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Discussion Starter · #1 ·
I just wanted some opinions from people here that have had experience building motors (ie pacman, brian g, etc). Im building a daily driver setup. Looking at 12.5:1 compression, crower full race cams, crower/eagle rods, planning to balance/knife the crank, blueprint the block...that sort of stuff. What i really want to know is it worth using the k24 block & crank, over the k20 motor...the reason i say this is that would a motor make more power from a k20 @ say 10000rpm over a k24 @ 8000 with the same build listed. I would think that the k24 would have better midrange, but i just wanted input from everyone else...im thinking the k20 would make more power based on this:

a k20 makes about 150 lb-ft, and from some articles i came across k24/k20 made 180 lb-ft

now 10000 * 150 / 5252 = 285
and 8000 * 180 / 5252 = 274

is it wrong to base the power like this? can someone please correct me, thanks.
 

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Big bore goes with big valves and BIG rpm. The F1 engines are running bore/stroke ratios around 1.6, a 100mm bore and a 60mm stroke (just an example),..... This allow them to cram several large valves above the bore. Ferrari did 5 valves several years ago. This coupled with their springless pnuematic "springs" helps to allow 17,000 rpm now. And a power band as wide as a hummmingbirds beak.....


I have had bore motors and I have had stroke motors, and in my opinion, for a regular driver, nothing beats a stroker motor.... Stroker motors produce awesome torque and are so easy to drive. The leverage of the crank will effortlessly pull the car around everywhere, and will pull stock gears or a heavier car with little effort. Further.....,
you can get away with more cam with a stroker motor...


Engines that require you to wind them out into the higher rpm to produce power tend to wear out faster, and can be a bit tiring to drive on a daily/regular basis. It all depends on what you want out of it.........

"There ain't no subsitute for cubic inches"

This very true for street engines, and "the longer the stroke, the more the poke" :wink:


If you think about the actual physics envolved a longer stroke does more work for roughly the same amount of energy.......


K24 is the way tooooo goooo...

Look at Skunk, ME :p HEHHEE, BISI, and others...What do you think they have...? :wink:
 

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Now the question i have is, with the increase amount of revving that the k24 block is going to see. How long will it last, and when you rev that high with that long stroke how does piston speed come into play with reliability?
 

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Discussion Starter · #4 ·
thanks for the advice...i was wondering if you could help me with something else. I found this article:

http://succ.shirazu.ac.ir/~motor/page7f.htm

It talks about tuning the intake and exhaust manifold. I was wondering if you would agree with this article? When i tested it out (there is also a applet) with a temp of 323 K (or 50 C) and it says that the intake runner length should be 30cm at 8000rpm. Is this correct? 30cm seems kinda long? Any thoughts about this...thanks, I apprecaite your help. :D
 

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http://succ.shirazu.ac.ir/~motor/fluid/pipe/pipe.htm

Put this For the INTAKE TEMP 313.7

Then for the EX TEMP 593.15...


Mine says 10.485 inch so close

Yours is 11.725inch


Temperature conversions between the three temperature scales:
kelvin / degree Celsius conversions (exact):
kelvins = degrees Celsius + 273.15
degrees Celsius = kelvins - 273.15
degree Fahrenheit / degree Celsius conversions (exact):
degrees F = degrees C x 1.8 + 32.
degrees C = (degrees F - 32.) / 1.8
 

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There are 3 main factors in determining just how big is "too big".

1. Cylinder displacement. In reality, cylinders of up to 900-1000 cc are quite doable without any reliability or manufacturing issues.
However, most designers shoot for cylinder sizes of 500-600 cc max
if they're designing a high performance engine. 8) Smaller displacement per cylinder tends to be more efficient when it comes to power production (and sometimes economy). Currently, when it comes to car production, Honda's biggest cylinders are indeed, right under that 600 cc limit (K24 at 587 cc, J35 at 583 cc). .......

2.Ok let's talk about Bore size - Generally a bigger bore allows for bigger valves, which means the engine is capable of breathing better, particularly at higher rpms (read good for high rpm power). However, for a given cylinder displacement, a bigger bore also makes it difficult to achieve higher compression ratios without a significant piston dome - this can inhibit flame front propagation and therefore combustion efficiency. Additionally, the time it takes for the flame front to cross a larger bore is, naturally, longer. Therefore, more ignition lead may be required which reduces net work done by the cylinder. That said, bore sizes up to 100 mm are not unheard of and can still achieve excellent power efficiency (see Porsche 911 3.6 engines for example). ECT>>>>>

3. Stroke - This is probably the one to be most concerned with when it comes to discussing the J-series family future. A longer stroke motor puts more stress on rods, wrist pins, cranks, etc. than a short stroke engine of similar displacement. The upside is that its easy to achieve good compression ratios and you can get a small combustion chamber w
ith good flame propagation
characteristics. You can also generate very good midrange torque since the long stroke (often associated with a short rod) has some effects on the dynamics of the induction system.......BLAHHHHH

Now, if we assume that the J-series can not reliably take any more bore (we know it can handle more bore by at least 1-2 mm, just not if it can meet Honda durability standards.), a 3.8 liter J-series with an 89mm bore would require a stroke of 102mm. Knowing Honda, a 3.8 might be a bit smaller (really a 3.75) which could get the stroke down in the 99-100mm region. Either way, we're talking small differences.

