The_Phantom

Don't be juvenile, you should be better than that. You would be right if I was trying to prove that 911s have a drivetrain loss of exactly 11.2787635464% and Corvettes has a drivetrain loss of 17.35475894635%. That's not my point. There is a big difference is drivetrain loss between the two cars. The Porsche is lower. The difference is due in large part to the fact that the engine in the 911 is in the rear and the engine in the Corvette is in the front. The dyno results while no where near precise are so vastly different between the two cars that they make my point. You are acting as if I had two dynos where one of the cars seemed to have a drivetrain loss of 15% and the other had a drivetrain loss of 16%, and was using those results to make a point. However, the difference here is big enough so that perfect or not perfect the difference is obvious.

Viken

Gary, there is no grey area. The rubber compounds are the same. It's the grooves that make the difference. The Corsa System is designed to perform well in the wet and they do quite admirably. There is always a trade off between dry and wet performance as placing more grooves pretty much means less rubber on the ground.

E. J. - 993 Alumni

Okay, this is my last reply to you.

You already know the answer (in your mind), so you aren't hearing anything to the contrary.

I am not proving a particular exact driveline loss either. I am saying that your whole premise is wrong based on the information you are using or proposing to use.

Let me spell it out for you.

1. You can't compare factory HP numbers for a motor - they are vague, inexact and each motor makes a different amount of horsepower.

2. You can't compare HP figures gleaned from two types of measuring devices.

3. You can't make a general statement like you are without some sort of proof. Lots of people here with lots of automotive experience are telling you that you are wrong.

4. You asked for opinions on your premise, were told your premise was bunk by some smart people with experience, and still hold firm to the premise. Too quote you, you said:

and
We tell you that it doesn’t make sense, provide solid, real reasons why it doesn’t make sense, yet you continue to believe what you want. Why? Because you read it in some small time car rag and because you believe it to be correct. You want to be correct in front of your peers, and will go down fighting. That’s why this is my last post to you regarding this silly premise. If I were Greg Fishman, I would change my username…

If you were to admit you were wrong, and admit that maybe it is really only the friction of the gears, U Joints, bearings et al that make for a 1 or 2% driveline loss we could all move on a little smarter for the conversation. But you would rather go down with the ship – which is your right to do.

Have a nice day.

e6tme

What?! First off, you originally claimed that Porsches incur "approx. 7% loss" now you are saying 11.5% is "damn low." Which is it?

Secondly, you originally gave the example of the 2001 Z06 with the 11.5% "loss". Now you're saying they can't be that low?


The quoted losses are guesses and assumptions. They have shown no more scientific proof than you.

You are missing the forest for the trees. All that those articles prove is that rated outputs are generally moot because they vary so much. Many have suggested that Porsche underrates their motors- the GT3 is a perfect example. Perhaps GM takes the mean of a sample of their engines and rates them that way. Who knows? But that goes a lot further in explaining your original contention that Porsches seem to have "stronger horses" in their motors than other cars.

As I and others have repeatedly said, trying to figure out actual drivetrain losses would require you engine dyno the motor, then chassis dyno the car. Ideally you would do this with several cars because as this discussion has proven, there is too much variance from engine to engine, car to car, to be able to draw any legit conclusions.

The_Phantom

Oh, no, I can admit when I'm wrong. And it definitely seems like you guys are right about one thing, that the driveshaft is not what causes the drivetrain losses.

Sure, factory hp can be inflated, but they're close enough for the purposes of this conversation. Do you realize the problems with the FTC a car company would have if they grossly inflated a hp number?


"Proof", let's get this straight, I'm the only person that has cited anything.

You need to realize to believe your position which is supported by 'I'm right because we're smart' instead of based on the available evidence would be to fall victim to the ad hominem logical fallacy. So far you guys haven't produced anything that proves me wrong.

Yeah, European Car Magazine with its large circulation of hundreds of thousands of copies is just a rag and not as credible as you.

