Planet 9

**Slatfatf** · #41 09-02-2008, 04:15 AM

Originally Posted by K-Man S

Hey I am shooting for a GT400 but not sure if I will ever get there or not. Fort, what drivetrain loss figure would you like me to apply to my 332 rear wheel hp?

I can see 2 approaches that make sense.

One would be to deduce a drivetrain loss from a baseline dyno of the unmodified car, and stick with that loss consistently. One could argue that the % drivetrain loss should go down as the power goes up, but we'll set that aside until better data is available. This approach neglects the fact that each engine with produce a different power than its nominal rating - but the amount of this difference is unknowable.

In your case, I seem to recall you had something like 265 RWHP in your baseline dynos. That would imply a drivetrain loss of about 10%. On that basis you could reasonably claim that your engine now makes 370 FWHP, which is pretty damn impressive!

The other approach would be to talk about increased RWHP from a baseline, and not try to speculate about what FWHP might be present. As I recall, you've added something like 65 RWHP above your baseline, which is also fantastic! In this approach, since the drivetrain loss is unknowable, we just avoid talking about FWHP altogether.

**titanic** · #42 09-02-2008, 04:23 AM

According to Rototest Research Institute, the drive train loss for a manual Cayman is 8%, for a Tiptronic Cayman S is 12%.

Powertrain Performance Graphs - Rototest Research Institute

**Slatfatf** · #43 09-02-2008, 04:27 AM

Originally Posted by elmo91789

Fort,

It seems like after you have made two edits and additions to this post I now agree with you that a baseline of 275RWHP makes the dyno plausible and would be an indication of a 14RWHP gain for the exhaust and is very much in line with results from the addition of the Remus to a stock Cayman S..

I frequently edit long-winded posts after they're posted. I have a hard time with the tiny posting editor window. Sorry for any confusion...

Originally Posted by elmo91789

Fort the dyno shows 317RWHP and 317/.89 = 356.179 and that is closer to a
RS350 than the RS340 don't you agree ?

My concern is that the dyno might be reading high across the board. For example, if the data were acquired on a Dynapack dyno, where the dyno is connected directly to the wheel hubs, then the "driveline loss" would be expected to be much lower. Thus, an unmodified car might dyno at 280 HP on a Dynapack, implying a drivetrain loss of about 5%. In that case they have a GT334 (317/0.95 = 334). Without seeing a baseline we don't really know how much power has been added.

Originally Posted by elmo91789

I see you are asking for a stock baseline before you can feel happy with the results so do you think they should strip the RS350 back to stock and then basline for you or do you think they should just invest in another test Cayman S and start all over again to substantiate the dynos for you?

I'm not asking them to do anything... especially not for me. I'm just pointing out that there is some uncertainty in their results since no baseline has been posted.

**Slatfatf** · #44 09-02-2008, 04:33 AM

Originally Posted by titanic

According to Rototest Research Institute, the drive train loss for a manual Cayman is 8%, for a Tiptronic Cayman S is 12%.

Powertrain Performance Graphs - Rototest Research Institute

That's a fantastic link Titanic! Thanks! Note that their data was for a base Cayman. Also, their dyno was a wheel-hub type dyno. Thus, their 8% loss is less than what one usually sees on a rolling-drum type dyno, where 10-11% is more typical.

**titanic** · #45 09-02-2008, 04:41 AM

Originally Posted by Fort Felker

That's a fantastic link Titanic! Thanks! Note that their data was for a base Cayman. Also, their dyno was a wheel-hub type dyno. Thus, their 8% loss is less than what one usually sees on a rolling-drum type dyno, where 10-11% is more typical.

You are welcomed.

elmo91789 · #46 09-02-2008, 05:24 AM

Originally Posted by Fort Felker

That's a fantastic link Titanic! Thanks! Note that their data was for a base Cayman. Also, their dyno was a wheel-hub type dyno. Thus, their 8% loss is less than what one usually sees on a rolling-drum type dyno, where 10-11% is more typical.

