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Old 04-06-2013, 10:51 PM   #1
SubaruWrxNewb
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Default Horsepower and trap speed relation

I understand all dynos are different and read differently. I understand that they are just a tuning tool and some read lower/higher than others. I see a lot of people saying that if you run it at the track the trap speed will tell you what you're making. So, what is the real relation between trap speeds and horsepower?

I ran my car for the first time today at a local 1/8 mile track. 1.78 60ft time, 7.8 et @ 91. I had a run at 92 mph, but the et was higher. I'm just trying to get a realistic idea of what kind of power my car is making.

Thanks!
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Old 04-06-2013, 11:44 PM   #2
freddy121389
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Can you list what you have done to the car and what the rest of your drag info was, like 60ft etc. If you pulled off around a 1.7 60ft. My guess is you would trap around 120mph @ 11.8-11.9 1/4 mile. Power can vary since I have no idea what you drive. If its a 2011 Wrx like my car I would guess like 350-360whp.
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Old 04-07-2013, 12:09 AM   #3
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Quote:
Originally Posted by SubaruWrxNewb View Post
I understand all dynos are different and read differently. I understand that they are just a tuning tool and some read lower/higher than others. I see a lot of people saying that if you run it at the track the trap speed will tell you what you're making. So, what is the real relation between trap speeds and horsepower?

I ran my car for the first time today at a local 1/8 mile track. 1.78 60ft time, 7.8 et @ 91. I had a run at 92 mph, but the et was higher. I'm just trying to get a realistic idea of what kind of power my car is making.

Thanks!
The people that tell you trap speed will tell you all are just as ignorant as the dyno people.

Traps are much better but are not something to gauge off except personal gains... Just like a dyno.

Just like the dyno can read low or high, traps speeds are highly dependant on driver and weather. The same car with no alterations can vary 1-5mph easily. The driver can vary it 1-10mph. I've seen both extremes of both variables.

With that soapbox spiel over with, yes you are somewhere in the 350-400 range of that is an average wrx on an average day.

91mph 1/8th mile is no slouch. That's at least a 120+ 1/4.
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Old 04-07-2013, 09:15 AM   #4
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Quote:
Originally Posted by freddy121389 View Post
Can you list what you have done to the car and what the rest of your drag info was, like 60ft etc. If you pulled off around a 1.7 60ft. My guess is you would trap around 120mph @ 11.8-11.9 1/4 mile. Power can vary since I have no idea what you drive. If its a 2011 Wrx like my car I would guess like 350-360whp.
The car is an 04 STi. It's a built 2.5L, GTX35R, FMIC, Injectors, etc.... Running on a pump gas tune right now and it made 450/396 at 21 psi on a dynojet. It has an e85 tune and it made 540/460 on 25 psi on the same dyno, but since e85 is so scarce around me, I'll be getting retuned on VP 100 or something similar very soon.

I was very happy with the passes I made, just curious as to what my traps tell people on here than know more about them and the correlation they have with HP. Like I said above, hopefully I'll get a tune on some better gas and get to make some 1/4 mile passes!

Thanks guys!
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Old 04-07-2013, 10:21 AM   #5
juanmedina
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The ralationship is power to weight ratio to trap speed... not just power
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Old 04-07-2013, 12:23 PM   #6
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Quote:
Originally Posted by juanmedina View Post
The ralationship is power to weight ratio to trap speed... not just power
That's still only partly true. They are directly proportional, but that's a scatter plot that will still be all over the place.
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Old 04-07-2013, 01:24 PM   #7
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Quote:
Originally Posted by SubaruWrxNewb View Post
The car is an 04 STi. It's a built 2.5L, GTX35R, FMIC, Injectors, etc.... Running on a pump gas tune right now and it made 450/396 at 21 psi on a dynojet. It has an e85 tune and it made 540/460 on 25 psi on the same dyno, but since e85 is so scarce around me, I'll be getting retuned on VP 100 or something similar very soon.

I was very happy with the passes I made, just curious as to what my traps tell people on here than know more about them and the correlation they have with HP. Like I said above, hopefully I'll get a tune on some better gas and get to make some 1/4 mile passes!

Thanks guys!
your #'s are fairly accurate, the 04 is the lightest of the years for the sti and it usually takes 500-520whp on a dj to go 10.90's @ about 126 with a good driver and good 60ft(high 1.50's).I assume you are still on stock cams and heads.good luck on your next trip to the track.
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Old 04-07-2013, 11:48 PM   #8
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i went 126mph this weekend with 490whp and 440wtq dynojet numbers. 1.67 60ft.
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Old 04-08-2013, 08:41 AM   #9
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Quote:
Originally Posted by juanmedina View Post
The ralationship is power to weight ratio to trap speed... not just power
Quote:
Originally Posted by ProfessWRX View Post
That's still only partly true. They are directly proportional, but that's a scatter plot that will still be all over the place.
This is correct that it will be a huge scatterplot depending on driver, track conditions, etc. But in general terms you can predict the ideal 1/4 mile time and trap if you know the HP and weight of the car. Here's a calclator that have I have found to be quite good compared to the results I've seen online with a "good" driver and "good" car setup (tires, etc).

