Heavy...
I understand your logic and somewhat agree. As most would agree, it doesn't matter what the number is, but what the differences in the numbers are after the changes, on the same dyno.

As far as driveline loss, this is my take. For the average guy, it's not practical to dyno an engine, nor necessary. This was a great source of frustration for me when I started looking around the '6' for info on modding. I was curious (like most) to know what I could expect for baseline hp and from certain mods. All I kept reading about was "600 kit" this, "650 kit" that and "700 kit" again. It's kind of misleading for a new guy to think he can flash a car and stick on a couple mufflers and pickup 200hp at the wheels. To me all that matters is what hits the ground. And I realize that number is a moving target, depending on tuner, parts, dyno, etc.... I personally take Porsches word for it that my engine makes 415hp, if it doesn't, oh well. I have built engines and dynoed them more for breakin purposes, not to see how much power it makes. I guess my point is, To ME, it only matters what the engine makes for power IN THE CHASSIS. Thats why I accept the fact that MY car has a 19% driveline loss based on Porsches rating of the engine in my car and the reading we got at the wheels on this particular dyno. I realize that I could go to another dyno and only have 17.5% loss or maybe I'd have 21% loss.

I also realize that not all people have access to a chassis dyno and maybe get all their stuff, including a tune, through the mail. Thats why I think it's more realistic to pass around real world info like actual mods and the corresponding chassis dyno numbers so people don't think they have 700hp because they bought a certain kit from someone.

 

whatever the loss is from crank to wheels in a car will not change for that setup. I think it would be great to know what the difference in hp when going from AWD to RWD in the same car on the same dyno. Those are relevant results and you could calc the difference in the two regardless of what the total loss is, Has anyone done that and if so what was the loss.

 

It was our intention to do that as we had my car (AWD) and an exactly modded RWD car in the shop almost at the same time. Tony might actually have that info as he tuned both cars. I think the numbers we posted earlier in the thread (20-30whp?) are very real world. I will try to find out though.

 

That means the dyno being used would determine the drivetrain loss. The drivetrain loss is probably more consistent that the power output, but I do understand why some people use that but IMO that's the worst way you could use because even differences in the same car would mean that if you put two stock 996 TT's on the same dyno, and one dynoed 433, and one 443 that the drivetrain loss would be the variable and not the power output.

Not to mention getting on a dyno dynamics, then the drivetrain loss goes to 30% or more. Or if you have slight problem on your car that you dont find initially, then you are being mislead on the drivetrain loss.



Edit: Sorry, had not seen the replies. But I am in agreement in using the dyno as a baseline and the most important thing is finding the wheel hp. Completely agreed.

 

Thanks Seal,
Ultimaty we are all right. we all agree that the number is not what is important, but that driveline loss on EACH car is consistant assuming all things are the same, tire type and size, awd, rwd etc. Yes, the ONLY variable is the dyno. The number we get after our exciting dyno session means nothing, until the next time we go make a change. Hopefully we put the car back on the same dyno, where all things are STILL equal depending on temps and such, but as far as dyno and a certan car, the difference in numbers is what we are looking for.

 

I think in order to draw a scientific conclusion as to drivetrain loss the engine dyno is needed, because if we look primarily at performance numbers, for the most part you can get a couple mph in a 1/4 mile etc in going from AWD to RWD, but a huge part of that is drag, which has some big effects.


However for baseline numbers, it's not that big of a deal. And not much of what we do today on dyno's is scientific regarding all the different variables.

 

I absolutely agree, however, I didn't know we were gonna get "scientific". That automatically disqualifies me .
However, as I said, most people agree that the engine dyno is the "correct" way to quantify ACTUAL hp at the flywheel, but no one is going to dyno their engines and are content to accept what the chassis dyno says. If Porsche is actually wrong about the power output of this engine, then our driveline loss "guestimate" is off by a percent or two. I'm OK with that. All "we" care about is what the "xyz" dyno says now and what "xyz" dyno says after we flash, install mufflers, install bigger turbos, etc... The numbers we all brag about really mean nothing as I'm sure we've all seen 500rwhp cars beat up on 600rwhp cars. With respect to 951's thread, I don't believe anyone is going to RWD expecting feel a 100hp gain. I also don't think anyone is going back to AWD because they are dissappointed with the power "gain" (for lack of a better word). I think everyone that went from RWD to AWD did it for street "safety" reasons, as I know I would, hence the reason I am NOT gonna do it .

 

I have no arguements with that. I just think that with the wide variety of drivetrain loss numbers floating around these day, somebody has to have actually tested a drivetrain in this method before. I know it wont be done for many cars, but it would be nice to know that someone has actually tested one somewhere so we could have an idea of what that constant number is. I dont expect for everyone to do it. Only one car needs it to be done to establish a constant.

But with all the numbers we throw around, from one car to the next, one drivetrain to the next, and with the complexity and technology involved in todays drivetrains it would be nice to know. Otherwise it's a guess on everyone's part. And will still be for any car that's not tested.

 

I`m changing my mind about the RWD once a week..

 

I would totally agree with you. I also think that for dyno numbers to mean something they need to be done on the same car as HC pointed out, there are variables between cars. For example I know for fact, that 2003 Seal Gray TT's have considerably less loss than other years and colors

 

Dyno numbers as a rule don't mean squat, but when you are on a dyno, you need to know somehow whether you are going forwards or backwards with changes. As everyone says...2 cars and some blacktop are the real test.

 

I would love to see a comparison of the same car and same driver with AWD for 1/4 and 60-130. Then rear wheel conversion (no limited slip) and same tests. Finally that same TT with rear wheel conversion and the addition of the limited slip and same tests. This would be good. Even better if the driver was able to express his experience with all 3 tests. Asking for a lot, I know..LOL

 

the one example listed on this thread was by TXgold and the difference was substantial. With AWD the car ran 60-130 in 9.22. With RWD the car ran an 8.40. that is 0.82 seconds which is huge time. What I don't know is if there was any other changes or how complete the RWD conversion was. Good data non the less. I would say that it definitely shows a big increase in Hp.

 

The only variable was about a 65/35 mix of 93/MS109 gas, with no race file. In other words I put in about four gallons of MS109 and ran this time with a UMW 93 Flash. The Temp was actually either the same or warmer the day of the 8.40 run.

I know this is gay, but I ran this run the morning after I met my Fiance.

 

It is a totally different experience! Personally, I would never go back to AWD.
Happy Holidays
Robert