Wheel Horsepower from Trap Speed

BilletGarage

BilletGarage

Diesel Addict
Joined
May 10, 2007
Messages
723
Alright, I am trying to make heads or tales of the difference between wheel horsepower determined on a DynoJet or other inertia dyno and wheel horsepower determined from 1/4 mile trap speed . . .

I recently dyno'd on a DynoJet 224X and put down a max 441hp to the wheels. Second pull was 438hp I believe. Two months prior, on another inertia dyno, I pulled 443hp.

Now . . .

Based on every calculator I found by googling (wheel horsepower from trap speed) I am putting 545hp to the wheels. :doh:

Vehicle Weight w/driver: 7,650lbs
Trap Speed in Bakersfield on multiple runs: 97mph

Can someone please explain this descrepancy? Is the dyno just not loading the truck (spooling the turbo)? I have played with these calculators with other peoples times and trap speeds and some jive with their dyno numbers and some don't . . .

What gives here? Which is more accurate? Do the comparison yourself and see if your numbers jive! I want to know! Also curious if numbers on a load dyno such as a Superflow or Mustang jive more with inertia dyno numbers or with the calculators.

http://www.tunercalcs.com/hp-from-quarter-mile-trap-speed.html

Thanks in advance guys/gals!
 
My truck weighs 6500lbs, and would run 16.2's@81mph with a setup that dyno'd 281hp/693tq. I put the trap speed in that calculator, and it says 269.6hp, so it was only about 11hp off on my truck. I havent ran my current setup at the strip, so I cant compare it to my latest HP numbers, but it seems pretty close on my old numbers. Oh, and my dyno #'s came from dunbars dyno. I would suggest sticking your truck on his dyno.

Eric
 
Cummins Driver said:
My truck weighs 6500lbs, and would run 16.2's@81mph with a setup that dyno'd 281hp/693tq. I put the trap speed in that calculator, and it says 269.6hp, so it was only about 11hp off on my truck. I havent ran my current setup at the strip, so I cant compare it to my latest HP numbers, but it seems pretty close on my old numbers. Oh, and my dyno #'s came from dunbars dyno. I would suggest sticking your truck on his dyno.

Eric
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Good information Eric! Thanks! I'm starting to think too that maybe the operator needs to be very experienced in running a turbo diesel on an inertia dyno (proper turbo spooling, etc). In general the numbers that come off of Dunbar and Maddog's dynos seem to be much more in line with trap speed indications. Of course that's just a general observation . . .
 
Yeah, dyno's can vary a lot. Honestly though, other than for show, as long as you are putting down the numbers on the track, then the dyno numbers dont mean anything:rockwoot:
 
Same thing with me. My trap speed indicates a lot more power than the truck is putting down on the dyno. That's why next week I'm going back to the track and seeing how she runs. I ran a 14.6@96mph with no boosted launch on 35's at 7600lbs.
 
BgBlDodge said:
Same thing with me. My trap speed indicates a lot more power than the truck is putting down on the dyno. That's why next week I'm going back to the track and seeing how she runs. I ran a 14.6@96mph with no boosted launch on 35's at 7600lbs.
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Wow! Yeah, with your MPH it sounds like your leaving alot on the table on the short side of the track . . . I ran 13.63@97mph for reference. What were your 60' times like? 1/8th mile?
 
The calculator in your link shows over 100hp more than my highest dyno number. 6700lbs @117mph
 
Land and Sea. There is another HP calculator program out there that I used once that was almost dead on from my roller numbers. I can't remember what or where the calculator is though.
 
Double J said:
Land and Sea. There is another HP calculator program out there that I used once that was almost dead on from my roller numbers. I can't remember what or where the calculator is though.
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I just actually heard about Land and Sea dynos for the first time last night. They seem well built and accurate based on what I've read. If you find that calculator, I would like to see it for sure!
 
The only acurate HP calculator is the HP by 1/4 mi. trap speed located at Smokemup.com. The HP calculator here at Comp D in the upper menu also seems to come up with the same numbers as Smokemup.

7650 @ 97 = 474 rwhp.

Also, these numbers will almost always only match dyno results from a Dynojet 248. This is just my opinion based on experience, but a 224 is not a good dyno to get acurate numbers on from a diesel. It is too small to run in inertia mode and also the numbers are greatly effected by the load settings when using the load mode. Same goes for other load typ dynos. Unless the inputs used to determine the amount of load are specifically calibrated precisely for each individual truck, the numbers are rarely acurate.
 
