Does a dynamometer tell the turth ?
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
Does a dynamometer tell the turth ?
Would to expects to get the same results with these setups ?
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Anyone have any before and after to show results ?
Assuming you can figure out the losses thur the drive train you should be able to get the same results for the gross HP of the engine and only RWHP would vary based on drive train configuration.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Anyone have any before and after to show results ?
Assuming you can figure out the losses thur the drive train you should be able to get the same results for the gross HP of the engine and only RWHP would vary based on drive train configuration.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Opened a can of worms here 
The only way to figure out what your particular C3 has in drivetrain loss is to do what I did. Take the engine engine out and put it on an engine dyno and then put it on a chassis dyno. Mine resulted in a 23% loss.
Manual transmissions will have less loss than automatics with the TH400 topping the list. You can figure 20-25% or more. I would use a figure in the 22-23% for most C3's with manual transmission and 25% or more with the TH400 transmission.
The only way to figure out what your particular C3 has in drivetrain loss is to do what I did. Take the engine engine out and put it on an engine dyno and then put it on a chassis dyno. Mine resulted in a 23% loss.
Manual transmissions will have less loss than automatics with the TH400 topping the list. You can figure 20-25% or more. I would use a figure in the 22-23% for most C3's with manual transmission and 25% or more with the TH400 transmission.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
The chassis dyno tells the ugly truth. It tells you how much power you're actually putting to the ground. Does it matter that you have a 600 hp motor if it only puts 400 to the ground?
Many dreams have been shattered by the chassis dyno.
Many dreams have been shattered by the chassis dyno.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Use the dyno for a tool, not for absolute numbers. The true test of how much power a car is making or how fast a car is, is by trap speed in the 1/4 mile...
On a chasis Dyno, there is way too many variables to skew the readings, a stall converter can kill 50-75hp on a chasis dyno, yet make you faster at the track.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Would to expects to get the same results with these setups ?
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Assuming you can figure out the losses thur the drive train you should be able to get the same results for the gross HP of the engine and only RWHP would vary based on drive train configuration.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
On top of that, environmental conditions would need to be the same (humidity, temperature, elevation). Pretty easy to guarantee the elevation part, not so much the other two.
Every dyno is different. Dynos of the same manufacturer/model will be close to each other, but one could have worn bearings or be running a bit hotter vs another and although the software will correct for that, it's not perfect.
So it's still a big guessing game.
Dynos are fun for bragging about which engine has more power.
They're a useful tool for determining whether or not your modifications have made an improvement in power.
They are not going to tell you whose car is fastest, though.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
While chassis dyno data are very useful in tuning a given car on a given day, there are too many additional variables in play to accurately extrapolate HP differences at the flywheel between differently set up cars, especially if there's no conditional correction...
As for engine dyno data, unless any two sets of results are corrected to a particular standard, such as those prescribed under SAE J1349, the numbers generated for any two engines can only be considered reference points. Think that's no big deal? I submit that 1) if you happen to be guarantying a build's HP/TQ production, it certainly would be, and 2) you definitely wouldn't want for the spec series mill you've been assigned for the season to have been tuned on a 'high-HP" day without correction (BTDT). My $.02 worth, earned at significant greater expense.
.
As for engine dyno data, unless any two sets of results are corrected to a particular standard, such as those prescribed under SAE J1349, the numbers generated for any two engines can only be considered reference points. Think that's no big deal? I submit that 1) if you happen to be guarantying a build's HP/TQ production, it certainly would be, and 2) you definitely wouldn't want for the spec series mill you've been assigned for the season to have been tuned on a 'high-HP" day without correction (BTDT). My $.02 worth, earned at significant greater expense.
.
Last edited by TheSkunkWorks; Sep 28, 2014 at 02:15 AM. Reason: sp
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If YOU owned a dyno shop, and some local boyz wanted to see how much power their cars could produce, how would YOU calibrate your dyno?
a) calibrate it to give accurate results (knowing that they will be terribly disappointed); OR
b) 'rig' the calibration to give them some 'nice answers'.
Dyno shops can calibrate their equipment to give any kind of results they want. If you want accurate results, tell them you want proper calibration for the dyno.
Be aware that some 'fly-by-night' dyno shops may not even know how to properly calibrate their stuff. They just run the equipment and hand you some paper.
a) calibrate it to give accurate results (knowing that they will be terribly disappointed); OR
b) 'rig' the calibration to give them some 'nice answers'.
Dyno shops can calibrate their equipment to give any kind of results they want. If you want accurate results, tell them you want proper calibration for the dyno.
Be aware that some 'fly-by-night' dyno shops may not even know how to properly calibrate their stuff. They just run the equipment and hand you some paper.
Safety Car
Joined: Jan 2009
Posts: 3,736
Likes: 56
From: anchorage ak
A 700r4 is up there with the 400. The guy that use to have the chasis dyno here in Anchorage said that the 700r4 was the worst. Others here on the forum beg to differ and say the turbo 400 is the worst. Most agree that for autos the power glide wins for least amount of loss in an auto.
