Opinions Please
Discussion
I intend to test my GTR on a rolling road to establish BHP at the wheels . Informal opinions please . Will my g/50/03 gearbox take the strain or break up ?! The engine is circa 500 BHP but when I drive it the gearbox doesn't take much strain because the wheels spin before the engine delivers it's full power .
Frank
Frank
The rolling road operator should apply the power progressively and will already have brought it up to speed and into a higher gear so the load will not be as harsh as you pulling away from the lights.
You need to talk to Lucky as I believe he suffered bent suspension mounts as a result of his runs but this may just be down to how it was restrained.
Others may also have been on the rollers and can offer advice on how it should be tied. I'm thinking Jeff S will have the answer.
Steve
You need to talk to Lucky as I believe he suffered bent suspension mounts as a result of his runs but this may just be down to how it was restrained.
Others may also have been on the rollers and can offer advice on how it should be tied. I'm thinking Jeff S will have the answer.
Steve
Edited by Steve_D on Saturday 18th April 06:31
BHP at the wheels is a completely meaningless figure. Often used as pub bragging, but completely dependent upon transmission losses.
Transmission losses are heavily influenced by tyre temperature, tyre pressure, tension in the straps, single vs dual roller setup etc. They are different for every car, on each RR session and hence can influence power readings by +/-15% - maybe even more.
ONLY if the operator does a run down test to establish transmission losses will you get any real indication of the engines power at the flywheel, and then only for comparitive purposes at that specific rolling road.
You should ask your rolling road operator for the version of the software (i.e algorithm) being used the day your car is tested, and also for any figures used in correction for air temp etc. Then you can go back if you make changes to your engine and get meaningful comparative results. (assuming said operator is still using or prepared to reinstall the same software algorithm version.
On a GTR you will also get a huge difference due to the charge air temp under the rear clip. Take the rear clip off and you will see your power figure rise signifcantly.
Road & Track in South Ockenden (Nr Dartford Tunnel) do a good job.
Transmission losses are heavily influenced by tyre temperature, tyre pressure, tension in the straps, single vs dual roller setup etc. They are different for every car, on each RR session and hence can influence power readings by +/-15% - maybe even more.
ONLY if the operator does a run down test to establish transmission losses will you get any real indication of the engines power at the flywheel, and then only for comparitive purposes at that specific rolling road.
You should ask your rolling road operator for the version of the software (i.e algorithm) being used the day your car is tested, and also for any figures used in correction for air temp etc. Then you can go back if you make changes to your engine and get meaningful comparative results. (assuming said operator is still using or prepared to reinstall the same software algorithm version.
On a GTR you will also get a huge difference due to the charge air temp under the rear clip. Take the rear clip off and you will see your power figure rise signifcantly.
Road & Track in South Ockenden (Nr Dartford Tunnel) do a good job.
738 driver said:
If you want to preserve your tyres Frank, would you consider a hub dyno? ....a bit more accurate as well as controlled!
Maybe ask Can-Am Dave as he has current knowledge and details.
Hi FrankMaybe ask Can-Am Dave as he has current knowledge and details.
I have run my car on several dynos. I would take your car along to www.thor-racing.co.uk they are near Warwick. I have yet to run my car with them but I have been to visit them I had a good long chat to the dyno operator. He was very knowledgeable. They run a Dynopack hub dyno which is much safer for you and your car(wheels removed and hub adapters fitted). The power at the wheels is the figure you are looking for not at the flywheel as this is never going to be completely accurate. On a hub dyno power runs are very repeatable but not on a standard rolling road. I'm afraid that Arnie has got it the wrong way round(no offence meant Arnie). Power at the flywheel is less the meaningfull figure and that is the pub bragging figure as it is the higher figure. Power at the wheels on a hub dyno has no losses, requires no algorithm and it is simlpy an accurate figure. I always run mine with the rear clip removed. They may have lots of powerfull fans but they will never simulate the air movement on the road. I would not worry about your transmission as said before the power is ramped up. I hope to take mine along to thor racing once I have fitted my new cylinder heads. Best of luck Frank.
