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Discussion Starter · #1 · (Edited)

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I wonder if the crowd liked the Jeep TH blowing away everyone or did they think it was a rich guy showing off?? People can be funny when a new vehicle dominates so effortlessly.
 

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Michael
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I had 4 runs at atco yesterday, against 2 coyote Stang GT’s, a stock SRT8, and modded civic, and It still wasn’t close.

And 2 of these cars were on drag radials and I have all season tires.

Street or strip, beating this truck isn’t easy.



And I weighed it yesterday as well, without me in it, 5,233lbs, about an 1/8 tank gas.
 

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Trackhawk
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#6659 foot brake, no launch control

Wanted to try a few more techniques with launching, but ran out of time.


View attachment 184282
Excellent, thanks for sharing. One more question, how do those numbers compare to what the performance pages reported on any of those runs? FYI, your numbers are very close to mine when I've used just a little bit of power braking.
 

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Michael
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The performance page 1/4 mile et was quoting 11.7 on all the runs I believe.

Basically high by a full tenth to a half.
 

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Michael
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Same conditions, I’d wager I could have knocked full tenth or more off that ET.

11.4’s with this truck will be the norm. Just didn’t have the time.

I drove an hour to track, went thru tech and within 15 minutes of arriving, ran that [email protected]
This truck is remarkably consistent and doesn’t seem to suffer heat soak, at least in these conditions.
 

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Same conditions, I’d wager I could have knocked full tenth or more off that ET.

11.4’s with this truck will be the norm. Just didn’t have the time.

I drove an hour to track, went thru tech and within 15 minutes of arriving, ran that [email protected]
This truck is remarkably consistent and doesn’t seem to suffer heat soak, at least in these conditions.
11.4s you say. Mom driven with baby seat in the back...lol

https://youtu.be/ek9xNWcRVmY
 

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What were the ambient conditions when you guys ran? My Performance Pages showed a consistent 3.8 seconds 0-60 time.

I am in Tucson and ran consistent 12.2's @ 113 mph at 68 F. I didn't have RH or barometric pressure, but the dragstrip track is at 3000 ft.

It seems everyone else is running mid 11's! Could it be temperature and altitude make that much of a difference?

I found launch control at 1800 rpm better than 2400 rpm. I guess that would be tire slippage. I'll be going back in a couple of weeks for more experimentation.
 

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I am in Tucson and ran consistent 12.2's @ 113 mph at 68 F. I didn't have RH or barometric pressure, but the dragstrip track is at 3000 ft.

It seems everyone else is running mid 11's! Could it be temperature and altitude make that much of a difference?
Yes.........DA (Density Altitude) has a lot to do with it.
The good runs are occurring at tracks that are near sea level and temps in the 40's.
 

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The DA with my slips above was -1443.
So that means the equivalent air density would be greater than the standard altitude by 1443 feet, which translates to about 2.25 psi, or 4.5 in-Hg increase.

This makes sense to me. Using the calculator link below, that should increase the air density by 15%, which would add about 80 HP to the rated power, which should give you 118 mph in the quarter. This is all based on rules of thumb.

https://www.ajdesigner.com/fl_horsepower_elapsed_time/horsepower_elapsed_time.php

I feel better about my 12.2 sec in the quarter now.


Where did you get your altitude density number?
 

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Michael
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So that means the equivalent air density would be greater than the standard altitude by 1443 feet, which translates to about 2.25 psi, or 4.5 in-Hg increase.

This makes sense to me. Using the calculator link below, that should increase the air density by 15%, which would add about 80 HP to the rated power, which should give you 119 mph in the quarter.

https://www.ajdesigner.com/fl_horsepower_elapsed_time/horsepower_elapsed_time.php

I feel better about my 12.2 sec in the quarter now.


I wouldn’t put to much faith in those calculations.

You can correct any run, with either a negative DA or a positive one, to a 0 DA level. It’s called a corrected run, much like a sae corrected dyno run, and it let’s you compare two runs apples to apples. It’s a correction factor that is widely accepted. I believe even the NHRA uses this correction.

Just to be clear, even with the negative 1440 run above, the correct run to 0 DA is only about a tenth and 1-2 mph slower for a Supercharged engine.

http://www.dragtimes.com/da-density-altitude-calculator.php
 

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I wouldn’t put to much faith in those calculations.

You can correct any run, with either a negative DA or a positive one, to a 0 DA level. It’s called a corrected run, much like a sae corrected dyno run, and it let’s you compare two runs apples to apples. It’s a correction factor that is widely accepted. I believe even the NHRA uses this correction.

Just to be clear, even with the negative 1440 run above, the correct run to 0 DA is only about a tenth and 1-2 mph slower for a Supercharged engine.

DA Calculator - Density Altitude Calculator - DragTimes.com
Firstly, awesome web page calculator. Thanks. I wondered what the difference would be between a non- and supercharged engine effect. On reflection I think the impact of barometric pressure change on a SC engine maybe due to it being a smaller percentage of SC manifold total pressure than a non-aspirated engine (e.g. 1 psi change to 14.7 psia > 14.7+ 8 psia thus larger impact).

Secondly, as I stated the numbers were the result of rules of thumb to give me a sense of my performance - not meant to be exact calcs. They were, however, consistent with your track results which is what I was trying to convey, meaning they corrected my results much closer to yours. I did not intend to mislead anyone.

My point was that I was trying to put my track numbers in perspective to what others were reporting. Not knowing the ambient conditions - or even geographic locations of others made me wonder why my results seemed to be relatively high.

Thanks to your post I now know what altitude density is. I am a mechanical engineer and in my previous job at a utility we tested and reported gas turbine performance for a utility. Our corrections were usually correction curves for individual parameters (such as barometric pressure, temperature, humidity, exhaust pressure, etc.) which were then totaled for the corrected performance.

Never have I dealt with (or heard of) altitude density which I guess was developed for flight applications. However, it seems to be an easy way to relate corrected results. That web page is convenient and makes short work of the calcs. I am very curious as to the algorithms for corrections and ET and speed conversions.
 

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Michael
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Exactly correct, DA was originally pioneered for the aviation industry.

I apologize, didn't intend to come off harsh. Some of those HP calcs have a habit of generating more questions than answers at times. All a good conversation in the end though.
 
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