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Air temp fuel corrections old EJ20

Road Tuning

Discussion and questions related to the course Road Tuning


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Hi,

EJ20 rally car. My M800 historically has a fuel air temp comp table with 2 % change per 10°C, but between 20°C and 50°C it has zero comp changes.

I can understand the desire to have some extra fuel/cooling/protection as air temps rise. Only issue now is variable lambda at non competition zones. Obviously the important zones are the hi load zones etc.

An example on stage in middle of summer would be: ambient: 36°C /air temp : high 50's°C even with inter-cooler spray. (More commonly 40's)

Seems like it might be good to keep the 0% change in maybe the 40 to 50°C bands but make the 20-40 bands compensating. Maybe the existing is just safe!

Many thanks for suggestions.

I've seen temp correction tables set up like this plenty of times but it's going to result in an AFR change across that range in temps. Ideally under load I'd recommend a 2-2.5% change per 10 deg C. Many tuners think that you can't dial in the fuel table properly if you set this correction first, however it's actually the opposite. If you have the IAT correcting doing nothing over a . 30 deg range then you're going to be chasing fuelling variations based on IAT in your main fuel table which means next time you hit those zones, if the IAT is different then your AFR will vary. There is an argument for varying the correction table so that you're allowing the AFR to move richer at higher IAT for protection but that's a different subject.

Andre on the "different topic" being: allowing the AFR to move richer at higher IAT for protection

This table has increasing comp above really high AT for that reason, but do you think the comp table should be flat at say 40-50? Could the "time above a certain temp"(math function) be used on another axis as an alternative?

It really depends what you want to achieve and ultimately you need to test and find out exactly what you're getting. Let's say that you're running 0.80 lambda at 40 deg C. If you held the IAT correction flat from 40 deg and above then by the time the IAT reaches 60 deg the lambda 'should' be about 5-6% richer, so you could expect the measured lambda at this IAT to be about 0.75. If you want to run richer than 0.75 at 60 deg IAT then you could add to the correction table. There would be very few situations where I'd find myself wanting to add a positive trim as IAT increases though and you need to be mindful of the lambda becoming so rich that you induce a rich misfire or start fouling spark plugs.