Hi guys,

been lookin but can't find it. in a magazine article called "ram that tpi". they took the car to the track and ran about a 12.6 with air temp at in the mid 80s.

they then had the car dynoed tuned and took it back and ran a 12.3. they picked up about 30hp from the tune but on the trip back the air temp was around 48 if memory serves.

my question is how much difference in an et will that temp make with this car vs how much was from the dyno tune?

the chip was stock so there was a lot of hp still left to be had but i am just interested in how much dif the air temp makes.

i know there are other factors just looking for a wag here.

thanks!!!

ps... worst part is they were suppose to take it back to the track after they had a chip burnt but i can't find a follow up article anywhere!! guess 3 rd gens are becoming the rodney dangerfields of cars.

 

Sure it makes a big difference if its 50 or 90 degrees out. I don't know exactly how much power but I can tell you that my car is noticable faster on a cool night at 1am.Also one thing that I really have noticed is that the temperature really can hurt or help traction at the track.When its really hot it seems to me my car has less traction but I could be wrong. The tires seem to be sliding more when it gets to 100+ here in Texas. I want to run my car at the track when its in the 70s but I have to wait for a cold front or winter. Its mid 80s easy at night here.Last month it was 90 at night tell 10pm it sucks.

 

Heat increases the density altitude. Dropping from 80 to 48 will greatly decrease the DA. Lower altitude means the engine makes more HP.

Dragstrip results are never an accurate way of doing testing unless the runs are all on the same day and the DA doesn't change much during the day. If they were able to make more HP on dyno pulls then that's good and shows an improvement. Not doing any changes to the car but going to the strip every week can show a different ET just because of the weather.

If they first tested on a 48* day then did a dyno tune and went back on an 80* day, the ET would probably have been the same or slower.

 

My T/A is running on the rich side, so air temp makes a huge difference for me. It chirps the tires when I punch it from a stop when its above 65*. The other night when the temp dropped to like 57*, it would screech the tires from a 15mph roll and chirp them hard into second. My friends T/A was also the exact same way.

Cold air seems to make a big difference, especially if your car is running rich.

 

thanks for the input guys. my car is rich and cold air seems to make a rather substantial difference too. now that it's nearly fall i have a even bigger grin when i crank the beast.

what i am trying to ascertain is could air temp be the diff in the 12.3 vs 12.6runs. if it is, why didn't the dyno tune help more? i know this is a wag on my part but, it would seem that dropping the air temp (increased density) some 30 degrees would account for the .3 et diff. so again, why wasn't the car even faster after the dyno tune? i can see 30hp being equal to the .3 but coupled with the large drop in air temp should have seen an even better et.

could the dyno tune have been at a different temp and therefore not have been as effective on a colder day? in the article they dropped the fuel pressure by a few points at the dyno tune, would it have helped to up the pressure on a cold day?

at the risk of complicating this more, when does hp start to become more important that torque?

 

Tuning on a dyno means you're getting the best performance based on that days weather conditions. The dyno results should be converted to sea level so you can compare your car to someone in another part of the country.

Now you have a dyno tune. You go to the track however the weather conditions are not the same as the day you were on the dyno. The dyno tune is only the best under specific conditions. To get the most power out of the engine in different conditions, you need to adjust the tune to match the current conditions. That's why racers are always playing with jetting. Don't touch the timing. Once that's set to where the engine likes it the best, you never change it. Jetting is the most common tune adjustment since that affects how much fuel the engine gets. If the density altitude increases (hot day), there's less air to burn so the fuel is jetted down. The car still won't make as much HP as it did on the dyno because of the poor air but if jetted correctly, a 1/4 mile run can be converted to what it should run at sea level and it should have the same results as the dyno.

A dyno tune isn't the last tune you do. It only gets you to the best starting point for fine tuning adjustments based on the weather conditions. There's a lot of numbers involved in knowing how to tune for the weather. At least with a dyno tune, you eliminate a lot of guesswork as to where to start.

