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Discussion Starter · #1 ·
Hey everyone,

I am in the process of building an all motor K24. It's currently still at the machine shop, hasn't yet been balanced. These are the specs:

-K24a4 (04 accord) block, with oil squirters and k20 oil cooler added
-12.5:1 Nippon Racing Pistons (They are cast but they are QUALITY, this is a very reputable brand)
-Scat forged rods
-K20z3 Cylinder head, stock port
-Drag Cartel drop in cams
-RBC intake port matched to 72mm throttle
-PLM header
-3in custom exhaust w two straight through mufflers
-3.5in intake
-Action stage 3 clutch and lightweight (7.5 lbs) flywheel
-ATI Dampener
-K20a2 oil pump
-VR1 oil (high zinc)

I have seen stock bottom end k24a2s on here that turn 8k+ rpm, but I can't find any info on reliability. What is a good max rpm if I want to get about 80k miles out of this engine? The pistons I chose while cast, are just as strong if not stronger than stock. Anyone hear have long-term experience w a higher revving k24 on stock or non-forged pistons? I'd love to hear yalls thoughts.
 

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2002 DC5 Type S
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welcome to the forum. 8000rpm is a max shift point for a K24 if you want reliabilty. Food for thought, a K20 at 9,000 rpm is the same piston speed as a F1 engine at 18,000rpm. The K24 at 8,000 rpm is the same piston speed as the F1 engine. A K24 spinning at 10,000rpm requires the intake valve to open 63 times per second, so if you back it down to 8,000 rpm the intake valve is still opening an insane amount of times per second. This makes it hard for the engine to fill the cylinders with air the higher you go, the increased piston speed creates friction from the skirts of the pistons hitting the cylinder walls due to the longer stroke 99mm (which is greater than a 2018 Z06 Vette or Viper V10), and if you look at a dyno of a K24 the way the TQ falls off quickly is evidence of what I am saying. There is more to it but this sums it up.

Above 8,000 rpm in a K24 is straining the engine.
 

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96 civic HX K24a
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Hey everyone,

I am in the process of building an all motor K24. It's currently still at the machine shop, hasn't yet been balanced. These are the specs:

-K24a4 (04 accord) block, with oil squirters and k20 oil cooler added
-12.5:1 Nippon Racing Pistons (They are cast but they are QUALITY, this is a very reputable brand)
-Scat forged rods
-K20z3 Cylinder head, stock port
-Drag Cartel drop in cams
-RBC intake port matched to 72mm throttle
-PLM header
-3in custom exhaust w two straight through mufflers
-3.5in intake
-Action stage 3 clutch and lightweight (7.5 lbs) flywheel
-ATI Dampener
-K20a2 oil pump
-VR1 oil (high zinc)

I have seen stock bottom end k24a2s on here that turn 8k+ rpm, but I can't find any info on reliability. What is a good max rpm if I want to get about 80k miles out of this engine? The pistons I chose while cast, are just as strong if not stronger than stock. Anyone hear have long-term experience w a higher revving k24 on stock or non-forged pistons? I'd love to hear yalls thoughts.
I would get it on the dyno and let the graph tell you where to rev it. But I also am of those guys that is ok with the piston speeds. My stock k24a1/z1 frank went to 8100 with a type s pump every time I drove it. My tsx motor is limited to 7600 currently due to injectors hitting 100% well before then but once I get the type s pump and bigger fuel setup it’s going to rev as high as it wants while making power. Your cams and RBC likely won’t take the powerband past 8k so I don’t think you need to worry if it’s a street or drag car.
 

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What is a good max rpm if I want to get about 80k miles out of this engine?
This right here, ask how many people revving over 8000rpm have engines that lasted this long without starting to burn oil or develop excessive blowby or leakage? The answer will be none. There's a good reason every engine manufacturer keeps their average piston speeds at 25m/s or less.

@ 8krpm you're already over 26m/s average piston speed. You're in high wear territory.
 

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2002 DC5 Type S
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This right here, ask how many people revving over 8000rpm have engines that lasted this long without starting to burn oil or develop excessive blowby or leakage? The answer will be none. There's a good reason every engine manufacturer keeps their average piston speeds at 25m/s or less.

@ 8krpm you're already over 26m/s average piston speed. You're in high wear territory.
many MIA high rpm K24 guys that never came back to share the end results to insane piston speed. I will give credit where credit is due and running top grade oil in these Kseries is important to get what some want from them. Giving credit to tuners that give it to people straight about where each particular engine should be shifting at if the customer is not aware so much about what is a high piston speed.
 

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Discussion Starter · #7 ·
So here is my new question. Will a high-zinc oil like VR1 prevent some of the high rpm wear? Zinc supposedly forms a sacrificial layer between metal parts.
 

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So here is my new question. Will a high-zinc oil like VR1 prevent some of the high rpm wear? Zinc supposedly forms a sacrificial layer between metal parts.
dont know. I know they will stay together longer.
 

