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Old 04-03-2015, 07:31 PM   #1
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Curious about HP loss through the drivetrain.

Porsche says my cars has 258 HP from factory. I know this is not at the wheel HP, but how would I account for HP loss on a Tiptronic trans drivetrain? I believe the whp on a manual 2003 Boxster S is 229 HP and figure the Tiptronic would be less then that?

I never did a dyno on it in stock form, so I'm not sure what the car's HP was at the wheels. I've done some upgrades and plan some more and would want to know how much HP I got out of the upgrades.

Thanks!
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Old 04-03-2015, 07:57 PM   #2
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Just read a thread at 6speedonline.com and a member there stated that the Tiptronic will "eat up about 10% more in the drivetrain over the manual trans". So that would put the stock whp at 206, does that sound right?
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Old 04-03-2015, 08:25 PM   #3
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If I had to guess that sounds about right. It feels like a 200 whp car to me. I guess if I ever get bored one day I might hit up a dyno day.
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Old 04-04-2015, 02:44 AM   #4
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I've got a related question...
I've often seen the figure "15-20%" drivetrain loss, but I wonder how that works when making comparisons after engine upgrades. If my stock 250 hp engine makes 210 at the wheels, I question why a higher hp engine loses more hp with the same driveline. Instead of being a percent, it seems like it should be a discrete figure.
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Old 04-04-2015, 08:38 AM   #5
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Not sure I'm following you on that?

2003 Boxster S with 258 bhp losses 11% through the drivetrain to 229 whp. (manual trans)

On your car with 250 bhp losses 16% through the drivetrain to 210 whp.

I got the 2003 Boxster S whp number from this video. It's Fabspeed showing how their parts can increase the HP, so I figure they would show the stock whp as low as possible lol.

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Old 04-04-2015, 09:46 AM   #6
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I have two engine dynes and a chassis dyno all within 50' of each other. We can pull an developmental engine off the engine dyno and install it into the car the someday, then test it on the chassis dyno. I see 18-22% losses generally from a manual car.

Pay zero attention to the factory power rating, often times they are posted in DIN and not SAE anyway.
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Old 04-04-2015, 04:02 PM   #7
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Originally Posted by Jake Raby View Post
I have two engine dynes and a chassis dyno all within 50' of each other. We can pull an developmental engine off the engine dyno and install it into the car the someday, then test it on the chassis dyno. I see 18-22% losses generally from a manual car.

Pay zero attention to the factory power rating, often times they are posted in DIN and not SAE anyway.
Never expected that much of a loss with the trans axle mated directly to the transmission. Unlike a Camaro or Mustang having a drive shaft between the trans and trans axle.

Do you have any numbers to share on the loss with a Tip trans?
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Old 04-04-2015, 06:12 PM   #8
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Originally Posted by Jake Raby View Post
Pay zero attention to the factory power rating, often times they are posted in DIN and not SAE anyway.
Yep, HP numbers on shiny brochures from Porsche should be read as "at least xxx HP".
HP varies quite a bit depending on elevation, air temp and atmospherics. Also ignore all the dyno numbers from aftermarket parts mfg companies who freely rig the results because they are also quite variable.

Chasing dyno numbers from others is like herding cats. An exercise in futility. The only ones that really count are on your car.
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Old 04-04-2015, 06:24 PM   #9
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Originally Posted by Topless View Post
Yep, HP numbers on shiny brochures from Porsche should be read as "at least xxx HP".
HP varies quite a bit depending on elevation, air temp and atmospherics. Also ignore all the dyno numbers from aftermarket parts mfg companies who freely rig the results because they are also quite variable.

Chasing dyno numbers from others is like herding cats. An exercise in futility. The only ones that really count are on your car.
Exactly why I picked that Fabspeed video. Figured they would post as low as possible on the stock HP number, which they showed 229 whp. That's about a 11% loss from Porsche's 258 bhp number.

I thought that was actually pretty good, then Jake rained on my parade lol. Maybe that's what j.fro was referring to as I'm sure Jake's engines were producing more then 258 bhp.
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Old 04-04-2015, 07:08 PM   #10
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Originally Posted by KRAM36 View Post
Exactly why I picked that Fabspeed video. Figured they would post as low as possible on the stock HP number, which they showed 229 whp. That's about a 11% loss from Porsche's 258 bhp number. Because that motor is probably producing 280 at the crank bone stock.

I thought that was actually pretty good, then Jake rained on my parade lol. Maybe that's what j.fro was referring to as I'm sure Jake's engines were producing more then 258 bhp.
Chasing others dyno numbers is a fools errand.
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Old 04-04-2015, 08:18 PM   #11
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Originally Posted by Topless View Post
Chasing others dyno numbers is a fools errand.
I'm not chasing anyone's dyno numbers. I'm trying to find out the percent of HP lost in the drivetrain.

So a 2003 Boxster S has 280 bhp?
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Old 04-04-2015, 08:51 PM   #12
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The best way to know what you have is to perform a bone stock dyno test and then re-dyno after every mod using the same dyno to minimize variability. Temp, pressure, etc, will still make even those comparisons hard enough.

