Martin D
Enthusiast
My Final answer. you will lose 2.5% of your power on the dyno if you switch gears to 3.55. But it's ok....Trust me.
Regards.
Martin
Regards.
Martin
Dynos, Gears and RWHP?
- Thread starter ViperRichRT10
- Start date
Joseph Dell
Enthusiast
So Martin, when are you going to take those "best flowing set of GENII heads ever" and put that beast on a dyno??
Isn't it Sept yet?
JD
Isn't it Sept yet?
JD
00prowler
Enthusiast
There must be something wrong with you car if a 911TT went by you with 600RWHP with those gears at that speed..I have 640 RWHP with 3.55s and I can tell you it aint even close past the launch..hard to beat em off the line for sure...Al
VIPER GTSR 91
Enthusiast
There is nothing wrong with my car and I hope you too get to compete and get your ass kicked with a much finer car, i.e. Porsche twin turbo. There was no threat until past 130 mph and then he was GONE. My point is the gears, and I am sure it would have been a better chase with my old stock 3:08 gears. With your 3:55s you would have been really TOASTED on the long end with this Porsche. Dont think the Viper is the best and fastest car out there.
[/QUOTE] There is nothing wrong with my car and I hope you too get to compete and get your ass kicked with a much finer car, i.e. Porsche twin turbo.
[/QUOTE]
When you say finer car do you mean more expensive? Seems to me I have seen sevaral videos of a stock 96 GTS spanking a brand new at the time x50 package twin turbo porsche. I too find it hard to beleive that a Viper with over 200 more RWHP is going to have trouble with a stock 996tt at any point but a dig.
[/QUOTE]
When you say finer car do you mean more expensive? Seems to me I have seen sevaral videos of a stock 96 GTS spanking a brand new at the time x50 package twin turbo porsche. I too find it hard to beleive that a Viper with over 200 more RWHP is going to have trouble with a stock 996tt at any point but a dig.
DEADEYE
Viper Owner
My 3:73's definately slowed me down. Cars with less hp kept up with me. My car pulled harder, but for much shorter distances.
joe117
Enthusiast
This is the formula for horsepower.
(Torque * RPM) / 5252 = horsepower
If the dynojet isn't making these measurements, it can't tell you what your horsepower is.
If there is a flaw in the way it measures torque, perhaps the inertia you speak of, then that may give you errors that are an artifact of the test equipment.
What I mean by that is,
Inertia is not in the formula. If inertia changes the torque readings on a dyno, then the dyno is not giving you real torque data.
But again, there is only one formula for horsepower and you need to measure torque at rpm.
And from the formula, you can see that gears don't change the horsepower.
(Torque * RPM) / 5252 = horsepower
If the dynojet isn't making these measurements, it can't tell you what your horsepower is.
If there is a flaw in the way it measures torque, perhaps the inertia you speak of, then that may give you errors that are an artifact of the test equipment.
What I mean by that is,
Inertia is not in the formula. If inertia changes the torque readings on a dyno, then the dyno is not giving you real torque data.
But again, there is only one formula for horsepower and you need to measure torque at rpm.
And from the formula, you can see that gears don't change the horsepower.
Answers to 2. First, no a dynojet does not measure torque. It calculates it. The way it does it requires it to be a dynamic measurement (vehicle speeding up). That is how the vehicles inertia comes into play. Hone up on your physics and you will be able to see how inertia can be the device that allows measurement on on side and affects the results on the other side. If you do not believe inertia has an impact then answer the question why a light flywheel allows the car to perform better (in some situations).
As to the turbo Porsche I have gone at it with a modified turbo and just barely beat him. And I have 690 RWHP. They can be wickedly fast. Note mods are not always obvious either. Can you call a twin turbo a sleeper?
As to the turbo Porsche I have gone at it with a modified turbo and just barely beat him. And I have 690 RWHP. They can be wickedly fast. Note mods are not always obvious either. Can you call a twin turbo a sleeper?
joe117
Enthusiast
"If you do not believe inertia has an impact then answer the question why a light flywheel allows the car to perform better (in some situations)."