Fort,

In this thread just a few post back (see #43) you were sugesting these type dynos had a 5% loss.

This seems to be the same type dyno and is reporting 8% loss is your quess just off by 160% on the amount of loss or is the wheel-hub type dyno you mentioned that much different.

***DaveN007*** · #47 09-02-2008, 05:34 AM

As I have stated several times, I believe that a rolling start comparison is the only thing that matters. Take a video of a GT350 versus stock. From 25mph tp 125mph. Or pick your favorite speeds.

Isn't that what you are looking for? An increase in acceleration? More torque?

If a "GT350" is quicker than a "GT390", but each comes with a certified Dyno sheet...which would you want?

I say we standardize on GTxxx, where xxx = 1/4 mile time expressed as xx.x seconds.

**Slatfatf** · #48 09-02-2008, 05:39 AM

Originally Posted by elmo91789

Fort,

In this thread just a few post back (see #43) you were sugesting these type dynos had a 5% loss.

This seems to be the same type dyno and is reporting 8% loss is your quess just off by 160% on the amount of loss or is the wheel-hub type dyno you mentioned that much different.

I just made up the 280 RWHP number (and the resulting 5% loss) as an example of what might happen. I did use the word "might" in the earlier post. I didn't mean to suggest that 5% was the right number. Jeez... For the record: I don't know what the differences are between the dyno used in the link and a Dynapack. They do seem superficially similar. I don't know what the driveline loss would be on a Dynapack, but it should be lower than on a rolling-drum type dyno.

elmo91789 · #49 09-02-2008, 06:12 AM

Originally Posted by Fort Felker

I just made up the 280 RWHP number (and the resulting 5% loss) as an example of what might happen. I did use the word "might" in the earlier post. I didn't mean to suggest that 5% was the right number. Jeez... For the record: I don't know what the differences are between the dyno used in the link and a Dynapack. They do seem superficially similar. I don't know what the driveline loss would be on a Dynapack, but it should be lower than on a rolling-drum type dyno.

Fort,

Sorry my bad, I thought that you had first hand knowlege of the Dynapack machine and I can see in the above post you do not so thanks for making that clear and forgive me for being mistaken and hope there is no hard feelings.

**Slatfatf** · #50 09-02-2008, 06:15 AM

Originally Posted by elmo91789

Fort,

Sorry my bad, I thought that you had first hand knowlege of the Dynapack machine and I can see in the above post you do not so thanks for making that clear and forgive me for being mistaken and hope there is no hard feelings.

No worries, it's all good. Thanks for the note.

**titanic** · #51 09-02-2008, 06:39 AM

Originally Posted by DaveN007

I say we standardize on GTxxx, where xxx = 1/4 mile time expressed as xx.x seconds.

That won't work. What if I fall asleep in the middle of the run, wake up 5 seconds later to complete the run. I would have a lousy 1/4mi ET even if I were driving a Bugatti.

***DaveN007*** · #52 09-02-2008, 07:03 AM

Originally Posted by titanic

That won't work. What if I fall asleep in the middle of the run, wake up 5 seconds later to complete the run. I would have a lousy 1/4mi ET even if I were driving a Bugatti.

GT180 as in 18 seconds.

Rodrigo · #53 09-02-2008, 07:29 AM

Alex,

Did I understand correctly that you will have the car in your shop sometime in the next week or two? If so, I would love to come by and check it out. Am definitely interested in the RS350 mods. The factory CS could definitely use a bit more power to match the superb handling.

Pint of Brew · #54 09-02-2008, 11:35 AM

I'm quite mystified with how much everyone obsesses about Drivetrain Loss and dynos not being reliable...

Why not stop fiddling with 11%, or 13%, or 15% drivetrain losses and instead comparre RWHP like men, without reverting to "but the ENGINE is pulling more, so it's MORE!".

