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I've completed almost all of the tuning courses and had a question about IAT correction. I understand the 2.5% change for every 10 degrees in change, but in 2 of the courses Andre is making the adjustment from 68 deg F. Is this the "standard" IAT temp that you should always make your correction table from, or should your 10 degree correction be adjusted from what your IAT temps are at when you tune the car?
It's not strictly critical as long as you're using the same consistent change for each 10 degree change in IAT. I normally take 20 deg C as a zero point simply because we tend to see ambient temps around this level. Of course the actual temp during tuning is always changing so it's not critical in my opinion if you use 20 degrees of 30 for example.
Ahhh got ya! Thanks Andre!
Are you guys discussing fueling or ign timing? I am curious how many deg of timing you guys usually pull out per 10 deg C.
It's fueling. You should have a IAT temp compensation table
@kschwei the timing trim with regard to ignition needs to be dealt with on a case by case basis. Technically as the IAT increases the inlet charge density decreases so we 'should' actually need more ignition timing. At the same time though the higher IAT makes the engine more prone to knock which would obviously require less ignition advance. In most instances I don't trim the timing at all over a range of perhaps 0-40 deg C. Above this I may start to remove a small amount of timing if the engine is knock sensitive.
@Andre thanks for that explanation. I am tuning a TVS supercharger where the inlet temps get pretty high on the 17 psi pulley while WOT up to redline. Was just wondering how much timing pull you let the IAT compensation table take care of in this situation if any at all. Or would you set your IAT compensation table to start working above the peak IAT you see while tuning.
Hi Kevin - Just want to add - I run a twin turbo V8 non intercooled . What i find with high-ish inlet temps is i have to add fuel to not go lean . Just wanted to say so that you didnt go pulling fuel out without knowing this is also a possibility .
Kevin - that is a tricky situation and you could really deal with it in either way. Generally though you'll get a feel for whether the IAT at high rpm and WOT is affecting the ignition timing the engine will accept. The general trend is that as rpm increases, we need to advance the timing so if you're seeing a trend in the timing table where you advance it to a point and then need to start pulling timing again as the IAT rises at higher rpm then I'd personally start using the IAT trim table to deal with this as if the high IAT is affecting the optimal timing at high rpm then it will also be affecting it elsewhere.
A good way of checking the IAT trim table with a supercharger is to blank off the intercooler/heat exchanger and perform a couple of back to back dyno pulls to generate higher IATs. This will allow you to confirm your IAT trim table is set correctly above the normal IATs you're seeing during a single pull which will mean the tune is going to be safe out on the road or track.