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Determining Performance Gains from Log Files

iso100

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#1
I decided to try to quantify the gains I've felt between my car with the stock airbox and an older COBB OTS tune and the way it ran recently after I installed my custom intake (before heat shield).

I loaded my logs into Datazap and then compared 3rd gear between both.

I created a spreadsheet and recorded:

  • Start Time
  • Start RPM
  • End Time
  • End RPM

... for both runs.

I calculated the delta time and delta RPM for each.

Then I calculated a value of RPM Rise per Second. This is essentially the rate of RPM change every second.

I was careful to choose similar segments of the RPM band and made sure that the actual throttle position was 100% throughout.

Old log = 341.32 RPM gained/sec (took 4.005s to gain 1367 RPM)
New(er) log = 452.68 RPM gained/sec (took 3.075s to gain 1392 RPM)

By my calculations it's a 33% increase in performance.

Did I really gain this much performance? Is there something I'm missing or is this calculation otherwise flawed? (I didn't note fuel tank % on either logs... so one could be with an empty tank and the other, full) Both runs were within 2 degrees in terms of charge temps.

Wonder if I should go out at lunch and do another pull now that I have exhaust on...

Here's my Google Docs Spreadsheet in case anyone wants to double-check my data:
https://docs.google.com/spreadsheets/d/1VbgQIdbSLaFG7LYzzNqr0tzP2Z-LVC9Hscgp3aOtbs4/edit?usp=sharing
 


dyn085

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#2
Performance increase can't be measured as a percentage in regards to reduced times because it's not linear.

Do it over a much larger rpm range and it'll give you a better idea of what I'm talking about. Instead of comparing ~1380 rpm, try and do 2k-6.5k (4500 rpm).
 


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iso100

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Thread Starter #3
Yeah, my main reason for not using a wider range is that my oldest log didn't cover a wide range. I included only similar ranges since I assume the rate of acceleration is the same across the two.

As a result, I only included (in groups 1 and 2) the narrower band.

I believe, however, that the time it takes to get from one RPM point to another in the same gear and under similar conditions can be an indicator of performance change. If it takes 33% less time, then that's an improvement in my opinion.

Now that I did another log today I'll see if I can compare log #2 with it over a wider RPM range.
 


dyn085

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#4
I'm not saying it's not an improvement, just saying that the measure you're trying to use isn't linear. Assuming the percentage gain you think you're getting in such a small range would not equate equally over a longer distance.
 


razorlab

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#5
Yea, it's like getting a 15wtq gain at 4000 rpm to 5000rpm only. Doesn't show the whole picture.

It's like looking at ATP's newest dyno chart with a short blip from 300whp to 330whp at the very end and claiming the car made 330whp. I laugh every time I see this chart.

 


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iso100

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Thread Starter #6
Yea, it's like getting a 15wtq gain at 4000 rpm to 5000rpm only. Doesn't show the whole picture.
Sadly I have no full-RPM early logs that span a larger RPM band. I don't plan on doing much more in terms of power mods either. Maybe a ProTune but not an FMIC, DP etc anytime in the next few years.
 


Siestarider

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#7
I settled early on 2500-6500 rpm 3rd gear 100% WOT test pulls on datalog, stock with Cobb Stage 1 about 8.6 sec. Currently with 2J dp, Cobb IC and Stage 3 tune, right at 7.5 sec. Tried 3" exhaust, no gain over stock exhaust, so put stock back on. No idea how this approach applies to anything else, but maybe a useful comparison for someone out there.
 


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