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Discussion Starter #1 (Edited)
I'll start out by giving a run-down of the engine plans and build philosophy, then will move onto the progress thus far. I'll give you guys some pictures for now, but may hold off on some until I can more conveniently access stuff, since for the winter it's cramptly parked in a single car garage. However, I will try to accommodate special requests.

I started working on the car about 10 years ago when I first got my license, modifying it without my parent's knowledge. One day, after many months of modding the car right under their noses, my mom went to get in the car and saw that it had a non-reclinable bucket and harness. She yelled "what the heck!". My Grandma stopped driving right about then so we got her car and my parents began to use that instead (because of the mods). My parents drove the Civic less and less, and I modified it more and more until it basically became my car. It still is.

The idea for the car is to use it on the awesome roads we have just northwest of Madison, in the "driftless region" of Wisconsin, and at nearby tracks, probably blackhawk farms raceway in South Beloit, IL. These roads can be somewhat bumpy, and have corning speeds that range from 40 to about 100 mph. My brother and I have explored this area for years and logged hundreds or thousands of behind-the-wheel hours. We've found many sections of road with excellent visibility and a large margin for error that make it very possible to safely enjoy practicing driving.

I think the EP3 has one of the best price to performance ratios of any tuning base, with adequate potential for having fun with much more expensive machines on the track. I want to show that anyone can built certain cars, like the EP3, that give a competitively safe, secure, fast ride at a price that's affordable for many, many people.

Decisive advantages versus older hondas:

1. Greater chassis rigidity: 95% better torsional, and 22% better bending rigidity than em1.
- Roll cages can increase rigidity, but can cost $1000 for a weld in roll cage, plus the work to remove everything, repaint the welded areas, modify the dash, etc. Unless the cage were high quality, the cage may make only bring the rigidity of the EP3. This would offset or negate the weight advantage.

2. Low Cost:
For example, the 02-03 EP3 uses the same ABS proportioning valve as the DC5 Type-R. The 02-03 EP3 OEM front sway bar is the same 25.4mm diameter as the JDM EP3 and DC5 type Rs. The rear sway bar from a 05-06 RSX Type-S is 21mm versus the 22mm type-r sway bar, which is more than double the price. The overhang weight and length is the smallest of any Type R. The EP3 comes with EPS (electronic power steering) making the car easier to work on, lighter, and more powerful. Seat bases, engine mounts, brake lines, exhausts, suspension, chassis braces, etc. designed for DC5 can be used for EP3 (with few exceptions), making parts easier to find and more likely to be cheaper.

3. Suspension Design:
The unique feature of the EP3 and DC5 that the older civics and integras lack is that deflection is used to improve geometry. The front compliance bushing is located on the front of the arm, resulting in toe-in under side load. That toe in, while cornering, reduces ackerman, increases caster by more than 1 degree, and increases camber as well. It causes the front contact patches to become larger and more parallel, and to pull in the same direction. It improves grip as well as function of the LSD.

The faster you can accelerate out of corners, the more weight can be transferred to the rear. The rear compliance bushing is also located on the front of the arm, therefore also results in toe-in under cornering load, which is helpful for rear traction and stability. 4-wheel-steering is used very successfully on most of the worlds fastest cars to accomplish the same geometry change as the EP3's more simple, lightweight approach. The 1st generation Honda Prelude was the 1st to use 4ws, and back then, had the fastest 60mph slalom time in the world - faster than the Ferrari F40.

The design requires the suspension to operate in a very specific range of it's suspension stroke in order to load the suspension correctly for optimal deflection. This would explain why the Type-S, Type-S A-Spec, and Type- R models all have very progressive spring rates. I think the somewhat poor tuning reputation of the EP3 and DC5 may mostly come from lowering too much or using the wrong springs - errors that may be much less noticeable on eg,ek,dc2, etc.

OK, moving on to the build:

Current mods:

K20a3 Bc Stage 3 cams
Insulated Airbox w/ Cold Air Snorkel
PLM Header with Custom 3" Flange
3" Custom Exhaust
Oil Catch Can
Innovative Engine Mounts (85a side, 75a front/rear)
Sunroof Delete
Sound Deadening Removed
A/C Removed
Rear Seats, Carpets, Interior Panels (Except door cars and Dash) Removed
Lightweight Battery + Relocate
R. Wiper Delete
Drilled Impact Beam
Drilled Custom Rear Bumper Beam
Drilled Front Bumper Beam
OMP Front Tower Bar
OEM F. Sway Bar (25.4mm)
22mm JDM DC5 Type R Sway Bar (22mm)
RSX A-spec suspension (new top hats, bearings)
Hardrace front LCA bushing
Energy suspension rear LCA bushing (80a)
Hardrace Front RLCA bushing
Powerflex Rear Shock Eye Bushing (95a)
Superpro Knuckle Bushings (80a)
Prothane Rear URLCA Bushing (85a)
Hardrace Pillow Ball Rear Inner Bushing
Whiteline R. Sway Bushings (80a)
05-06 RSX Type-R R. Tower Gussetts
Custom Rear Tower bar
OMP Steering Wheel
Cobra Suzuka Pro-Fit Seats
5 Point Harnesses (OEM Belts + Airbag Delete)
F/R 06 Type-S 5-lug Swap
JDM DC5 Brembos + EBC Yellowstuff pads
4x AP2 Front Wheels (17x7 +55) w/ 22mm spacers (+2cm Track Width f/r)
Michelin Pilot Super Sport 215/45/R17
S2000 299.6mm F. Rotors

Carbon Hood

Right now, it makes 180whp and 145tq. There was a poor design for the intake snorkel that I think robbed several horsepower, nevertheless its really fun and actually kind of fast.

