guardsred951S

I've heard everything from a 15% loss in the drivetrain to a 30% loss when it comes to rear wheel vs. flywheel HP.

My 89 951 was put on a dyno and has 260 rear wheel HP (and more torque) and I usually say it has just over 300 HP at the flywheel but I don't really know.

Does anyone know what the real deal is?

M758

I asked this question a little while back.
Report then was about 17% for the 944/951.
You can do a search in this forum and the main 924/944/951/968 forum.

My 88 S stock got 230hp & 240ft-lbs at the rear wheels. when i dynoed it a couple years back.

Russ Murphy

Check this thread out: <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=18&t=000474&p=" target="_blank"> Dyno Transmission Losses</a>

QUICK'44

Here's My two cents worth....


A friend who owns a well respected porsche tuning shop in Arizona did a fairly "imperical" test on a turbo 944.
he built the race motor and tested it on an engine dyno,then installed it into the car and ran it on a dyno jet (i believe)...results: 12% loss through the drivetrain,that's the figure i go by these days.

Another interesting point is frictional loss due to TIRE DIMENSIONS.
last year i ran my car on a dyno jet to test some mods i had just done. the results were very very bad. i just could'nt understand it and was quite dejected...
Suddenly the dyno operator asked me what tire pressure i was running in my rear tires..hmmm
Upon checking this i found there was only 19 psi in the 12.5" wide goodyear slicks!
we aired them up to 36 psi...and gained 22 hp!

My point here is that MUCH depends upon the rolling resistance between the tires and the rollers. i suppose if you want the "purest" dyno numbers on your motor...run the skinniest tires you can on the rear...or atleast something close to stock.

M758

Hmm, Interesting actual flywheel vs rear wheel dyno tests verified at 12% tranmission looses.

I think I know the "well respected porsche tuning shop in Arizona". If I am correct then I definitly will sign-up for 12% as that dude is good and knows 944 Turbos!!!

So my 230 rearwhp = 257.6 Flywheel hp

Not too shabby for a stock Turbo S with 109k

Danno

"My point here is that MUCH depends upon the rolling resistance between the tires and the rollers. i suppose if you want the "purest" dyno numbers on your motor...run the skinniest tires you can on the rear...or atleast something close to stock. "

Hey QUICK'44 , great testing, thanks! I always suspected there was some tire-slip and stuff from the rollers as well. That's why these guys use a dyno that bolts directly to the hubs: <a href="http://dynapackusa.com" target="_blank">Dynapack dyno</a>.

M758

Damn Danno,
Looking at that dyno pack website really make me want to get one of those in my garage.

It good they don't have price 'cus I probably would need to sell my house to pay for it

christian

Don't think a stock S has 230 rwhp. 15 % would be 270 HP, you have to divide by 0.85.

M758

[quote]Originally posted by christian:
<strong>Don't think a stock S has 230 rwhp. 15 % would be 270 HP, you have to divide by 0.85.</strong><hr></blockquote>

My 'S' did produce 230 hp at the rear wheels and I have the dyno chart to prove it.
I have had the car since feb '97
As far as I know the car does not a have chip. It was not sold that way and none of the records show a chip purchase. I could be wrong as I have not opened the DME boxes to check it out. I do remember seeing another 'S' owner quote 230 rwhp on a dyno.

On the same day I dynoed mine I saw a 964 RS America put 250 hp down at the wheels... Those things are only factory rated at 250lbs at the flyweel. He was the original owner and the motor was completly stock. Remember that factory power ratings are minumum. On occasion some cars can be higher due to the stack-up of tolerances.

christian

The 964 RS america has about 250 HP flywheel - same engine as in all other 964. If you had it on the dyno and it showed 250 HP

1. The dyno reading is wrong or it translated the rear wheel HP into flywheel HP

2. Both of the cars are modified and you didn't know it, but this is very unlikely as the RS would need to be heavily modified in order to show those HP.

Anyway, no offense taken. BTW the 964 has a higher HP loss than the 944, about 20 %, so 250 would be 312. You would need a 3.8 to get that kind of HP.

M758

Well Christian,
I did seem very strange when the RSA put down 250 rwhp. I did see it as I was there when it happened. It was PCA dyno day a local Porsche tuning shop. The owner is well respected Porsche racer & tuner. There those the board who will vouch for his knowledge and skills.

Any way we were all shocked when the RSA chart came back. We all asked the owner. A retired gentleman and avid DE driver "So what did you do?" He promply said "Nothing except for some holes in the air box." This guy is the original owner of the car and was surprised about the power output.

The shop owner was somewhat surprised, but then relayed stories about the RSA program. Apparently the motors are stock 964 units which are rated at 250 hp at the flywheel. Except that for RSA cars Porsche handpicked the "best" 964 motors and steered them in to the RSA. Apparently it was more of surprise to the car owner rather than the experieced shop owner.

christian

Sorry but I haven't heard about handpicked 964 RSA as they where (at the time) cheaper versions of the normal 964, cheaper in goodies and about USD 10 K cheaper in price. I believe you, but 250 rwhp is not possible. A standard 964 should have about only 205 to 210 rwhp. I measured 210 on mine with the stock chip but K&N cone filter and first muffler bypass (a drilled airbox doesn't bring any performance) and 228 with the custom chip. My car goes 180 mph on the speedo. Maybe the dyno was modified <img src="graemlins/nono.gif" border="0" alt="[nono]" />

Ski

and so since you haven't heard about it isn't true? Hmmm.......he might actually be one of the cars that got a slight oversize in piston diameter, which did happen if the blocks were found to have defect at 100mm. That can be fortunate for hp but very unfortunate if you have to replace a piston, oversize that is.

How many people have weighed their car before putting it on the dyno and input the correct information or just put generic? Might make a slight difference in hp.

The only really GOOD people at dyno, same same setup,,,are the guys building the IROC series race cars,,those guys do it well.

christian

Bret:
There was a long discussion some time ago on the 964 forum. I also have some 911 books. Of course I know a sh... - I agree with you there, just trying to keep my eyes and ears open. And about 40 to 45 rear wheel HP is not just a little bit of a stronger engine. We are not talking turbo here.

I am with you when you suspect that probably all results that day where wrong.

Ski

Well,,I'm not really saying they were wrong; and maybe you shouldn't question so hard, no offense meant at all. I think every engine is different,,different air fuel ratios CAN change hp readings as much as 10%; so results can vary. There have been 951s opened up and found oversize pistons. Did these cars run better than the ones with 100mm? There was one of our Gurus who had a rwhp of 230 running very rich. Got it down to 12.1 and had 262.

When you dyno your car, you would think that we all want a real time figure for our hard earned $$ that we have spent, no matter large or small! It would be in our own best interest to put in the correct data before starting the run. So, with that in mind: what were the temps on the dyno day,,what tires were being run,,what actual % of driveline loss,,and how good was the A/F ratio of the car. I have a dyno reseved next week(they owe some time because of the O2 sensor failing last week)for 1/2 day, $275, to change three different sets of chips and allow some cool down time between runs. I will weigh the car, put in the ambient air temp, and hopefully put their nice big fan in front. I have put a few dollars into the car so I want it right.