Removing weight from the flywheel will reduce the load on the engine.
If the car weighs x and the drag is x then it will require a certain amount of power to accelerate it to some given speed.
If you remove weight from the flywheel, then more of the engine horsepower will be available to accelrate the car.
Reduced flywheel weight will allow the car to slow down quicker also.
The weight of the flywheel will have no effect on engine horsepower or rear wheel horsepower.
"a dynojet does not measure torque. It calculates it. The way it does it requires it to be a dynamic measurement (vehicle speeding up). That is how the vehicles inertia comes into play."
If the dynojet calculates torque in a way that allows inertia to enter the torque data, then the dynojet is simply not giving you a true horsepower measurement.
No acceleration is required to measure horsepower. Only a measurement of torque at any given rpm.
"Hone up on your physics and you will be able to see how inertia can be the device that allows measurement on on side and affects the results on the other side"
How about you give me that physics lesson.
Tell me how inertia would be involved in making horepower measurements using a standard dyno.
A standard dyno uses a load that does not require acceleration.
Removing weight from the flywheel will reduce the load on the engine.
If the car weighs x and the drag is x then it will require a certain amount of power to accelerate it to some given speed.
If you remove weight from the flywheel, then more of the engine horsepower will be available to accelrate the car.
Reduced flywheel weight will allow the car to slow down quicker also.
The weight of the flywheel will have no effect on engine horsepower or rear wheel horsepower.
"a dynojet does not measure torque. It calculates it. The way it does it requires it to be a dynamic measurement (vehicle speeding up). That is how the vehicles inertia comes into play."
If the dynojet calculates torque in a way that allows inertia to enter the torque data, then the dynojet is simply not giving you a true horsepower measurement.
No acceleration is required to measure horsepower. Only a measurement of torque at any given rpm.
"Hone up on your physics and you will be able to see how inertia can be the device that allows measurement on on side and affects the results on the other side"
How about you give me that physics lesson.
Tell me how inertia would be involved in making horepower measurements using a standard dyno.
A standard dyno uses a load that does not require acceleration.
Tom F&L GoR
Enthusiast
Work is force times distance.
Power is the rate of doing work, or force times distance per time.
1 Horsepower is 550lbf-ft/second
You can measure the torque output as a load (lbf) on the torque arm at a fixed distance and one speed.
You can also accelerate a known mass and measure the time it takes to change it from one speed to a higher speed. The inertia of the chassis drum is constant, but the rate (RPM) changes. You can still calculate power.
power = (force * distance)/per time
and force = mass * acceleration, so
power = ({mass * rotational acceleration} * distance)/per time
An inertial dyno measures force as acceleration of the known mass of the roller. Inaccuracies come in when the assumed inertia changes, like different engine flywheels, wheel diameter and weight, etc.
Visit any dyno website for more info.
Power is the rate of doing work, or force times distance per time.
1 Horsepower is 550lbf-ft/second
You can measure the torque output as a load (lbf) on the torque arm at a fixed distance and one speed.
You can also accelerate a known mass and measure the time it takes to change it from one speed to a higher speed. The inertia of the chassis drum is constant, but the rate (RPM) changes. You can still calculate power.
power = (force * distance)/per time
and force = mass * acceleration, so
power = ({mass * rotational acceleration} * distance)/per time
An inertial dyno measures force as acceleration of the known mass of the roller. Inaccuracies come in when the assumed inertia changes, like different engine flywheels, wheel diameter and weight, etc.
Visit any dyno website for more info.
joe117
Enthusiast
My point is,
gears do not change horsepower.
If the dyno says they do, it is wrong.
(Torque * RPM) / 5252 = horsepower
If your gears double the torque, the rpm will be cut in half.
So the number over the 5252 will be the same whatever the gear ratio.
gears do not change horsepower.
If the dyno says they do, it is wrong.
(Torque * RPM) / 5252 = horsepower
If your gears double the torque, the rpm will be cut in half.
So the number over the 5252 will be the same whatever the gear ratio.
Tom F&L GoR
Enthusiast
Oh. I thought you were asking about physics. If only I had known so many dynos are doomed to be eternally "wrong."
