piston?

[Adam]

i have a 97 5sfe and wanted to know if high compression pistons were safe to run with a supercharger and if so what is the safest ratio to run?

[andyman61]

uh, i think that would be a bad idea. if you're gonna run boost, you want low compression pistons, not high. the 5s-fe wasn't meant to be boosted, so you have to compensate for the added pressure by lowering the compression ratio.

[Deep]

Go for it, but spend a shitload of time/money tuning it.

[Adam]

im am swapping in a rebuilt engine and the engine that im taking out i am going to build the hell out of. i just wanted to know what pistons to go with.

[CrawlingEye]

Originally posted by Adam
im am swapping in a rebuilt engine and the engine that im taking out i am going to build the hell out of. i just wanted to know what pistons to go with.

I've been looking into pistons/rod combo's for over a week now (my plans are a built NA camry), it wouldn't be a good idea to use high-compression with boost.

A lot of people here even lower their compression to an 8-1 ratio to allow them more boost.

[zoni]

check out the latest rippmods thread in the camry forum... he talks about pistons there.

i would say 8.5's

[allblackalltrac]

Originally posted by andyman61
uh, i think that would be a bad idea. if you're gonna run boost, you want low compression pistons, not high. the 5s-fe wasn't meant to be boosted, so you have to compensate for the added pressure by lowering the compression ratio.

on the contrary....17psi @ 9:1 will make more power than 20psi @ 8:1...

the 5S is a pretty stout motor and isnt giving the credit that it deserves most of the time...

if you intend on boosting a 5S at a minimum have the con rod shot peened and polished, use ARP hardware where ever you can...

in my Corrado I run 14-15psi @ 9:1 CR....the maximum amount of boost I could run is 20psi...

here are some quick calculations

((boost psi / 14.7) + 1) x motor compression = effective compression.
((20/14.7)+1)x 8.5:1= 20.0646

((20/14.7)+1)x 8.0:1= 18.8843

((17/14.7)+1)x 9:1= 19.4081

((18/14.7)+1)x 9:1= 20.0204

((20/14.7)+1)x 9:1=21.2448

mind you it is possible to run more boost than what the given effective compression negates...enter standalone, water injection, nitros oxide, intercooler, race gas....remember as boost goes up so does the price and the likelyhood of breaking something...

for a streetable car your best option would be to run as much compression as possible with less boost...this will keep the power under the curve, which is where it should be.

[allblackalltrac]

Im currently looking for high compression pistons for the 5S as well however I intend on using a 3S-GE head so the valve reliefs at the top of the dome have to be cut different.

Anybody know of a piston manufacture that makes these?

[Adam]

i've wanting to do a head swap, but i want the ripp s/c and dont know if it will still fit the same. so im just rebuilding the engine, port and polish the head and get a valve job. ripp also made cams for the 5sfe so i'll see what he wants for those.

[luisitol]

tony has 10.5CR and he will be running upwards of 20psi. yes its the V6 but jsut wanted to pint out that high CR and boost can be done, jsut make sure you tuen the crap out of it. Try the E-manage, thats the route i'm goign for my 5sfte.

[allblackalltrac]

Well Tony has alot of money to throw at such a project.

High CR and high boost is not impossible...more improbable. Like I said more boost more money more chances things can go wrong...not everyone can afford to run around with high CR and boost. Especially when the car wasnt forced inducted to beging with...for most of us high CR and boost is an improbablility.

Effective compression(EC) is best in the 18-20% margin, by my calculations Tony's EC will be in the 24.7 range. The heat and cylinder pressures that are going to be created with such numbers are going to melt something fast. I assume he plans on using a very large very efficent IC coupled with water injection at the least to kwell some of the heat. Standalone goes without saying. This will be by no means streetable.

[luisitol]

it is true it will be very expensive but it can be done.

I think 9.5 (the stock 5sfe CR) is a good compromise between high and low CR with boost. 9.5 still leaves you some low end and also allows from some decent boost till you run into problems.

Using the EC forumula you can run 16psi and still be within the sweetspot (19.84). 16psi on a 5sfe would be a pretty quick car.

[allblackalltrac]

Yup now you know why all the MR2 guys are turbo'in their 2.2's or going 5S-GTE.

More torque, more HP, quicker spool, broder power band, more efficent.

Hell turbo'ing a stock 3S-GE will make more power than a stock 3S-GTE