Unfortunately, trying to use someone else's loss estimate or dyno values to calculate loss is just a best guess. Why do I say this?

I have seen various Spec Boxster stock 2.5L engines tested on the same dyno on the same day vary from 172hp to 188hp. That variability is larger than the hoped for horsepower gains from most mods. That is why Topless said that this is a fools errand - the error is larger than the value being measured.

Moving forward, get a good baseline and then compare that to any future mods. Trying to build the horsepower history backwards is generally an unreliable approach.
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Old 04-04-2015, 09:05 PM   #13
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Originally Posted by thstone View Post
The best way to know what you have is to perform a bone stock dyno test and then re-dyno after every mod using the same dyno to minimize variability. Temp, pressure, etc, will still make even those comparisons hard enough.

Unfortunately, trying to use someone else's loss estimate or dyno values to calculate loss is just a best guess. Why do I say this?

I have seen various Spec Boxster stock 2.5L engines tested on the same dyno on the same day vary from 172hp to 188hp. That variability is larger than the hoped for horsepower gains from most mods. That is why Topless said that this is a fools errand - the error is larger than the value being measured.

Moving forward, get a good baseline and then compare that to any future mods. Trying to build the horsepower history backwards is generally an unreliable approach.
Guess I'll never know then, cause I'm not pulling my mods out to do a stock dyno run. Was way too much work to get them in there.
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Old 04-05-2015, 08:45 AM   #14
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Originally Posted by Topless View Post
Yep, HP numbers on shiny brochures from Porsche should be read as "at least xxx HP".
HP varies quite a bit depending on elevation, air temp and atmospherics. Also ignore all the dyno numbers from aftermarket parts mfg companies who freely rig the results because they are also quite variable.

Chasing dyno numbers from others is like herding cats. An exercise in futility. The only ones that really count are on your car.

Don't forget the fuel used too.
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Old 04-05-2015, 09:19 AM   #15
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You guys make things way too complicated. Porsche says the HP is to 258, Topless says it's 280. All I needed was a baseline number for drivetrain HP loss, that's all I'm looking for. Right now the Fabspeed video shows a 229 whp for a manual trans 2003 Boxster S. I'm pretty sure they did everything in the book to make that as low as possible.

So far Jake is the only one to come out and give a number to me without spouting this, that and the other has an effect on the HP numbers.

His engine dyno is 50" from his chassis dyno, so he has the setup to give me this info. I hope he replies back on the Tip drivetrain HP loss he has observed.
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Old 05-06-2015, 01:27 PM   #16
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Got this info from a Pelican article.

Porsche Boxster Dyno Testing - 986 / 987 (1997-08) - Pelican Parts Technical Article

Driveline Losses: Since the dyno testing is performed using rollers on your car, there are going to be forces that are going to slow down and reduce the power in-between the flywheel and the rear wheels. These driveline losses include friction from the transmission, losses from brake discs dragging slightly, and friction in the wheel bearings. On the Boxster, typical driveline losses are often estimated at about 15%, although modifications to the chassis can raise or lower that value. Through a complicated process of calculations that are computed by the dynamometer, you can calculate your driveline losses by counting the time it takes the dyno rollers to stop when you let out the clutch. Using these calculations, you can then estimate what your horsepower output is at the flywheel.

So you can calculate the drivetrain loss. I don't know how you could do that with a Tiptronic though. Moving the shifter to neutral wouldn't be the same as letting out the clutch, would it?
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Old 05-06-2015, 04:08 PM   #17
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Originally Posted by KRAM36 View Post
Through a complicated process of calculations that are computed by the dynamometer, you can calculate your driveline losses by counting the time it takes the dyno rollers to stop when you let out the clutch.
Is this true for all dyno's? Anyone have a specific formula that they'd like to share?

I'll go and get another dyno and do a run down just to see what it calculates.
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Old 05-08-2015, 05:14 AM   #18
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Is this true for all dyno's? Anyone have a specific formula that they'd like to share?

I'll go and get another dyno and do a run down just to see what it calculates.
Make a call to your dyno shop and see if they can do that. When you make that, if you don't mind, ask them how they would do it with an automatic transmission.

Please.
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Old 05-08-2015, 05:43 AM   #19
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Make a call to your dyno shop and see if they can do that. When you make that, if you don't mind, ask them how they would do it with an automatic transmission.

Please.
Sometimes I wonder about the total fixation on maximum HP output. At our local auto cross, the perpetually dominant Boxster is a 2.7L bone stock (other than an IMS Solution) 986 with a five speed. He regularly hammers highly modified cars with seeming ease. It ain't always about horsepower............
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Old 05-08-2015, 05:50 AM   #20
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Make a call to your dyno shop and see if they can do that. When you make that, if you don't mind, ask them how they would do it with an automatic transmission.

Please.
I think you'd have to contact one of the dyno manufacturers like Dynojet, Dyno Dynamics or Maha. There will be an algorithm/formula in the software which will allow user input of a restricted amount of input parameters.
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