http://vexer.com/automotive-tools/1-...MPH-calculator

It even shows the distribution curves that it uses to calculate the results. The results on this plot generally seem to line up well with cars that have sticky tires (probably drag radials for the higher powered setups) and good drivers. Probably in the 1.5s 60' range or better. You can definitely have a high powered car that goes a lot slower than this calculator if you're driving or tires aren't up to snuff.
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Old 04-08-2013, 07:43 PM   #10
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Quote:
Originally Posted by xluben View Post

This is correct that it will be a huge scatterplot depending on driver, track conditions, etc. But in general terms you can predict the ideal 1/4 mile time and trap if you know the HP and weight of the car. Here's a calclator that have I have found to be quite good compared to the results I've seen online with a "good" driver and "good" car setup (tires, etc).

http://vexer.com/automotive-tools/1-...MPH-calculator

It even shows the distribution curves that it uses to calculate the results. The results on this plot generally seem to line up well with cars that have sticky tires (probably drag radials for the higher powered setups) and good drivers. Probably in the 1.5s 60' range or better. You can definitely have a high powered car that goes a lot slower than this calculator if you're driving or tires aren't up to snuff.
Shift time is also a huge variable. You can usually tell the grade of driver off the 60' too, but sadly the best launch can still be granny shifted. And I learned a long time ago that most track goers are pitiful, and even self proclaimed "good drivers" are usually terrible. I've been to the track too many times to believe otherwise.
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Old 04-11-2013, 07:16 PM   #11
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Google "Moroso Power-Speed Calculator".
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Old 04-11-2013, 11:00 PM   #12
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got a 00rs coupe with 04sti longblock, 06 6mt with a GT3076 .63 rotated, made 380whp/360tq @ 20psi on Precision Tuning Dyno "DynoJet" Reads legal from what i see.

best pass so far 11.9 at 117mph, need to get better at launching, tried 5k-6krpm dumping the clutch and feels like wheel hop in the back, tried slipping the clutch and got slightly better launches, still not a single 1.6x 60f. last year i got a 1.6x with my old engine that ran not this great, same suspension and worst tires, idk...
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Old 04-11-2013, 11:46 PM   #13
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Quote:
Originally Posted by snake32 View Post
got a 00rs coupe with 04sti longblock, 06 6mt with a GT3076 .63 rotated, made 380whp/360tq @ 20psi on Precision Tuning Dyno "DynoJet" Reads legal from what i see.

best pass so far 11.9 at 117mph, need to get better at launching, tried 5k-6krpm dumping the clutch and feels like wheel hop in the back, tried slipping the clutch and got slightly better launches, still not a single 1.6x 60f. last year i got a 1.6x with my old engine that ran not this great, same suspension and worst tires, idk...

The best I got on my '04 was a 1.71 short time, and that was launching on the 2 step. I did a total of 3-4 passes, best was a 13.2 at 103ish. I was all pissed off at the time because it seemed like everyone on here does about the same in a stock STi. Then again, the DA that night was 6500 feet, not to mention it was in the 90's and for 5 minutes, I was sitting in the staging lanes heatsoaking the hell out of the TMIC. I agree with the wheelhop thing, mine only stopped when I lowered the 2-step to 5000 RPM and put slightly more air in the tires so give that a try. This was stage 2/E85 with a broken ringland on cyl #3 I later came to find out. Never went back after that, a timeslip to me isn't worth possibly trashing my drivetrain.
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Old 04-12-2013, 12:19 AM   #14
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Here is a great spread sheet of horsepower on different dynos, the weight of the car and the ET and trap speed it ran.


Last edited by Boosted Tuning; 04-17-2013 at 12:30 AM.
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Old 04-12-2013, 07:41 PM   #15
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I went 7.6@92 in the eighth and Im making 324/372 on a dynojet but my cars light, so you're probably making similar numbers.
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Old 04-16-2013, 05:59 PM   #16
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Quote:
Originally Posted by xluben View Post
This is correct that it will be a huge scatterplot depending on driver, track conditions, etc. But in general terms you can predict the ideal 1/4 mile time and trap if you know the HP and weight of the car. Here's a calclator that have I have found to be quite good compared to the results I've seen online with a "good" driver and "good" car setup (tires, etc).

http://vexer.com/automotive-tools/1-...MPH-calculator

It even shows the distribution curves that it uses to calculate the results. The results on this plot generally seem to line up well with cars that have sticky tires (probably drag radials for the higher powered setups) and good drivers. Probably in the 1.5s 60' range or better. You can definitely have a high powered car that goes a lot slower than this calculator if you're driving or tires aren't up to snuff.
This vexer calculator was unbelievably close to the all the numbers my car makes. I put in my ET and these were the numbers...
Measured Vexer Calcuator
MPH- 116.36 - 116.14
ET- 11.735 - 11.735
WHP- 390 - 385

Sweet so according to xluben I'm a good driver!
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Old 04-18-2013, 09:31 AM   #17
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If you make sure you aren't having timing pulled with logs, from knock/heat/shift knock/etc. then the hp/trap data should be pretty succinct.

Also, if you aren't keeping yourself in your powerband (this is why road logs and vd are cool) then your hp/traps won't match, either. I remember driving my sti like a noob at the strip, just not critically thinking, wasn't that long ago (gut check, 2006) I was going to redline on the vf in 3rd and 4th when I should've shifted, that hurt the trap, surely, hindsight is 20/20.
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