The durometer of the bushings is optimized for proper deflection. I chose a hardened rubber bushing for the front LCA bushing so that it would maintain it's original deflection characteristics while using 140 treadwear tires. I chose a urethane bushing for the rear front arm bushing so the suspension would move more freely. All of the urethane bushings in the system were bored to match the inner sleeve diameter more closely, lubricated with Shin-Etsu Silicon grease and fitted with zerk ports to keep them slippery and moving as freely as possible. I think this setup could move even more freely than the pillow-balls that are used instead of bushings on most racecars, and with zero play. I also experimented with various tie-rod ends and end links to find which move most freely. OEM tie-rod ends are BY FAR the smoothest and most free. OEM end links are better than knock-offs, but much more bound that the OEM tie-rod ends. I may end up going with a pillow-ball setup unless the OEM end links free up with use. I chose not to use hardrace just because they look like the same design as OEM and were about twice the price. Moog were the least free, became pitted very quickly, and were much heavier than OEM.

After watching some youtube videos of EP3 and DC5 rear suspension deflection...

I concluded:

The knuckle bushings are used primarily for shock loads (i.e. bumps, potholes, etc), therefore I chose a urethane bushing that was the same or softer than the remainder of the bushings and a bit harder than the compliance bushing, allowing deflection while keeping the pivots as free as possible.

The front RLCA bushing is by far the biggest bushing in the system and is the biggest factor in rear deflection. I chose to use a hardened rubber bushing to keep the deflection characteristics the same as OEM when using stickier tires, just like in the front. The upper control arm bushings and rear inner bushings must deflect simultaneously for the geometry change to occur - the flat metal plate that connects the knuckle to the rear inner bushing is actually as thin as possible in the middle [and thicker where it attaches to the knuckle and inner rear bushing] so that it can bend to aid in front RLCA bushing deflection.

I chose 80a urethane upper control arm bushings, and a pillow ball for the rear inner bushing. The shock eye bushing is 95a. I had to use different manufacturers for many different locations depending on their durometers and availability (prothane upper inner, superpro upper outer, hardrace lower inner, etc.).

In the videos you can see that quite a bit of defection occurs are the rear inner bushing, generating toe out. The OEM compliance bushing has relief cuts, to allow it to deflect more than other bushings. Of course the bushings become softer with use... I think the inner rear and inner front RLCA bushings wear the most because of the combination of twisting and load... I think the inner rear bushing wear may eventually surpass the front bushing, simply because there is so much less rubber and it is a smaller diameter. As more and more deflection occurs at the inner rear bushing, and less and less at the front, the toe-in geometry change becomes less effective. Furthermore, it's likely the guys in these videos had urethane bushing kits, which include the compliance bushing. All available rear urethane compliance bushings are >90a, therefore there is a 100% chance your suspension deflection will result in toe-out instead of toe-in! Don't use hard compliance bushings (or use harder bushings everywhere else)! Same goes for in the front - even a front compliance bushing with the same durometer as the rear front arm bushing will behave like it's stiffer than the rear, since while cornering the bushing is already twisted from the arm articulating, unlike the rear which rotates coaxially.

It's also possible that the aftermarket LCA's in these videos came with a soft bushing - I called several companies and learned that most or all company's arms come with bushings 70a-80a. Most or all urethane bushing kits use 80a at that location (Powerflex uses 95a ("street" and "race" powerflex bushings are THE SAME for the EP3/DC5)!) The guy in the first vid has skunk2 LCAs, which have 70a bushings, and you can see that's where most of the deflection is occurring.

The factory Type-R shocks/springs are close to perfect - usually times go up when the suspension is altered in JDM specimens. Likewise, the NSX-R was close to perfect - the fastest light-tuned specimens use the stock setup, or merely lower the car by about an inch, even when using slicks. The design of OEM suspensions for this chassis puts the strut bearings inside the spring whereas all available coilovers use a smaller diameter spring which requires the bearing to be positioned on top of the spring, increasing the overall height of the bearing assembly, reducing suspension stroke. I think the only way to improve on Type-R suspension, in a way that retains it's versatility on bumpy surfaces, is a custom setup that retains the full suspension stroke, or to extend the strut tower somehow (the BTCC car did this).

My research indicates the 05-06 A-Spec suspension for the RSX is approximately identical to the 05-06 Type-R, with spring rates adjusted for LHD. I think a aftermarket damper paired with OEM springs is the only good suspension upgrade option other than a fully-custom setup. Therefore I am, for now, using A-Spec suspension. At $600 new, it is another major cost advantage of using this chassis.

