Power loss.

[T66]

Is there any truth in the rumour that you loose plus minus 35% of power on a FWD car from the flywheel to the wheels? (N/A that is)

[curtis73]

Its usually a bit more on the order of 25%, but yes. Every step you take, like transferring power from one cog to the next in the tranny, transmitting power through the CV joints, bearings, etc. They all cause friction which converts the torque into heat and sound energy.

BTW, that doesn't change for turbo, supercharger, nitrous, or anything... its there no matter what you do.

[T66]

Would the power loss be more on a RWD application?

[curtis73]

Typically a touch less in RWD. The power in a FWD gets split into four CV joints which tend to suck up a bit of power, whereas a rear wheel drive puts the power through two smaller Ujoints and one direction change in the ring gear. Independent rear suspensions on RWD cars tend to take a little more than live axles since they go back to 4 Ujoints on the drive axles.

Overall, they are all pretty much a wash. And I was a bit high on my estimate of 25%, I'd say 20% is more realistic. In general, engineers and designers don't take it into much consideration when it comes to things like fuel economy or efficiency, so its not a huge difference between layouts.

[T66]

Thank you. The reason why i ask this is due to the fact that I bought a motor (Mazda 2L 16v FE3) from the east and the engine seem to be in good nick ( compression wise, 10.1 on all four cylinders) but the book states that the motor makes plus minus 141Hp on the flywheel but I only managed 83 Hp on the wheels. RWD application. Aftermarket management system. Now this is not write, is it?

[beyondloadedSE]

drivetrain losses on the mtx-75 in the ford contour is about 18%. 35% sounds extremely high for mtx or atx.

[drdisque]

Mazda automatics have notoriously high drivetrain loss. All of this loss comes inside the transmission itself. Its so bad that the manual probe GT runs the 1/4 mile over a second faster than the automatic one.

[Moppie]

Originally Posted by curtis73

Typically a touch less in RWD. The power in a FWD gets split into four CV joints which tend to suck up a bit of power, whereas a rear wheel drive puts the power through two smaller Ujoints and one direction change in the ring gear.

I have to totaly disagree here.

Applications where the engine is mount transversly (so there is no change in drive direction) generaly lose considerably less than 20%, the average is around 15%, and for simple manual gearboxs it can be as low as 10-12%.

Applications where the engine is mounted longtudinaly suffer far greater drive train loss as the drive has to be converted through a sharp angle.
This is usualy done through a pinion gear in the differential.
These are notoriasly bad at efficant power transfer, generate lots of heat and tend to be very noisy.
In some cases they can provide as much power loss as the rest of the drive train combined.
Typical RWD drive train power loss is around 20-25%, but 30% is not unheard of.
Things like drive shaft length, number of joints in the shaft etc, as well as how complex the rear axle are all add to power loss through heat and noise.

AWD is of course the worst, early systems could suffer as much as a 50% power loss between the engine and wheels, adding things like a transfer case and a second differntial just adds more drag on the system, and more power is lost to heat and noise.
Modern systems in cars like the Subaru Imprezza are much more efficant, but still lose around 30% to the drive train.

[CBFryman]

50% is unlikely.

and your typical Manual Transmission Total Drivetrain loss is 10-18% FWDand RWD and automatic 15-25% maybe a tad higher if its an ineficent tranny, all AWD's have other than FWD's is a differential to transfer pwoer to the rear and then one to split it to the two rear wheels. i havent seen figures on this but stock STi's arent dynoing 150whp... typical is 220-230whp. which is around a 27% loss for a manual.
Evo VIII's typically dyno around the same and are rated (probably underrated) to 286bhp which yeilds a 23% drive train loss for a manual transmission.
i could continue on to the SRT-4, Audi's, orther subaru's but i wont...
a tiburon which a transversly mounted v6 engine has 171bhp and typically dynos consistnatly around 145whp... so around a 15% power loss for a manual.

[Moppie]

Originally Posted by CBFryman

which is around a 27% loss for a manual.

And 27% is around 30%, which was a rough esitmation based on my expeirance comparing wheel numbers with quoted flywheel numbers
So I was out by 3%, not to bad really.

50% on a modern AWD would be extreme, but try dynoing and old Series One land cruise and see what sort of results you get

Of course as knowledge improves and new ideas are tried drive train losses will go down, I doubt any of the figures in this thread will be relevant to a new car in 10 years. Especialy when talking about AWD.

[T66]

Originally Posted by T66

Thank you. The reason why i ask this is due to the fact that I bought a motor (Mazda 2L 16v FE3) from the east and the engine seem to be in good nick ( compression wise, 10.1 on all four cylinders) but the book states that the motor makes plus minus 141Hp on the flywheel but I only managed 83 Hp on the wheels. RWD application. Aftermarket management system. Now this is not write, is it?

Please be so kind to reply on the above.

[Moppie]

Is it a manual or an Auto?

If your engine is making 141 then your getting a 42% power drop to the wheels.
Either the dyno wasn't set up properly, or you've a problem with the engine and its not making the power it should be.

Working on a power loss of say 22% (average of what everyone thinks it should be) then you should be seeing around 110hp at the wheels.

[curtis73]

I think something is amiss with the engine. Maybe some re-tuning on that aftermarket computer?

[T66]

The engine's cr is what the book states. Custom intake manifold (because the unit use to be an FWD, now RWD) and custom zorst. Guys, I am loosing 26hp somewhere and I do not know where to go and look. It is so frustrating!! Except for management, where would you oaks start looking?

[Moppie]

Well your custom exhaust and inlet manifolds would be a good place to start, then look at how the ECM is tuned, is the fuel pump big enough etc etc.

With a better idea of what its in, how its installed and what your level of knowledge is there isn't a lot we can do to help with out just making educated guess'es.