Ok, if you know your Honda’s pretty good I’ve got a good question for you.
I’m talking D series SOHC stuff, no DOHC ppl please, you will only make it worse…
The D15B3 carb’d engine is listed at 9.9-1 CR. Where does that engine get all its compression ratio from, mostly pistons or mostly the head???
After the question is answered, I’ll have another. Thanks!
zerodaze is your man
I believe that was from the pistons, but I don’t remember it being that high. Keep in mind D15 pistons are different from D16 pistons. They have different wrist pin locations.
The early SOHC heads were all the same, and only the cam was different based on what model you had.
most the heads are the same except the obd2 all have squared off combustion chambers which bump the compression (similar to gsr head)
its definetly in the piston, if you want a high compression d series i would get the d16a1 pistons (from 88ish d16a1)
Thank you!
Like Earl mentioned, if you go with a1 pistons make sure you pay attention to what year you get. They changed the when they went from the zc to the sohc. Make sure you clay it just to be safe. The valve reliefs don’t line up perfectly, but there are a bunch of guys running the setup with no issues.
You could also run a set of GX pistons if you wanted to get silly with the compression. You would need after market, or machined ls rods though.
Thanks for the info!
What I’m really looking for is THE piston that I can drop into a z6 on stock z6 rods to up compression ratio, while still being able to run it on a stock p28 ecu.
Either of the A1 pistons should work. I assume this is for circle track car.
Use the earlier zc pistons if you can find them.
yup, circle track car.
they are p29 pistons if you want the honda code for them fyi
and are you allowed to run a programmable ecu for circle track or racegas for that matter?
High Octane yes, ecu no.
so you think you can get by with just high octane and only base timing adjustment? if thats the case i wouldnt go very high unless the motor is strictly disposable
what would you suggest?
i couldnt really tell ya, but i know 12’s compression isnt the easiest to tune with a programmable ecu, and if you can only run stock header etc the high compression wont help much if you cant get rid of it or get enough air for it
the motor can only flow as much as its worst part allows, so basically what im saying is that maybe a lower compression motor that you can adjust timing through the dizzy to fully take advantage of the race gas might be your best option
Hmm, I see your point, so maybe I should pass on putting higher compression pistons in the motor then huh?
if you have to use stock header etc then ya, i would update to the y8 header though (better flowing stock) y8 intake manifold
what head are you using, im sure a little higher compression wont hurt, maybe mill the head a little bit
i would do:
itr intake tube/filter
y8 intake manifold
z6 longblock
shaved head to bump compression a little bit
y8 exhaust manifold
no exhaust
then i would just adjust the timing through the dizzy to take advantage of the high octane gas (check plugs etc and run a 6 series plug to start out)
def use a z6/y8 trans for the shorter gearing
The y8 intake manifold wasn’t better flowing, it just had a larger plenum. Both it and the y8 head were designed for more swirl… for a performance app, I would stick with the z6 runner. They were a little longer and fatter, but the plenum was a bit smaller.
Can you use any honda injector? I can think of a couple of sneaky ways to get more fuel into the engine. Timing shouldn’t be that big of a deal as long as you stick with the P28. The maps weren’t very aggressive to start with.
I suppose we could use a different size inject, as long as they are honda injectors and I didn’t have to modify the harness or fuel rail… .
honestly with these cars and from experience on my friends car like this i would say keep it simple and reliable, in a honda chassis with the right trans(ex) you shouldnt have a problem being faster than most out there
from what we have done it seems that gearing as well as proper tires will help more than a high hp motor that will make it harder for traction