Dodge Viper GTS on the rollers
Discussion
Hi Carl
I know my stepson, Keith who took the pic I used did not do a video, am awaiting to see if my son took any videos and will ask if Ollie did one when I see him Tuesday. My son left the unit after the first few runs before I did the run graphed. The pressure changes at the back of the car gave him a kind of motion sickness and a headache!
Nice car Carl and quite brutal, even more so with the second stage of boost I imagine! Carl N and Ollie must have balls to map it on the road! The car only just fitted in the unit and on the rollers...what a monster!
Problem I have with transmission losses, all guess work. I am not sure the transmission will lose more under load, with more power the car will accelerate faster imho. My understanding is it takes x to turn a gear if you input more then that it turns and I am not sure the losses apart from friction and load against bearings goes up with power input or speed,depends on quality of transmission build, it is the tyres that cop it. We are not holding the load, rapid runs dont let the tyres work hard. Carls Viper runs from 1500 rpm to 5500 were 5 seconds start to finish. Race folk use inertia dynos to get the coast down losses as low as possible so that more power gets to the wheels, that is what wins races. I feel folk get bogged down with the losses, at the end of the day, if there isn't enough power at the wheels for you, tune it more as it is the wheel power which does the work for you, not the flywheel power. We tune cars for road and track and try to get losses down to safe levels( thin oils not safe in endurance cars but ok in sprint and hillclimb), we can influence the losses dramatically with oil viscocities. No one ever seems to talk about oil viscocities, gear used, tyre pressures, sizes or compound when they are 'percentaging' the losses. I think the percentage game is a red herring. We use direct top gear to do the tests so we are reducing the effect of under or overdriven gears in terms of losses. What we have, which I keep saying, is a means of measuring wheel power and a means of measuring drive losses. The two together allow us to compare like for like cars and look for reasons why power is low, eg had bad uj bolts which were rubbing and taking 10 extra bhp to turn, extra thick gloop to stop oil leaks in diff...5 bhp more!
Peter
I know my stepson, Keith who took the pic I used did not do a video, am awaiting to see if my son took any videos and will ask if Ollie did one when I see him Tuesday. My son left the unit after the first few runs before I did the run graphed. The pressure changes at the back of the car gave him a kind of motion sickness and a headache!
Nice car Carl and quite brutal, even more so with the second stage of boost I imagine! Carl N and Ollie must have balls to map it on the road! The car only just fitted in the unit and on the rollers...what a monster!
Problem I have with transmission losses, all guess work. I am not sure the transmission will lose more under load, with more power the car will accelerate faster imho. My understanding is it takes x to turn a gear if you input more then that it turns and I am not sure the losses apart from friction and load against bearings goes up with power input or speed,depends on quality of transmission build, it is the tyres that cop it. We are not holding the load, rapid runs dont let the tyres work hard. Carls Viper runs from 1500 rpm to 5500 were 5 seconds start to finish. Race folk use inertia dynos to get the coast down losses as low as possible so that more power gets to the wheels, that is what wins races. I feel folk get bogged down with the losses, at the end of the day, if there isn't enough power at the wheels for you, tune it more as it is the wheel power which does the work for you, not the flywheel power. We tune cars for road and track and try to get losses down to safe levels( thin oils not safe in endurance cars but ok in sprint and hillclimb), we can influence the losses dramatically with oil viscocities. No one ever seems to talk about oil viscocities, gear used, tyre pressures, sizes or compound when they are 'percentaging' the losses. I think the percentage game is a red herring. We use direct top gear to do the tests so we are reducing the effect of under or overdriven gears in terms of losses. What we have, which I keep saying, is a means of measuring wheel power and a means of measuring drive losses. The two together allow us to compare like for like cars and look for reasons why power is low, eg had bad uj bolts which were rubbing and taking 10 extra bhp to turn, extra thick gloop to stop oil leaks in diff...5 bhp more!
Peter
Edited by PeterBurgess on Sunday 24th May 07:32
If you were to free spin the input shaft on a box by hand you'd feel it would turn fairly easily, no real resistance ?
I'm sure if you then tried to turn that same shaft at 5000rpm, even unloaded it would take a huge amount of effort even if only from the oil drag inside the box.
Now start loading up gears, creating friction, heat etc even more losses.
Then add your tyres on the rollers...I'm sure you could easily turn a tyre by hand slowly with the tyre not pressed into the roller.