So I'm winning you over as well. You are now admitting that there is a 1-2%. Progress has been made. Another three perecnt and you'll agree with me.

The_Phantom

Perhaps, perhaps, perhaps. And until we do know, I will continue to believe the experts at European Car Magazine and to believe that the dynos support this principle.

E. J. - 993 Alumni

Dont even know why I am bothering, but here you go.

My info comes from an automotive engineer who HAS done these kinds of tests using the SAME engine (in and out of a car) with both tests getting temp and humidity controlled air and dynos that were calibrated using the same equipment. When you can provide data that is equally well controlled, you would have a bit of credibility vs. citing garbage from a car magazine.

Seacrest out

The_Phantom

Don't know why I'm even bothering with you, but here you go. You have an engineer who has done tests on rear engine rear wheel drive and fron engine rear wheel drive cars and concluded that there is no difference in drivetrain losses. How convenient! Where does he work, what is his name?

Don't talk about data, when you have none yourself.

tdf360

Thanks Viken, I didn't know the compounds were identical. I would guess, based on that, that the Corsa system would be closer to the Corsa than to a street tire, the grooves can't hurt THAT much.

Gary

SundayDriver

I will probably regret posting here but here goes anyway...

I am that Engineer. I spent ~3 years at a major fuel systems development vendor doing engine calibration and performance work. While in school, I did research on automotive engines, both chassis dyno and engine dyno work. Some was even published by the SAE. Further, I spent ~10 years in the Automotive testing field at a firm called EG&G Automitive Research in San Antonio. That said, here is what is wrong with your assertions:

1) Drivetrain length has virtually nothing to do with drivetrain loss. Loss comes from bearings, gears, bushings, etc. The weight of one driveshaft vs. another has no bearing on this. Now a long driveshaft, with the same characteristics as a short driveshaft would certainly provide more aero drag, but you would be hard pressed to even identify that factor as it is so small it can be neglected.

2) Your approach to using published engine power vs. someone's chassis dyno results is virtually worthless. Engines vary. They can vary quite a bit. A 350 HP rated engine may actually be 330 HP in one case and 370 in another 'identical' engine. Using published HP destroys the entire argument, but I will continue.

3) Were both dynos properly calibrated with tracable standards? If not, then you have no idea if you are really comparing 1ft-lb to 1ft-lb. Maybe 1 ft-lb on one dyno is really 1.1 ft-lb.

4) Were the test conditions the same? Were both tests suppying temperature, pressure and humidity controlled air to the engine? Were both the same?

5) Were the oils (brand, viscosity and age) as well at temps the same for the engine and chassis tests? If not, you have significantly changed the overall friction losses.

6) Now if that is not enough, lets move away from the small errors that could account for 5-10% error and go for the biggie. What speeds/gears were these tests conducted in? Drivetrain loss is a function of fixed losses plus variable (Speed dependent) losses. If one test has an overall gear ratio of 1:1 and the other was 1.5:1 they are not even close to the same test.

I have personally participated in tests where we dynoed the same engine both in the car and on the engine dyno. In both cases controlled air is supplied. Dynos are calibrated daily. Oil temeratures are contorlled via external coolers. Even then, variability can be a couple of percent. I have seen what magazines do for testing and personally I would not trust their data to beter than +/- 15% or so.

arenared

This is such an entertaining thread (except for the part where the bodies were flying). I wouldn't trust the dyno charts on the EVO website. I was looking at it today, and in one place it said to correct for 10% drivetrain losses. In another, it said to correct 15%. This was for the same model/trim/year, but the baselines were different by 10HP. Some obvious variablity that Evo didn't know how to explain. Of the Boxster dyno charts I've collected, 16% seems to be about the best "difference" from advertised HP. I gotta imagine the 996 (4WD excepted) is darn similar. Speaking from an underpowered, but nicely handling (modified) Boxster S, I'd sure like to see Porsche put in more HP (across the line). The 986S and 996S HP are more like base model HP to me. From my surfing, a GT3 is probably the only P-car in my upgrade path when the time comes.