I'll be positioning the seats closer to the middle and farther back compared to stock. I'll use a steering extension to let me sit as far back as possible using the factory pedals. I'll determine the driver's seat height based on visibility and feel, and will mount it on sliders, because my brother will be using the car as well. I want the roll axis of the car to correspond to the roll axis of the driver's body to maximize feedback transmission. This is a similar approach to what can be observed on the BTCC EP3 and most race cars at high levels of competition (GT, JGTC, etc.) - lower seats isn't always better. The passenger seat will be mounted directly on the base and as far to the middle and rearward as possible.

I've cut the front bumper in front of the tires and installed a custom splitter that I made out of plywood and painted using sailboat hull paint. The shape is similar to what we see on on the BTCC car, and Rikli Motorsport EP3, which are the most successful and fastest EP3's that I've seen.
Rikli Motorsport EP3
I'll post pictures of how I made and attached the cowls and installed the splitter ASAP. This will work in combination with a 60" APR single-foil rear wing, mounted to the hatch near the license plate using 2 plates of 6061 aluminum 9/32" thick, similar to the BTCC car. For now I'll be using black 04-05 EP3 side skirts, but plan to use a flat underbody with integrated front quarter panels to allow venting of the air coming through the front bumper cowls and around the inside of the front wheels. I'll post pics of the wing, skirts, and installation process/design as soon as possible. The rear bumper is cut about .5" above the level of the bumper beam, similar to the Rikli Motorsport car.
Rikli Motorsport Cut Bumper. There is a custom bumper beam replacing the stock piece so that it no longer protrudes past the bottom of the bumper edge, and reduces weight.

OK, Now Onto The Engine:

The engine is a complete k24a1 with new pistons, rods, oil pump, cams, etc. I chose the a1 because it's cheap, and because the head flows better or as good as any of the other k series heads. My goal is for torque to peak over 210 lb/ft, and to have at least 260 whp, with an emphasis on lightweight components and minimal parasitic loss. I think a powerband like that will make the car even faster for my use than a 290 or 300whp car with 190ft/lb. The BTCC car only made 250whp, but a whopping 200 lb/ft toque out of the 2.0 liter!

I'll be doing a VTEC-killer setup with '06-'08 TSX cams and RBC (now RSP) manifold. Half the reason for choosing TSX cams is because they're cheap. The second half is because I remember seeing very, very good torque on more than one setup - about 210-225 ft/lb. That's more torque than most or all 99mm stroke making greater than 300 whp.

VTEC killer allows me to keep the a1 head, reducing the cost. Using single lobe exhaust rockers reduces reciprocating weight by ~900g. Thelost motion spring in 3-lobe heads also causes parasitic loss. Plus, the VTEC solenoid removes weight as well!


I'll be using STD Supertech exhaust valves (30mm), and +.5mm (35.5mm) Crower flat-face intake valves, with 3-angle job of course. I chose to do new exhaust valve just to refresh my valve stem clearances, and because the original valves were really dirty. I chose 35.5mm intake valves mostly for experimentation. The Crower flat-faced type were the only option that I could find in stock in that size.

As you can see, I smoothed-out the surface of the combustion chamber, before the valve work and decking, using a wire wheel bit on a dremel. The idea was that a smoother surface would reduce carbon deposits, and possible help flow circulation and fuel evaporation.

Here's my port work. I used machining dye to port match to the hondata gasket, mounted as high as possible on the mounting studs, to remove more material from the tops of the ports than the bottom in order to make the port shape a bit more vertical, and therefore the change in direction of the airflow a bit more gradual. I tried to keep it close to congruent with OEM, mostly just adapting the shape to the wider 35.5mm valves. Admittedly I narrowed the divider quite a bit, seeing that that is a common trait of most cnc port jobs, even mild ones. Hopefully it works well lol. I used a pneumatic rotary tool with a carbide bit, followed by a rotary sanding bit on the intake side, and the sanding bit only on the exhaust side, just to smooth it out. I'm thinking about polishing the exhaust side to reduce carbon buildup and reflect heat.



Since the cams are only 12.35mm lift, and I have AP2 seats, retainers, and keepers laying around, I chose to use Ballade Sports springs for an S2000. They are designed for use with the AP2 retainers that I already had, and are actually very stiff, almost as stiff as Supertech's HD1021 springs, which are by far the most common springs in engines making ~300hp or more. I think these springs should be safe to at least 13.5mm, which is probably the most I might ever need.

Here are the Ballade springs next to AP2 intake springs. AP2 cams have 12.65mm lift (.35mm more than TSX), the same rocker ratio, and a more massive valve than K24, so I may actually just use AP2 springs until I need to switch cams, reducing parasitic loss and reducing valvetrain wear.


I drilled holes for oil squirters into the block using a drill press. I checked the flatness of the squirter-to-block interface using machining dye. I could fit a .008" feeler gauge under Number 3 so will require refacing the mating surface by 0.7 degrees. I chose to use oil squirters to increase piston lubrication and for reduced temperature, so that I can run a tighter p-w clearance for longer engine life, and since track sessions may be 20 minutes or more at WOT, they may otherwise get hot.