Strap the axle down so the tyre is buried hard into the roller...and I'm sure it will become a lot more difficult...and this is what should happen during a pull.
There really are so many reasons why the more load that's applied through the drivetrain, why it requires even more effort to make it all keep going
And Stan's also correct, once in neutral only the output shaft is spinning, so if a coastdown is done this way, at best you can only guess the losses of the output shaft, propshaft, axle and wheels/tyres
There should be very little drag from the transmission itself.
Really, who cares though ? The numbers will be what the numbers will be, just never compare them to other dynos etc and tune for the best results you can get with the gear you have.
After that it's real world performance that matters
I'm sure if you then tried to turn that same shaft at 5000rpm, even unloaded it would take a huge amount of effort even if only from the oil drag inside the box.
Now start loading up gears, creating friction, heat etc even more losses.
Then add your tyres on the rollers...I'm sure you could easily turn a tyre by hand slowly with the tyre not pressed into the roller.
Strap the axle down so the tyre is buried hard into the roller...and I'm sure it will become a lot more difficult...and this is what should happen during a pull.
There really are so many reasons why the more load that's applied through the drivetrain, why it requires even more effort to make it all keep going
And Stan's also correct, once in neutral only the output shaft is spinning, so if a coastdown is done this way, at best you can only guess the losses of the output shaft, propshaft, axle and wheels/tyres
There should be very little drag from the transmission itself.
Really, who cares though ? The numbers will be what the numbers will be, just never compare them to other dynos etc and tune for the best results you can get with the gear you have.
After that it's real world performance that matters
chuntington101 said:
Is there a build thread for this car? Would be nice to see a little more of the detail.
a lots of Carls original build pics are still showing, no doubt been modified a bit since these were takenhttp://www.viperalley.com/forum/viper-discussions-...
Great numbers Carl, you must be happy !
Hi Stan
This article says we are all talking rubbish
http://www.superstreetonline.com/how-to/engine/mod...
Peter
This article says we are all talking rubbish
http://www.superstreetonline.com/how-to/engine/mod...
Peter
PeterBurgess said:
Hi Stan
This article says we are all talking rubbish
http://www.superstreetonline.com/how-to/engine/mod...
Peter
I think it agrees with me...This article says we are all talking rubbish
http://www.superstreetonline.com/how-to/engine/mod...
Peter
Ignore the PUBHP figures and at best use WHP figures.....but only as a before/after guide whilst tuning.
I think one thing that is being missed is the difference in coast down test methodology.
"In the end, there's no easy way to estimate the drivetrain loss your vehicle experiences on the road or even on the dyno. Coast-down tests are sometimes used on a dyno to attempt to measure frictional losses, but because this test is not dynamic (meaning they're not done while accelerating, but rather while coasting to a stop with the direct drive gear engaged but the clutch depressed so that the engine and transmission aren't linked) it really only captures steady-state drivetrain losses as well as rolling resistance. So rather than attempting to convert your vehicle's dyno-measured wheel horsepower to a SAE net horsepower figure using a percentage or a fixed horsepower value, you're far better off accepting the fact that these two types of horsepower measurements aren't easily correlated and forego any attempt at doing so."
This will show a greater power lose than using neutral.
Stan
"In the end, there's no easy way to estimate the drivetrain loss your vehicle experiences on the road or even on the dyno. Coast-down tests are sometimes used on a dyno to attempt to measure frictional losses, but because this test is not dynamic (meaning they're not done while accelerating, but rather while coasting to a stop with the direct drive gear engaged but the clutch depressed so that the engine and transmission aren't linked) it really only captures steady-state drivetrain losses as well as rolling resistance. So rather than attempting to convert your vehicle's dyno-measured wheel horsepower to a SAE net horsepower figure using a percentage or a fixed horsepower value, you're far better off accepting the fact that these two types of horsepower measurements aren't easily correlated and forego any attempt at doing so."
This will show a greater power lose than using neutral.
Stan
Hi Stan
For obvious reasons I do not like to hold clutch depressed and wait while the transmission comes to rest, however, when I have coasted down like this I get a marginal difference of less than 1 bhp on a 22 bhp losses car. I think what that article is trying to say, and Steve is, don't try and guess what flywheel is, it doesn't matter, wheel power propels the car. Same as Steve says stick to a dyno so you know if you gain or lose or if a problem. I use the wheel power and coast down losses for comparison purposes. Just strange that the addition of wheel losses and wheel power is in the ball park for tested flywheel power. The obvious retort would be we are measuring too high a wheel power and not enough losses....but, we get repeatable results so it is, as I keep saying, a useful tool. As things are I will happily publish interesting graphs and cars as we do them. Not many other tuners seem bothered to publish graphs but I am happy to share the enjoyment of my work and some of the cars we do with Piston Head readers/posters.
