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Dragstrip and Launch Techniques Discussion 1/4 mile, 1/8 mile, launch discussions.

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Old 07-16-2012, 02:47 PM   #1
E.T.


 
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Trap speed (and other 1/4 mile data)

It was my first time at the track the other night, and I'm interested in what all that data on my timeslip can tell me about my car. For example, my best trap speed was about 109 mph. Is that in the normal range for my mods and an L99? I upgraded to 3.70 gears, which I've heard can lower trap speed a little.

Also, does anyone know about calculating HP from trap speed? I found this formula, but not sure how accurate it is:

Flywheel HP = weight x (trap mph/228.4)^3

This leads to one more question...what is the weight of our cars? Does the curb weight in the wiki include fuel? Just wondering if I should use curb weight plus 155 lbs (me) for the calculation...
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Old 07-16-2012, 06:20 PM   #2
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**UPDATE**

So this is interesting. I weighed my car on a truck scale after work and it came in at 3880 lbs without me, and about 1/4 tank gas.

On track night, I had:

Camaro = 3851.5 (no gas) lbs
5/8 tank gas = 71.4 lbs
Me = 160 lbs

Grand total = 4083 lbs

If I use the formula above, I get 444 HP at the flywheel. Considering ~20% drivetrain loss, that's 355 rwhp, which is almost exactly what I dyno'd the day before under similar temps/humidity. I'm assuming if the weather conditions were better, I'd actually be making a little more HP, correct.

Anyway, sorry for all the math, but I'm a physicist....I can't help it
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Old 07-16-2012, 07:00 PM   #3
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I don't know all the math behind them... BUT i ran your numbers through some of the online HP estimators... their numbers seem to all be a bit lower than the number you came up with... some sites will give you HP based on ET and HP based on Trap Speed... seems to be quite a difference between your ET HP and your Trap HP...

(ok... so lately i've been trying to calculate the Brick's HP based on my timeslips... )
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Old 07-16-2012, 08:17 PM   #4
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Yeah, I've noticed there are quite a few calculators out there. They don't always specify if they're calc'ing HP or WHP. I don't really know which one is the most accurate, but this one seemed pretty close based on my dyno numbers. On some of them, I noticed if I put in trap speed and weight I get one result, but then if I put in ET and weight, I get another result. So...who knows what the real answer is. It's just interesting to see what kind of information can be extracted from a timeslip.

This was where I found the HP equation above:
http://www.stangnet.com/mustang-foru...d-here.567417/
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Old 07-16-2012, 08:33 PM   #5
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Quote:
Originally Posted by E.T. View Post
Yeah, I've noticed there are quite a few calculators out there. They don't always specify if they're calc'ing HP or WHP. I don't really know which one is the most accurate, but this one seemed pretty close based on my dyno numbers. On some of them, I noticed if I put in trap speed and weight I get one result, but then if I put in ET and weight, I get another result. So...who knows what the real answer is. It's just interesting to see what kind of information can be extracted from a timeslip.

This was where I found the HP equation above:
http://www.stangnet.com/mustang-foru...d-here.567417/
That's some very interesting info!!!

I would think HP based on MPH would be closer than ET, since your ET is so dependent on how well you can launch your car.
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Old 07-16-2012, 09:02 PM   #6
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That's some very interesting info!!!

I would think HP based on MPH would be closer than ET, since your ET is so dependent on how well you can launch your car.
That makes sense. Here is another one I found. The formula is slightly different but it appears that the result is in rwhp. It would put me over 400 at the wheels though, which seems too high. Although they do mention accuracy degrades over 4000 lbs.

http://books.google.com/books?id=znQ...launch&f=false
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Old 07-17-2012, 12:12 PM   #7
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Did you run your car before the gear swap ? Interested if you seen any gains in ET .
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Old 07-17-2012, 12:57 PM   #8
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Did you run your car before the gear swap ? Interested if you seen any gains in ET .
Unfortunately no, so I have no basis for comparison. Ive read that they should be good for a few tenths, but they probably make it a little harder to get traction.
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Old 07-17-2012, 07:00 PM   #9
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Based on what I've read, I'd doubt 400rwhp.
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Old 07-17-2012, 07:53 PM   #10
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Based on what I've read, I'd doubt 400rwhp.
Yeah, that does seem high. I basically have the JRE 415 package, although I bought it all separately Anyway, it's supposed to be good good for 415 rwhp on the LS3 and 375 rwhp on the L99. I dyno'd about 355. Could just be the dyno, but it was also 93* and humid when I did the pulls. I figure if I dyno'd in colder temps, it might pull a few more ponies.
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