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Old 09-13-2012, 01:19 AM   #14
Scooby Specialist
Member#: 59837
Join Date: Apr 2004
Chapter/Region: SWIC
Location: Nor Cal
2004 Spec-C Type RA
What MAF? -Speed Density!


If safe power could be made at leaner AFRs why would the factory roms run fueling below 11-1? Take the JDM 207 rom from the v8, they have better fuel than we do but they choose to run ~10.4/1 AFR with 17psi of peak boost. Their timing never goes below 27 so you can pretty clearly see they chose timing vs AFR as the preferred method to increase cylinder pressures and make torque.

Here is a log from a JDM motor and you can see it knocking a bit at high RPM since it is running on 91 here in AZ

The extra fuel should drop EGTs while the advanced timing increases cylinder pressures so you can still make good torque without overheating your heads from high EGTs. Leaner AFRs push EGTs up quickly, going from a 11-1 AFR to a 12-1 AFR is a 200-300C increase in flame temperature and that is heat your heads, valves , cooling system has to deal with. Retarding the timing to prevent detonation at these leaner AFRs also pushes up EGTs since the burn spills over into the exhaust ports.

Its your car, do as you like. If the goal is high cylinder pressures to increase torque you can do it with AFR, boost and timing. AFR increases EGTs significantly so using boost and timing to increase cylinder pressures has become a more preferred approach for durable power. I tend to think the engineers at subaru that picked richer AFRs had some good reasons so I just follow their lead when I tune my car.

I like desert track days and non broken motors so I run on the richer side to keep EGTs down. Gas is cheap compared to a new motor.
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