I used the crank and block codes to determine a yellow-green-green-green-yellow bearing combo as my starting point for measuring clearances, which I then checked multiple times using a mitutoyo .0001" bore gauge + micrometer, as well as plastigage. Interestingly, my plastigage measurements were about .0001" below my bore-gauge measurements. My measurements varied microscopically each session; no two sessions produced identical measurements. This was caused by the conditions in the room (temp, etc.) I chose to represent my data my as the following: .0019"(1), .0018"(2), .0020"(3), .0018"(4), .0019"(5). Using this data, I chose to go with the following final bearing order: TOP - blue, black, brown, black, blue BOTTOM - black, brown, green, black, brown. My new clearances are perfect at .0016", .0016", .0019", 0016", 0016". Using this bearing order also keeps the clearances symmetrical top and bottom.

I see that many people run slightly larger than this (i.e. 0.002"), I chose the highest end of oem spec to allow very safe use of 30 weight oil, whereas 40 may be more well-suited for a .002" clearance. My research shows that it's possible to gain 2-10hp using certain brand oils over others, and a similar amount using thinner oil. I'm thinking about using Eneos 10w-30 oil. Scott at King Motorsports, who's worked with me before on the tune and exhaust, also told me they use "30 weight Red Line oil" on all their endurance engines.

I used BC lightweight sportsman rods, which weight about 458g each (36g over claimed). I chose these for the price, and because I think most rods are overbuilt for a setup like this. I'm starting to think these may be the weak link in the engine, just because everything else should be so durable - the oiling design is somewhat different than OEM and looks somewhat inferior. (LMK and I'll snap pics)


I sent the Supertech 88mm 12.5:1 pistons to Calico Coatings to have a skirt coating applied. I did this to reduce piston to wall clearance. Years ago, back when I bored the block, I had read that Supertech spec'd the pistons at .0040", then, after slapping issues (see many forum threads), revised it to .00315", which is what the spec sheet said, and is what I used. Since then, I've noticed that the largest spec for this engine, in any bore, by any manufacturer, is .0025", and that is for 2618 alloy (these are 4032) which expands about 14% more. JE and Mahle, who are the only other companies who make 4032 pistons for this engine, spec .0020" and .0016", respectively. I called Supertech and asked them about this, I was told that down to about .0020", or even slightly less, is actually fine for NA! He did say less than that may be risky if the engine were to overheat or experience detonation (of course). Calico told me the thinnest they can do the coating is .0008", so we are shooting for .0008"-.0012", therefore the piston-to-wall clearance will be .0019"-.0023".

The Supertech pistons came with a wrist pin that has a .2" wall thickness. This is the same pin that's provided with all of their pistons for this engine, which makes me think they are overkill for a NA setup like this. I see that people upgrade to thicker-walled pins somewhat often, even on NA builds. The pin, especially with .2" walls, should be way stronger than the pistons or the rods. I think going thinner is better because it is lighter, therefore helps engine response, and reduces loads on the piston skirt and pin bores, probably increasing engine life. These advantages would be more significant in a 2.4l than a 2.0l. I had custom pins made with a .15" wall. Precision Performance Products in NC modified one of their off-the-shelf pins to my specified length and chamfer; they cost about $19 each and PPP was an absolute pleasure to work with! The new pins are a stronger material and weigh ~19g less per pin. I thought about a tapered bore pin, but the cost was about double



Calico Coatings will also be doing a DLC coating to the rings. Instead of using a traditional ring filer, I made a jig using random bits I had laying around, including R/C car bearings. The ring gap is positioned over a groove, in which I place a fine diamond file that is used to remove material for the gap. I place this setup under a binocular microscope that I happen to have laying around. This way I can be sure that the edges are perfectly square and parallel.


With the lighter oil pump with no balance shafts, lighter pistons, rods, flywheel, valvetrain, etc. the total engine weight should be about 20lb lighter than the k20a3 it's replacing.

Stay Tuned

30 Posts
Discussion Starter #2 (Edited)
Weaver Auto Parts here in Madison has been awesome and inexpensive, taking care of business for all my machining needs. Their bigger machine shop in Sauk City, WI (25mi away) is equally badass. My friend Paul here in Madison does head work, decking, cleaning, etc., and Sauk City does the block and balancing work. The Sauk City shop offers a 5g "street" balance and a 2g "race" balance. They were totally game for doing a 0.1g crankshaft balance!... with the flywheel, pressure plate, and harmonic balancer attached!! Yes, the entire rotating assembly is balanced to within 0.1g!!! They said the crank was almost perfect, so here you can see it only took a bit of grinding, no drilling. However, the Clutchnet pressure plate required 10g of material to be removed! Remember, Spoon's engines are balanced to within 0.2g and make >10hp over stock, with no other changes besides very precise oil clearances.




They needed to deepen the existing balance drilling of the flywheel just a bit. You guys will probably end up seeing the PRC pulley later on. They removed about 1g. I used the PRC pulley from a 06 Type-S because it is more than 1lb lighter than the original k24 CR-V pulley, plus is 5.4" in diameter instead of 6.125". This is an easier ratio for the accessory drive, which is only running the water pump and alternator anyway right now, gaining at least a few hp.

The flywheel is 8 1/4 lb.


Unsurprisingly, I'll be using a k20a2 oil pump. Here you can see where I ported it. Rumor has it that porting like this increases the threshold for oil cavitation, so the engine can rev a approximately 300-500 rpm higher with equal safety. Basically it just means the oil flows better, more smoothly, and more easily. It was actually really, really easy and quick to do using a Dremel with a sphere-shaped grinding-stone bit.