So, what does a 100 mm stroke (give or take) mean? Well, it means you'll have to keep the revs down. I'd say 6500 rpm maximum, and probably a bit lower. It'll also mean you'll have to step up the rod strength a bit, much like what Acura did with the K24 in the TSX. That engine has a 99mm stroke and easily exceeds 7000 rpm. To get piston speeds in a "J38" down to levels similar to that of a J32, you'd need to keep revs under 6000 rpm. Although we're more concerned with piston acceleration, which means you could bump the engine speed up a couple hundred rpms more. Call it a 6200 rpm rev limiter. With lighter weight construction in the pistons/rods, stresses could be kept low, but costs would go up.

BTW, the K24 does use balancers. Any time a 4 cylinder starts to get above 2.0 liters, second order shaking forces start to become objectionable. Hence the shafts in the H22A and the K24. A 60 deg V6 is better balanced to begin with, so fewer issues to deal with.

Whether Honda goes to a 3.8 liter for the RL remains to be seen. I'd rather see a V8. Or maybe Honda engineers will squeek out an extra 1-2mm of bore and bring stroke down to a less extreme level. An increase to 91mm would allow a stroke of 96-97 mm without difficulty - not too much more than the current J35. Hopefully we'll find out soon enough. :wink:
 

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Professor15 said:
Now the question i have is, with the increase amount of revving that the k24 block is going to see. How long will it last, and when you rev that high with that long stroke how does piston speed come into play with reliability?

Oh ya The K24A2 uses a 15% longer stroke than the K20A2 to obtain 18% more displacement (the larger bore helps too).

Assuming similar cylinder heads, optimized cams, etc. the primary determinants of power are displacement, rpm and compression. We can eliminate the latter in this case (although the k24 will need less of a piston dome for the same displacement - this is good for flow).

So, the K24 provides, on balance, more in displacement than it loses in rpm (theoretically, if you put a cap on piston speed). Additionally, the taller deck height of the K24 block allows Honda (should they choose) to improve the rod ratio on the K24 vs. the K20. This reduces side loading stresses, another good thing.

Additionally, the 1mm larger bore on the K24 allows Honda (should they choose) to run larger valves for improved flow. Another good thing.

In the end, I wouldn't expect a production worthy "hot" k24 to produce much more peak power (if any) vs. a hot K20. However, it will produce lots more torque everywhere below the hp peak. And in anything but a flat out drag race (and even then if you were traction limited), it would make the K24 car faster than its K20 bretheren.

Not saying it should happen this way, but the numbers are pretty self evident once you delve into them. :p
 

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Stroke (inches) 99
RPM 8500




Results

--------------------------------------------------------------------------------
Average Piston Speed 140250


Formulas for piston speed

piston speed in fpm = stroke in inches x rpm / 6

rpm = piston speed in fpm x 6 / stroke in inches
:wink:
 

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Discussion Starter · #9 ·
how did you get 10.4 for the runner length? Also, how does the volume of the plenum effect the intake? I would imagine with ITB's theres no plenum, so runner length and diameter (whether its conical or not) would play a major role...Im sure that your busy, so if you dont have time to explain this, do you know any good articles that i could read so i could learn more about intake manifold design...and also since it hasnt been discussed, exhaust manifold design? thanks, i really apprecaite you sharing your knowledge.
 

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How to Fabricate an Intake Manifold


This article details the complete fabrication process on a custom intake manifold for a developmental Mazda RX7. The basic design can be easily adapted for almost any engine design. Tools needed to fabricate this part would include a drill press, lathe, bandsaw, hole saws, files and a TIG welder. This manifold was constructed from mild steel for ease of assembly but it could also have been made from aluminum.

Basic Design

This plenum type design uses a single throttle body attached to a plenum with separate intake runners for each port. Port type injectors are mounted in each runner.







Head Flange

The main flange which would be bolted to the cylinder head in the case of a piston engine, is made from 1/4 inch steel plate to reduce warpage during welding. An intake manifold gasket can be used as a guide to trace the flange outline and mark the port and bolt holes. The flange plate can be cut out using a bandsaw or plama arc torch. Bolt holes can be drilled on a drill press. Intake runner tube holes can be done with a hole saw or plasma arc if they are not round. Try to design the port holes so that the ID of the tubing used for the runners is the same of that for the finished port size in your head. The runners should be spigotted inside the flange hole for ease of jigging.