Regards Dave
Frank,
If you do go for a hub dyno i'm sure you would be very happy working with these guys
TORQUE DEVELOPMENTS INTERNATIONAL
If you do decide to use them & wouldn't mind a spectator please let me know
If you do go for a hub dyno i'm sure you would be very happy working with these guys
TORQUE DEVELOPMENTS INTERNATIONAL
If you do decide to use them & wouldn't mind a spectator please let me know
I put my statement a bit the wrong way round perhaps . What I want to establish is an approximate BHP figure for the engine without taking it out . So if BHP is say 250 at the wheels then it's probrably not 500 BHP engine . If however it was 425 BHP on a hub dyno then you could say that it could well be a 500 BHP engine . Yes/ No?
Frank
Frank
I would have thought with a hub dyno run Frank, losses of 15-20% would be a conservative deduction.
Overall clip temps are 'very' important, not just the intake air temp....especially around the upper clip.
Air warms up very quickly via conduction,convection,radiation etc.
10% loss in air density = 10% loss in power....(N/A engine)!
Overall clip temps are 'very' important, not just the intake air temp....especially around the upper clip.
Air warms up very quickly via conduction,convection,radiation etc.
10% loss in air density = 10% loss in power....(N/A engine)!
60mph said:
I put my statement a bit the wrong way round perhaps . What I want to establish is an approximate BHP figure for the engine without taking it out . So if BHP is say 250 at the wheels then it's probrably not 500 BHP engine . If however it was 425 BHP on a hub dyno then you could say that it could well be a 500 BHP engine . Yes/ No?
Frank
Hi FrankFrank
Your figure of 425 BHP would be about right! My first dyno session with my Can-Am was measure at 400 BHP at the wheels which equated to 478 BHP at the flywheel. This was on a Dyno Dynamics rolling road. As Dave says it's usually between 15-20% loss through the transmission.
Regards Dave
[quote=CanAm Dave
Your figure of 425 BHP would be about right! My first dyno session with my Can-Am was measure at 400 BHP at the wheels which equated to 478 BHP at the flywheel. This was on a Dyno Dynamics rolling road. As Dave says it's usually between 15-20% loss through the transmission.
[/quote]
This is exactly the assumption which is so woefully misleading.
The type of tyres will make a difference to the power figure
The temperature of the tyres will make a difference to the power figure
The force with which the tyres are pressed onto the rollers (i.e how tight the staps are) will make a difference to the power figure
The effective spring rates of the read suspension will make a difference to the power figure
The tyre pressures will make a difference to the power figure
The compound gear ratios (tyre surface speed relative to cranksahft speed) will make a difference to the power figure
Need I go on? You can add the word 'significant' to most of the above.
The only way to get an accurate figure (and this is down to the calibration of the rollers, so same rollers, same day, same air and ambient temps need to apply) is to do a run down or coast down test.
After the engine hits peak rpm, the rollers are used to measure the torque (converted then to power) required for the car to maintain steady speed (the transmission losses). In effect this is a complex algorithm which calculates these forces based upon the slowing rate of the car when the clutch is disengaged.
Its worth remembering that power is the rate at which the torque is doing work. Power, despite common opinion is just an expression fo torque factored by speed. The torque figure is converted to power using the following expression:
Torque * RPM
Power = -------------
5252
So you end up with a chart which looks like this:
Here the power plot (pink)'P-norm' is calculated from 'P-wheel'(blue) and 'P-Drag'(green), both being calculated from the torque measured by the rollers relative to the engine RPM.
NOTICE HOW THERE IS NO LINEAR (percentage) RELATIONSHIP BETWEEN THE WHEEL AND NORM POWER PLOTS!!!!!
In short, anyone saying there is a guideline percentage for transmission losses, is very wrong.
Moving to charge air temp and flow rates, when using my Caterham on rollers I found with the confined ram air airbox attached (in static air) I got readings as low a 259bhp (uncorrected). When running minutes later with the airbox removed (venturi's in frree air) I got 290 odd bhp.
Putting the airbox into an 80mph airstream (realistically simulating real world use) power increased to 316bhp.
So a lack of free air will knock power figues significantly, and a lack of +ve air pressure if there is a direct sealed induction path from scoop to engine will increase that gap even further.
I'm sure that if the GTR scoop generates a +ve air pressure, a similar test can be conducted. Using a decent airbox which connects the scoop to the induction system will make a huge difference to your cars performance.
.