Here's a pic of the car right now. It's been sitting like this in the garage for several months.


Here you can see a quick snapshot of the bumper cowl. I still need to attach the airdam (between the splitter and the bumper), and make a gasket to take up the small gap between the cowl and splitter.


I drilled out the reinforcement beam and structure inside the dash, saving at least 10lb! I'll probably removing the blower assembly from inside the dash, which weighs at least that much. I'll then 3d print some adaptor cowls to attach computer fans to the factory defroster ducts to prepare myself in case the windshield ever fogs.


Stay Tuned

30 Posts
Discussion Starter #4 (Edited)
Several days ago I removed the Sparco Sprint Junior that had been in the car several years. It was a base-mounted design, manufactured in 2003. I wanted the seat positioned higher and tilted back; mounting the seat directly to the rail was so low that the bump in dash over the gauge cluster began to obstruct the view, and the driving felt better with it positioned higher as well. Movement is transferred to the body in a more rotational direction the closer to the floor the seat is positioned, and a more lateral direction the higher it it positioned, because the rotational axis of the body roll of the car is located near the floor and middle of the car. I think movement in a lateral direction can be easier to detect and use.

The old seat used a series of spacers to change the seat's angle. Eventually I realized that in order to achieve the height and angle that I wanted, I would need to make large, wedge-shaped spacers to go between the seat and the base. I thought adding that much height would begin to compromise the strength of the mount somewhat significantly, plus, tilting the seat farther back more would cause the seat of the seat to interfere with my legs when operating the pedals.

Obviously, the tilt of the seat can be more easily adjusted with side-mount versus bottom-mount. Side mounts also come in tall versions, so a side-mount system seemed to fit my needs perfectly. Plus, my friend wanted to buy the Sparco for his Miata, and frequently passengers would mention that the stock seat was insufficiently supportive.

So, I sold the Sparco to my friend after finding Cobra Suzuka Pro-Fits that appeared on Craigslist after several months of scanning. These seats have taller thigh bolsters that should give more contact area for more feedback and support. The butt-area of the seat doesn't extend as far under my legs, so extending my legs should be fine, even with the seat quite reclined. My dimensions are 6'3" 170lb 31" waist - I think 33" waist is a good maximum , although up to 36" may be able to fit in a pinch. They weight about 18lb and cost $700 for the pair. They are also very breathable, and I think will be cool and comfortable, which I think may improve driver speed.

Sparco and Planted mounts were the only convenient options, I found OMP on a european website at a similar price, even including international shipping. The final 2cm or so of every edge of the seat base surface is curve downwards about 1cm below the plane of the seat base surface, which is a unique feature as far as I know. Even with just slightly better fitment, installation and removal is MUCH easier, especially when doing solo.

Ebay yielded a used tall OMP HC/733E and a discontinued Sparco tall mount. I test fitted the bases a couple days ago and the angle was way too far forward using both top holes.
Lowering in the rear caused the mount to interfere with the plastic around the belt holes.

With the bases installed, I sat in the seat and tilted it back to where I wanted it, then measured the distance between the ground and the front of the base by placing an object under a certain spot under the seat, which I could then reposition after exiting the seat to replicate the angle. I determined that it would be possible to achieve my position by drilling new holes and removing material to avoid belt hole interference.

Here are the new mount shapes, and stencils I used to guide the cutting edge. I wanted them to pass as unmodified designs for when I go to the track; they're stronger now, after all. The raw edges were painted with a Duplicolor black touch-up marker to prevent rust.



Here we see the back angle and height difference between the driver (OMP) and passenger (Sparco) seats.



I took the engine block to Paul today to have the oil squirter faces leveled. He said he'll be using a pilot into the hole and and a cutting surface that rotates coaxially and perpendicular to the pilot to remove just enough material to make them new oil squirter mating surfaces perfectly perpendicular to the holes for zero leakage.

Also, today someone in Europe accepted my ebay offer for an RSP intake manifold. I'll be port-matching, smoothing and enlarging the runners very slightly to match the growth factor of the 35.5 intake valves, plus will smooth the transition at the throttle body. 35.5mm valves increase the area of the valve faces by 55.376 mm per cylinder over stock; thats a 2.8% difference in area. Therefore I wish to increase the diameter of each runner by approximately 2.8%.

I talked to a new person at Calico coatings today; I hadn't received a response to my email that I sent the day I sent the pistons, received the invoice from Calico, and relayed the information I received from Supertech that day determining the final thickness spec. We are aiming for .0010"-.0012" of CT-3 / .00215-.00195" piston to wall clearance, limited by the machine's spray thickness parameters. They said their equipment only allows DLC coat to the outer face of the rings, and that that capability depends on whether they have the correct tool for this ring size.

Stay Tuned


30 Posts
Discussion Starter #5 (Edited)
The pistons are now coated and the piston to wall clearance is confirmed at 0.0020"-0.0022". DLC-ing the rings cost $120-$300, so I decided to leave them uncoated. DLC-ing rings results in a much greater sealing area on the face of the ring. I think spending $120 would have been equally satisfactory.

