Planet 9

wpmjr · #1 02-20-2007, 05:55 PM

I've de-snorked and just ran my first dyno run today. On a Mustang dyno I got 277 RWHP. As I understand it a Mustang dyno is the way to go because it doesn't require tapping into the engine to monitor rpm. With 15% losses, that means we are running 325 HP at the crank, not 295! I think this is very interesting, and think it would be useful to have an archive of dyno runs from different members to get an average for stock cars and bench marks for various mods, all in one place. So I'll post mine, and would like to see others do the same.

I've read that Vipers and new Z06's both undersell their output by 30HP too. I can't believe this is for some silly reason like tricking the insurance industry. I wonder why they do it, and I wonder which cars do it and which don't.

PS: don't bother saying they usually run more than 1 pull on the dyno. My tech didn't know what to make of the computer warnings after the first pull so we stopped, but I later found out these were expected and can be ignored. They cleared up by the next day. Anyway, I have yet to see a big change between multiple runs anyone else has posted, and my number is in line with others who have posted here. I'm confident it is a good test.

**Santa Fe** · #2 02-20-2007, 06:27 PM

Did you test before the mod? Not many tests of a stock box car available.

wpmjr · #3 02-20-2007, 08:49 PM

No, I was not doing it to evaluate the mod. Of course it would be nice to know the difference. Perhaps I'll have a real slow day again with 60 bucks to burn...

I still think the result reflects our base engine power, though. I don't consider such a tacked-on artificial impediment as the cig baffle to be part of our engine spec.

russian porsche · #4 02-21-2007, 12:31 AM

I think the toyota supra turbo, nissan skyline, and mitsubishi 300gt turbo had more hp than the manufacturer said. I think they said that they all make 276hp, they actually made 320hp, thats what I've read in many mags when I was into the tuner stuff. If you think about it all of those cars did a 4.8 0-60 so I don't think 276hp whould be enough for those cars, they all way good 3500lbs. at least, but thats cool about the cayman maybe guys at stuttgard tricked the porsche people and maybe the cayman better anyways. wonder if the 997 has the same luck.

wpmjr · #5 02-21-2007, 07:49 AM

I just looked at some corvette forum dyno data on a regular C6- rated 400HP, RWHP tested at 345, with 15% losses it works out to 405HP- so no real trickery there.

Also, on RWHP, crank HP, and losses:

RWHP would be a better number for manufacturers to publish. Crank HP is useless unless you might drop a crate engine in another car- very few of us ever do that. But if we want to compare power levels from car to car and are forced to think in terms of crank HP, then choosing a single standard loss assumption is a good idea. I've been consistently told losses are 15%-20%. One mag suggested some might be as low as 12%. I think for my purposes it makes sense to assume 15% for everything.

Apollo · #6 02-21-2007, 08:22 AM

Mustang brand dyno is merciless and usually gives you lower numbers than some of the other more popular brands. So these numbers look very very good.
A guy at one of the muscle car forums I go to has tested his HEMI and got about 15-20HP difference at the rear wheel when compared between Mustang and some other dyno he ran. Mustang rated him lower that the other dyno. They did do 3-4 runs on each, since the guy had money to burn.

So again, looks like Germans are not playing the game domestics here play by over-rating their engines.

trebien · #7 02-21-2007, 12:24 PM

Originally Posted by russian porsche

I think the toyota supra turbo, nissan skyline, and mitsubishi 300gt turbo had more hp than the manufacturer said. I think they said that they all make 276hp, they actually made 320hp, thats what I've read in many mags when I was into the tuner stuff.

Back in those days, there was an understood "secret" agreement between japanese manufacturers to limit power to 280HP in their vehicles... hence the understated numbers.

hormelbin · #8 03-04-2008, 12:15 AM

Originally Posted by wpmjr

I just looked at some corvette forum dyno data on a regular C6- rated 400HP, RWHP tested at 345, with 15% losses it works out to 405HP- so no real trickery there.

Also, on RWHP, crank HP, and losses:

RWHP would be a better number for manufacturers to publish. Crank HP is useless unless you might drop a crate engine in another car- very few of us ever do that. But if we want to compare power levels from car to car and are forced to think in terms of crank HP, then choosing a single standard loss assumption is a good idea. I've been consistently told losses are 15%-20%. One mag suggested some might be as low as 12%. I think for my purposes it makes sense to assume 15% for everything.

As much as I'd like to believe in a sub-10% rwhp loss, I think that WPMJR is probably right in his/her (sorry, I'm a noob...wasn't sure which, and wanted to be gender neutral) assessment of a 15% hp loss. From the quarter mile times that I've seen posted of stock CSs, they fall somewhere between 13.0 and 13.5 seconds. Using an online "quarter mile time estimator," I was able to input the run time and an assumed gvw of 2950lbs and come up with a whp figure of about 250. That's roughly a 15% loss from the SAE rated 295 at the crank.

