This guy with a Greddy Turboed RX-8 took it to a rotary mechanic that tuned it to 12.5 afr but it's hitting as high as 13.5 at redline!! He's boosting 7psi and using 10.5 heat range spark plugs to be able to be this lean and prevent detonation or so the mechanic said.

He got anywhere from 265 to 272 whp over several dyno runs. Do you think this is dangerous for the engine? I always see people shooting for afr's in the 11:1 or richer, never heard of these lean conditions on a turbo rotary. What do you think will happen?

 

My first thought would be...BOOM!!

 

anybody else tuned lean and used colder sparkplugs to be safe??

 

If you were really being safe, you wouldn't tune it so lean. The sparkplugs are a work-around for the problem, not a fix for it. Retune the engine and give it the fuel it needs.

 

it's not my car, I saw it on the RX-8 forums and thought it was very interesting because I never saw this lean tuning before

 

Running richer than the ratio of maximum power for the fuel is a work-around as well. 12-13 is a great place to be as far as power with gasoline (where do you think most NA rotary race engines are tuned to), unfortunately it's also a great way to blow a motor due to preignition, or detonation.

On the other hand, I wouldn't trust your average mechanic to give tuning advice.

 

Too much other variables...

Fuel octane?
IC...intake temps?
Type of wide-band sensor?
EGT?
Ignition timing?

This is one reason why shooting for a particular AFR number is not an exact science.


-Ted

 

That A/F ratio should be ok for that boost level 7psi. I would worry about 13.5 readings.