DO MA NEU!
DO MA NEU!
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
Ok lets say the engine has 400 HP TH350 with a 3.08 and the dyno peaks at 325 HP and 350 Torque. Should you get the same results if you change to a 3.73 Rear ? Anyone have some real results.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
......Yes......when I had my 383, with 3.55 gears, it dynoed at 373 rwhp. After a change to 4.11 gears (no other changes), it dynoed at the same 373 rwhp. No change. The dyno operator told me that the rear gear ratio in high gear ( 1 to 1) makes no difference in readings. You have the same engine, it cannot magically gain in horsepower. Because of the torque the stiffer gears give you to accelerate faster, what changes is the time to get to your higher rpm. But the horsepower reading at the same rpms is constant on both charts. I checked my numbers and saw this to be true.
Instructor
Joined: Nov 2013
Posts: 220
Likes: 17
From: Pasadena MD
Would to expects to get the same results with these setups ?
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Anyone have any before and after to show results ?
Assuming you can figure out the losses thur the drive train you should be able to get the same results for the gross HP of the engine and only RWHP would vary based on drive train configuration.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
Assuming the same car and the same engine.
1. Auto Trans 3.08 rear vs 3.73 rear
2. Manual Trans 3.08 rear vs 3.73 rear
3. Manual Trans same rear but different gear ratio's.
I know auto vs manual will have difference results but do other changes also produced different results ?
Anyone have any before and after to show results ?
Assuming you can figure out the losses thur the drive train you should be able to get the same results for the gross HP of the engine and only RWHP would vary based on drive train configuration.
How well do dynamometer's, or can they even figure out drive train losses, or is this just a guess / estimate.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
If YOU owned a dyno shop, and some local boyz wanted to see how much power their cars could produce, how would YOU calibrate your dyno?
a) calibrate it to give accurate results (knowing that they will be terribly disappointed); OR
b) 'rig' the calibration to give them some 'nice answers'.
Dyno shops can calibrate their equipment to give any kind of results they want. If you want accurate results, tell them you want proper calibration for the dyno.
Be aware that some 'fly-by-night' dyno shops may not even know how to properly calibrate their stuff. They just run the equipment and hand you some paper.
a) calibrate it to give accurate results (knowing that they will be terribly disappointed); OR
b) 'rig' the calibration to give them some 'nice answers'.
Dyno shops can calibrate their equipment to give any kind of results they want. If you want accurate results, tell them you want proper calibration for the dyno.
Be aware that some 'fly-by-night' dyno shops may not even know how to properly calibrate their stuff. They just run the equipment and hand you some paper.
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I like using the G's curve which shows me how its pulling and at what RPM the g's start to fall off. The phone app I could never get it to work but I am still using the old 3GS phone.
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
......Yes......when I had my 383, with 3.55 gears, it dynoed at 373 rwhp. After a change to 4.11 gears (no other changes), it dynoed at the same 373 rwhp. No change. The dyno operator told me that the rear gear ratio in high gear ( 1 to 1) makes no difference in readings. You have the same engine, it cannot magically gain in horsepower. Because of the torque the stiffer gears give you to accelerate faster, what changes is the time to get to your higher rpm. But the horsepower reading at the same rpms is constant on both charts. I checked my numbers and saw this to be true.
Last edited by cagotzmann; Sep 28, 2014 at 09:39 PM.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
By gear, do you mean trans gear?......I have a TH400 auto trans, so the runs were done in high gear (3rd on 3 speed auto), 1 to 1 like driving on the street. If you have an overdrive trans or manual, runs are usually done in your 1 to 1 ratio gear.
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
So how do they prevent the auto transmission from down shifting. Do you need to disconnect the kickdown cable ?
Last edited by cagotzmann; Sep 28, 2014 at 09:35 PM.
Racer
Joined: May 2011
Posts: 484
Likes: 10
From: Newcastle NSW
Factor these comments in to stated figures from some of the performance 'crate' engine suppliers and the real truth is often somewhat s-t-r-e-t-c-h-e-d. Known of such engines supplied for race purposes where customers been disapointed with results - had the engines subsequently put on a dyno and being nowhere near suppliers figures - 15% less than stated is not unusual!
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
I find that interesting, but using your 1:1 gear doesn't makes sense you would need to reach top speed of the car to cover the complete RPM Range. I would think you could use any gear and get the same results.
So how do they prevent the auto transmission from down shifting. Do you need to disconnect the kickdown cable ?
So how do they prevent the auto transmission from down shifting. Do you need to disconnect the kickdown cable ?
Driving with an auto trans is tricky, there is some technique involved as you have to get above the rpm that would downshift with the pedal floored before your measurement begins. For me, that was between 3500 and 4000 rpm. Or, as you mentioned, you could disconnect your kickdown cable. There is no kickdown cable on a '69 TH400, hence the tricky driving. Also, with a high stall converter, it will flash, and torque readings may spike before settling down. Despite the wicked looking torque curve, the HP curve was steady.
Pic........
