Dyno Guru's is this normal?
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 994
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From: Jamison PA
Dyno Guru's is this normal?
Just had my Stock LT4 Dyno'd on a mobile dyno. Had it done a year ago, also on a mobile dyno but not the same one as this year. Last year my numbers were 298.2 HP-307.2 Torque. HP and Torque curves crossed at 4950rpm. AF averaged 11.5 from 3500-6500. This year it dyno'd 285 HP-289.7 Torque. HP and Torque curves crossed at 5250rpm. AF was 12 from 3000-6500. The only thing different with the car is 4.11 gears just put in. Question is, is the difference in readings caused by the different dyno or did the gears cause the change or is it a combo of both?
[Modified by Tony.96LT4, 7:03 PM 6/27/2004]
[Modified by Tony.96LT4, 7:03 PM 6/27/2004]
Le Mans Master
Joined: Feb 2002
Posts: 5,970
Likes: 20
From: San Marcos Texas
Re: Dyno Guru's is this normal? (vader86)
hp and tq should always cross at 5250. When they dont on a dyno graph its because the hp and tq are not scaled the same by the dyno computer. But if you look at the hp and tq seaperatly you will see that the numbers are equal at 5250.
Thread Starter
Burning Brakes
Joined: Apr 2001
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From: Jamison PA
Re: Dyno Guru's is this normal? (chriswtx)
hp and tq should always cross at 5250. When they dont on a dyno graph its because the hp and tq are not scaled the same by the dyno computer. But if you look at the hp and tq seaperatly you will see that the numbers are equal at 5250.
Thread Starter
Burning Brakes
Joined: Apr 2001
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From: Jamison PA
Re: Dyno Guru's is this normal? (Vic'89)
Vic, I went from 3.45's to the 4.11's and I expected they would but not 13 HP worth. Can I "assume" that the HP and Torque numbers are correct on my dyno from last year even though the graphs aren't scaled correctly?
Le Mans Master
Joined: Feb 2002
Posts: 5,970
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From: San Marcos Texas
Re: Dyno Guru's is this normal? (Tony.96LT4)
Its not that the graphs aren't scaled correctly. They just are not scaled the same for hp and tq.
Heres an example. My 93' NSX dyno on 2 different dynos.
First one, notice the scales on the left and right are different.
Not too shabby for a Normally aspirated 3.0 267rwhp/206rwtq
Second one they are the same and cross at 5250.
The hp and tq curves just cross at different points but the numbers are correct.
[Modified by chriswtx, 9:55 PM 6/27/2004]
[Modified by chriswtx, 9:56 PM 6/27/2004]
[Modified by chriswtx, 9:57 PM 6/27/2004]
Heres an example. My 93' NSX dyno on 2 different dynos.
First one, notice the scales on the left and right are different.
Not too shabby for a Normally aspirated 3.0 267rwhp/206rwtq
Second one they are the same and cross at 5250.
The hp and tq curves just cross at different points but the numbers are correct.
[Modified by chriswtx, 9:55 PM 6/27/2004]
[Modified by chriswtx, 9:56 PM 6/27/2004]
[Modified by chriswtx, 9:57 PM 6/27/2004]
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Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 994
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From: Jamison PA
Re: Dyno Guru's is this normal? (chriswtx)
OK! I got it now. Thanks for clearing that up. I didn't notice the HP and Torque were different. I was reading both off the same scale. Thanks!
Race Director
Joined: May 2001
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Re: Dyno Guru's is this normal? (Tony.96LT4)
The difference in A/F ratio can simply be a difference in the sensor or in weather conditions. That's why you can't just say matter of factly "every car should be tuned for 12.8:1 A/F ratio for peak power" Although a statement like that may be techincally correct, the 02 sensor on your dyno might not be 100% accurate. So you just have to fiddle with it until you find the point where your car makes peak power.
11.5:1 on one dyno can easily be the same a/f ratio as 12:1 on another dyno, so I really wouldn't worry about that. As for the horsepower lost? It's all about the gears and weather. Wanna try a neat trick, next time you're at the dyno make a pull in third gear. The graph will have the exact same shape but you'll have lower numbers clear across the board.
11.5:1 on one dyno can easily be the same a/f ratio as 12:1 on another dyno, so I really wouldn't worry about that. As for the horsepower lost? It's all about the gears and weather. Wanna try a neat trick, next time you're at the dyno make a pull in third gear. The graph will have the exact same shape but you'll have lower numbers clear across the board.
Safety Car
Joined: Sep 2000
Posts: 3,524
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From: Hinckley Ohio
Re: Dyno Guru's is this normal? (Vic'89)
I know this has been
But I still don't get it.......So we are saying 4.10's are less efficient gears than 3.45.......for same motor rpm the half-shafts, wheels, & tires are turning slower so should they take up less power?????
Ok, so 1:1 is most efficient transmission performance, but again in 1st, 2nd or 3rd the entire drive line is turning a LOT slower, again sucking up less horsepower......seems like you should get higher horsepower unless a lot of heat is going into the tranny...
I am a slow learner....maybe someday I will get it????
Le Mans Master
Joined: Mar 2000
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From: If you read this, you'll go blind
Re: Dyno Guru's is this normal? (LT4BUD)
Different Dynos can yeild slightly different results.
Weather plays a very big role in performance.
Another big factor is what temperature was the engine before the run? You'll see more power when the engine is cooler.
Thread Starter
Burning Brakes
Joined: Apr 2001
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From: Jamison PA
Re: Dyno Guru's is this normal? (Nathan Plemons)
Nathan, I had a pull in third gear and yes it was lower 273.7 HP and 274.0 Torque. I also had a run, the first one, thrown out cause the E-brake was on. When I saw 174 HP come up on the screen my jaw dropped but then when we found the E-brake on, the guy doing the dyno got a quick lesson in Vette E-brakes.
Thanks guys.
Thanks guys.
Le Mans Master
Joined: Mar 2000
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From: If you read this, you'll go blind
Re: Dyno Guru's is this normal? (lead foot 85 vet)
so you want to dyno in the highest gear to get the highest hp numbers? 6 th gear or in my case overdrive?
You can do lots of things make a run look better/more power.
Burning Brakes
Joined: Aug 2000
Posts: 984
Likes: 1
From: Cincinnati OH
Re: Dyno Guru's is this normal? (LT4BUD)
I know this has been
But I still don't get it.......So we are saying 4.10's are less efficient gears than 3.45.......for same motor rpm the half-shafts, wheels, & tires are turning slower so should they take up less power?????
Ok, so 1:1 is most efficient transmission performance, but again in 1st, 2nd or 3rd the entire drive line is turning a LOT slower, again sucking up less horsepower......seems like you should get higher horsepower unless a lot of heat is going into the tranny...
I am a slow learner....maybe someday I will get it????
This phenomenon only affects inertial dynos such as a Dynojet, which require a drum to be accelerated. A brake dyno can measure steady state power, taking driveline inertia out of the equation. Gear friction is also a factor, but not so much as driveline inertia when you are talking about an inertial dyno.
I always wondered why no one did a dyno run in 6th gear, until someone pointed out the tire speed at redline in 6th gear
. Your engine doesn't have enough power to ever hit that speed in 6th on the road, but nothing would stop it on a Dynojet.