Peter
For obvious reasons I do not like to hold clutch depressed and wait while the transmission comes to rest, however, when I have coasted down like this I get a marginal difference of less than 1 bhp on a 22 bhp losses car. I think what that article is trying to say, and Steve is, don't try and guess what flywheel is, it doesn't matter, wheel power propels the car. Same as Steve says stick to a dyno so you know if you gain or lose or if a problem. I use the wheel power and coast down losses for comparison purposes. Just strange that the addition of wheel losses and wheel power is in the ball park for tested flywheel power. The obvious retort would be we are measuring too high a wheel power and not enough losses....but, we get repeatable results so it is, as I keep saying, a useful tool. As things are I will happily publish interesting graphs and cars as we do them. Not many other tuners seem bothered to publish graphs but I am happy to share the enjoyment of my work and some of the cars we do with Piston Head readers/posters.
Peter
PeterBurgess said:
Hi Stan
For obvious reasons I do not like to hold clutch depressed and wait while the transmission comes to rest, however, when I have coasted down like this I get a marginal difference of less than 1 bhp on a 22 bhp losses car. I think what that article is trying to say, and Steve is, don't try and guess what flywheel is, it doesn't matter, wheel power propels the car. Same as Steve says stick to a dyno so you know if you gain or lose or if a problem. I use the wheel power and coast down losses for comparison purposes. Just strange that the addition of wheel losses and wheel power is in the ball park for tested flywheel power. The obvious retort would be we are measuring too high a wheel power and not enough losses....but, we get repeatable results so it is, as I keep saying, a useful tool. As things are I will happily publish interesting graphs and cars as we do them. Not many other tuners seem bothered to publish graphs but I am happy to share the enjoyment of my work and some of the cars we do with Piston Head readers/posters.
Peter
Peter,For obvious reasons I do not like to hold clutch depressed and wait while the transmission comes to rest, however, when I have coasted down like this I get a marginal difference of less than 1 bhp on a 22 bhp losses car. I think what that article is trying to say, and Steve is, don't try and guess what flywheel is, it doesn't matter, wheel power propels the car. Same as Steve says stick to a dyno so you know if you gain or lose or if a problem. I use the wheel power and coast down losses for comparison purposes. Just strange that the addition of wheel losses and wheel power is in the ball park for tested flywheel power. The obvious retort would be we are measuring too high a wheel power and not enough losses....but, we get repeatable results so it is, as I keep saying, a useful tool. As things are I will happily publish interesting graphs and cars as we do them. Not many other tuners seem bothered to publish graphs but I am happy to share the enjoyment of my work and some of the cars we do with Piston Head readers/posters.
Peter
In no way have I meant to imply that the wheel reading that you have posted are in anyway not accurate.
Stan
Hi Stan, not for one moment did I think you were implying that. It is what many other folk think and say and like to think and like to say I think it is a minefield as I said earlier and don't think we will get closer with the SF901 up and running! We would have to use the sf dyno then bolt it all to a chassis dyno etc etc ad infinitum. I tend to tell folk the inertia testing we carry out shows accelerating power available if that makes any sense? For example, lighter flywheel shows slightly more wheel power which is the case out on the road as a car will accelerate faster with lighter flywheel as the power is delivered faster to wheels instead of being used to spin up heavy flywheel.
It would be interesting if you did do some testing on boxes in neutral then in direct top for differences in effort to rotate, oiled, non-oiled etc. You would have some first hand knowledge not many other folk would have.
Peter
I think it is a minefield as I said earlier and don't think we will get closer with the SF901 up and running! We would have to use the sf dyno then bolt it all to a chassis dyno etc etc ad infinitum. I tend to tell folk the inertia testing we carry out shows accelerating power available if that makes any sense? For example, lighter flywheel shows slightly more wheel power which is the case out on the road as a car will accelerate faster with lighter flywheel as the power is delivered faster to wheels instead of being used to spin up heavy flywheel.It would be interesting if you did do some testing on boxes in neutral then in direct top for differences in effort to rotate, oiled, non-oiled etc. You would have some first hand knowledge not many other folk would have.