The_Phantom

Ok, forget about driveshaft length and weight and respond to what was stated in European Car Magazine.

"On the other hand, a Mustang dyno will correct with a 21% loss figure. Actual over-the-road loss is probably in the 17-20% range. A lot of front-wheel-drive cars do not have any 90-degree gear changes. All gearing is straight transfer. Losses are less; I'm going to guess at 11 to 12%."

http://www.europeancarweb.com/tech/t...02d/index.html

What specifically is wrong with this statement taken from European Car Magazine? You admitted that Loss comes from bearings, gears, bushings, etc. The drivetrain in a front engine rear wheel drive car is more complicated that one in a front engine front wheel drive car and a rear engine rear wheel drive car (more "bearings, gears, bushings, etc.", no?) Then you agree with me that the more complicated drivetrain in a front engine rear wheel drive car results in greater drivetrain losses than a front engine front wheel drive car or a rear engine rear wheel drive car? If there is a difference in drivetrain losses, how much is it?


Secondly, did you ever test an engine that was used in both a rear engine rear wheel drive car and then a front engine rear wheel drive car? (Probably not) If so which engine and in which cars? If you haven't then in light of your inductive skepicism about the results of dyno testing, how can you say that you know that there isn't a difference? Did you ever test any rear engine rear wheel drive car? If so what were the drivetrain losses?

e6tme

Talk about beating a dead horse...

The european car tech letter does not help your case.

Let me surmise: You started this discussion by asserting that A) Front engine/rear drive cars have a driveshaft which alone accounts for 25-35% of total drivetrain loss. B) Since Porsche has a rear engine, rear drive layout, and no driveshaft, it has less drivetrain loss.

Now you admit that the driveshaft alone does not account for the 25-35% of total parasitic losses, but you state that "a front engine/rear drive layout is more complicated than a front/front or rear/rear layout."

This comment is completely erroneous.

First off, the layout depends on whether the engine, gearbox, and diff are mounted transversely and/or longitudinally.

The most inherently efficient layout that is commonly used is a transverse engine with a transverse gearbox and transverse diff. (Most FWD cars) Because all the componants are lined up in the "same direction" the power doesn't need to go through any 90-degree gear changes as referanced in the European Car tech letter.

In the case of a longitudinally mounted engine and gearbox with a transverse diff i.e. the layout in a Corvette, Viper, BMW, etc., crankshaft power flows from the engine to the gearbox, and then encounters a 90-degree change at the rear diff.

This is why the author of the tech letter contends that most FWD layouts are more efficent than others.

Fishman, what you need to understand is that all RWD 911 layouts are longitudinally mounted engines and gearboxes with transverse diffs, the same as Corvettes, BMWs, etc.

Furthermore, for all intents and purposes the Porsche layout is LESS efficient than the Corvette simply because power is routed forward from the engine to the gearbox and then back 180-degrees to the differential. This is done via an extra set of gears and shafts not required in the 'Vette.

It is important that you understand the above is a gross oversimplification of things. When you consider the transmission as a whole, the gears, the shafts, how many forward gears, bearings, seals, what type of lube, etc. etc. the 90 and 180-degree gear changes don't count for that much.

You also need to consider that most FWD cars are relatively light weight with less power, therefore their transmission componants are smaller and weigh less than the typical transmission from a powerful RWD car.

To recap- a "mixed" layout such as a Porsche or Corvette is less efficient than a "uniform" layot, such as a Civic. I will concede that a 90 degree change is less efficient than not. But at the end of the day, there are innumerable factors you need to consider when trying to determine drivetrain losses, that is why no one really knows, and why those losses differ from car to car.

DJ

Well said, e6.

Greg Fishman

Ditto.