I run my engine at 36* timing. Is it the best? I don't know but it works good enough. Perhaps a dyno tune will say I can make 20 more HP if I bump it to 38* or drop it to 34*. Should I change the gap on my spark plugs? It's hard to tell if changing things like that at the track are actually doing any good. A dyno will find the best settings easier and more accurately.

At the track, there are too many other variables involved that a dyno can't compensate for. Tire pressures, wind strength and direction. Something simple like a cloud going over the track just before you make a pass can change your results. If you can eliminate a lot of the guesswork tuning things on the dyno, you can concentrate on the other stuff at the track.

Just because a dyno says you have ### hp and your car weighs 3500 pounds doesn't mean you'll run a specific ET based on the power to weight ratio.

Don't go believing all those magazine articles. Once you pick up a lot of knowledge, you can see how far fetched the articles become. Some articles are ok but for stories like you're mentioning, they need to compare apples to apples.

You could write a story about some fictional stock import v6 beating a hopped up big block Camaro but fail to mention that the import is also 2000 pounds less weight. Ever see the features showing ProStreet type cars with 32-34" tall tires. Read the specs, if they're published, to see they only use 3.42 or worse gears in the diff. They never give 1/4 mile performance. The cars look impressive but without the proper performance parts, they're designed as show cars or highway drivers. Anyone with tires that tall that wants true performance would have something like 5.13 gears or more in the diff. Little things like that are never mentioned in the articles.

I've only see a couple of articles about dragstrip tuning. They take a car to the track and spend the entire day trying different things to make it go faster. At the end of the day, they may gain an extra second from just doing simple things but it's all tuning on the same day under roughly the same conditions. If they go back a week later, the performance results will be different.

 

thanks again for the input. always nice to get it from someone who's been there done that.

the article was in gm hi tech performance and seems to be legit.

so if i am reading your answer correctly the .3 could have just come from the 30+ degree diff in air temp when they went back to the track. also, since the didn't make any changes during the run i.e. increase fuel pressure for the colder air, they may not have taken full advantage of what they had from the dyno tune.

first they took the same car to the track running a modifed tpi set up (big runners, intake manifold etc) and ran a 12.9 with the air temp being about the same as when they ran the stealth ram the first time at got a 12.6. i also noted then only made minor changes to the tune for the tpi and never did a dyno tune for the tpi set up either.

one of the questions about that was the only advanced the timing with the tpi to 8* or 10* btdc but on the stealth ram runs ran the timing all the way to 16*. so my next question is....if the had continued to mess with the tune on the tpi could it have hit a 12.6? yea, i know it's a wag, but if you would mind at least it will be an educated wag.

they concluded that the switch from tpi to hsr was good for about .3 and 3 mph in the 1/4 but now after studying the article i am begining to wonder. i have seen the dyno results for the hsr vs tpi and it does add hp but if it don't git-r-done in the real world why spend the money?

 

When tuning on the dragstrip, ignore the ET. There's too much that can affect the ET. Watch to see how much the MPH changes. That's the best indication to the amount of HP. You could hook up or spin off the line. If you spin, you'll lose ET but the MPH will be the same as if you hooked up.

When I make a pass down the track, I break my run down into sections. How quick was the 60' time. How much time did it take to go from the 60' mark to the 1/8 mile. How long did it take to go from the 1/8 to the 1000' and how long from the 1000' to the 1/4 mile. That way I can see exactly where the car picked up or slowed down. Maybe you get a great 60' time but ran slower than a previous run when you should have been slower. By breaking the run down, maybe you lost all the time you should have gained between the 60' and 1/8 mile. That tells you that you slowed down during your shifting. I put all the numbers into a spreadsheet and graph each run to see the changes.

As for the HTP tune, EFI works a little different than carb tuning. The EFI system has the ability to do minor changes based on weather conditions. O2 sensors can tell if the engine is running too rich in a high altitude situation and will compensate. Depending on the EFI system, it may have a barometer sensor plus any other sensor that can adjust the car's performance. I guess it just depends if it's running in open or closed loop while at WOT.