Also, I've heard rumblings about the CSs bhp being underrated, but the highest credible figure that I've seen has placed this understatement at no more than 10hp (from 295). Anyway, I just got past my engine break-in about a month ago (The longest period of my life!). If I can find some spare cash or time, I might have to take a trip to the local dyno shop or drag strip to get some more data, but my money is on 250 at the wheels. As always, thanks for the info and enthusiasm.

P.S. - If anyone wants to check out the "Quarter Mile Estimator" that I used, you can find it at TunerCalcs - Estimate Quarter Mile ET from Wheel Horsepower and Vehicle Weight. No guarantees about its accuracy, but it's fun to play around with.

**Slatfatf** · #9 03-04-2008, 10:07 AM

Originally Posted by hormelbin

From the quarter mile times that I've seen posted of stock CSs, they fall somewhere between 13.0 and 13.5 seconds. Using an online "quarter mile time estimator," I was able to input the run time and an assumed gvw of 2950lbs and come up with a whp figure of about 250. That's roughly a 15% loss from the SAE rated 295 at the crank.

Porsche's value for the drivetrain loss is 12%, so we should expect about 260 RWHP. There have been many dyno results posted for stock cars that are within a realistic 2% measurement error of that value.

Also, your 2950 lb weight would be about right for an empty car with few options. Add a driver and some gas and you'll be close to 3200 lb. If I plug 3200 lb and 260 HP in the online estimator, I get a 1/4 mile time of 13.4, which is consistent with observed times.

wpmjr · #10 03-04-2008, 10:25 AM

Originally Posted by Fort Felker

Porsche's value for the drivetrain loss is 12%, so we should expect about 260 RWHP. There have been many dyno results posted for stock cars that are within a realistic 2% measurement error of that value.

Also, your 2950 lb weight would be about right for an empty car with few options. Add a driver and some gas and you'll be close to 3200 lb. If I plug 3200 lb and 260 HP in the online estimator, I get a 1/4 mile time of 13.4, which is consistent with observed times.

Fort:

I would like to know where to find Porsche's 12% number- can you tell me where?

Thanks

**Slatfatf** · #11 03-04-2008, 10:47 AM

I'll see if I can find that again...

PS I've looked and can't find it now.

Jim Michaels · #12 03-04-2008, 11:41 AM

I've seen the 12% drivetrain loss estimate somewhere as well, but I don't remember that coming from Porsche AG. I think there were several drivetrain loss estimates several years ago using 996s and Boxsters. The lowest estimate I recall was 11%, with several at 12%. Since then I've been assuming about an average 12% loss for most newer Porsches. The 15% loss estimate has been around for a long time, but it may be time to re-think that with newer cars.

wpmjr · #13 03-04-2008, 11:51 AM

I want to know the real number, but as far as comparing to other cars, especially non-porsches, using one arbitrary number like 15% is best. Those cars that have less frictional loss have more effective hp than those with 15% losses anyway. And I don't think many modern cars are much better than 15.

**Slatfatf** · #14 03-04-2008, 11:51 AM

Here's an interesting post that claims measured losses in Porsche drivetrains of 12-18% depending on vehicle age and condition How dynometers work.... - Saabscene :: Saab Forum. I'd assume that a new Cayman would be at the low end of that range. The 15% rule of thumb for RWD vehicles may be a little high for Porsches - their integrated transaxle should have lower losses than the more common configuration of separate transmission, drive shaft with U-joints, and rear differential.

**Cold Croc** · #15 03-04-2008, 02:30 PM

Originally Posted by Santa Fe

Did you test before the mod? Not many tests of a stock box car available.

Here's my dyno from last month..... bone stock '07 CS

***DaveN007*** · #16 03-04-2008, 03:04 PM

Originally Posted by Cold Croc

Here's my dyno from last month..... bone stock '07 CS

260 was right about where several stock cars ran on this day on this dyno if I remember correctly.

**Cold Croc** · #17 03-04-2008, 04:08 PM

Originally Posted by DaveN007

260 was right about where several stock cars ran on this day on this dyno if I remember correctly.

Yup... and one guy had done the de-snork and little else and had a great output....can't recall who....

Maybe there's more to this de-snork stuff than we're giving credit for...

**Slatfatf** · #18 03-04-2008, 04:16 PM

It was CURV ETR. He got a little over 280 RWHP with desnork and a Remus catback. Here's the dyno chart http://www.planet-9.com/zone-7/178...tml#post223040

**DriveS4spd** · #19 03-05-2008, 07:48 AM

I found the post for CURV ETR re: dyno results:

http://www.planet-9.com/cayman-dyn...-dyno-jet.html

Gator Bite · #20 03-05-2008, 09:35 AM

Comparing RWHP from one dyno to another is pretty much futile. You could visit three different dynos in one day and have a wild spread of results. Dynojets, Mustangs and Dyno Dynamics all deliver different results.

See my dyno charts: http://www.planet-9.com/cayman-dyn...tml#post234018