Drive train losses...Vixpy1?
Discussion
Inspired by another thread...drive drain losses are often expressed as a percentage of flywheel BHP.
But are the losses more of a static amount, ie 25bhp in top gear etc whatever power is being fed in, or a linier %age - double the HP going in, double the losses???
Reason I ask, is that if you have a 100bhp at the fly engine, and 80bhp at the wheels, you have a 20bhp and a 20% loss.
If you then transplant a 200bhp engine, do you have 180bhp at the wheels as the drive line has stayed the same, and a 10% loss or 160bhp and still a 20% loss, or somehwere in the middle??
Cheers,
Virgil.
But are the losses more of a static amount, ie 25bhp in top gear etc whatever power is being fed in, or a linier %age - double the HP going in, double the losses???
Reason I ask, is that if you have a 100bhp at the fly engine, and 80bhp at the wheels, you have a 20bhp and a 20% loss.
If you then transplant a 200bhp engine, do you have 180bhp at the wheels as the drive line has stayed the same, and a 10% loss or 160bhp and still a 20% loss, or somehwere in the middle??
Cheers,
Virgil.
Basically, you need to ignore flywheel guesstimates, and use wheel HP figures from rolling roads.
Drivetrain losses will depend on many things, and most rollers cannot accurately determine these, so why people insist on doing it, baffles me.
Most just like the higher numbers for pub talk, doesnt actually matter if it relates to a cars performance.
Its what is at the wheels that matters.
Drivetrain losses will depend on many things, and most rollers cannot accurately determine these, so why people insist on doing it, baffles me.
Most just like the higher numbers for pub talk, doesnt actually matter if it relates to a cars performance.
Its what is at the wheels that matters.
Edited by stevieturbo on Wednesday 29th August 18:12
stevieturbo said:
Basically, you need to ignore flywheel guesstimates, and use wheel HP figures from rolling roads.
Drivetrain losses will depend on many things, and most rollers cannot accurately determine these, so why people insist on doing it, baffles me.
Most just like the higher numbers for pub talk, doesnt actually matter if it relates to a cars performance.
Its what is at the wheels that matters.
Agree ATW is what really matters, although as you say unless the RR can accurately measure them. Mine whilst having a headline 23% losses at high revs actually has less than 14% lower down, I would have settle for a flat 20% type guestimate type RR as it would have put the peak Torque at over 410lbs Drivetrain losses will depend on many things, and most rollers cannot accurately determine these, so why people insist on doing it, baffles me.
Most just like the higher numbers for pub talk, doesnt actually matter if it relates to a cars performance.
Its what is at the wheels that matters.
Edited by stevieturbo on Wednesday 29th August 18:12
The drivetrain losses will depend on the drive train surprisingly enough rather than the power the engine has. treating them as a 20% is pure guesswork, and about as usefull..
for example if I were to put the 4ltr engine back in the tuscan as apposed to the 5ltr the same gearbox and diff will require exactly the same amount of power to turn over at the same RPM...
G
for example if I were to put the 4ltr engine back in the tuscan as apposed to the 5ltr the same gearbox and diff will require exactly the same amount of power to turn over at the same RPM...
G
I'm gonna write a book.
BHP for idiots..
No really.
Want more HP .. interested.
20p.
Yep - that's how much my local garage charges for air..
Over inflate your tyres by say 10psi and watch your power figures on the RR go up..
Why..
Friction losses on both sides of the tyre - also the operator straps the car down, further increasing the friction.
The real road has only 1 contact area..
Not suggesting Dyno makers cannot figure this out but they do insist that the tyre pressure is fed into the system..
Wonder how often that's done.
Still wanna buy my new book
BHP for idiots..
No really.
Want more HP .. interested.
20p.
Yep - that's how much my local garage charges for air..
Over inflate your tyres by say 10psi and watch your power figures on the RR go up..
Why..
Friction losses on both sides of the tyre - also the operator straps the car down, further increasing the friction.
The real road has only 1 contact area..
Not suggesting Dyno makers cannot figure this out but they do insist that the tyre pressure is fed into the system..
Wonder how often that's done.
Still wanna buy my new book
Graham said:
for example if I were to put the 4ltr engine back in the tuscan as apposed to the 5ltr the same gearbox and diff will require exactly the same amount of power to turn over at the same RPM..
Part of the losses are torque dependant, so with the same load the losses would be the same. Losses however would be higher with the 5.0L at full chat compared to the 4.0L.The question is not which one to brag aboout, or which shoudl you talk about, or which is more realistic...
Yes, I know in the real world wheel hp matters over fly hp. (actually torque matters most :P). That's partly the reason for the question. Not so I can go and brag that my car has a 1000hp, (just 790 of it are lost in the gear box) so it must be faster than your 50cc scooter! Doh!
You can measure the exact output of an engine without guessing - it's called an engine dyno. So if you take an egine that produces 200HP on a dyno rig then stick it in a car on a rolling road...blah blah blah. Then take a 100hp engine and do the same, are the drive train losses on the same car, the same??
That, as Shakspeare once said, is the question...
Yes, I know in the real world wheel hp matters over fly hp. (actually torque matters most :P). That's partly the reason for the question. Not so I can go and brag that my car has a 1000hp, (just 790 of it are lost in the gear box) so it must be faster than your 50cc scooter! Doh!
You can measure the exact output of an engine without guessing - it's called an engine dyno. So if you take an egine that produces 200HP on a dyno rig then stick it in a car on a rolling road...blah blah blah. Then take a 100hp engine and do the same, are the drive train losses on the same car, the same??
That, as Shakspeare once said, is the question...
rev-erend said:
I'm gonna write a book.
BHP for idiots..
No really.
Want more HP .. interested.
20p.
Yep - that's how much my local garage charges for air..
Over inflate your tyres by say 10psi and watch your power figures on the RR go up..
Why..
Friction losses on both sides of the tyre - also the operator straps the car down, further increasing the friction.
The real road has only 1 contact area..
Not suggesting Dyno makers cannot figure this out but they do insist that the tyre pressure is fed into the system..
Wonder how often that's done.
Still wanna buy my new book
Yeah it's all a bit difficult to work out what is going on. Losses are, ultimately, all over the place depending on I/O speeds of the gearbox and so on, and then the tyres, they get hot and change pressure etc, drivetrain lubricants changing temperature etc.BHP for idiots..
No really.
Want more HP .. interested.
20p.
Yep - that's how much my local garage charges for air..
Over inflate your tyres by say 10psi and watch your power figures on the RR go up..
Why..
Friction losses on both sides of the tyre - also the operator straps the car down, further increasing the friction.
The real road has only 1 contact area..
Not suggesting Dyno makers cannot figure this out but they do insist that the tyre pressure is fed into the system..
Wonder how often that's done.
Still wanna buy my new book
Dave
virgil said:
So if you take an engine that produces 200HP on a dyno rig then stick it in a car on a rolling road...blah blah blah. Then take a 100hp engine and do the same, are the drive train losses on the same car, the same??
That, as Shakspeare once said, is the question...
Simple answer....no.That, as Shakspeare once said, is the question...
Are losses related to power output...yes, but not the same.
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