Dockboy said:
The only acurate HP calculator is the HP by 1/4 mi. trap speed located at Smokemup.com. The HP calculator here at Comp D in the upper menu also seems to come up with the same numbers as Smokemup.

7650 @ 97 = 474 rwhp.

Also, these numbers will almost always only match dyno results from a Dynojet 248. This is just my opinion based on experience, but a 224 is not a good dyno to get acurate numbers on from a diesel. It is too small to run in inertia mode and also the numbers are greatly effected by the load settings when using the load mode. Same goes for other load typ dynos. Unless the inputs used to determine the amount of load are specifically calibrated precisely for each individual truck, the numbers are rarely acurate.
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Ok, now that makes alot of sense and is in line with most of the 6.0 guru's assertions that the stock 135cc injectors are good for right around 500 WHP. Using the calculator above with the exact mph (97.91mph) I get 487whp. I can live with that for now. LOL

My fuel only number based on my trap of 92.45mph is 410whp and consistent for most Race Tunes with a crappy '05 turbo.

Thanks Greg for that information! Very helpful!
 
Then there's the 2wd (on a dyno) vs 4wd boosted launch. You shouldn't be able to get the same boost pre-load on a dyno at 55mph/locked OD then you can sitting on the torque converter and brakes.

If you wheel spin, you'll tend to get a higher MPH, and slower et vs no wheel spin.

All you autos running 13.6 @ 96.. I ran a 100 at 13.9.. 4mph is a big difference, on a 248 I did 512 with the Edge combo. Now, I've also ran 14.4, 14.2 14.1 at 100mph and even a 14.9 with a 2wd tire spinning 2nd and 3rd gear run. Always managed 100, and one 99mph run. I'll have to double check my time slips to get accurate numbers, but in a nut shell. I should of been around 7200# maybe 7300#. never weighed that day. I had to run a over 1/4 tank due to the AirDog big line pickup.

Put in the numbers, I'm at 495hp at 7300#. If you factor in the fact that I bogged most of them runs as the clutch just grabbed, or it slipped. it's rather close if you take into account the mass amounts of human error I had :)

So, I suspect the 450hp range is accurate.
 
I still think the old "area under the curve" argument needs to be taken into consideration. A 500hp small block chevy might be making it's peak power at 6500rpm, but take that motor down to 4500rpm and it might only be making 375hp. A diesel (which has more gears to take advantage of it's narrow power band) might be making 500hp at 3800rpm, but take that same motor down to 2300rpm (a 1500rpm drop) and as long as there is still a load and the boost is still up, I'm pretty sure power would still be close to 500hp. Therefore a diesel might have the same average horsepower in it's powerband as a much more powerful gas motor. Since the hp calculators work in a gasoline world, I'm willing to bet that the real power numbers are closer to dyno numbers than we might think. We brake-boosted the crap out of an 06 Ram with light mods and it made 425rwhp on the dyno from like 2000rpm on up, just a flat line, no power curve. Anyways, just something to consider.
 
Well, I just ran my truck for the very first time last night.....Jeff Garmon did the math two different way with my quickest run and came up with one that said 590HP and one that said 598HP.....

I just got through taking all 8 time slips and running an average MPH. I'm just over 106mph for an average.....I weighed my truck full of fuel (34 gal.) with me in it (250lbs) and it weighs 7420 lbs.

Last night I was just over 1/2 tank (approx. 17 gals.) with me and some junk in the cab. So I figure I was a conservative 7300 lbs.....

Using the CompD calculator up top, It shows that I'm making 595 RWHP.......Given that I dyno'd 530/1050 before I installed my Flux 2's and Stg. 2 CP3, That should be just about right......Jeff Garmon agrees.....

BTW, They were all 10 lb. Boosted 4x4 lauches...I stayed in 4wd. the whole way down the track...

I think its Very Accurate!!!!
 
Dalpilot said:
Was that "The Jeff Garmon"? LOL
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LOL Yes it WAS!!!

Every time he calls me or I call him, I Always answer "hello, THE Jeff Garmon"......He laughs everytime!!

He was the man WAY BEFORE Diesel was Cool!!!!!!!!!!!
 
The calculator here is right on. Less than 1hp from my Trap to Dyno on Maddogs. Well there was a head wind so I might have gained another mph. but close enough.
 
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