Calico kept me informed on the status of the order, and showed perfect coordination with another local company who offered the capability of doing DLC, and was equally good at keeping me informed.

UPDATE: "I just looked at my receipt email from calico for the first time... It says .0008-.001 PER SIDE. This is after repeated clarification that it was .001 TOTAL we were shooting for. I noticed on the packing slip it said .0008-.001" and I thought it was ambiguous. I was told "light coat", the receipt says "heavy coat". Now I want to know how or if an error was made measuring p-w. If it is too thick, I think recoating the piston is the only good option, since at 88mm, boring it more is definitely undesirable. I'll make some phone calls in the morning and update."

8 of the 18 engine bearings came damaged and needed to be warrantied; they're now here and ready. Once the oil squirters are ready I can begin assembly. Note that there are 2-3 part numbers for each rod bearing size, each indicating a different location of manufacture. I got all three version just to see, and will post details of that during assembly.

Last weekend I bought a transmission from a salvage yard in Indiana. The engine bay of car that it came from looked extremely clean with very little corrosion, making me think the car had been used mildly. It had new-looking 18" mags, cheap tires, and aftermarket tailights, making me think it was crashed in the act of celebrating the new car. It was a 2002 Type-s with 48,900 miles (CRASH). I'll use the stock synchros, which look almost pristine, then eventually rebuild with carbon synchros. This car hopefully will never be launched or dragged, and I'll be as delicate as I can, so I'm not that concerned about wearing them out.


I'll have it cleaned in Weaver's tank. I'll give you pictures of the inside during installation as soon as the final drive gets here. Remember, there's a 1-Way MFactory clutch LSD going in. The LSD calls for a specific transmission fluid for correct operation of the clutches; I think getting it spotless will be good so that the diff can immediately begin running with undiluted fluid.

All along I though I'd use a 5.062 final drive, possibly with a TSX 6th, because it's the same ratio as the FD2 Civic, which was developed to set a Suzuka lap time, which seems similar to the roads around here. 5.062 is the closest factory ratio for these transmissions, and at about half the price of aftermarket options, is the shortest final drive that I'm willing to consider.

I figured the closer, the better, while still being able to drive for up to at least 3 hours at a time on the highway. However, it concerned me that the FD2 Civic uses 18" wheels, and it's 2L engine revs higher than this engine will. I wondered whether highway rpm would be ridiculous, and how the difference in redline would change the shift points.

It turns out a FD2 revving to 8600 shifts at about exactly the same speed as RSX with a 4.7 final drive revving to 8100. In other words, if you want FD2 shift points using a k24, use a 4.764 final drive!

I'll note that the DC5 Type-r uses a 4.764 final drive, but with different 4th, 5th, and 6th gears (1, 2, and 3 are the same throughout). I found that this results mostly in just a taller 3rd gear!

Shift MPH:

(5.062 8600rpm) : RSX K24 (4.764 8100rpm) : DC5R (4.764 8600rpm)
shift mph
1. 40 : 39 : 43
2. 62 : 60 : 65
3. 87 : 84 : 92
4. 114 : 112 : 115
5. 143 : 139 : 143
6. 178 : 174 : 179

This is comparing a 225/45/18 (fd2) to a 235/45/17 (this car) - 255/40/17 (very popular size) makes it slightly shorter.

You can see that DC5 Type R (4.764) 4-6 shift MPH is approximately the same as the FD2 (5.062), however the FD2's shift point from 3 to 4 occurs at 87 instead of 92. I think a short third gear makes more sense for around here, since even the low speed corners are fast enough that it may be possible to eliminate ever needing to use 2nd.

I'm still wondering if I should just go for the 5.062, at least for educational purposes. I probably will. The 5.062 may render 2nd gear really short and ridiculous, and require sensitive throttle control when in 3rd... but will the 5.062 give useful acceleration in 4th and 5th 70-120mph ? I think it might. The consensus on US-based forums seems to be that 5.062 is too short for a k24... I'm wondering if this may come just from drag racing... Most Youtube videos of EP3 and DC5 in Europe have final drives shorter than 5.062!

30 Posts
Discussion Starter #6 (Edited)
The block is still in the shop. The oil squiter faces were resurfaced parallel to the bolt holes. I measured the new gap at 0.002". I imagined the mist of oil spraying through the gap, effecting the crankshaft and piston balance and wanted to reduce the gap. I did this by finding the angle for resurfacing (about .07 degrees), then placing the engine on a plate with an equal tilt to its surface. I then placed this in a large mill. The result was perfect flatness, but when I did the identical process to the adjacent oil squirter, which was equally crooked, the alignment was no longer correct. The machine is at a public "makerspace" here in Madison, so I think the angle adjustment may have been loosening during use. I decided to bring it back to weaver to reface it with the pilot technique again.

The wing for this car is 60" and will be mounted to the hatch, like the BTCC car. I'll be using 5/16" (maybe 3/8") 6062 aluminum plates. I decided on the shape after many fiberboard prototypes. The material was very easy to cut and sand to shape in the huge woodworking area at the same public workshop. I used miscellaneous tripods to hold the wing to determine the correct height, then made the shapes for the support and tested them by taping them to the car then looking at it at every angle.