Peter
Hi Stan
I ran an Escort x-flow sprint engine on the rollers today and tried coastdown in neutral from 94 mph and coastdown in 4th (direct top so only going through mainshaft) from 94mph by holding down clutch. Losses in neutral 17.6 bhp, losses in 4th with foot on clutch 17.4 bhp, difference probably extra drag down on engine at idle with clutch engaged! Wheel horsepower was 107.8...125.4 at engine.
Peter
I ran an Escort x-flow sprint engine on the rollers today and tried coastdown in neutral from 94 mph and coastdown in 4th (direct top so only going through mainshaft) from 94mph by holding down clutch. Losses in neutral 17.6 bhp, losses in 4th with foot on clutch 17.4 bhp, difference probably extra drag down on engine at idle with clutch engaged! Wheel horsepower was 107.8...125.4 at engine.
Peter
PeterBurgess said:
Hi Stan
I ran an Escort x-flow sprint engine on the rollers today and tried coastdown in neutral from 94 mph and coastdown in 4th (direct top so only going through mainshaft) from 94mph by holding down clutch. Losses in neutral 17.6 bhp, losses in 4th with foot on clutch 17.4 bhp, difference probably extra drag down on engine at idle with clutch engaged! Wheel horsepower was 107.8...125.4 at engine.
Peter
Peter,I ran an Escort x-flow sprint engine on the rollers today and tried coastdown in neutral from 94 mph and coastdown in 4th (direct top so only going through mainshaft) from 94mph by holding down clutch. Losses in neutral 17.6 bhp, losses in 4th with foot on clutch 17.4 bhp, difference probably extra drag down on engine at idle with clutch engaged! Wheel horsepower was 107.8...125.4 at engine.
Peter
If I read this correctly you got a greater HP lose in neutral than you did in gear with the clutch depressed on your coast down test. Very strange.
Stan
PeterBurgess said:
Hi Stan
Think of the clutch as an engine isolator and if engaged you have an element of engine inertia to contend with. The inertia dyno is very very sensitive!
Peter
But if the box is in neutral it's isolated from the engine anyway ?Think of the clutch as an engine isolator and if engaged you have an element of engine inertia to contend with. The inertia dyno is very very sensitive!
Peter
As are the laygear etc from rotation in the oil bath
With clutch pressed and in gear, all these gears are still being turned along with the output shaft so losses should be higher.
The results stand as measured and tested, folk will have to work out themselves why the losses are about the same. Points to losses in box being very low doesn't it? In direct top power is transmitted through mainshaft, same as coasting down in neutral or coasting down in 4th with clutch depressed, mainshaft is turning and subject to frictional losses from oil, bearings and seals. It is probable that good modern boxes are 99% efficient in direct top, less good ones 97% efficient.
before I bought an inertia dyno I thought losses were percentages but the inertia dyno is an eye opener. As I keep writing, losses seem to be directly proportional to tyre speed, width and pressure. Cars with loads of ujs such as TR6 lose higher proportion through transmission, olde worlde live back axles lose less.
Peter
before I bought an inertia dyno I thought losses were percentages but the inertia dyno is an eye opener. As I keep writing, losses seem to be directly proportional to tyre speed, width and pressure. Cars with loads of ujs such as TR6 lose higher proportion through transmission, olde worlde live back axles lose less.
Peter
PeterBurgess said:
I think the percentage game is a red herring. We use direct top gear to do the tests so we are reducing the effect of under or overdriven gears in terms of losses.
I completely agree power at the wheels is the only measurement that matters (and the only one that is being accuratley measured). However I've always read you're supposed to be performing the power run in a gear with the closet to a 1:1 ratio rather than just sticking every car in top gear.Disclaimer : I work for a dyno manufacturer, but am trying to be impartial here
Estimated flywheel horsepower figures are a can of worms.
Driveline losses vary with diff and trans oil viscosity, which in turn varies with temperature.
Tyre losses depend on width, compound, temperature, and how the car is strapped down.
We ran a research program some years ago, which involved back-to-back testing of the same engines on both engine and chassis dynos. The results were interesting : tyre / transmission losses vary considerably according to both the speed of rotation and the torque being transmitted. You cannot just multiply the measured power by a single number and get an accurate curve, as the losses are not a constant factor of either torque, power or revs.