Intake Runners
Runners are made from .050 to .065 tubing. Runner lengths can be adjusted within the space constraints to help boost torque within the desired range. Short runners are good for high rpm torque as in a racing situation. Long runners are more applicable for street use at lower rpms. For most street engines, try to keep the length from the end of the runner to the valve at least 9 inches long and preferably longer. Available space usually limits this dimension when using straight runners so curved runners using 90 degree mandrel bent tubing can sometimes be used to increase the runner length. As applied to engines with oval or square ports, you will have to form the tubing into the port shape which is considerably more complicated. Tubing should be cut off at precise lengths with a tubing cutter and carefully deburred. For maximum airflow, tapered runners with velocity stacks inside the plenum can be made if you are capable of this type of work. This is very time consuming but this design shows a 20-25% increase in flow over straight tubing runners.

Plenum, End Plates


Depending on engine displacement and the throttle body used, the intake plenum is usually constructed from .065 wall exhaust tubing in either 3 inch for engines under 1600cc or 4 inch for most other engines. Holes must be cut in the plenum tubing with hole saws for the intake runner tubes and in the case of a side mounted throttle body, for the throttle body tube also. The throttle body may also be placed on one end of the plenum in place of an end plate, depending on component layout. Our RX7 manifold used 4 inch tubing. The plenum should be made at least 2 inches longer than the dimension of the front to rear outside intake ports to allow better airflow into the outer ports. Also plan for any vacuum taps for brake boosters or MAP sensors etc. at this point.

End Plates, Throttle Body Plate

End plates cap the plenum ends and are made from .050 to .065 plate stock. Cut them out with a bandsaw or plasma arc. Make them about the same size as your plenum tubing OD. If you plan to put the throttle body on one end of the plenum, this end cap will need to be made from 3/16 to 1/4 inch plate to allow for tapping of threads to hold the TB as well as have a hole cut the size of the outlet TB bore. If the throttle body is to be mounted as in our RX7 manifold, use 1/4 plate for the TB flange. We like to tap right into the plate with fine threads for maximum strength.

Throttle Body

Throttle body choices are numerous. One should be selected which can flow the desired amount of air and fits within the space limitations. Thought should be put into the ease of connecting either an air filter or turbo plumbing to it. Too large of a throttle body for street use will often mean very sensitive "tip in" throttle response which could be annoying. There is also no need of a 3.5 inch TB when your turbo plumbing is only 2.25 inches. Getting a throttle body with a potentiometer type TPS already installed will save time and trouble. For many applications, the Ford 5L V8 and 4.6L DOHC throttle bodies work well. They are cheap, available and relatively compact. Ford Motorsport and Edelbrock make larger sizes in 5mm increments. The 4.6L TBs are very compact and have a minimal amount of extra garbage on them. All Ford TBs have potentiometer type TPSs also. Ford Explorer 4L throttle bodies can be ordered from your dealer. These are relatively inexpensive and are 65mm with minimal garbage on the outside. Put some thought into a throttle linkage at this point also.










Injector Bosses





We usually make these out of 1 inch bar stock. We like to seal the vacuum side of the injector with a 5/8 ID- 3/4 OD O-ring slid over the nose of the injector body. This will work on any standard injector. You can pull off the stock O-ring and pintle cap. Bore the bar stock to .640-.650, straight through. This allows a slight air gap between the boss and injector to reduce heat transfer and fuel boiling. A .740 counterbore, .040 deep is machined at the end for O-ring retention and sealing. We usually cut off the bosses at 45 degrees so that they are about 1.35 to 1.5 inches long. This is a good entry angle for many injectors into the runner and is an easy angle to saw at.





Fuel Rail

The fuel rail is usually made from 3/4 square tubing with a .050 to .065 wall. This shape allows much easier drilling and jigging. 1/4 inch holes can be drilled at the port spacing interval. Over top of these holes will be welded the upper O-ring bosses machined from 3/4 bar stock. These will usually be about 1/2 an inch long and have a .540 to .545 hole drilled for the O-ring to seal on. Carefully chamfer the entry side for easier O-ring fitment. End caps for the rail are made from 1/4 plate and tapped for 1/8 NPT fittings. For a more detailed description on building a fuel rail, go to the article on our tech page.

