M758

Ok Question,
I understand that there are power losses from the flywheel to the wheels.

1) Are these the same for all cars? I assume some drivetrains are more efficient than others so they would have different loss values.

2) Is this loss a fixed hp per drivetrain or does it increase as power goes up? I understand how it can change depending on drivetrain, but how does it take more power to get a higher power level through a gearbox?

3) What is typical for Porsche? 22% or fixed hp?

Thanks

PorscheG96

1) No.
2) Power loss results from friction so the function is linear.
3) After seeing the results from both Bill and my own dynos I'd say ~17%.

M758

[quote]Originally posted by PorscheG96:
<strong>1) No.
2) Power loss results from friction so the function is linear.
3) After seeing the results from both Bill and my own dynos I'd say ~17%.</strong><hr></blockquote>

Ok Thanks... Got it now!

After thinking about it a while you are right. The losses are liner.

Friction in General is fuction of the normal force and coefficient of friction.

As the normal force goes up so does the friction.

Now loading in gearbox goes up as the power through it goes up. This is due to the reaction loading at the gear teeth which is reated out through the bearings.

OK got it!

Thanks <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

Deepice

I asked this same question not to long ago...

I was told that it is 15% for 911's and 17-18% for our cars....

944Fest (aka Dan P)

My dyno guy, who has extensive Porsche dyno experience, puts the 951 drivetrain losses at 16%. That 1% is close enough to the other 17% mentioned, and could easily be varied by synth fluids. He said the WORST drivetrain losses he's seen was the GM LT1 package, at 25%. Sure, it's a seperate tranny and rear end, built heavy to stand up to abuse, but can you imagine flushing one QUARTER of your power before getting to the road??? No wonder a Porsche vs. a Chevy with similar power to weight ratios yields an advantage to our marque! There is a 10% difference in the power that gets to the ground!

Then again, if is 17%, then I'm making almost 4 more HP then we calculated at 16%!! (286 at the wheels) <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Danno

Wow... I'm getting a major case of déja vu....

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=010438" target="_blank">Topic: HP...flywheel to wheels? </a>
[quote]Check out this thread: <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=000474" target="_blank">transmission losses on dyno run</a>.
And also check out the charts on <a href="http://www.novustelecom.net/~fkassam/dyno/dyno.html" target="_blank">Farzaan's Dyno Day</a>. Compare the charts of the stock cars with known specs and draw your own conclusions... <hr></blockquote>

abduln

I am not sure how your guy came up with 25% for an LT1 pacakge (what is that by the way, there are several cars that use that engine?).

On the various FBody sites there are numerous cars dynoed there and the stated corrections are always 14 to 19% depending on being a stick or automatic, rear end type (ltd slp vs. ATB), and tire frictional cf. Those guys actually post their dyno charts, so it's pretty easy to find out what's going on in their world.

At 25% you couldn't possibly get the gas milage that those cars get, plus you wouldn't get the speed or acceleration they get per their rated horspower and torque. GM simply wouldn't let the car on the road because of the CAFE penalties.

Abdul

M758

Danno,
Guru as always. Thanks for the info. Unfortuantly as many things are there is no "easy" simple answer. Comparing rear wheel hp vs flywheel hp is not really the best thing to do. Even comparing rwhp from various different dyno is not perfect due to all the factors that introduce errors. Clearly Chassis dynos are a very good tool for the tuner who has one in his shop. By doing before and after runs on the same unit to similar conditions (ie gear, ext engine fans) he can determine to fair degree of certainty how he has impacted perforance. Once he does enough cars he can get a "baseline" for a particular type of car with certain modifications and the know if any particular car is higher or lower than expected for that type.

As with most measurement systems Dyno's do not Lie, but one needs to be carefull to properly understand what numbers really mean.

I have read some you threads on your MAP sensor stuff and have been pleasantly surprised how you have been relying on the DYNO and a/f measurements to "Tune" your chips and MAP sensor. Good Call on this. As long as you are using the same Dyno and approx the same external conditions you should be able to properly understand your gains. Of course I assume you already know this and have been following this idea as well.

Danno Thanks for the input!

951 badger (if you are out there)... Saw your "S" made 230 rwhp on the dyno... Intesting... Mine did too when tested about 2 years ago at 109k. Cool