overrun fuel cut on or off??
 

What is the norm for a race car? Heard some say leave it off to cool things down whilst off throttle, others say leave it on to prevent bore wash.

What are your views and reasons for/against?

How does turning it off cool things down? When decel fuel cut is on, there is no combustion and thus no heat made. The only reason I could com up with for turning it off is if the extra engine braking upsets the handling of the car somehow. Or if having normal combustion during off throttle events decreased spin up time of the turbo by a measurable amount.

On, shorter delay if you are endurance racing, longer if you are awesome. I run a 1s delay. I leave mine off because after four years of awesome in my green car with the turbo, the cylinder walls looked great.

The car is used for sprint racing so fuel consumption is not an issue. So you suggest i leave mine off and get some nice flames going?

I'd leave it on since this is not a rotary. You'll have to add a shitload of fuel to blow flame.

IMO, you're more likely to shoot flames with it on. If you dont have a cat the extra O2 into the exhaust makes the unburnt fuel already in the exhaust to light off. May or may not flame out of the tailpipe.

Flames are always a bonus but not the goal. just want whatever is best for the motor. i can have it so it comes on below a certain rpm and is off above.

I run a 2 sec delay IIRC.

What ecu? I havent played with one with that setup, normal its rpm and speed enable disable to turn it off at low rpm/speed to prevent stalling and bucking.

its a motec m4

software is terrible but works fine.

dont think i have an option to add a time delay, will have a look now.

the only options i have are:

overrun inactive rpm
overrun active rpm
overrun throttle position
overrun recover fuel

Wait... their tuning software is in DOS? DAFAQ?

you are correct! got to love DOS!

Motec used DOS until recently.

resurrection bump, do you guys still leave overrun-cut on in your track cars (not injecting on off-throttle like stock tuned cars)?

Some online literature I've come across suggests turning it off helps cool valves, piston, turbo through evap. cooling and the fuel efficiency hit won't be too much since there isn't much time on track where you should be off throttle

One example: Learn To Tune - High Performance Academy

i run with mine turned off now for this reason.

FLAMES HERE I COME

Cant shoot flames with out air. Add a clutch switch that retards the timing 50 degrees and enriches 30% thats activated +4k rpm.

tell me what your VE is in overrun and decide for yourself.

I suspect it is somewhere around PW TOO LOW TO SQUIRT anyway.