Rather than compare two separate products with different loss coefficients, resulting in a comparisson which contains two errors, I'd be much happier if we reserve the Crank HP readings to whoever has stripped their engine, mounted it with it's exhaust on an engine dyno, and got the graph from a real dyno to prove it, rather than playing around with assumed drive losses.

This is particularly relevant when a few percent mean the difference between "worlds best" and "world's second best".

The convention for calling products "GTxx", much like other car names, is whatever the manufacturer likes. It's quite arbitrary that we've decided to call things "GT(horsepower)" and I for one find it quite boring. As though there's some kind of common genealogy, modding philosophy or target market between all the tuner's GT badged products.

Want an original name? Call it something else I say. Look at Gemballa: Avalanche. Otherwise you're risking getting into e-penis wars with "but Bob's GT-375 is more powerful than Evo's GT-385, because they use more drivetrain loss to derive the number so they suck".

Not to mention, GT is supposed to be Grand Touring. Not really the design brief with any of the tuned machines we commonly call GTs. Want a GT? Get an Aston.

**K-Man S** · #55 09-02-2008, 01:58 PM

Hmmm Gebmalla Avalanche, in that case I'll have to call mine either the Cayman Summit or Cayman Peak.

**sharkster** · #56 09-02-2008, 05:18 PM

Originally Posted by Rodrigo

Alex,

Did I understand correctly that you will have the car in your shop sometime in the next week or two? If so, I would love to come by and check it out. Am definitely interested in the RS350 mods. The factory CS could definitely use a bit more power to match the superb handling.

Hi Rodrigo, absolutely. It should be back from EVO by late next week and I'll be glad to show you. She's still got a couple more tests/toys to go this week (pulley, cats/headers).

**sharkster** · #57 09-02-2008, 05:25 PM

Just as an FYI, the car was baselined but months ago (and on a couple of occasions) at 273-5rwhp but not on that same day nor location (although the dyno set up was the same) and so forth so it wasn't something I felt viable for inclusion. However the point here was to show specific gains on the same day/dyno/conditions by changing certain hardware. We really wanted to know the difference a plenum vs plenum/software sicne we all already know how much an exhaust adds

The drivetrain loss on the EVO dyno is 9% but the real proof is what she drives like and how she performs at the track. The dynos are indeed useful for tuning (although Todd also tunes on the street as well) and just a representation of our particular car on a particular day.... We'll know what the changes are between those runs and adding the cargraphic headers/cats (hopefully that'll help Fort and others) shortly as well as the ESR pulley and of course what 93 does....

**Ian@EVOMS** · #58 09-02-2008, 07:33 PM

Thank you to everyone for their patience, we got power returned to the building at 10pm lastnight... it was a rough few days!

I also appreciate all of the debate that was brought to the table while I was unable to communicate. Since there are so many posts to respond to I will give a general response to everyone!

The only real way to find the exact drivetrain loss of the Cayman would be to take the motor out of every Cayman and strap it on an engine dyno to have a real engine baseline for each car. With the factory rated (note how they say "rated" and not "actual") horsepower of 295 we assume a drivetrain loss dependent upon our assumption that our stock car makes 295hp at the crank. Porsche, just as all car manufacturers do, under-rate their cars. Thus my claim of 45 crank horsepower gain, which was underrated, was over an assumed stock 306 crank horsepower (273/0.89=306.74) from the baseline dynos we have seen. If I, or Porsche, promised you guys a particular number and there was less, there would be some angry Cayman drivers. Under-promise and over-deliver and you have some seriously happy Cayman drivers! With 317rwhp on 91oct at an 11% loss you are looking at 356.18 crank horsepower... seems to me like RS350 is a reasonable claim.

We can get caught up in drivetrain loss debates for hours on end, but we chose a logical number so we could accurately compare the results. I will have more dyno results here in the next few days when we get the headers/cats and ESR Pulley installed. We will also have 93oct dynos for the car as well.

Hang tight!