CR Equally perportioned with Fuel rate?
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My cars louder than yours
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From: Augusta, GA
CR Equally perportioned with Fuel rate?
The title might be a bit confusing, but I'll try my best to explain what I'm trying to figure out.
Im rebuilding a turbo motor with 9.4:1 rotors instead of the stock 8.5:1 rotors. Ill be using the stock TII ECU at stock pressure levels for now and a S-AFC for fuel corrections. The percent of difference between the 9.4 and the 8.5 is 9.6% (someone correct me if I'm wrong).
All things being equal (they won't I know, this is just theory) if I took the 8.5CR rotors fuel map and adjusted it say +10-12% (for the 9.6% change in compression ratio) for the 9.4CR rotors, would this be the same A/F percentage as the stock 8.5CR rotors?
It sounds right on paper, but my real question is if the amount of fuel increase needed for the difference of CR Rotors is equally perportioned with each other, or is there some kind of formula I can roughly follow. This is just until I can get her to a real dyno, not a bandaid. One thing I'm worried about is the difference in heat between the two rotors and how much I need to adjust from that.
Excuse my ignorance of this whole situation. I'm just trying to figure it out on my own with no first hand experience or previous knowledge of tuning.
Thanks
Charles
Im rebuilding a turbo motor with 9.4:1 rotors instead of the stock 8.5:1 rotors. Ill be using the stock TII ECU at stock pressure levels for now and a S-AFC for fuel corrections. The percent of difference between the 9.4 and the 8.5 is 9.6% (someone correct me if I'm wrong).
All things being equal (they won't I know, this is just theory) if I took the 8.5CR rotors fuel map and adjusted it say +10-12% (for the 9.6% change in compression ratio) for the 9.4CR rotors, would this be the same A/F percentage as the stock 8.5CR rotors?
It sounds right on paper, but my real question is if the amount of fuel increase needed for the difference of CR Rotors is equally perportioned with each other, or is there some kind of formula I can roughly follow. This is just until I can get her to a real dyno, not a bandaid. One thing I'm worried about is the difference in heat between the two rotors and how much I need to adjust from that.
Excuse my ignorance of this whole situation. I'm just trying to figure it out on my own with no first hand experience or previous knowledge of tuning.
Thanks
Charles
I'm a boost creep...
Joined: Jan 2002
Posts: 15,608
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From: Auckland, New Zealand
Re: CR Equally perportioned with Fuel rate?
Power does not increase proportionally with compression ratio. In fact the curve of power potential vs. CR starts quite steep at very low CR (3-4:1) and flattens off quite quickly as CR increases. This is why there have been no major changes in the CR of production engines for the last 20 years. The benefits are far outweighed by the downsides. Once you get up to 10-11:1 the difference is quite small. So a 10% increase in CR doesn't give anywhere near 10% more power. You'd be lucky if it's near 5%.
Remember the stock mixtures are very rich, so you'll probably find you won't need to increase fuelling at all. You'll still be leaning them out when you get on the dyno. Just make sure you keep the intake temps down with a proper cold air intake and decent intercooling.
Remember the stock mixtures are very rich, so you'll probably find you won't need to increase fuelling at all. You'll still be leaning them out when you get on the dyno. Just make sure you keep the intake temps down with a proper cold air intake and decent intercooling.
Thread Starter
My cars louder than yours
Joined: Oct 2001
Posts: 1,969
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From: Augusta, GA
Re: Re: CR Equally perportioned with Fuel rate?
Originally posted by NZConvertible
Power does not increase proportionally with compression ratio. In fact the curve of power potential vs. CR starts quite steep at very low CR (3-4:1) and flattens off quite quickly as CR increases. This is why there have been no major changes in the CR of production engines for the last 20 years. The benefits are far outweighed by the downsides. Once you get up to 10-11:1 the difference is quite small. So a 10% increase in CR doesn't give anywhere near 10% more power. You'd be lucky if it's near 5%.
Remember the stock mixtures are very rich, so you'll probably find you won't need to increase fuelling at all. You'll still be leaning them out when you get on the dyno. Just make sure you keep the intake temps down with a proper cold air intake and decent intercooling.
Power does not increase proportionally with compression ratio. In fact the curve of power potential vs. CR starts quite steep at very low CR (3-4:1) and flattens off quite quickly as CR increases. This is why there have been no major changes in the CR of production engines for the last 20 years. The benefits are far outweighed by the downsides. Once you get up to 10-11:1 the difference is quite small. So a 10% increase in CR doesn't give anywhere near 10% more power. You'd be lucky if it's near 5%.
Remember the stock mixtures are very rich, so you'll probably find you won't need to increase fuelling at all. You'll still be leaning them out when you get on the dyno. Just make sure you keep the intake temps down with a proper cold air intake and decent intercooling.
How much do you think i would need to increase over the RPM range with the N/A computer?
Thanks
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