just wondering how much of a static compression ratio can you run before having to run premium 93 octane. somewhere around 10:1???

 

up

 

Bump.

 

There is no set maximum compression ratio. The tune, cam profile, chamber/piston design, etc. all affect the minimum octane rating you should use.

 

ok then looking more generally. iff you go buy a new car, at around what comp. ratio do they start saying you need to put premium fuel in it?

 

Let's look at it from another angle: what are you trying to accomplish?

 

b20 with bolt ons in my daily driver what compression for pistons can i use. basically can i get away with 10:1 or so without premium gas

 

you can use any gas you want, hell you can use 85octane and 10.5:1 but your gonna take a power hit your gonna have to retard the timing so much.

best thing, talk to your tuner, but honestly stop being a cheap bastard! dont build a car your trying to make fast with the intention of using crap gas.

 

im not trying to build anything fast. i already have a car that goes plenty fast, this was just something to replace the 185k ls motor in my daily driver to perhaps have a lil more tq to make daily driving a little easier with large hills and ****, considering i drive over a few thousand foot elevation mountain every day to work.

this thread was taken out of context, and its original title probably should have been around what compression ratio do car companies recommend premium gas. it was just curiosity

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">
this thread was taken out of context, and its original title probably should have been around what compression ratio do car companies recommend premium gas. it was just curiosity</TD></TR></TABLE>

well every car company is different, evos have like 9.X:1 compression and there service manual says to use 94octane while honda fit is also around 9.x:1 and there manual says to use 87. its just not that cut and dry.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">what compression for pistons can i use</TD></TR></TABLE>
What will be the design of the piston face? How about the combustion chamber? What will be the piston-head clearance?

Like I (and others) have said before, there is a lot more to it than static compression ratio.

 

OP what motor do you plan on putting in your daily? i think this can help us a bit more to get you what you want, i understand your desire for a bit more grunt on the hills. what ecu will you be using? factory ecu or something you can tune?

from what your saying i think you would be most happy using an LS motor with a GSR trans and stock LS ecu... or LS trans if you drive on the HWY a lot.

 

ah probably pick up a b20 for it. replace the intake manifold with an aftermarket one and then the normal bolt ons. id really like to use stock ecu just for no worries, it has to start at 5am when its 3 degrees outside.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">ah probably pick up a b20 for it. replace the intake manifold with an aftermarket one and then the normal bolt ons. id really like to use stock ecu just for no worries, it has to start at 5am when its 3 degrees outside.</TD></TR></TABLE>

**** then just do that, a stock b20 should be more than adequate, you dont even need bolt on parts. rock it stock with a stock ecu and GSR trans, you will have ZERO problems going up hills

 

Well it seems as if an implication should be made, a 10:1 compression ratio is certainly not stock on a B20. So, you're going to make limited power on 87-89 octane versus 93 octane with a higher compression piston, depending most importantly on the tune.

And the reason why an EVO asks for at least 93-94 octane fuel, is due to the fact that it's boosted and that's what the engine needs to run properly.