Ha ha Tom. I do not think he gets it. Joe, the actual power is NOT changing. It is the measurement of it that changes. And that measurement is affected by system inertias. If you could make a massless drivetrain an inertia dyno could be created to be 100 percent accurate. Unfortunately real drivelines are not massless and thus introduce error. And what I was trying to tell you is that a higher numerical gear increases the error.
I have spent my educational life and work life in and around power creation and measurement. From water brake to electrical absorption to eddy currrent to inertial. They all have their pros and cons and degrees of inaccuracy. In this case the inertia dyno issue is that it requires acceleration to make a meqasurement, which by definition brings inertia into the equation (remember Newton law about a mass in motion tends to stay in motion ...).
I have spent my educational life and work life in and around power creation and measurement. From water brake to electrical absorption to eddy currrent to inertial. They all have their pros and cons and degrees of inaccuracy. In this case the inertia dyno issue is that it requires acceleration to make a meqasurement, which by definition brings inertia into the equation (remember Newton law about a mass in motion tends to stay in motion ...).
joe117
Enthusiast
OK, fine.
Let's stop all the nonsense.
We know the horsepower formula.
We know that inertia has nothing to do with horespower.
So let us agree that gears do not change true horsepower.
Is that correct or not?
That's what the question was.
Let's stop all the nonsense.
We know the horsepower formula.
We know that inertia has nothing to do with horespower.
So let us agree that gears do not change true horsepower.
Is that correct or not?
That's what the question was.
Tom F&L GoR
Enthusiast
Actually, the question was whether gears changes RWHP...
(geez, anal engineers are hard to deal with.)
But the horse is dead, so we can stop kicking it.
Let's pick on Don, I think it was his post that made this two pages wide. We need a forum button to shrink wide posts back to one page width...
(geez, anal engineers are hard to deal with.)
But the horse is dead, so we can stop kicking it.
Let's pick on Don, I think it was his post that made this two pages wide. We need a forum button to shrink wide posts back to one page width...
joe117
Enthusiast
Yes, a way to look at the post without chasing it across the screen would be very nice.
"Actually, the question was whether gears changes RWHP..."
Other than a small change in gear tooth friction,
gears do not change horsepower.
Not engine hp or rwhp.
Anyone want to fight that?
Even with really long strings of text? ;-)
"Actually, the question was whether gears changes RWHP..."
Other than a small change in gear tooth friction,
gears do not change horsepower.
Not engine hp or rwhp.
Anyone want to fight that?
Even with really long strings of text? ;-)
ruckdr
Enthusiast
Ya, lets pick on Don, it must have been that long link that didn't break up into multiple lines.
Lets you become proficient with your mouse (hehe)
Got my car fixed, off to a track day tomorrow.
Later,
joe117
Enthusiast
"I am starting to understand that. Arguing against the laws of physics in this realm was a difficult job but Joe was up to the task"
Ok, that's cute. But let's see what you really know about physics.
Do gears change your RWHP?
Yes or No.
I'm not talking about small friction variations.
Ok, that's cute. But let's see what you really know about physics.
Do gears change your RWHP?
Yes or No.
I'm not talking about small friction variations.
No. They change the measurement of it.
But inertia does reduce the amount of useful hp when the device being measured is changing rotational speed. That is the useful hp is reduced exactly by the amount of energy that is stored in inertial energy (ie flywheel energy). Remember we are talking about a dynamic condition and not steady state.
For example if you install a heavier flywheel and conduct a hp test with a fast rpm sweep you will show lower hp, whether flywheel or rear wheel. That is why real dyno measurements are done with a slow sweep or at steadyu state points. But, the fast sweep like a dynojet actually reflects the acceleration potential of an engine/driveline combo better.
But inertia does reduce the amount of useful hp when the device being measured is changing rotational speed. That is the useful hp is reduced exactly by the amount of energy that is stored in inertial energy (ie flywheel energy). Remember we are talking about a dynamic condition and not steady state.
