Exhaust Change

[Guest]

Ok fellers,

To settle this debate simply go put your car on a chassis (aka rolling road) dyno and get a true figure. Flywheel figures are not accurate because that is not a true measurement of what power you are getting TO THE GROUND.

CJF - a stock XR6 Turbo is around the 190 Rear Wheel KW so go do us a favour and put your car on a dyno to see what improvements in power you have got as I am sure many people would be interested. B)

[richdave]

CJF - a stock XR6 Turbo is around the 190 Rear Wheel KW so go do us a favour and put your car on a dyno to see what improvements in power you have got as I am sure many people would be interested. B)

I hear the thud of a gauntlet hitting the ground....

A better test would be for the mod'ed car and a stock car to be tested side by side so that conditions are as close to as possible.....

The outcome would be VERY interesting.

[psi_guy]

I agree with u richdave. But if it aint possible, at least why not try and test a stock & the moded car on the same dyno (chassis of course) like vik said, on the same day, one after the other? That probably is effected less by driver style etc than a track drive.

[Guest pmacleod]

That's not correct.

Think of a 1000kw GTR or something similar. A standard GTR might put down 150kw at four wheels and 230kw at the flywheel. Hence, by your reasoning, GTRs lose a fixed 80kw from the flywheel to the wheels.

Obviously, the 1000kw GTR does not have 920kw at the wheels.

Also, by your reasoning, it would be quite possible to have a car that has a negative power

output to the wheels if it were say, running badly and down on power.

Adam

Agreed. Your frictional and heat losses will increase as you try and put more power down to the increased energy that each component has to transfer. It may appear to be a fixed percentage loss - however in reality a formula incorporating an exponential factor would be more accurate.

Adam,

Of course it's not possible to have a negative output, if the car was that sick it wouldn't turn the rollers and you wouldn't get a reading. Taking your GTR example, a 1000kw GTR would not have the same gearbox and diffs as a stockie, so the loss would be different again. If by some miracle it did have the stock box yes it would lose the same through the drivetrain just before it went bang

DZ,

It takes X amount of force to turn the drivetrain. Why would that change just because you have more force available to turn it ? As far as heat and friction go, well you only get more of those when you turn the drivetrain faster. Again, the heat and friction in the drivetrain is the same at any given RPM regardless of the force applied. The engine itself may be generating more heat when modified but the transfer of that to the rest of the drivetrain is almost unmeasurable.

It took me a while to get my head around it, but it does make sense. I can probably find the technical discussion if people are interested.

Cheers,

Paul.

02 STi which will have an honest-to-god 300kw ATF/230kw ATW (4) when I'm finished with it

[Turbo6man]

As far as heat and friction go, well you only get more of those when you turn the drivetrain faster. Again, the heat and friction in the drivetrain is the same at any given RPM regardless of the force applied. The engine itself may be generating more heat when modified but the transfer of that to the rest of the drivetrain is almost unmeasurable.

It took me a while to get my head around it, but it does make sense. I can probably find the technical discussion if people are interested.

Cheers,

Paul.

02 STi which will have an honest-to-god 300kw ATF/230kw ATW (4) when I'm finished with it

Incorrect again - you are not listening!

It is not simply the engine speed - it is the TORQUE that you are trying to control and disperse through the components.

The only losses that are fixed are the engine driven ancilliaries like water pump, alternator etc.

From the flywheel back there are losses which vary according to the torque transfer and the inherrent efficiency of each item including clutch plate, gearbox, diff, even tyres.

Manual gearboxes for example are generally accepted at close to 90% efficient whereas autos are a bit less at around 80%. This is because of the extra clutches in the auto together with larger, heavier gearsets. Also a torque convertor is less efficient (until lockup) than a clutch. LSDs are also less efficient than an open diff. Underinflated tyres are less efficient than overinflated.

Edited 06/01/03 10:20 PM by richdave

[Guest ladieslookout]

Someone get there XR6 turbo to a remus sports exhaust depo and have them suss something out for the car, remus r the best when it comes to exhaust systems.

[Boost6]

When you've got 1000kw in a GTR, you wont worry about losing some power through the driveline!!!

My XR6T ute (auto) made 190rwkw completely std, then 272rwkw the following day after a Cobra stage II kit was fitted.The exhaust is still std. I agree it is no point to compare figures from other dynos but at least I know we got an 80 rwkw increase from the mods.

I have a fresh GTR engine build happening at the moment & it will be engine dynoed before going in the car. I dont know if it will be chassis dynoed afterwards once the engine is in the car - but it would sure be interesting cause then we would know for a fact what the actual losses were for that particular driveline setup.

Ultimately, track dyno is the best way to measure power.

[Guest]

Well done Boostie,exactly 12 months since the last post on this topic.

vik

[NYOPA]

I have a completly stock engine/ exhaust system in my 1 week old car and would be happy to put it up for a dyno test against another to see what power differences there are.

Just PM me if you want to do it sometime.