What compression ratio do the turbocharged M3 owners have and what boost?

mert

8.5:1 here

8.5:1 same here

ditto, 8.5:1

you guys should specify how much boost you run... and whether you're running any kind of W/A injection...

Boris

8.3:1

I am currently running 14psi

I'm surprized you guys lower compression for the low boost most of you run... I don't know what boost everyone runs... but I'm assuming it's not more than 15psi...

I have friends that run that type of boost on stock Integra engines... (well, 10psi+)... it's all in the tuning... just look at AA's MCoupe that's running 19 or 21psi with W/A on stock internals... maybe a headgasket or something.. I know of M3's running 10-12psi on headgasket/stock internals easy....

I bet M3 engines are just as indestructable as 2JZ if you run the same compression as they do, and run forged pistons/rods... the only reason 2JZ hold so much boost "stock" is because they're forged stock... and have lower compression stock... they don't impress me that much... and they get too much credit... (although, it is deserved... I'm just anal! :)).

Boris

I agree...I am running 10-12psi in my del sol with 10:5:1 comp. I have a spare block im building up and im going with 10:1 forged pistons for it, and these are honda blocks, which everyone seems to think are the weakest things around:rolleyes: Higher compression + Big turbo = Sick power:D Lowering teh compression that much is just used as a bandaid to aid in tuning the car safetly.

There are people running low boost (10-12psi) and higher on stock compression. Usually people will opt for LCR to be on the safe side, specially those without 93 octane gas readily available. Usually the reason for LCR's is because with a higher one you are more susceptible to pinging/detonation, but this can also be remedied by retarding the timing or running a bit rich. The point I am trying to make is that your final compression ratio (i.e., FCR = [(Boost/ 14.7) +1] x CR) has to be adequate for the available fuel octane. Also, LCR's usually allows for more boost before the onset of detonation/pinging, which usually results in higher peak HP figures.

Just to give an example (Vortech compressor on both setups):

Stock CR of 10.5:1 :

Lets say we run about 8 psi of boost, this will equate to a FCR of about 16.2:1. This usually leads to RWHP figures of about 260-300 depending on intercooling/etc for S50/S52 engines.

LCR of 8.5:1 :

Lets say we run 14 psi of boost, this will equate to a similar FCR of about 16.6:1. This setup usually leads to RWHP figures in the neighborhood of 370-400+ for S50/S52 engines.

The AA MCoupe does have a head gasket to lower the compression at his boost levels and he is still with stock internals.

As for the 2jz motor, if you compare the pieces and block of that engine to the ones used in the S50 or S52 you will understand why that car is capable of the numbers it puts out on stock internals and I agree that the M3 at the same CR is capable of similar numbers, the only thing is that the chassis, subframe, and some drivetrain pieces probably wont be able to take the power without re-enforcement. I guess we will find out as people keep on pushing the envelope with these cars.

Mert: Same as you, 7.7:1.

Putting in strengthened internals should not be a detonation bandaid. If for a particular power goal/fuel detonation is getting in the way, you must lower compression. But I do agree that tuning could be better and raise this ceiling in many cases. - Beau

Originally posted by ///3oris
I bet M3 engines are just as indestructable as 2JZ if you run the same compression as they do, and run forged pistons/rods...
Boris

8.5:1...surprise. I'm currently dialed in on 10 pounds.

I tried till now 15 set ups:

Euro M3

11,3 cr 3,7 psi ASA Supercharger
10,5 cr 7 psi ASA Supercharger
10,5 cr 8 psi ASA
10,5 cr 10 psi ASA
8,5 cr 6,6 psi ASA
8,5 cr 10 psi ASA
8,5 cr 14,7 psi ASA
7,5 cr 14,7 psi ASA
7,5 cr 13 psi ASA
7,5 cr 8,8 psi ASA
7,5 cr 16 psi Vortec T Trim
7,5 cr 19-20 psi Garrett Turbo

The 7,5 cr was achieved with forged pistons bought from SPS. The damn pistons cracked with the supercharger after 1500 miles. I am shocked.
On the other side for miles and miles, 20000 miles I drove on stock pistons either 11,3 or 10,5 ( African version) and made so much detonation when I knew nothing about fuel enrichment and BMW OEM pistons were so good.

Now with 11,3 stock pisytons and thicker head gasket I ll have 10,0 cr and boost ??. I ll start with 11 psi and go up as much as possible.

I have 95 octane fuel but bought Toluene. Will mix it 40 %. Retard timing.

Thanks God intake tempearture was 48 F and ambient was 42 F. Turbo is both water and air cooled and my intercooler is very big.

