I went to the track a my times were slower this time my best was 15954 and rest were 16020 the last time i went the temps were cooler and i ran a 15343 temp was around 50 deg. this time it was 84 deg with 51% humidtiy. Plus i put some doug thory try-y on my truck.I didnt think the weather would make that much of a differnt my mph fell off to usally run around 88 mph this time i was running 83mph i was very disappointed.

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... this time it was 84 deg with 51% humidtiy

That would be a big factor

i had rhe very same experience,i was beginning to think my headers made my truck slower,but im confident now it was the weather.

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Originally posted by Rich B:
I went to the track a my times were slower this time my best was 15954 and rest were 16020 the last time i went the temps were cooler and i ran a 15343 temp was around 50 deg. this time it was 84 deg with 51% humidtiy. Plus i put some doug thory try-y on my truck.I didnt think the weather would make that much of a differnt my mph fell off to usally run around 88 mph this time i was running 83mph i was very disappointed.

Bring on the cooler weather. I like it and so does the HEMI.

My hemi loves the cooler weather. I can feel a huge difference when it cools off.

My best was 14.59 before headers in 50-60 degree weather. I went back a month later with headers and it ran a 14.52 with a slower 60' time but it was about 70-80 degrees and humid. It makes a huge difference. My 0-60mph dropped over a full second with my header and exhaust swap

yeah,i think the hemi likes cool,that explains why my truck is 1.2 seconds faster in the 1/4 mile in hot weather with a little 75 hp zex kit.

What is a plasma booster?

I won't race my truck unless it is cool because I know that I will be disappointed in the ET's. It is a night and day difference the way the truck pulls on the way to work in 50 degree weather vs the way it pulls on the way home in 90 degree weather.

I am waiting for some cold weather and then I'll go back with my 17's on it and the short belt and shoot for a 14.8.

I wish they were more consistent. It starts to slow down when you go rounds too.

Craig

Weve had some nice 70's here and it was crazy how much a difference it made.

It really sucks how much these things slow down in the heat. I'll have to do some datalogging on a really hot day and compare it to a cold day and see if I can tell what the hell the difference is. It must pull a lot of timing and maybe add a bunch of fuel too. So, you could trick it by adding the power wire, but the question is will that cause detonation. I think that whatever the computer is doing is overcompensating for the heat, but how do we add some back in without going too far. I am afraid to lower my intake air temp readings with a power wire since I am already running more timing with my Diablo. I just want it to pull less timing when it heats up, but it needs to not add in any more in the cold temps since I have it on the edge already with the Diablo.

I sure wish that I could see the fuel tables and spark tables that use the intake air temps in their axis. I wonder if Diablo can give me that?

I can see all of those tables in my Mustang's computer with my Tweecer. I disable all of them at the track and it has made the car much more consistent. I do have to make sure that I start out with lower timing though so it isn't overly advanced in the later rounds when I am hot lapping it or it will detonate.

Craig

I'm betting it pulls timing slightly and subtracts fuel. If you think about it, when it's hot and humid outside you're getting less air. Less fuel would keep the fuel ratios about right.

I know on my truck, when it's cold and not humid outside, this thing will run 500 times better than it does in 100 degree humid weather. Like day and night

I was thinking that it would command a richer mixture in order to keep cylinder temps down and fight off detonation in the heat. My overhead was reading 98 degrees today on the way home so I did a quick 0-70mph datalog. I looked at the log and the timing seems as high as I ever remember it getting to.

I just compared my log today which had ACT temps of 115 degrees to an older log where it was 60 degrees out and the ACT was 77. It hit 24.5 Actual Spark at 5850 in both cases and the Open Loop AFR (which I am assuming is commanded AFR) was at 11.67 in both cases. It was 20.5 degrees and 11.9 at 4k in both cases and 21 degrees and 11.6 AFR at 5k in both cases. This can’t be right. The adders, subtracters, and multipliers for WOT timing vs temp must not be included in the Actual Timing and in the Open Loop FA. How could it be the same under such different conditions? As far as I know, the “Actual Spark Cyl1” which I logged is supposed to be the actual timing after all of the above are added in. This is datalogging with the Diablo. I am running the Diablo 93 tune on 91 octane but I have taken out a degree of timing. I may have even taken out 2 degrees in the mid range because I saw some short term spark retard there before on the shift. Now I don’t see any short term or long term knock retard. I can’t find my tune notes so I am not sure how I currently have it adjusted.

I guess that I need to do more investigation on what all of these parameters are that the Diablo is logging. The problem is that even when I ask the Diablo guys, they don’t even know half the time. They didn’t even know that the Long Term Fuel Trims are used at WOT until I pointed it out to them. They didn’t believe me until I posted what my measured AFR was with the Wideband with the 93 tune with 5% LTFT and then immediately after reflashing the 93 tune with 0%LTFT. The AFR went up by 0.4. They finally got back to me and said that they verified this to be true, but only when the LTFT is positive. I guess that they never dyno’d the Dodge’s again after a road test and saw that the AFR was different than how they had it tuned before it left the dyno with 0%LTFT. I guess these trucks do like to be rich because mine slowed down with the fresh flash that cleared the LTFT and leaned it out by 5%. I know this by checking the time to 90mph in the datalogs. I started from the same exact spot on the road and just launched from idle to keep wheel spin down.

I also need to get a wideband on this thing again and see how rich it is really running. Those are really rich commanded AFR’s. That is where I have my blown Mustang running. I can’t remember how much fuel I am adding with the Diablo, but it isn’t much. I also don’t remember if the LTFT’s are included in the Open Loop FA in the logfile. I know that they are used at WOT if they are positive and mine are at 5%.

Craig

That's a good point. I would assume it pulled timing but does not add fuel.

Get a gauge, I added some fuel (maybe 5% like you did) before I got my AF gauge. I ended up leaving the low and mid ranges at 0% and actually subtracted fuel in the high rpms. I was running like 11.7ish at WOT at 5000+ RPMs. I'd say the diablo canned tune is pretty close to what you should be running. I'm at about 12.2-12.5 at WOT throughout the whole RPM range.

My AFR stays around 12.3 hot or cold, i didn't check timing but there is no KR.
the way i see it the cold dry air it's lighter and moves faster so it's easier to vacuum and creates a more powerful explosion in the combustion chamber, it might also help aerodynamics it's easier for our "bricks" to cut through the less dense air

But cold air is more dense. I don't think it affects the aerodynamics much if any.

I've only messed with my timing and AFR once and that was when I first got my diablo maybe 6-9 months ago when it was cooler out. It's starting to cool down but I never checked it this summer. But it runs way better when it cools off. I ca't believe the difference it makes.

Makes me think our trucks could really benefit from a forced induction set up.