Your figure of 425 BHP would be about right! My first dyno session with my Can-Am was measure at 400 BHP at the wheels which equated to 478 BHP at the flywheel. This was on a Dyno Dynamics rolling road. As Dave says it's usually between 15-20% loss through the transmission.
[/quote]
This is exactly the assumption which is so woefully misleading.
The type of tyres will make a difference to the power figure
The temperature of the tyres will make a difference to the power figure
The force with which the tyres are pressed onto the rollers (i.e how tight the staps are) will make a difference to the power figure
The effective spring rates of the read suspension will make a difference to the power figure
The tyre pressures will make a difference to the power figure
The compound gear ratios (tyre surface speed relative to cranksahft speed) will make a difference to the power figure
Need I go on? You can add the word 'significant' to most of the above.
The only way to get an accurate figure (and this is down to the calibration of the rollers, so same rollers, same day, same air and ambient temps need to apply) is to do a run down or coast down test.
After the engine hits peak rpm, the rollers are used to measure the torque (converted then to power) required for the car to maintain steady speed (the transmission losses). In effect this is a complex algorithm which calculates these forces based upon the slowing rate of the car when the clutch is disengaged.
Its worth remembering that power is the rate at which the torque is doing work. Power, despite common opinion is just an expression fo torque factored by speed. The torque figure is converted to power using the following expression:
Torque * RPM
Power = -------------
5252
So you end up with a chart which looks like this:
Here the power plot (pink)'P-norm' is calculated from 'P-wheel'(blue) and 'P-Drag'(green), both being calculated from the torque measured by the rollers relative to the engine RPM.
NOTICE HOW THERE IS NO LINEAR (percentage) RELATIONSHIP BETWEEN THE WHEEL AND NORM POWER PLOTS!!!!!
In short, anyone saying there is a guideline percentage for transmission losses, is very wrong.
Moving to charge air temp and flow rates, when using my Caterham on rollers I found with the confined ram air airbox attached (in static air) I got readings as low a 259bhp (uncorrected). When running minutes later with the airbox removed (venturi's in frree air) I got 290 odd bhp.
Putting the airbox into an 80mph airstream (realistically simulating real world use) power increased to 316bhp.
So a lack of free air will knock power figues significantly, and a lack of +ve air pressure if there is a direct sealed induction path from scoop to engine will increase that gap even further.
I'm sure that if the GTR scoop generates a +ve air pressure, a similar test can be conducted. Using a decent airbox which connects the scoop to the induction system will make a huge difference to your cars performance.
.
In a basic carburated SBC-Ultima install, its not such a great idea to fit 'sealed' ram-air induction.
A sealed filter box with cool ram-air input and bypass would be the better solution.
The velocities and pressures present at say 6500rpm@80mph differ greatly from those experienced at 6500rpm@180mph. So to set up a carb with hypothetical air velocities in a sealed airbox would be potentially quite harmful in this particular application.
In a N/A engine, should the manifold pressure ever reach ambient?
It was my understanding, from a dyno engineer friend, that run down calcs are normal on inertia type dyno calibration.
Was this the type you are referring to Arnie?
The hub dyno does not have as many of the variables, needing calculation/correction.
A sealed filter box with cool ram-air input and bypass would be the better solution.
The velocities and pressures present at say 6500rpm@80mph differ greatly from those experienced at 6500rpm@180mph. So to set up a carb with hypothetical air velocities in a sealed airbox would be potentially quite harmful in this particular application.
In a N/A engine, should the manifold pressure ever reach ambient?
It was my understanding, from a dyno engineer friend, that run down calcs are normal on inertia type dyno calibration.
Was this the type you are referring to Arnie?
The hub dyno does not have as many of the variables, needing calculation/correction.
Fat Arnie said:
CanAm Dave said:
Your figure of 425 BHP would be about right! My first dyno session with my Can-Am was measure at 400 BHP at the wheels which equated to 478 BHP at the flywheel. This was on a Dyno Dynamics rolling road. As Dave says it's usually between 15-20% loss through the transmission.
This is exactly the assumption which is so woefully misleading.I have the data of plenty of Ultimas on rolling roads and they all fall between these percentages! Not so woeful after all!
Regards Dave
There are some interesting white papers at http://www.tdi-plc.com/index.php?pge=C_dynocam that help explain the drive train losses issue and the problems with rolling roads.
Edited by TDIPLC on Monday 20th April 09:15
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