Assembly

Once all of the pieces are cut out and deburred, clamp the head flange to a scrap head if possible to reduce warpage. Carefully jig the plenum and runners to the flange and measure for straightness. Tack weld the pieces lightly and re-check for straightness. You should still be able to move things around a bit at this stage. Tack the opposite side of each joint and re-check again. Once you are satisfied, TIG weld all of the joints. Weld on your end caps and TB flange. Let everything air cool.
Now you must cut holes in the runners for the injectors to poke through. Scribe a line across the runners where you want the center of the injectors to be. Now intersect each mark on the runner with another line down the center of each tube. Punch mark and drill a 1/4 hole. Now drill straight through with a 1/2 inch drill. Once you pierce the tubing, slowly lean the drill over at 45 degrees to oval the hole. The injector bosses will be positioned over these oval holes so make sure before starting that you have enough room around the boss to the flange that you will be able to get the welder in there. Assemble the injectors into the rail and slide the bosses over the injectors. Carefully align the assembly so that the injectors are dead center through each injector hole in the runners. Clamp in position and re-check. Lightly and quickly tack each boss in position. As soon as this is completed, either pull the injectors out or water quench each tack to avoid heat damage to the injectors. Once you are satisfied that everything is straight, finish welding the bosses without the injectors in place. Be aware that the bosses must be welded in very straight and at the same depth for proper sealing.

Finishing

You can weld on bolt down tabs on the fuel rail and attachment points for the bolts on the manifold. A couple of long, 1/4 inch bolts usually suffice here. The manifold can now be thoroughly cleaned with soap and hot water, then lacquer thinner. A good quality engine enamel can be used to finish or better yet, get it powder coated.






Here are some photos of an intake manifold for a Toyota 20R for more idea









http://www.sdsefi.com/techinta.htm :wink:
 

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Discussion Starter · #11 ·
thanks for the article. I was just wondering, is there a big difference between side enterance (like regular honda) or middle enterance (seen in the article) when it comes to flow? Pros, Cons to each?

Also, i was wondering if you knew any articles for exhaust manifold design...I would imagine the basic design would be the opposite of the intake manifold; like, instead of tuning the exhaust manifold so that the pulses reach the exhaust valve when its open...you would want the pulses to reach the valve when its closed. I was wondering if you could help me expand on designing a exhaust manifold. Thanks, once again, i really appreciate your help.
 

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The Exhaust Pulse
Ok let me see here for To gain a more complete understanding of how mufflers and headers do their job...
We must be familiar with the dynamics of the exhaust pulse itself.


Our Exhaust gas does not come out of the engine in one continuous stream. Since exhaust valves open and close, exhaust gas will flow, then stop, and then flow again as the exhaust valve opens. The more cylinders you have,
the closer together these pulses run.,....

When we made our Headers we did a lot of testing..

Keep in mind that for a "pulse" to move, the leading edge must be of a higher pressure than the surrounding atmosphere. The "body" of a pulse is very close to ambient pressure, and the tail end of the pulse is lower than ambient. It is so low, in fact, that it is almost a complete vacuum! The pressure differential is what keeps a pulse moving.
A good Mr. Wizard experiment to illustrate this is a coffee can with the metal ends cut out and replaced with the plastic lids. Cut a hole in one of the lids, point it toward
a lit candle and thump on the other plastic lid. What happens? The candle flame jumps, then blows out! The "jump" is caused by the high-pressure bow of the pulse we just created, and the candle goes out because the trailing portion of the pulse doesn't have enough oxygen-containing air to support combustion. Neat huh :wink: ?


Just as Paula Abdul :shock: will tell you that opposites attract, the low pressure tail end of an exhaust pulse
will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines
Rev at various speeds, the exhaust pulses don't always exactly line up. Thus, the reason for the Try-Y header, a 4-into-1 header, etc. Most Honda headers are tuned to make the most horsepower in high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 header, such as the ones sold by Gude, are optimal for that high winding horsepower you've always dreamed of. What are exhaust manifolds and stock exhaust systems good for? Besides a really cheap boat anchor? If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! Something to keep in mind, though, is that even though an OEM exhaust may make gobs of low-end torque, they are not the most efficient setup overall, since your engine has to work so hard to expel those exhaust gasses. Also, a header does a pretty good job of additionally "sucking" more exhaust from your combustion chamber, so on the next intake stroke there's lots more fresh air to burn. Think of it this way: At 8,000 RPM, your Integra GS-R is making 280 pulses per second. There's a lot more to be gained by minimizing pumping losses as this busy time than optimizing torque production during the slow season.


Ok, now that we know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.
 

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Discussion Starter · #13 ·
wow, this thread is getting really informative. Do You actually do your designing for your header? I would imagine that you do...and since this is a competitive market...im sure that you wouldnt declose all your knowledge about tuning a header...but thats understandable. I wanted to know one more thing about the length of the intake manifold runners. Remember how I got 11.7" for the length...if i was using ITB's, would that be 11.7" to the butterfly plate, or 11.7" to the beginning of the velocity stack (and the butterfly plate is contained within it). Once again, Thanks for your help...feel free to continue with a encore where you left off about progagating forward motion in a exhaust pipe :wink:
 
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