I used a lathe to make aluminum cylinders out of scraps of aluminum rod, which will be for bolting it onto the car. I'll bevel the edges of the plates, then cut reliefs in the aluminum plates in the shape of the cylinders, then weld them in, then sand blast everything, then anodize them black.


The RSP manifold arrived several days ago. The RSP manifold is well-known for having torque levels at least as high as the more expensive RRC. This is because of it's unique design -Velocity stacks protrude into empty space inside a plenum. The advantage of the design is the precise aerodynamic shape of the runners, especially at the opening. The RSP manifold generally becomes much weaker above 8000 - 8500 rpm.

RBC left, RSP right

I predict the TSX cams will max out from 8000 - 8500 rpm. I wanted to enlarge the runners to adjust for the larger engine displacement, then optimize the shape and length to increase the power threshold of the manifold just enough to match or exceed the cams. I kept the design very close to original to cash in on Honda's r&d, then improved the surface texture, and slightly shortened the runner length.


There was a ledge and increase in diameter of the runners at the transition between the removable snorkels and the manifold body. While increasing the diameter, I made the transition flush. This means the change in diameter was greater in the removable snorkels than the remainder of the runner inside the manifold body. The diameter of the runners increased approximately 1.8mm in the snorkels, and 0.7mm in the manifold body.

This pic was from today. All of the inlets are like the one highlighted here, now. From most to least coarse, I used a carbide rasp, then a rotary sanding bit, then light sand blasting to achieve the texture. I may post more pics.

People have experimented with many, many porting techniques in the thread about the RSP. Shortening the snorkels even 10mm can lower torque, and raise peak torque rpm by 500-600. I wanted to raise the maximum useable rpm while keeping the torque the same, raising torque and/or lowering peak toque rpm.

I removed about 1.5mm of material from the top of the original shape, then rounded the lip inwards as I increased the diameter. The shorter height and new shape will have an effect similar to shortening the runners about 3-6mm, I think. Compared to the original, the new shape has a more constant rate of taper throughout it's length, but especially at the straight portion of the shape we're looking at, before the elbow.

The TSX cams, like the manifold, max out at less than 8500 rpm. I think the larger ports and 35.5 valves could raise the maximum rpm of the TSX cam, as well as decrease the rate of torque decay, and that max torque and low max torque rpm are therefore very important for this engine. Long runners can increase torque because of the aerodynamic phenomenon that is caused by their length, therefore there can be greater potential advantage to shaping and porting a long runner than a runner designed just for max flow.

This pic was after I removed material from the rim by using a sanding belt on the top face, but before I began removing material from the snorkel interior. You can see the original interior surface on the right, next to the others which have had nearly all of the shaping work finished. The new shapes are all now more precise and matched, smoother, and lightly sand blasted, like in the previous pic.

There is consensus that the positioning of the throttle opening restricts flow, especially for cylinders 1 and 4. I changed the shape of the throttle port to allow air to more easily travel around and over the snorkels, and circulate inside the plenum. The shorter runner length helps for this as well.

The new intake will be 3d printed, and will basically be a long, straight velocity stack going from the throttle into a plenum with cold air feed, filter, etc. I want to do a long, gentle taper throughout the length, going from over 3" at the mouth to ~62mm at the throttle. The snorkels are basically directly in the path of that air, and the interior of the plenum behind the snorkels has lots of protrusions, so I think the air will be pretty turbulent no matter what. I think using the intake to make the air as dense/least turbulent, and fast as possible, and using the throttle port and plenum shape to allow the air to circulate and tumble and release energy more easily should help compensate for throttle location; enough to create power up to less than 8500 rpm.

Note the big casting imperfection on the inside right side of the opening in the first pic.



Material was removed around the throttle opening and in the far corner near the plenum cover bolt hole boss. Several millimeters of material were removed from those areas, and the surrounding areas shaped to match. The plenum cover bolt hole boss comes very close to the runner opening, and so does the plenum wall nearest that opening. I think that tight space and protrusion would interfere with the air circulating and energy dissipating in the air throughout the plenum, as well as upset the balanced airflow to that cylinder, therefore that area should be smoothed and opened as much as possible.


Hopefully I'll be able to do combinations of RSP and RBC manifolds and 3D printed and non-3d printed intakes on a dyno. The runners of the RSP are shaped really similarly to ITBs, except the airway isn't obstructed by throttle plates, and the air may be better than drawing from the bay or hood, so I think the manifold may have potential to be at least as torquey as some ITBs. Remember, this setup can probably run 50 degree VTC as well. And I want to see how a gently-tapering velocity stack + airbox setup compares to a 3.5" or 4" tubular intake on a dyno, which seems to be what the vast majority of people are using on the most powerful n/a k series. A guy at King Motorsports said they've tested tons of 3.5" and 4", which are the sizes that make the most power, he said... He said 4" is usually better, and that just changing or adding an angle, the location of the angle(s), and the length of the intake, can effect horsepower by "9".

5 Posts
Great build thread. Wanted to ask what you are going to do for your oiling system? I ask, because I follow a shop that is running a boosted K24 setup in an NSX for road course racing, and they were seeing oil pressure drop down to around 30 psi in multiple turns. They found that the only thing short of a dry sump to resolve that was an aftermarket baffled pan from Unit2Fab. Hope that helps.

