My thought is that it is more fixed, with just a bit of variable thrown in.
I just don't see how a car loses an extra 80hp going from 315whp to 615whp.
If environmental factors remain relatively constant(or standardized) the only loss is thru the drivetrain, and that hasn't changed.
I'm no mechanical engineer, so all theories welcome!

 

I think you are focusing on a fixed number loss in hp. It does not work like that. an 18% loss will have more hp lost in a higher hp car just plain math.

lets use the 20% number loss.

car A 315/0.80=393 hp loss is 78hp

car B, 615/0.80= 769 hp, loss is 154 hp.

Car B looses 76 more hp, but only because the ratio is higher, kinda like our taxes.


putting it another way if Car A has 78 hp loss because it looses 18%, and if you say that Car B looses 78hp as well then it would only have a 13% loss. How can the same car have two different drivetrain loss numbers at different hp levels? not possible.

 

Thanks Marty, it wasnt a new tune just a tweaking of the fuel system. My car was running too( in the 9s at WOT) rich so we tossed the factory FPR and now have much more consistent control of fuel pressure with an aftermarket unit. The weather was much better as well. At the end of the day the mile will tell the tale...

 

If you only consider it to be a fixed %, then I can see your point.
But I am suggesting that as a percentage of flywheel hp, the % changes as flywheel hp increases.

Let's say you dyno a car at .8bar, and it makes 400whp, for a loss of, say, 100hp.
Let's also assume the dyno run takes 10 seconds to run from 2500rpm to 6500rpm.

Now you turn up the boost to 1.5bar, and the car puts down 800whp.
Let's also assume the run takes 7 seconds from 2500rpm to 6500.

The result between the two runs is that the higher flywheel output gives a run that takes 3 seconds less to complete , which registers as greater hp at the wheels.
That is why you see the increase on the dyno chart, because the run was quicker using the same given mass rotated over time.

Remember that the dyno just takes into the consideration the time it takes to rotate the drum(a given mass) from X rpm to X rpm, and measures the torque generated at each rpm, which generates the hp curve.

The quicker it rotates, the greater the hp registered at the wheels.

Nothing in the driveline has changed, only the output of the engine has increased.(assume you standardize all temps prior to the individual pulls)

Again, I agree there will be some additional parasitic losses from heat generated by the greater torque applied to the driveline/gears, etc, but to use a fixed % to back into the flywheel estimate would suggest that total driveline loss would effectively double.

I'm trying to look at this in a way that makes sense to me, and it makes sense to me that the resulting increase in rwhp does not necessarily carry with it a two-fold loss in flywheel horsepower.

That is why I suggested that the percentage loss figure changes as flywheel hp is increased, with at least the baseline 100 hp loss as a starting point, and some additional parasitics added as hp goes up.

There is no real way to know(unless the engine is dynoed outside the car, reinstalled and redynoed in the chassis), and since I tend to be conservative by nature, I lean towards suggesting that if the stock driveline loses about 100hp based on a dyno pull, then as hp is increased the total loss stays around 100hp, give or take a few(which we will never really know, anyway).

Again, for these reasons, I tend to shy away from estimating any flywheel numbers.

Found a decent quote that helps explain my understanding.
http://www.ferrarichat.com/forum/sho...9&postcount=18

 

Gear losses increase w/ load. Remember all practical gears have sliding contact faces. FWIW, There is ~0hp loss when you're turning a transmission by hand.

 

You mean frictional losses?
Please explain a bit!

 

Yes. Almost all modern gears are involute based. The entire gear face is NOT in contact, but a single point that moves/slides from the tip to the root and back. Helical/hypoid gears complicate that even further as they wipe horizontally too.

I quick article on losses I found (the pictures of gear teeth are helpfull too if you've never seen an involute gear shape):
http://www.geartechnology.com/pa/mem...7/section4.pdf
The first page introduction is easy enough for anyone to follow before they delve into math. Even if you don't read it, the most important statement:
"the main portion of losses are load-dependent gear losses."

The losses are not linear. There are fixed losses, losses associated w/ rpm, and losses associated w/ load (torque). These all sum to create a total curve. When divided by the in/out shaft power they are a %. The % is NOT the same at 2000rpm as it is at 1000rpm. The % is NOT the same at 1/2 load than full load. The % is NOT the same in 3rd vs 4th gear. The % is NOT the same at different oil temperatures. Since each transmission is different and the line too complex, most approximate it as a fixed % based on some empirical data. Nothing wrong w/ that approach but it is only a rough approximation.

If you want to know (way) more about gears the "American machinist gear book" has been scanned by google books. Warning: its basically how to make gears. Probably no one here (but me) would be interesting in reading it I can read that sort of stuff cover to cover. "Gears and gear cutting - #17 Workshop practice series" is also riveting (but not in public domain yet)

 

Thanks.
That helps to understand it.
I'm not much of a mathematician, so I'm sure I'll get lost along the way there, but I'll read the article referenced above.
Thanks for the insight.

 

So if you decrease the two associated gears contact surface area you there-by have a lower % of loss?

 

If you really want to discuss HP, torque, and quick response, then think about a combination of Garrett 35s, GT3 RS heads, 3.8 Mahle conversion, and RSR throttle bodies. You can talk HP all day, but you ought to feel the quick response of those 6 throttle bodies connected to production of 930HP at the rear wheels. Incredible!!! Check out the thread "A Very Custom 996 GT2 RSR" for more info.

 

Question ...... why would you use RSR throttle bodies which have the rod going through the throttle body versus the barrel type which have no obstructions or pieces that can come lose and destroy your motor? In addition stroker motors will give far greater response. EVO is doing a 4.1 liter right now. Add the barrels to this and wow!

This aside ....... I believe the topic of this thread is 1000 hp is available without going through the extreme costs of big heads, ports, individual TB's or stroker motors.

 

That is a work of art
Robert

 

Nah ....... art didn't use these.

 

Chad
Can I borrow them....
Robert

Sure.

 

Rob

You have stock heads right?

Jag