Just kidding.

Cheryl, my friend with his SRT4, and myself all had our cars dyno'd again today(first time for the SRT4). My gains were +7/+22tq. Cheryl's gains were +1/7tq.

What were the differences between these runs and the previous runs? Obviously, it's a lot cooler. On the order of 30 degrees cooler. Also, the first time, my car had roughly 4k miles, now it's got 10k. Since the first set of runs, I've added a k&n drop-in, and a set of used kinetix cats. One last difference was the dyno procedure itself. It was the same dyno, with the same operator. But we measured coolant and intake temps before the first run, though we didn't let it cool down between runs. Also, all three previous runs were in 4th, while today's runs were in 4th, 4th, and 5th. The difference between run #2 and run#3 was -1/+7, so negligible differences.

One could assert that the gains my car showed were more from conditions than anything else. However, Cheryl's car did not respond *nearly* as well to the same change in conditions. Also, the numbers are supposedly SAE corrected for both sets of runs.

This time we didn't receive any print-outs of the graphs. However, we *did* receive the actual data files for the runs. To top it off, they had saved the data from our previous sets, so we have the actual data files for all six runs.

Attached for everyone's analysis pleasure are our actual data files. You need WinPEP to view/interact with them.

Explain/Blast/Flame/Congratulate/Postulate/whatever-ate away...

My updated numbers:
248whp/233wtq

 

LMAO. You just told every person who's ever bought any full exhaust for $800-$1500 that their mod was "negligible". hahahahahahaha..........

Great post!

 

Maybe negligible wasn't the best possible term to describe what I meant. What I was trying to point out was that the numbers for 4th and 5th were within expectations. All my previous runs were in fourth, and for the heck of it I wanted to see what difference 5th would make. Technically, it should have been just a few percent. In the case of horsepower, I lost roughly 1ph. But in the case of torque, I gained *roughly* 7 pound feet. That's a difference of of 3.1%, well within expectations of dyno'ing in a different gear. Negligible.

 

I have a few updates for anyone interested in my dyno numbers. First off, you can download the current version (7.1.3) of WinPEP here:
http://www.dynojet.com/downloads/zip/Winpep7.1.3.zip

The next thing I noticed is the difference in gear ratios. Yesterday, Cheryl's car was dyno'd in 4th, at my request. I have since learned that that may have not been a good idea because of possible lock-up issues with the converter in fourth. So I opened up the runs from August, and the gear ratios were different(the WinPEP software extrapolates gear ratio's by comparing engine rpm to wheel speed); in August, her car was dyno'd in 3rd gear.

Now, before everybody flips out and tells me that the gear shouldn't make much of a difference, please take some time and analyze my runs. I had originally thought that my runs in August were made in 4th, but they weren't. It appears they too were made in 3rd. My first two runs yesterday were in 4th, and the last was in 5th. So I have 3 runs in 3rd, 2 in 4th, and 1 in 5th, totalling 6 runs. Not an exhaustive sampling by any means, but enough to begin drawing conclusions. It appears that the gear ratios did not impact the indicated HP numbers, but had a pretty large impact on torque numbers. As I stated earlier, I gained about 7lb/ft of torque simply by running in 5th versus 4th. From the 3rd gear pulls in August to the 4th gear pulls yesterday, I gained about 16/17 lb/ft of torque. Some percentage of that gain, as demonstrated by the 4th/5th comparison, is attributable to the change in gear ratios from 3rd to 4th. But, just how much? Despite atmo corrections(SAE), some of the gains should be from lower temps. So what about the rest of the gains? How much were a result of the cats, and how much were the result of running in 4th?

It doesn't really matter. All I've established is *another* baseline for measuring future mods. At this point, my two dyno's are *not* comparable.

 

And one last thing. I found this page online discussing variables in dyno's. It primarily oriented for bikes, but I'm sure the same principals apply. Interesting read nonetheless:

http://www.bishopsperformance.com/dynoinfo.htm