BigBlueCruiser

Really?

is that why NASCAR runs rear diff coolers?

or why SB and BB powerboats run coolers on their outdrives?

Heat = parasitic power loss.

it is not static nor quite linear, but the percentage correction is far more accurate than the 50hp myth.

HAZ-Matt

How much power do you think it really takes to increase the temperature of the gear oil over the course of a 500 lap race?

BigBlueCruiser

OK let's see what we have again.

M6 LS2 dyno around 360RWHP(not 340 as I claimed earlier)
M6 LS3 dyno around 395RWHP

Now at a 15% loss

The LS3 is about 464 and the LS2 is about 424.

but look at what happens when we take a 10% loss.

The LS3 calculates out to 439 at the crank.
And the LS2 calculates out to 400 at the crank.

I think that perhaps the vette transaxle is even more efficient than the standard RWD layout.

the SAE certified numbers certainly match up at a 10% loss on the C6.

Which is perfectly fine by me.

BigBlueCruiser

Just a WAG but it's somewhere north of 350hp. Not 350hp for 14sec like a dragstrip. But 350hp WOT for tens of minutes.

We've all driven 500+ miles somewhere at sometime. Who needed a rear diff cooler for that? No one because we're averaging 75mph not 185. Even if you drive your 600rwhp SC'ed Z28 cross country and you average 75mph, you're putting about 50-60hp into the drivetrain continuously.

Bob Cosby

Ok. I never said it was exact, but I do think the "~50 hp myth" is closer than an arbitrary "xx% myth". So you stick with your myth and I'll stick with mine.

Bob

PS...SAE corrected LS2 GTOs dyno closer to 340 RWHP than to 360 RWHP. Perhaps Vettes are different - I haven't done that research.

TrickStang37

i dunno, stock 5.0's put down 180-190 rwhp stock. your practically doubling the losses with 400-500 hp with most examples.

TrickStang37

and the LS3's have been in the 380's rwhp.

I think the drivetrain losses through the vette are about 12.5%.
The vipers, from what I've seen (they've been certified as well) are closer to 10%.
The GT500 is closer to 14%.

this is just observation, i havent compiled enough statistics on the subject to say any of that as anywhere near fact. plus, you have to remember that even gear ratio's change measured output as well, so thats another wrench to throw in there.

RussStang

Ugh.

RussStang

There was a pretty substantially thread about this a long time ago over on the advanced tech boards. Lots of evidence. I believe there was even an example of a engine being dynoed, then having it installed and dynoing at the wheels, and then pulling the engine, ramping it's output up, and dumping it back in the car (can't remember the original motive behind this). Seems the conclusion drawn was that there is no set percentage to drivetrain loss, but there is not set amount for a drivetrain to absorb, either. As power increases, so does drivetrain loss, but not in a linear fashion.

A good example someone brought up was taking a v8 powertrain that cosumed 75 hp through it's powertrain. What if a 75hp 4 banger was put in it's place? Would 0hp be recorded at the wheels? Probably unlikely. It might be worth a search, if you don't mind looking around for it. It was a really interesting and in depth thread. I would try to find it myself, but I don't think I will have the time this evening to do it. Hopeful it is on camaroz28.com. It could be on ls1tech.com, as they have an advanced tech section over there as well, and many of the posters over here post over there as well.

Bob Cosby

Ok. If you use 185 RWHP and convert to 205 rated HP, you're saying that the drivetrain loss is only ~10%?

And to throw another wrench in ALL of this % vs whatever idea....I've had 3 different transmission models in the same car (99 Cobra), and compared them with no engine changes or other chassis changes. The same dyno was used, and all were SAE corrected. The results are that a TKO/3550 took 13 more HP to turn than a T45, and the T45 took 4 more HP than a T5. I bet if I'd of done the same with a T56, it would have been more of a loss than the TKO.

Things that make you go hmmmmm.

RussStang

You are making many good ponts, but if GM really did announce the LS3's hp output under the new SAE protocol, as they did with the LS7, it is not an underrated engine. There is very little wiggle room under the condition of the certification.

Bob Cosby

That sounds like a reasonable conclusion to me. However, I would suggest that the drivetrain loss is largely due to the beefier driveline parts needed to handle the power - with perhaps some in extra heat.

HAZ-Matt

I am not following. 350HP just to go into heating the oil in the diff? Based on some assumptions, that power would heat 2.5L of oil like 50 K (or 90*F) per second. Seems kinda crazy, especially when you consider that if that sort of power was just going to heat the gear oil, how much power would the motor have to make to overpower all of the losses throughout the drivetrain and still overcome the air at several hundred mph.

bossco

Y'know that's wierd, the stick axle car should be the most effcient out of the three, since an IRS invloves more bits and pieces to get the power to the wheels. I wonder how much the driveshaft plays in that, I don't know about the viper, but doesn't the vette use some sort of aluminum/carbon matrix driveshaft? Where the GT500 uses a steel two-piece shaft.

Schismblade

Good post. Agreed 100%