Would this be safe ??

S

SuperCoupe007

Registered User
Is 9.6:1 compression too high ???? i'd probably run between 13 ~ 15 BOOST.. run a good head gasket as well as an ARP setup, what do you guys think ??? oh yeah stock its a 8.2 ratio...
 
From the looks of the opinions I read in a post the other day I think that will require some pretty high octane fuel to prevent detonation, especially in boost. The compression could almost double under full boost.
 
hhhmm so i guess if i went with a 9.6 comp ratio, i'd be asking for some serious trouble.... guess i'll have to go lower.. any suggestions ??? i want to raise the comp ratio from 8.2 to a hight safe ratio, what type of pistons would you guys recommend ?? .. thanks..
 
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generally it is 1 compression point for every 3lbs of boost. So you would be around 14:5:1 - 15:5:1 under full boost.
 
id say 9:1 is a nice ratio...You might need an EEC tuner or something to help with a new timing curve however. You also may need to play with boost.
 
actually 8.2 is great compression . the lower the compression the more air volume you can cram into the cylinder. = more power with blowers its volume of air as the blower will cram in what ever it can so more room for fresh air fuel more power. we only use compression to give us a better idle off idle cruizing power. while not under boost for all out power we can benifit from lower compressions and the added air fuel charge. :eek:
 
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Lets just say I made a substantial amount of hp by moving my compression from 8.0 to 9.0...Was with a v8 and a small ROOTS blower...Being the M90 only flows so much..The added compression can help with power output..Not saying Mannys wrong..But with our poor flowing blower..I feel a higher compression would be benificial..
 
higher compression ratio means you need higher octane to resist pinging "detonation"

compression is nice, but volume is where the power is,
you can compress 1 cubic inch of air fuel into a 14-1 ratio and it will give ,
X amount of power given you have the right fuel to resist detonation.

but when you supercharge you cram 1.5 cubic inches of air fuel into the same area more power per cubic inch .

now lower the compression and you can cram 2 cubic inches of the flamables into the chamber more fuel air more power.

a gas engine will run on as little as 4-1 compression .

you take the chamber volume and the piston hight , it gives you a definite volume of air call itKaboom now raise the compression now you have less room forKaboom so less Kaboom =
less power ,

now lower the compression and you can fit more of the famed
Kaboom into the chamber making more power x amount of Kaboom makes x amount of power more room for Kaboom more power to be made.
 
Manny I gotta meet you oen day you crack me up..Important to note though also that I didnt add..

Low RPM Drivability will decrease with a lower compression

9.0 to 1 is a happy median
 
Its all in the shape of the combustion chamber fella's.
With the right shape you can run darn near any comp ratio you want.
Do research on "Soft head technology" ;) :D
 
my car

I'm running 9:1 compression on my set up and pushing about 17lbs of boost through the car. I only run 93-94 octane. You can always lower your timing via eec tuner.
 
yes we know that low end drivability deminishes with lower compression ,
but 9.1 is rather high. ford did a good job with the 8.2 on the sc. a good compromise. for a street engine.

for a race car yes more compression will boost low end power.

but most here are street drivers and need a engine that will run on junk gas,
as the rm2 bs method of rating octane is for the most part bs,

and 9.1 compression may not be the best for a car that already needs gas better than we can get at our local gas station. once again on a race car who cares we can use high octane.

now im going back to my tech talk like Kaboom

and Vooorrrrooooomm
 
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I was wanting to find a good efficiency number for the eaton m-90 and then run that amount of boost and up the compression to a near max level 93 octane would support. That would be the best way to do it. If we have a properly sized SC or turbo, then Ya you want it low.

Planing the heads and increasing the bore will increase compression some. That is about all I would do. You want the intercooler to do its job and have some heat to disapate. With a 9.6 Cr I would think you would be lucky to run 6psi before ^^see mannys post
 
HHmmm thanks for the inputs guys... I am glad i asked, otherwise my investmenat would go "KABLOOOM"... and that would be no fun.. :( OK... what if i were to use the pistons for a 8.6 comp. ??? (like the 94-95 SC's) ????? or should i defenitely just go with the 8.2:1 comp.. thanks guys...
 
My swb went 20psi with no detonation that I know of. :cool: Of course with the M90 the Cougar used to detonate like crazy with only 13psi. Hmmmmmmm.....
 
boost compression ratio is going to be different from a N/A motor with high compression. Tell all the 03 cobra guys about kaboom.
 
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