Ba82Ep3 (et al): K24 from a K20?

[Hasbro]

As you know, I'm a bit behind the motor knowledge curve and I'm sure this is an old topic. I was thinking how the piston speeds of a K24 were so high and was wondering if it would be beneficial to bore out a K20 to it's maximum, say, to a 2.4 level or whatever. More cubes without the piston speed but with higher rpms and more torque. Is this done?

[lemonhead228]

haha yea i seen youtube vids of the guys in japan boring out type R motors to 2.4. Pretty sick

ima try to find the vid for you

EDIT: http://www.youtube.com/watch?v=RwRiPF_Qpcc

the fit is sick! lol All of them are k24

[lemonhead228]

Where you wanna rev a k24 to? The limiting factor is the rod bolts. They are limited 8500 rpm MAX but thats pushing it. 8k-8.2k rpm is a safe spot with an k20a2 oil pump. But there's a guy on k20a.org his sn is sicksliver_ep3 and had carrillo rods and rev his k24 to 10k no problems. Well of course he has done more things but you get the point. Kinda pointless reving it that high with no cams to back it up lol

[Ba82Ep3]

The k20z1 block im building now will be bored for 87mm (k24) pistons. Why am i going to an 87mm bore in a k20 block? I have a k24 head. The combustion chamber is larger. The larger surface area of the k24 piston will give me the CR i lost by going to a head with a larger combustion chamber on a k20 bore/piston.

The power is in the stroke, not the bore. So you would gain more going from a 2.0 to a 2.2 liter with stroke (lets say for generalizations sake the 2.0 is 86mm stroke and the 2.2 is 88mm stroke, both 86mm bore) than if you achieved the same 2.2 displacement with a larger bore and the same stroke.

As mentioned, k24 piston speeds are greater because of the stroke difference so rod strength and rod bolt strength become important factors. Bore isnt really an issue (generally speaking) unless you choose a hefty piston (lighter pistons make rods/bolts do less 'work') If you choose the better of the OEM rods/bolts (k24a2/TSX) then you can rev safely to 8000rpm (assuming your setup even makes power up there).

If you start with a k24a1(CRV) or k24a4(Accord) short block you save some coin... but only if your original goal is to build something 'new' or better than what a stock k24a2 (TSX) could give you. The weaker rods/bolts of these two short blocks would limit your safe rev limit to 7500rpm... but again the setup needs to make power up there to even bother revving that high. With the lower CR of both of these blocks, 7200rpm on stock cams and your everyday bolt ons is really all you will need to rev to. This same theory applies to hybrid k20a3 setups...

[Ba82Ep3]

... and tying in that thought... when i built my hybrid k20a3 i was reasonable with my expectations knowing the purpose of each part chosen for the setup. I knew the k20a3 pistons wouldnt offer near enough CR once i dropped on the k24a1 head. Thats the primary reason i used k20a2 pistons, one gain balanced the other loss. I also knew the purpose of the k24a1 head... midrange, not top end, its known to make less power after 7000rpm than a k20a2 head. Odds are my peak power would be around 7000rpm... and this was the case on the dyno this past week... peak power being at 6958rpm with a 7200rpm rev limit.

So, why did i use flipped pin VTEC? With the greater volume of air in the combustion chamber, since one intake and exhaust valve ride on the VTEC lobe all the time, i hoped the k24a1 head would make use of it part throttle and net me a fatter midrange than a regular k20a3/a2 setup could... and without k24 weight and install issues (hood clearance/header clearance) common with swapped cars. Admittedly these are all small and rather minute differences to some, for me they were everything... and a sizeable amount when combined as a whole.

Now that i have a baseline with the initial setup, i can begin to take advantage of the large gains i will see with exhaust and intake changes. And i fear as much as i WANT to go turbo... a supercharger will work best for my setup and its intentions. I already have power... its the powerBAND i want to control and suit to my needs. I feel the turbo will just be too much too fast with each press of the gas and hard to control for consistent power delivery and ultimately... supreme corner rapage. Lap times are measured in tenths... you can lose a grip of those with excessive wheelspin... in just one corner...

[Ba82Ep3]

... so now that i have found my setup meets my expectations without spending an assload of money on it... the next block is being prepped for all out durability and abuse. k20z1 block/crank/rods (balanced) bored to 87mm with 12.5cr Supertech pistons. This is with the intent of boost... otherwise the piston CR might be 13.0 with flat faced valves for 93 octane.

The more i look at the dyno info... boost will likely be in the form of supercharging... and i may spring for the RSX-S manifold so it will make solid power all the way to 8000rpm with a cooler/less turbulent intake charge.

Sorry if i rambled... but picking and choosing what will work best for you comes to knowing what you want. Ive been through too many engine setups and freely tuned other peoples cars with different setups just so i could learn what each one was like... to make a solid choice of what i wanted. :mwink:

[Hasbro]

:msmile:

My head hurts. I need to go back over your emails again to see how this compares to above. It's almost unfair that they weren't published on line for others to appreciate.

[Ba82Ep3]

Thats what were here for... one big (kinda lol) happy family!

I would like to say that i REALLY wanted a 2.0 block bored and stroked to a 2.2, as that would be in my eyes the best compromise in generated TQ, power, weight, and fitment (the 2.4 really does make a little too much IMO... but that also involves a transmission gearing/FD choice conversation). BUT... the cost and need of aftermarket involvement went against the grain (for me). The route i chose was inexpensive, parts were readily available and will be for years to come (considering the economy condition), and it didnt require an assload of machine shop involvement. Win, win, win. lol

[lemonhead228]

Thats what were here for... one big (kinda lol) happy family!

I would like to say that i REALLY wanted a 2.0 block bored and stroked to a 2.2, as that would be in my eyes the best compromise in generated TQ, power, weight, and fitment (the 2.4 really does make a little too much IMO... but that also involves a transmission gearing/FD choice conversation). BUT... the cost and need of aftermarket involvement went against the grain (for me). The route i chose was inexpensive, parts were readily available and will be for years to come (considering the economy condition), and it didnt require an assload of machine shop involvement. Win, win, win. lol

oh is that so?? hahah maybe for your ride since its so light but on the ep i think it's perfect

[Ba82Ep3]

LOL

Agreed, the EP is heavier... and a k24 is the easiest way to get her to get up n go. Throwin more power at the problem always seems to solve it.

By all means dont be afraid to try a k24... we all need to find what WE want in our own car (especially as a complete package). For me? I spent more $ trying to keep front tires on it... even when the k24 in my EP wasnt supercharged. I would buy two pairs of fronts to one set of rear tires. It was pointless to rotate them because i would just end up replacing all four tires. lol I think solving traction issues should be a primary goal for all FWD chassis, not power.

Admittedly, if i could easily fit a k24 in my chassis i would have kept it for my EJ... and went a different route for the trans and FD. I dont think i would be as happy with the end result though.

[Blah1219]

Ba82Ep3; Very knowledgeable. Most of my info for my build came from him. I specificly went with the PRC IM and k24a1 head for mid gains, and the k20z1 short block interals for the strength and a bit high comp. I was going to go for the PRC pistons, but there were none on the market at the time. The 70mm throttle body to compensate for when I go vtec killer.

But on the side note, I'm really get the itch to go with another k20 build, but this time with a f22c crank, custom rods, k20a pistons and blah blah blah