Moreover I agree that it matters at the end the effective compression ratio.
You can boost at 8,5 cr 14,7 psi and get a effective cr of 17 at the same time you may boost at 10 cr 10 psi to get the same effective cr.

The best performance I ever had was 11,3 cr and 3,7 psi and 10,5 cr 8 psi. Because when you lower the cr on a supercharged engine below 10,0:1 you overrev the blower and damage adiabatic efficiency.

I tried Vortec T Trim at 7,5 cr and boosted 16 psi but intake temps were very high because I was overrevving the sc. Should you wish not to overrev the supercharger you will boost low.

Finally, the best results were taken by 7,5 cr and 19 psi turbo boost. the 19 psi was at 3 rd gear and I had no chance to look at the boost at 6 th gear cause I was playing with a Porshce Turbo and was going at 200 mph. After a couple minutes of racing the engine sound weird and we found out the pistons have cracked (damn forgeds) and engine block cracked also. ( engine block cracked cause we had sleeved it)

Today I ll get my new blocked M3 and after a 700 miles brake in Ill try to boost at 10 cr and see????

I had to use stock 11,3 pistons and lower cr with a thicker head gasket because I have no confidence in forged pistons. Maybe I had the bad quality forgeds.

200 mph might be a dream but check my videos (used to be on my website www.da-motorsport.com, now removed to another server) where the M3 was only 415 crank ho and was easily running 193 mph. I ll make mpegs of 200 + mph.

Mert

9.0:1
14psi
Aquamist
but I'm supercharged

Keep in mind CR for a turbo generating X hp should likely be a bit lower than for an engine running a centrifugal. Cylinder pressure tends to peak near torque peak. - Beau

Originally posted by mertdastan
I tried till now 15 set ups:

Euro M3

11,3 cr 3,7 psi ASA Supercharger
10,5 cr 7 psi ASA Supercharger
10,5 cr 8 psi ASA
10,5 cr 10 psi ASA
8,5 cr 6,6 psi ASA
8,5 cr 10 psi ASA
8,5 cr 14,7 psi ASA
7,5 cr 14,7 psi ASA
7,5 cr 13 psi ASA
7,5 cr 8,8 psi ASA
7,5 cr 16 psi Vortec T Trim
7,5 cr 19-20 psi Garrett Turbo

The 7,5 cr was achieved with forged pistons bought from SPS. The damn pistons cracked with the supercharger after 1500 miles. I am shocked.
On the other side for miles and miles, 20000 miles I drove on stock pistons either 11,3 or 10,5 ( African version) and made so much detonation when I knew nothing about fuel enrichment and BMW OEM pistons were so good.

Now with 11,3 stock pisytons and thicker head gasket I ll have 10,0 cr and boost ??. I ll start with 11 psi and go up as much as possible.

I have 95 octane fuel but bought Toluene. Will mix it 40 %. Retard timing.

Thanks God intake tempearture was 48 F and ambient was 42 F. Turbo is both water and air cooled and my intercooler is very big.

Moreover I agree that it matters at the end the effective compression ratio.
You can boost at 8,5 cr 14,7 psi and get a effective cr of 17 at the same time you may boost at 10 cr 10 psi to get the same effective cr.

The best performance I ever had was 11,3 cr and 3,7 psi and 10,5 cr 8 psi. Because when you lower the cr on a supercharged engine below 10,0:1 you overrev the blower and damage adiabatic efficiency.

I tried Vortec T Trim at 7,5 cr and boosted 16 psi but intake temps were very high because I was overrevving the sc. Should you wish not to overrev the supercharger you will boost low.

Finally, the best results were taken by 7,5 cr and 19 psi turbo boost. the 19 psi was at 3 rd gear and I had no chance to look at the boost at 6 th gear cause I was playing with a Porshce Turbo and was going at 200 mph. After a couple minutes of racing the engine sound weird and we found out the pistons have cracked (damn forgeds) and engine block cracked also. ( engine block cracked cause we had sleeved it)

Today I ll get my new blocked M3 and after a 700 miles brake in Ill try to boost at 10 cr and see????

I had to use stock 11,3 pistons and lower cr with a thicker head gasket because I have no confidence in forged pistons. Maybe I had the bad quality forgeds.

200 mph might be a dream but check my videos (used to be on my website www.da-motorsport.com, now removed to another server) where the M3 was only 415 crank ho and was easily running 193 mph. I ll make mpegs of 200 + mph.

Mert


Glad to see a fellow Turk playing with the big boys, especially in a country where car prices, gas prices, parts prices and taxes are all rediculously high...

eyvallah kocum :D