I'm an NA junkie. I used to be all about FI, but tastes change as does everything. Now, given that i live in an absurdly hot climate (las vegas) and I'm limited to 91 octane. What is the highest (read: safest) compression I could get away with?

I'm not an idiot, I'm not trying to get away with 13:1 or anything, but does 12:1 or something like 11:7 sound reasonable. The last thing I want is detonation you know?


any help is appreciated.

 

I don't think I can see you running 12:1 on 91 octane fuel. I can't say that I'd be certain about it, but If I had to make an educated desicion..I don't know that I'd push it much over the 11.5, maybe the 11.7 mark on 91 only.

 

i think it really depends on how you tune the car. I think anything's possible but you are limited to the power you can run due to the lower octane numbers. Get a good tune, i think you can stretch it out and run a pretty high compression.

 

a better flowing head also helps with decreasing detonation. you can probably get away with bumping up the compression alittle with good head porting. bump up the fuel pressure some. ignition and cam timing adjustments etc.

key--->TUNING

--just my 2 cents

 

The JDM F20C runs a 11.7 CR and with aftermarket head gasket will raised the CR to 11.9:1. From my experience, you can run 12 CR with 92 bump gas but anything over then you have to consider to back off the timing cuz this will cause the engine to ping or knock if it's too lean.

Basically, proper engine set up + tuning.

 

When i had my gsr, i was running around 11.8:01 compression and i live in socal where we have 91 gas as well. Like people said, its all in the tuning if you want to make it work. I will have to say though, i probably could have made more power if i lowered the compression a little more so it would have allowed me to run a more aggressive tune. High compression and 91 octane just isn't really easy to tune and doesn't give you that much room to work with.

Another thing to consider with your tuning is that if you tune to the max so that it doesn't detonate, that doesn't mean you will never detonate. Even when my car was tuned, it would detonate slightly whenever i would blip the throttle. On extremely hot days, you might experience detonation that you wouldn't normally on a normal/cool day. A bad tank of gas would do the same trick.

So my answer to you is, yes you can run 12.0:01 compression, but with a very mild tune. I would recommend running a more aggressive tune on a lower compression. That might yield better results .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StinkyTofu &raquo;</TD></TR><TR><TD CLASS="quote">

So my answer to you is, yes you can run 12.0:01 compression, but with a very mild tune. I would recommend running a more aggressive tune on a lower compression. That might yield better results .</TD></TR></TABLE>

nice. thanks for the info man. and thanks to everyone else that replied

 

its been said already...but yes, you'd be surprised what you can do w/ proper tuning (particularly w/ a standalone)

 

yeah, AEM EMS is definitely part of the equation. not looking forward to that tuning bill though, haha

 

like everyone else said, tuning is key. What will you use the car for? daily?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vapor &raquo;</TD></TR><TR><TD CLASS="quote">like everyone else said, tuning is key. What will you use the car for? daily? </TD></TR></TABLE>

yep, daily driver.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by alex_b &raquo;</TD></TR><TR><TD CLASS="quote">

yep, daily driver.</TD></TR></TABLE>

since it's daily, don't raise the compression too high, high octane gas (100+) isn't cheap.