At the end of the day, it is wheel horespower that ALL chassis dyno's measure.
Flywheel figures are estimated from that, because customers ask for it, so salesmen ask for it, so management orders it. And the numbers are bigger, so the punters are happy
Interestingly, it is overwhelmingly UK customers who want flywheel power. Most of the rest of the world seem happy with power at the wheels.
Note : The SAE / JIS corrections are purely to adjust the power to what it would be at some nominal atmospheric condition (I prefer SAE J1995).
Incidentally none of the correction standards are really correct with modern turbo engines, as a constant (absolute) boost controlled turbo compensates for low atmospheric pressure.
Estimated flywheel horsepower figures are a can of worms.
Driveline losses vary with diff and trans oil viscosity, which in turn varies with temperature.
Tyre losses depend on width, compound, temperature, and how the car is strapped down.
We ran a research program some years ago, which involved back-to-back testing of the same engines on both engine and chassis dynos. The results were interesting : tyre / transmission losses vary considerably according to both the speed of rotation and the torque being transmitted. You cannot just multiply the measured power by a single number and get an accurate curve, as the losses are not a constant factor of either torque, power or revs.
At the end of the day, it is wheel horespower that ALL chassis dyno's measure.
Flywheel figures are estimated from that, because customers ask for it, so salesmen ask for it, so management orders it. And the numbers are bigger, so the punters are happy
Interestingly, it is overwhelmingly UK customers who want flywheel power. Most of the rest of the world seem happy with power at the wheels.
Note : The SAE / JIS corrections are purely to adjust the power to what it would be at some nominal atmospheric condition (I prefer SAE J1995).
Incidentally none of the correction standards are really correct with modern turbo engines, as a constant (absolute) boost controlled turbo compensates for low atmospheric pressure.
AW111 said:
Disclaimer : I work for a dyno manufacturer, but am trying to be impartial here
Estimated flywheel horsepower figures are a can of worms.
Driveline losses vary with diff and trans oil viscosity, which in turn varies with temperature.
Tyre losses depend on width, compound, temperature, and how the car is strapped down.
We ran a research program some years ago, which involved back-to-back testing of the same engines on both engine and chassis dynos. The results were interesting : tyre / transmission losses vary considerably according to both the speed of rotation and the torque being transmitted. You cannot just multiply the measured power by a single number and get an accurate curve, as the losses are not a constant factor of either torque, power or revs.
At the end of the day, it is wheel horespower that ALL chassis dyno's measure.
Flywheel figures are estimated from that, because customers ask for it, so salesmen ask for it, so management orders it. And the numbers are bigger, so the punters are happy
Interestingly, it is overwhelmingly UK customers who want flywheel power. Most of the rest of the world seem happy with power at the wheels.
Note : The SAE / JIS corrections are purely to adjust the power to what it would be at some nominal atmospheric condition (I prefer SAE J1995).
Incidentally none of the correction standards are really correct with modern turbo engines, as a constant (absolute) boost controlled turbo compensates for low atmospheric pressure.
Fully agree, and it is odd that many in the UK seem to insist on the guesstimated flywheel figures.Estimated flywheel horsepower figures are a can of worms.
Driveline losses vary with diff and trans oil viscosity, which in turn varies with temperature.
Tyre losses depend on width, compound, temperature, and how the car is strapped down.
We ran a research program some years ago, which involved back-to-back testing of the same engines on both engine and chassis dynos. The results were interesting : tyre / transmission losses vary considerably according to both the speed of rotation and the torque being transmitted. You cannot just multiply the measured power by a single number and get an accurate curve, as the losses are not a constant factor of either torque, power or revs.
At the end of the day, it is wheel horespower that ALL chassis dyno's measure.
Flywheel figures are estimated from that, because customers ask for it, so salesmen ask for it, so management orders it. And the numbers are bigger, so the punters are happy
Interestingly, it is overwhelmingly UK customers who want flywheel power. Most of the rest of the world seem happy with power at the wheels.
Note : The SAE / JIS corrections are purely to adjust the power to what it would be at some nominal atmospheric condition (I prefer SAE J1995).
Incidentally none of the correction standards are really correct with modern turbo engines, as a constant (absolute) boost controlled turbo compensates for low atmospheric pressure.
But I guess in the US they sort of do too by using a Dynojet which seems to read as high as these flywheel figures anyway lol
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