just wondering what the best compresion ratio is for turbo engines, murix uses 9:0.1 and hrc sells 8.8:1 and howel has 8.6:1..... ?

The lower the compression, the bigger the combusion chamber. The bigger the combustion chamber, the more air you can cram in there. More air + more fuel = more power.

Missing Car. . .
Contemplating Turbo. . . . .

http://hometown.aol.com/ohshootuhh/

Perf:
KYB AGX Struts
Neuspeed Sport Springs
5 Strut Bars (2 F/U, F/L, R/U, R/L)
Sprint Front Camber Kit
$15 Rear Camber Kit
Corbin's A/F Gauge
MSD DIS-2 Ignition System
Some Regrind Cams that need High Compression (which I don't have)
Ported Intake Manifold
Ported Throttle Body
Nameless Cold Air Intake with a K&N Filter
Custom 2 1/2 inch exhaust with Dual DTM Muffler
Empty Catalytic Convertor
Energy Suspension Motor Mount inserts
Hurricane_GS Short Shifter
Symborsky Shift Kit
Clutchmasters Stage 3 Modular
225/50/16inch Wheels and Tires


Audio:
Alpine CD Head Unit
Alpine Flex4 25W X 4 for Fronts and Rears
Alpine V-12 450W X 1 for Subs
Infinity Reference Series 5 1/4 and 1 inch tweeter component systems for fronts and rears
Blaupunkt 3 way 6x9's in the rears
3 MTX 5000 10" 12 ohm subs running 4 ohms mono

I have 8.6:1

You've hit on a topic that many people have differing opinions on. Higher compression ratios make the turbo spool up faster and give you more off-boost power. I am of the opinion that there comes a point where you can't cram any more boost into a high-compression engine to make more power without having detonation. I believe that you should lower compression at that point if you want to build more power (of course you'll have to cram even more boost in). I think the problem arrives when you try to figure out at what point you have to lower compression ratio to start making more power (with higher boost) while avoiding detonation. I borrowed a textbook from my IC engines professor that is all about turbocharging. After I've read it cover to cover, I'll probably have a more educated opinion. I believe that OEM turbocharged engines have low compression ratios for a reason, not just tradition. It might be to avoid detonation when the bonehead driver puts in 87 octane.


Corbin

'95 ESI-T
HRC+FMIC+ETC...

Has anyone here tried using a stand alone engine management system??? I know there was a miata in SCC and turbo a while ago that was pushing 400hp to the wheels on stock internals because he was able to tune the car perfectly with the tec-2

I heard that too on a honda/acura site, they were running 27psi and pushing 350+HP on stock internals and how the hell does Stephan Papadakis run turbo on a high compressioned engine??? (and I know he is not low-compressioned)

I guess the fact that the tec-2 costs over $1500 doesnt help much though, but it would be nice if someone could find out for sure

a 350+ horse miata? dood must wanna die in that car

here's how i see the situation. the 4g63 is low balled at 7.9 prolly for what corbin said. remember this also allows them to get to 400 hp without a rebuild. hahn uses 8.8 in the same motor and car wehave and he's doin low elevens. so the question is what do you want to do with this turbo? if you wanna drag race and go as fast as possible in a straight line than drop the compression to just over 8 like 8.2ish and boost the hell outta it. if you wanna daily driven beast follow brad (super20g) and go 8.6 after all he's pacing and beating corvette's, how's that sound? as for me, i'm prolly gonna follow brad to an extent as far as compression and turbo. think i'm gonna go with an S-AFC instead of the big injectors though. i just love mitsu turbos can't help it. plus i enjoy taking turns so i'm gonna wana be able to stop pretty easy and swing into a turn without having to worry to much about breakin the fronts loose and drifting off the road

that miata was making like 398hp to the rear wheels, thats like 450 to the flywheel with just bolt ons and the EMS. It runs 10 seconds in the quarter mile.

Add me to the "Unusual" compression list. I have a 9.5:1 ratio. And no, it isn't a typo, that's a custom 9.5:1 with JE pistons. Why 9.5? I dunno, coz I didn't feel like 9.6:1. And as for pistonm clearance, well I tested my engine and it is still non-interference :-)

Actually I wanted to avoid a lag risk.... I may be going up in life turbo-size wise.

Anyways, as someone noted if OEM turbo cars come 8.8:1 then, an engine can definitely take 9.5:1 I mean OEM specs are usually over-safe for dorks that do stupid stuff like fill the wrong type of gas :-) (As Corbin already pointed out).

Also if you can somehow measure knock, you can ideally go to an insanely high compression as long as you are not harming the engine. Most Turbo 8 and 9 sec drag cars who don't declare their compresion ratios are *definitely* running higher than 9.. (I heard some Honda Unlimited class people run 11:1 with 20+lbs of boost).

As for 400hp on a "well tuned" stock-internal 420A car - sorry. It's not a matter of tuning here, it's a matter of physical capability. The stock internals can't handle it, I believe in this order: Rings, Rods, Pistons... Although any can go at any time (Blame Murphy & the laws of probability for that!) you definitely increase the chances of Major damage at that level.