I found this interesting link while searching for a density altitude calculator:

engine tuning calculator

I'm in Florida and it get's brutal hot and humid here in the summer. I punched in some conservative numbers for an average summer day and came up with about a 10% difference in actual air density.

I have a Vinci tuner and I'm running the Hi Perf/stock cam tune with 10% timing advance (about 3*), which seems to be the best for my set up. (Tested by seat of the pants and by driving my standard fuel economy test loop.)

Here's my question, with 10% less air density for months at a time in the summer, do you think it would be safe to cut 5 or 10% off the fuel during the summer?

I have a 00 FRC with BBK shorties, flowmasters, and a K&N with cut box.

 

If you're running closed loop with the MAF, then it's not going to matter because it adjusts for the air on it's own.

In speed density mode you would want to adjust it some for the changing air.

 

Just gotta keep an eye on the tune...in closed loop, you'd probably notice your trims swinging around. In open loop (like me), you'd probably be doing some tweaking.

 

Do you think it's ok to run 5 or 10% less fuel anyway with my set up? Just to see how it runs?

What I'm asking I guess is would I be approaching dangerous lean #s?

I dont have a dyno or data logger so I'm going by seat of the pants and my economy loop.

My understanding is most of these cars are a little rich from the factory and I'm wondering if my set up would be more or less so.

 

I run a Closed Loop Speed Density tune on my 2001 Camaro SS, and I can regularly see DA fluctuations from 1500 to 3500 (as recorded by my PerformAire Weather Station). All my fuel trims are very close and always range from -3 to 0 at most DAs I have recorded. So the myth that SD tunes can not compensate for altitude conditions is false, they do have a MAP sensor for a reason, only OL tunes would you need to keep an eye on the fueling/timing.

 

Yup. If the air is less dense, you should see the difference in your MAP

 

yeah people seem to think that speed density wont adjust for altitude, but it does, because you are tuning the fueling based on a certain KPA, so the KPA will change at higher altitude, so the fueling will adjust.

 

Can anyone answer my question about trimming back my fuel 5 or 10%?

These cars are commonly rich, yes, no? []

 

What do your LTFT's tell you...?
At WOT what do your HO2S11V, HO2S21V say...?

 

I only have a Vinci tuner and no data logger. You may as well be speaking chinese.

You guys have looked at the air fuel ratios for plenty of set ups and plenty of cars, doesnt anyone have an idea if it's safe to back off the fuel 5 or 10% for my set up?

I've been searching for a couple days now and from what I can find (which is very little), it seems these cars run a little rich.

I'm running the Vinci "stock/hi-perf" tune with 10% advance, K&N, modified box, headers and cat back. I'm a little afraid to mess with the AFR and I'm asking the guys who've seen the numbers I havent if you think it's safe to lean it out a little?

Does anybody have faith in an old fashioned plug chop?

 

Without you or us knowing where your AFR is right now, then no we can't know the answer to that.

If you're trying to tune WOT only, then yeah you could go ahead and drop your PE modifiers a little and see how the car responds.

If you're thinking about dropping the VE or MAF, then you may as well forget it. You'll end up richer at WOT because of the PCM fuel corrections. The LTFTs can go up to 25% more fuel to correct whatever you've done.

If you want total control and go open-loop SD, then you're going to need a tuner, scanner, and a wideband.