30 Posts
Discussion Starter #8
Wanted to ask what you are going to do for your oiling system? Hope that helps.
It makes me wonder what tires they were using - grippier tires might cause more sloshing. The position of the engine, and the car's driving style would have some effect too. I'm thinking I'll just use a pan baffle, because it seems like tons of people use these safely on a big variety of tracks and its a ton cheaper than other options. I read that the BTCC cars all use the stock pump and baffled pan, and tons of time attack k series cars use that as well. There's a thread here or on clubrsx where many people tested and found that significantly more pressure loss occurs during left turns, meaning the oil must mostly slosh up near the chains. That would explain why Mugen uses a subtler baffle design that concentrates on the area under the chains. I'm thinking of basically copying that design. I'll be running an oil pressure gauge so I can investigate as well.

Bumps, etc. I guess are the difference on road courses that might cause new oil issues versus track use. A driving technique like Takumi in Initial D, who can go full speed without spilling a single drop from an open cup of water, may likewise keep oil from sloshing around too much in the oil pan.

5 Posts
It makes me wonder what tires they were using - grippier tires might cause more sloshing. The position of the engine, and the car's driving style would have some effect too. I'm thinking I'll just use a pan baffle, because it seems like tons of people use these safely on a big variety of tracks and its a ton cheaper than other options. I read that the BTCC cars all use the stock pump and baffled pan, and tons of time attack k series cars use that as well. There's a thread here or on clubrsx where many people tested and found that significantly more pressure loss occurs during left turns, meaning the oil must mostly slosh up near the chains. That would explain why Mugen uses a subtler baffle design that concentrates on the area under the chains. I'm thinking of basically copying that design. I'll be running an oil pressure gauge so I can investigate as well.

Bumps, etc. I guess are the difference on road courses that might cause new oil issues versus track use. A driving technique like Takumi in Initial D, who can go full speed without spilling a single drop from an open cup of water, may likewise keep oil from sloshing around too much in the oil pan.
Might be worth getting a datalogger, and giving that a go at least the first time on any track. From the sounds of it, most other baffled pans for the K series work well up to a point, and then like you mention above, when tires and loading increases, then those baffled pans apparently fall short.

30 Posts
Discussion Starter #10
Might be worth getting a datalogger, and giving that a go at least the first time on any track.
I will. Maybe just a fast-reading gauge and a passenger or camera to record the reading. If the baffle is insufficient, I may try a drop-in baffle to work together with the original baffles, a new baffle design, or foam, just because it's so much cheaper than a new pan.

Can you remember the name of the car or any details like that? I looked up "unit2fab k24 nsx", turbo unit2fab nsx, etc. I'm wondering what the setup is, just because I haven't heard of incurable damaging starvation problems, and there are so many k series using the oem pan.

Could the body movements caused by the road surface be enough to make the pump slurp?

5 Posts
I think it's an issue of sustained lateral loading, especially during left hand turns like you mentioned. In any case, see the link below. Increasing minimum oil pressure from 38 psi to no less than 63 psi seems well worth the expense in my opinion.
This is a long one, but may be helpful for those with K series engine. One of the primary goals of the @RSFuture X @Koyorad NSX is reliability. After every event, I try to find all of the weak areas and improve upon them. One of the biggest weaknesses with the Honda K Series engine is oil starvation. It's a known issue, and is particularly bad in left corners. There are countless baffles and pans available, but I have found that none of them cure the problem. The best solution is a dry sump system, but they often come with their own complexities and challenges.
In my search for a pan that would cure the oil pressure issue, I stumbled upon a post from @time_attack_typer showing his data from the @unit2fab oil pan, showing great results. I noticed major oil pressure issues at @globaltimeattack Finals. I had an oil pan from a reputable Japanese tuner that baffled the oil pump chain and the pickup, and over filled the pan. Despite this, pressures were as low as 38 psi at 7000rpm during full throttle and in the 40's for extended periods (light blue line). This is engine failure waiting to happen. The worst corners were Sunrise and Sunset, which are the two corners highlighted in the photo.
After GTA Finals, I contacted Unit 2 fab for a pan. I installed that pan before the last test day, and the results were awesome. The lowest pressure I saw was 63 psi with an average of 95 psi (dark blue line).
The next step would have been a dry sump, but thankfully this pan saved me the time and expense. Huge shoutout to @sportcarmotion for building an awesome engine. It’s been through hell and has had no issues.

30 Posts
Discussion Starter #12 (Edited)
This is super good info. I'm thinking about it.

I tried to put the crank in last night but there is MAJOR interference with the oil squirters. The nose of each rod journal whacks the oil squirter stem. Apparently no one's added oil squirters to a k24 before, or at least posted their failure - many people post that "it's possible" with all the k24s, which I assume they are assuming just because they see that squirter faces exist in the casting; pics show that only A2 cranks have smaller journal noses.

Most of the time since the last update has been waiting for the shop to touch up the oil squirter face, they take forever, I got it back just 2 days ago! Now I'll need to either bend the squirters, or get a tsx crank, hopefully one with the same journal codes... There's been progress on the wing and some other stuff. I'll post with pics as soon as I can.
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