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This may have already been discussed, (if so if anybody can point me to this) but looking for some tips on tuning idle on large cam, large CID engines that do not have a good idle AFR reading or an idle valve etc - meaning as it warms up things continually change (RPM and MAP) and its hard to know where you are at with AFR etc. This is a drag racing application, around 11.5 L engine, 1300 HP NA- the issue is we are now seeing summer temps that are higher, and staging at higher temps and having a few issues. After launch and down track things are really good on the tune.
In short, i am looking for methods and practices some of you may use to really tune this situation.
This can be a problem with some engines, particularly with a really wild cam. My own approach with the drag engines I tune that exhibit erratic or useless AFR readings at idle is to simply adjust the fuelling rich and lean until the engine idles cleanly. I know on the face of it this sounds likely less than useful advice but if you simply adjust the fuelling in the idle area rich and lean in 2-5% increments, you'll find a 'window' of fuelling values where the engine rpm will pick up. As you keep going in the same direction the rpm will start to drop off again. Not particularly scientific but I aim for fuelling numbers that resulted in maximum idle speed.
For a drag application you don't need to worry so much about the engine being a little rich at idle either since it doesn't see the time running at idle that a street engine will, and it will tend to get more regular oil changes.
This is useful feedback- Thanks. - the difficult part is that when you add/remove fuel it moves in the fuel map to a different portion and seems i end up chasing my tail. Let me tell you some more about the situation.
I tuned this engine on the Dyno, it runs on Q16 and the engine builder likes it to operate in the 130-140 degree range, at least on the dyno for max power. In these temp ranges I had tuned it for a good throttle response and the engine was happy. When we got the the track on a humid day at 100 deg F we started seeing temperatures that were more like 180-190 degrees. Not really what we wanted but that was the situation- the car had no response to come up on the rev limiter while on the trans brake, kind of sputtered a bit. I believe that as it had warmed up it moved to a part of the fuel map that was not really tuned (ie we had never really seen that part of the map) unfortunately we ended up with no log to review
Here are my thoughts for the approach going forward- take the car up to hi temps, and tune the base map. I am thinking that I do not want to try and mess with the accel enrich because it worked at different parts of the fuel map, probably want to try and look close at the base map first
A secondary question for a situation like this- With an engine that we like to run at 140F, but may see 180F depending on the situation, how do you address the fuel enrichments and other coolant based modifiers etc.? Do you target your' %100' at your target temps(140), or your max (180). I guess when tuned properly it should make no difference? On a street car once up to temp they generally stay in a pretty tight range- not so much with an engine like this.
This is more to do with your OP than with your last post but when tuning idle on cars that move around I try to get the idle to go to the highest vacuum or lowest MAP reading. So if it is swing at idle between 10-12 " vacuum tune it till it stays mostly at 12" (or higher if you can manage it), likewise if it is swinging between 50-60kpa tune it to stay in the 50 kpa range. This is more of a carb tuning thing but I have found it works with efi as well, although I don't know if it would with Q16.