For example if you install a heavier flywheel and conduct a hp test with a fast rpm sweep you will show lower hp, whether flywheel or rear wheel. That is why real dyno measurements are done with a slow sweep or at steadyu state points. But, the fast sweep like a dynojet actually reflects the acceleration potential of an engine/driveline combo better.
Tom F&L GoR
Enthusiast
"Ok, that's cute. But let's see what you really know about physics."
joe117
Enthusiast
"But, the fast sweep like a dynojet actually reflects the acceleration potential of an engine/driveline combo better."
Yes, I understand that.
The car will do a sweep from idle to max rpm quicker in second gear than it will in third gear.
This is not a change in RWHP, this is an artifact of the test procedure.
I understand how gears will change the acceleration on this dyno.
A higher gear ratio will always give a quicker sweep.
But the higher gear ratio will not always give you better performance on the road or track.
A 4.56:1 rear in a Viper, would give a quicker sweep with faster acceleration than a 3.55:1 rear.
But in the real world, that 4.56:1 rear end ratio would not give better performance.
Yes, I understand that.
The car will do a sweep from idle to max rpm quicker in second gear than it will in third gear.
This is not a change in RWHP, this is an artifact of the test procedure.
I understand how gears will change the acceleration on this dyno.
A higher gear ratio will always give a quicker sweep.
But the higher gear ratio will not always give you better performance on the road or track.
A 4.56:1 rear in a Viper, would give a quicker sweep with faster acceleration than a 3.55:1 rear.
But in the real world, that 4.56:1 rear end ratio would not give better performance.
answer this please:
If you use a dynojet to measure horsepower using 3.07 gears, swap to 3.73 gears, would the RWHP #'s be different?
Because the inertia is created faster with the 3.73 gears, would the dynojet dyno make the HP number larger or smaller??
this is good to know when picking a dyno facility.
no more E-PEEN measuring please, just real answers. i don't care who is right and wrong i just like getting to the REAL life answer as fast as possible with the most precise information.
If you use a dynojet to measure horsepower using 3.07 gears, swap to 3.73 gears, would the RWHP #'s be different?
Because the inertia is created faster with the 3.73 gears, would the dynojet dyno make the HP number larger or smaller??
this is good to know when picking a dyno facility.
no more E-PEEN measuring please, just real answers. i don't care who is right and wrong i just like getting to the REAL life answer as fast as possible with the most precise information.
Tom F&L GoR
Enthusiast
This is a test, Joe.
ViperRichRT10
Enthusiast
OK, since I am the one who posted this question, I will try to make clear what my question was.
Same car, same dynojet, same time. One run on the dyno with stock gears. Second run with 3.55 gears. Are the DYNO readings the same? Or is the 3.55 gear run lower? Simple question. If it takes you 4 paragraphs to answer, please don't. Please limit responses to three sentences or less, no formulas or theories!
Same car, same dynojet, same time. One run on the dyno with stock gears. Second run with 3.55 gears. Are the DYNO readings the same? Or is the 3.55 gear run lower? Simple question. If it takes you 4 paragraphs to answer, please don't. Please limit responses to three sentences or less, no formulas or theories!
ViperRichRT10
Enthusiast
Beautiful!!!! Do you know about what % lower?
THANKS!!
Joseph Dell
Enthusiast
[sentence 1] The dyno is pre-programmed to know (supposidely) what your final drive ratio is and the reason that we use 4th gear for a stock car dyno run is that it is relatively close to a 1-to-1 ratio.
[sentence 2] the dyno operator doesn't ever ask you for your drive ratio as he/she guesses.
[sentence 3] Since ratios aren't what they were stock, the readings will be lower and will vary from dyno to dyno.
[bonus sentence] exactly like i told you the 1st day you posted... but as usual, nobody listens to Joseph...
[sentence 2] the dyno operator doesn't ever ask you for your drive ratio as he/she guesses.
[sentence 3] Since ratios aren't what they were stock, the readings will be lower and will vary from dyno to dyno.
[bonus sentence] exactly like i told you the 1st day you posted... but as usual, nobody listens to Joseph...
ViperRichRT10
Enthusiast
But JD...If you only knew how much fun it is to push your buttons! What did you say???
