AL SS590 M6

iTrader: (1)

Well not really a problem but................it's got me doing this
2000 Formula race only, LS1 heads/cam, auto, 12 bolt/spool
Open loop tune.

While racing Saturday I noticed something that has me a little worried.
At 1878' DA on a 1.56 sixty foot I ran a 11.325 at 118.59
At 800' DA on a 1.53 sixty foot I ran a 11.312 at 118.
At 700' DA on a 1.53 sixty foot I ran a 11.314 at 118.

Now I know that this is an open loop tune but I still figured that the car was reading the IAC and MAF so it would change the calibration based on the amount of air and the air temp. If it ran 11.32@118.59 at 1878' it should have run almost 11.20-1@120 at 700'
I'm confused and a little worried. If it doesn't compensate for cooler air then it's not going to compensate for hotter air either. If it doesn't compensate for hot air then when I go to the track and it's 90° out and the DA is 3500 feet it's going to knock like hell and maybe even break something.
Or is it just not sensitive to DA anymore and I need to track VP or dew point?
Somebody please help me understand what's going on.

white2001s10

iTrader: (4)

I set my ECT/IAT bias 100% to IAT after engine warm-up.

When the engine is cool it is biased more towards the ECT. Once warmed up it is biased to the max towards IAT.

If this doesn't give you enough change that you're looking for then you could consider using an ECT tricker adjusting with a potentiometer allowing adjustment on the fly.

Your car seems to respond well to running leaner in low gear, but is missing the extra fuel in high gear.

AL SS590 M6

iTrader: (1)

Thanks for the input. But I don't understand the last comment. The afr is 12.5 thru the whole rpm range on the dyno.

white2001s10

iTrader: (4)

Cars usually don't run their quickest down the track by holding the same AFR through the entire RPM range, or from start to finish of track either.

The AFR and spark advance needs to match both the burn-speed and cylinder pressure.
Engine speed and loading are the big factors to consider.

I could tell you what some engines like, but it's best to test and find out what yours likes. The dyno isn't the best place to do this since loading and transitions aren't the same as actual driving.

KVU

iTrader: (1)

1. AFR changes from when you are on a dyno vs the street. The dyno puts more load on the engine that you will ever see on the street. This is easy to verify with a wideband a/f meter and a simple test on the street. The reason the afr changes is due to load. For example, check WOT AFR on level ground. Then go up a slight hill at WOT and monitor AFR. Then go down a slight grade. Things will become clear very quickly. I have another example, vacuum secondaries on a carb tend to not open on a dyno. Simulated load is not the same as ACTUAL load.

2. Your AFR might be 12.5 on the dyno in 3rd gear. BUT AFR changes in each gear(again, due to load, not PCM settings). So 2/3's of the run, you are leaner than 12.7, in first and second gear.

3. MPFI engines don't take a huge loss in power like a carb vehicle when the d/a increases. There is a loss but not .5-1.0 seconds. At least not on a good tune.

So overall I think the tune is most likely ok. If you want to make fine adjustments track side, you should invest in the equipment. It's possible to get more power in lower D/A but it'll take having equipment hooked up in that exact condition. You would need to make a log book showing D/A and % change to fueling and the track result. Once you have enough information it'll be possible to just look at the D/A and know what fueling changes to make. Then you will not need the equipment hooked up all the time. This is required if you are wanting to compensate for ambient conditions. You will knock off about 1-3 tenths and increase mph 1-3. That is the typical results...

AL SS590 M6

iTrader: (1)

Thanks for your input.
The car was tuned on a Mustang dyno so the simulated load is closer than on a DJ. And to restate this is not a street car it is never driven on the street. It only does drag racing.
As far as the power changes goes. I've had this car for 7 years and until this tune it would vary 3 tenths and 3mph over the course of the summer due to weather changes. Last year with a normal tune with simular conditions the car would have changed about a tenth and 1mph over the course of the night. It didn't change at all and that just seemed odd to me.