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Discussion Starter · #9 · (Edited)
The cams I chose actually make peak torque 500rpms higher than drag cartel 3.2s interestingly enough. Hopefully the powerband won't be climbing too much at 8000. They are "drop-in cams" but have an insane amount of duration. Theoretical max power w these is like 340. What do yall think my setup will put down? Also do you think high duration cams like these have major clearance issues w 12.5:1 pistons?
 

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Look to be honest I have revved and a few clients are running their k24s to 8500 some with the stock oem pumps and some with RRC pumps.
Its their daily drives so far none of them have broke, I even fitted my k24 and moved it into my spider swap then took it out because I fitted a built motor and sold it to another guy
that is also revving the car over 8000 till today. This is all over a 5 year period i have posted some dyno sheets in the all motor thread.

I think for track racing it would be different I reckon because you would tend to keep the car in the higher RPM for way longer than in a drag race scenario.

Also @jordon the valve relieves with 12.5 comp pistons usually have bigger valve reliefs I'm, currently running crower stage 3s on the ep3 and can easily run 40 degrees of vtc.
I dont though as the cams loses power and are happier at lower VTC
 

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Look to be honest I have revved and a few clients are running their k24s to 8500 some with the stock oem pumps and some with RRC pumps.
Its their daily drives so far none of them have broke, I even fitted my k24 and moved it into my spider swap then took it out because I fitted a built motor and sold it to another guy
that is also revving the car over 8000 till today. This is all over a 5 year period i have posted some dyno sheets in the all motor thread.

I think for track racing it would be different I reckon because you would tend to keep the car in the higher RPM for way longer than in a drag race scenario.

Also @jordon the valve relieves with 12.5 comp pistons usually have bigger valve reliefs I'm, currently running crower stage 3s on the ep3 and can easily run 40 degrees of vtc.
I dont though as the cams loses power and are happier at lower VTC
I had a scK24a2 that was a zero mile factory engine. I owned it for 42,000 miles and the rev limiter was set at 8000rpm. I drove it hard as a DD and it made it to two weekend track events and had many grudge races. It held together well adn the dyno showed that. it used the same dyno since birth. It only used AMSOIL turbo formualted 10-30W at 5,000-7,000 mile changes. I was impressed, it was a zero mile engine though. Guys buying used semi-clapped out longblocks then spinning them above 8,000rpm is not smart IMO. If one does not know the life of his or her engine, it is best to think reliable.

Building a block is a different scenario, still above 8,000rpm in a K24 is dangerous piston speed zone mixed with the increased stroke (that great than a Viper or Z06) the friction on the cylinder walls from the pistons's skirts is intense due to increase piston rod ratio. The K24 is not a long rod engine, it never was designed to be one. Driving it like one is what "we" are saying not to do.
 

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The DC DIC neither have insane amounts of duration nor lift.

The DC3.2 are a different beast altogether.


Still power is flat from 7500, so litte point reving beyond 8.
 

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Discussion Starter · #13 ·
Yes I gather now that my engine won't flow well enough to warrant being revved over 8k, nor will it have the reliability I desire so I'm going to take yalls advice.

The DC DIC neither have insane amounts of duration nor lift.
For cams that require no spring upgrade they are pretty aggressive @295 high cam duration. The theoretical max power achievable through these cams is 343whp, just shy of the 3.2s estimated 357. To me that's incredible for an $800 camshaft. Maybe not insane but incredible. Gotta love Drag Cartel :)
 

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Light Rectangle Azure Slope Plot


That looks decent to me for a drop in cam. 250 wHP will go like stink. Go for it... and keep that limiter at or below 8k on cast pistons for a k24.


The duration does not necessarily warrant upgraded springs, it is the lift. Stock springs coil bind at some point as lift increases. 12.7mm seems to work for drop in cams. Schrick even went to 12.8mm on stock springs. Toda A3 with 13mm lift already require upgraded springs. I think 12.8, maybe 12.9 is about the limit for stock springs.
Of course, combined with steep ramps on the cams, you might also need different spring characteristics. But duration alone is not an issue for the stock springs.
 

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Will a high-zinc oil like VR1 prevent some of the high rpm wear? Zinc supposedly forms a sacrificial layer between metal parts.
ZDDP additives supply a sort of extra low wear layer of some 1/1000 mm. This is especially helpfully at cup tappet systems. The Honda iVTEC system has rocker roller followers, which has much less friction in the system as the cup tappet system. These is the field were emergency lubrication is normally found first. The Honda K-series is not affected by this as long as spring forces are not too high and lobe profiles are not to bumpy. Skunk2 Tuner cam lobe proves in at least their version 1, that engine speed can't be the only wear parameter of the lubrication system weakeners. There bumpy design and low material quality caused cam lobe wear when higher spring forces were used. This was found on other brands too. Some changed to forged materials to get rid of such observations and is mostly standard now.

