MPH vs. HP

JohhnyFoxtrot

JohhnyFoxtrot

need a trailer
Joined
May 25, 2007
Messages
1,179
Well I have been up in the air on my hp vs what a dyno says for a couple years. It neve seems to matter wether I have a single of any size or my current twins that my 60' time is always 1.99 or 1.98 at the least. Like I said it didn't matter if I was running low 13's or my current fast time of mid 11's. I see guys running low or 11.2-11.6 et's with a lower trap speed than I was, but a faster 60' which I can understand.

Now where does a 7500lbs truck that can run a 1.99 60' and a trap speed of 118 and a 11.73e.t. with 35"'s really stand? My highest dyno runs have been only 760ish but been low on rail pressure or boost or both.

What does the majority say?
 
118MPH at 7500 lbs calculates to 836 HP. You need to be accurate with the weight to get a realistic number. Even a few hundred lbs can mess up the calculation.
 
Well I sled pull and hang 7 100lbs pound weights to make 8000 with a 1/4 tank of fuel and no tailgate. With a tail gate and half tank of fuel I am there. Liked I said I know my 60' kills me on the top end for e.t. Never had a good dyno or 1/4 run with a good 60 time.
 
Here's a video of the second to last time it ran. Its the red one of course.

[ame="http://www.youtube.com/watch?v=4L3naSTtzYA"]http://www.youtube.com/watch?v=4L3naSTtzYA[/ame]
 
Why so slow on the 60'? What boost are you leaving at? When are you locking TC?
 
The HP calculator at the top of the page works quite well when you use weight and speed.
 
Your truck should be very close to mine for race weight ...Mine weighed 7300 with me in it (250 ish)...

At 118+ mph...You're making more power than your sig. say...

Like said, the calculator above has always been spot on for me (My "Former" HP)
 
IIRC the Smarty was set to defuel at a certain boost level on launch, so it was a pretty soft launch. Aside from the big arse front frame bracket to hang the sled pulling weights, he also has a big air compressor mounted in the bed!
 
I've been fighting to get the 60' time down on my 98' daily driver 4x4 and all I've managed so far is a 1.97 60' time. I always thought my truck was under powered, but then I figured out it would run the same 2.0 to 1.98 time regardless of 10 psi boosted launch or 20 psi boosted launch. I finally figured out that my lowly 385 HP 4x4 7200 lb truck was spinning on the launch. I couldn't feel it spinning, I didn't think it had enough power to spin, but it definitely was when I finally got someone to watch the launch from outside the truck.

I'd imagine your problem is spinning as well. Have you tried airing down the tires to 30 psi front and rear? Also, what size tires are you racing with?
 
If you guys could lock the TC in a lower gear I think you would see a substantial decrease in 60' times.
 
Big Blue24 said:
I've been fighting to get the 60' time down on my 98' daily driver 4x4 and all I've managed so far is a 1.97 60' time. I always thought my truck was under powered, but then I figured out it would run the same 2.0 to 1.98 time regardless of 10 psi boosted launch or 20 psi boosted launch. I finally figured out that my lowly 385 HP 4x4 7200 lb truck was spinning on the launch. I couldn't feel it spinning, I didn't think it had enough power to spin, but it definitely was when I finally got someone to watch the launch from outside the truck.

I'd imagine your problem is spinning as well. Have you tried airing down the tires to 30 psi front and rear? Also, what size tires are you racing with?
Click to expand...

I was doing decent 1.8's at 11-13 psi launch at just under 6500 lbs. Tires were aired down a bit.
 
I do 1.60's at 15-17lbs boost with street pressure in the tires (40F 35R), locking TC with the 1-2 shift... at 7300lbs
 
after PRI i'm going to tinker with locking TC in the upper part of 1st gear
 
I lock tc just before the 2nd gear shift. Lanching at 18-20 psi I just always imagimed it was the tight convertor. It is a triple disk suncoast.
 
Yeah, something's up...

My truck weight had to be close to yours... 18-20 psi launch...1.63 best...1.66-1.70 were normal... Locking as soon as it hits 2nd...

1.9's aren't right IMO...
 
I lock at 10mph in 1st. 1.57-1.59 60'. Toyo Proxie ST's.

Paul
 
i was told the 47 can't for some reason. when i blow this trans, it might be worth to change up to a 48
 
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