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Nathan · 16th January 2004, 09:33 AM

You generally run as much compression as you can for the horsepower you require. Your limits are det and EGT. If they go up too far, you need to lower the compression. It can turn into a law of dimishing returns though. Running more and more boost enables more power but reduces the low down power as you have no off-boost cylinder compression left.

Your examaple figures would be far different from that IMO. A petrol engine on 9.5:1 would be quite high for a turbo, and you'd be lucky to run much more than about .5 bar. Go to 8.5:1 (Mk4) and shazaam you're already capable of 1.4 bar. It doesn't take a lot of compression drop. I would think that a Mk4 on 7:1 would be good for 2.5+bar no probs. Similar to what the big cossy boys run as it goes. They run about 7.2:1 IIRC. Obviously all figures are thrown up there as an example and theres a lot more to this than I have posted.

16th January 2004, 09:33 AM	#2
Nathan Senior Member None - Don't currently own a MKIV Supra. Join Date: Sep 2003 Location: Essex Posts: 605	You generally run as much compression as you can for the horsepower you require. Your limits are det and EGT. If they go up too far, you need to lower the compression. It can turn into a law of dimishing returns though. Running more and more boost enables more power but reduces the low down power as you have no off-boost cylinder compression left. Your examaple figures would be far different from that IMO. A petrol engine on 9.5:1 would be quite high for a turbo, and you'd be lucky to run much more than about .5 bar. Go to 8.5:1 (Mk4) and shazaam you're already capable of 1.4 bar. It doesn't take a lot of compression drop. I would think that a Mk4 on 7:1 would be good for 2.5+bar no probs. Similar to what the big cossy boys run as it goes. They run about 7.2:1 IIRC. Obviously all figures are thrown up there as an example and theres a lot more to this than I have posted. __________________ Nathan TDI PLC We like VVT-i's, especially ECU solutions :-)