When we talk about preferable redline levels for engines not only the valvetrain is a limiting system, which is at a 99 mm stroke engine by far not an issue when well chosen, also the crank assembly can show wear and overloading of different kind:
  • overstreching of parts like rod bolts
  • overloading of oil films especially at the piston pin and journal bearing at TDC
  • excessive liner wear because of side forces in combination with clampy piston-liner-clearances
  • overloading of parts due to inertial forces
  • excessive vibration forces due to imbalanced oscillating masses
  • ...
I hope you understand my wording, some of them are wordily translations from German to English. Please ask me if you have no picture in mind of one of my points because of that. A few of the listed points can be extended regarding durability by the right oil additives. Liner wear is one of them. But to make it clear, adding ZDDP comes with some disadvantages and without the right base oil it doesn't mean it adds wear reduction functionality. I have tested some low ZDDP oils with better results as highly containing ZDDP oils. Among them Amsoil SS 5W30, Ravenol VSW 0W30 and newest the Quaker State Full Synthetic 5W30. The wear measurement results are better compared to the Motul 300V 5W30, which has a very high ZDDP content. As most customers also use a race CAT and I like fair emission reduction not only for single testing, I recommend them to use one of the lower ZDDP oils with very good durability results on non-tappet engines.

What oils additives can't do is reduction of force induced wear, and here the 99 mm stroke engine has some bigger disadvantages. Most race guys balance from cylinder to cylinder, but only a few of them balance the oscillating forces, which is quite a challenge on the higher stroke. On the plus side the forged crank of the K24A2 or A3 is quite a pice of cake, very precisely finished regarding coaxiallity and small tolerances of dimensions, but the inertia caused forces rise up fast when engine speed increases.

Durability has much to do with built quality = clearance design for the application and material choice beside the system immanent manners like stroke length. To give you an example what else is system immanent. Even if you keep the rod bolt tension the same, which is on length depended equal weight rates around 800 rpm less from 86 to 99 mm of stroke, the side force increases about 10 % at same VE. But note the VE of an 99 mm stroke engine is system immanently higher compared to an 86 mm engine at same engine speed when alternation of load parts are adapted. So assume around 15 % increased side load at -800 rpm compared to an 86 mm engine. Oil additives and the right base oil my help there.

If one pull the oil pump integrated balancer the oscillating forces get more free and causes multiple effects of wear in addition, just by the fact the engine vibrates harder. But, one has to pull it because of the balancer forces itself, which causes effective vibration on the balancer itself and can destroy it's bearings or integrity. So if one wish to exceed 7800 rpm for e.g. racing no balancer is better then with balancer in respect to durability. Of course one can spin - how do native speakers say it, the shit out of - it over 8500 rpm to regularly at 9500 rpm, but the lifetime of engine will be on an immediate risk of multiple causes. Think of 8 to 9 tons of piston weight only which need to be pulled and pushed (a bit lower) every rotation of the crank around. Fatigue is always a question of load and amount of cycles. Accordingly parts will fail and damage other systems of the engine too (imagine a journal bearing seizure and wear -> change of deck height -> piston to valve contact -> eventually a rod and valve deformation, other path would be additional vibration induces deformation of the already overloaded rod and so on).

Finally no clear answer is possible, therefore I described a few of the possible paths of engine wear and damage caused by engine speed levels exceeding the rational. The rational is typical around 7600-8000 rpm, depending on load and amount of cycles at that load. But what rational means is individual, some would say every year a new block is normal for a street warrier who does drag racing on street on weekends. Let's say 40 pulls a week on 20 weeks for redline near time of 2 seconds with 2 shift events gives us 3200 s of highest loads. A track car, which runs e.g. on Green Hell would see a similar high load time on two track days only. Let us assume the engine blows up after that you see a WW engine which is expected to see every year a overhaul a track engine likely is not expected to have an overhaul just after double day action weekend at Green Hell. Therefore the redline has to be adapted to the application and acceptance for the lowest overhaul intervall. Just simple like that.

BTW, most Green Hell drivers set engine speed limit of their 99 mm stroke engine to 7800-8200 rpm. Some to 8500 rpm, but think of that, hobbyists don't run every weekend ;).
 

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Discussion Starter · #17 ·
Thanks for the well thought out responses everyone. This motor is still being balanced and honed by the machine shop. They have been in business for 40 yrs so I expect this motor w an 8000rpm rev limit to last me at least 150k miles. Seems reasonable given there are stock k20z3s pushing 250k.

Last question just for fun: on an imaginary dyno that registers 235whp on a straight k24a2 full bolt on pump gas (typical I'd think), what are yalls predictions for my builds power? I will be posting the results in the coming weeks so it will be interesting to see who has the closest guess.
 

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Thanks for the well thought out responses everyone. This motor is still being balanced and honed by the machine shop. They have been in business for 40 yrs so I expect this motor w an 8000rpm rev limit to last me at least 150k miles. Seems reasonable given there are stock k20z3s pushing 250k.

Last question just for fun: on an imaginary dyno that registers 235whp on a straight k24a2 full bolt on pump gas (typical I'd think), what are yalls predictions for my builds power? I will be posting the results in the coming weeks so it will be interesting to see who has the closest guess.
My guess is 265 whp given the extra CR and drop in cams 👍
 
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