KompressorLOgic

iTrader: (6)

i have an 87 t2 with full 3" exhaust, and TID mod, ported waste gate ,
i have the rtek 1.7 with the 720 injectors , and its designed for a s4 engine,

ive heard of a few people doing s5 block with s4 manifolds with that setup,which has higher compression and a slightly better turbo...


would the s5 short block with all the s4 parts on it, cause a lean condition with the rtek maps?? im not sure what would actaully happen, as i dont under stand how the computer works exactly....

the thought allways kind of worrys me that it might run lean with that motor....

reason i ask is im having a hard time fiding a good jdm s4 motor in my area, but i found a few really nice s5 ones..... rebuilding isnt a worthy option for me is all i can say.....

jacobcartmill

iTrader: (6)

the ecu is going to supply enough fuel for an engine running 8.5:1 rotors. the 9.0:1 engine is going to make more power, have a better turbo, and need a little bit more fuel per the same boost as the 8.5 motor.

so yeah, i'd guess it would be maybe a little lean. just put a wideband on it to verify

NZConvertible

Compression does not affect mixtures, so a wideband won't show jack. With higher compression the same amount of air and fuel goes in, it just gets squeezed a bit harder. The reason you may need to increase fuelling is that more compression generates more heat, which increases the chance of detonation. The extra fuel is to absorb that heat. But in this case the compression increase is small (~6%) and unless it was on the verge of detonation before it's unlikely to be a problem now. If you've paid attention to keeping intake temps down (cold air intake, FMIC) then the detonation shouldn't be an issue.

jacobcartmill

iTrader: (6)

*verify that with an EGT gauge

NZConvertible

Verify what exactly?

RETed

NZConvertible is right.
It's a compression ratio issue - not an AFR one.

Going from 8.5 to 9.0 isn't that bad, and I doubt you'd run into any problems.

Nothing that premium pump gas can't fix...



-Ted

KompressorLOgic

iTrader: (6)

do s4 and s5 have different timing settings??? im wondering if droping the cas back a few degress would put me more in a safe zone..
i was planning on running 10-12 psi with this setup.... but i worry about detonation


i allways use premium anyway.....
anyone using this setup to confirm??

Nismo Convert86

iTrader: (7)

with the rtek anything over 9psi it automaticly retards the timming, i can't remember if it's 5 degrees or one....

jacobcartmill

iTrader: (6)

that the EGTs raised due to the rise in compression all other things equal

NZConvertible

technically it would make it safer, but it would also defeat the purpose of having higher compression, since it would negatively affect engine performance at all revs and loads.