question on dyno runs

[Grimlock]

Is it true that sometimes you can obtain better numbers on your third dyno run as opposed to the previous ones. The place near me does 2 runs and I didnt know if I should have it dynoed 3 times in a row. The car has 1400 miles on it and its stock until after the baseline run. I thought too many runs would just heat up the car.:??:

 

[TRDNiteLife]

When I first got my car dynoed I actually pulled one more HP but about 5 less torque on the second run. I only let the car cool for about 10-15 minutes between pulls that time. Generally the car will progressively put down lower numbers because of the heat.

 

[VENOMOUS03COBRA]

Originally posted by TRDNiteLife
Generally the car will progressively put down lower numbers because of the heat. [/B]

exactly, the car will almost always drop power after every pull. if you have an after market heat exchanger , it will drop less , but it will still drop.

 

[Grimlock]

So then, I dont need to pay extra money for a third run. Two should serve just fine? Also, do I need anything special to check A/F ratios precisely (sp)?

 

[VENOMOUS03COBRA]

no , you dont need a third run. about checking a/f, they say its more accurate if they put in a bung. but i always checked it at the tailpipe, which most people do.

 

[CobraBob]

Originally posted by VENOMOUS03COBRA
exactly, the car will almost always drop power after every pull. if you have an after market heat exchanger , it will drop less , but it will still drop.

That is not really true as long as you allow a minimal cool down between runs. I have been to the dyno four times (three different dynos) and in all cases but one the second run was the best, with the first one being the lowest. In the exception, the third pull was the best. First has always been the worse. Here's my last set of numbers, with a 10 minute cool-down in between each (SAE).

#1 447 rwhp 467 rwtq
#2 457 rwhp 481 rwtq
#3 442 rwhp 465 rwtq

 

[VENOMOUS03COBRA]

wow bob , thats pretty cool. i never seen dyno #'s go up like that. cool down or no cool down. i know mine never did, the guy usually pulls the car one after the other , with hardly any cool down.

 

[PhillyCobra]

The answer to the question partly depends on how cold the car was before the first run. Until engine coolant temp reaches 160 degrees with stock computer, engine will not allow max timing and will stay in extra rich tune. Because of this, you can get more power as it heats up. However, the supercharger and intake tract heat up drastically with each run, potentially lowering power. Most people find the 2nd run the best. It would be unusual for power to go up on a 3rd run, unless the first run was perhaps run with the engine stone cold.

 

[n0xlf]

My latest dyno was:

450.54/483.07
451.65/482.09
451.01/480.10

Now, that's pretty consistent, especially considering I changed AF between 1-2, and changed timing between 2-3...

It was 8 degrees outside, with my dyno temps between 48-50, so that probably helped too...

 

[CobraBob]

Originally posted by PhillyCobra
The answer to the question partly depends on how cold the car was before the first run. Until engine coolant temp reaches 160 degrees with stock computer, engine will not allow max timing and will stay in extra rich tune. Because of this, you can get more power as it heats up. However, the supercharger and intake tract heat up drastically with each run, potentially lowering power. Most people find the 2nd run the best. It would be unusual for power to go up on a 3rd run, unless the first run was perhaps run with the engine stone cold.

Good explanation. I never knew the reason why. :beer:

 

[Grimlock]

So the best thing to do would be to buy a temp gauge and do the dyno as soon as it hits the 160 mark...:idea:

 

[PhillyCobra]

You can cycle the odometer to read engine variables, like coolant temp. Not sure how to do it, but should be able to find a thread here with search. There are some other variables that need to be met in addition to ECT to reach normal program, but they likely would be met once ECT is 160.

 

[Grimlock]

I think you just hold down the odometer on start up until it lets you cycle through the various functions. At least I think thats how I did it with the lightning.

 

[j card]

I've seen runs go up if all of the oil was cold in the drivetrain. Sometimes people warm up the engine in neutral and the trans and rear end are still cold - so the numbers can go up as the oil in the drivetrain warms up and flows more freely. I always warm the car in gear to try and get everything warmed up equally - much easier to get repeatable results this way.