toddk911

0-60 in low 4's??????? Sounds a little off on the fast side.

hosrom_951

He said high 4's, but gave him low 4's if it rocks

FSAEracer03

Jerome... not many people have dyno tested fricton losses due to 1) it's a major PITA to engine dyno then chassis dyno a moto and 2) each dyno has variances... so no, I have not. Like someone said, it's an industry standard.

Blueman, I left out any aero correction factors because 1) I don't want to jack up the "estimated" numbers, 2) drag is an exponenial loss and therefore would be WAAAYYYY to hard to calculate in this case and 3) I wanted to leave some room for estimated error with the 15% friction loss (like Jer said, not all are 15% losses)

The standard for a RWD loss due to the clutch and geartrain is 15%, FWD is slightly lower and AWD is 20-25% depending on the system used.

Eyal.... re-read what I said, bonehead aaaand you have a lot to learn, grasshoppper... your dyno pull when stock was good, but like I said, dyno's have different variances, the weather changes readings, and each engine has a different exact output, so you can't assume yours was exactly 217bhp.

EDIT: guys, this isn't biblical truth here... these numbers ARE estimated. I am not claiming to hold these numbers up for exactness. I am just curious as to what others got... thats all

....aaand as for 0-60, there is no way in hell I am launching my car

EDIT 2: oops, forgot to list the weight I entered... I put in 3300 lb for my '87 with just under a half tank of gas, a 170lb driver and 2 bags totalling ~30lbs. I believe the curb weight for the '87 and '88 non-S turbos was just under 3100lb, am I correct? (aka, who has the exact number handy??)

944Willie

I recently had mine corner balance after a huge susp upgrade and with 200# in the drivers position my 87 weighed 3232#. It has all standard options, without LSD. With my GT Pro I measured 189 hp. It's as stock as you will find (except the susp). I am changing to a 3" cat back SFR exhaust soon and will retry. My motor has recently been rebuilt but stock WG and turbo. New chips coming soon and then I'll test it again.

Laust Pedersen

Drive train loss: Gears are really more than 99% efficient in transmitting torque i.e. less than 1% loss, but it is mainly the gear oil that creates the loss, meaning that it is a viscous effect, which is strongly dependent on the rotational speed of the gears (squeezing out oil between the teeth) and therefore the speed of the car. So in short the transmission loss is strongly dependent on the speed of the car. The 15% is just an “average rule of thumb”.
It should actually be possible to measure that function by lifting the rear wheels off the ground, speed them up to maybe 100 mph, depress the clutch and read the speedometer as a function of time. The missing variable is the moment of inertia of the drivetrain, but it is reasonable to assume that the main components are the wheels themselves.

Weight: There was a thread about the weight of our cars a little less than a year ago and as I recall the vast majority was between 3000 and 3100 lbs. I had mine weighed on a truck scale at 3040 ± 20 lbs with half a tank, the usual fluids, spare-wheel and std tools.

mroberts

I'm curious why drivetrain losses are quoted as a % of power rather than a function of RPM.

I would have thought the frictional losses in the drivetrain would be a function of the speed at which they are turning. You shouldn't have more friction just because the engine is putting out more power.

Blueman33

Drag coefficient.

I forgot what it is, but it is already calculated for our cars. I forget the lister who has it, but they are one of our over-seas listers.

So somewhere on this board is the coefficient!

FSAEracer03

Hmm... maybe I'll have to rethink my weight estimation and do another test (ok, just an excuse for another test). I was under the impression that our cars weighed in around 3050 w/o fuel load. If I assume that it weighs that much WITH a half tank (like Laust stated) plus the weight of myself, the weight to be used should be about 3250 assuming the tools are still in there... so would 3300 be a probable weight with a full tank of gas or no? Opinions, people, opinions...

As for friction loss... metal-to-metal loss is in the range of 1% or less like Laust also said... the loss comes from different factors like the rotational inertia and friction surfaces of the clutch and flywheel as well as the loss from pneumatic tire friction.

EDIT: I'll fill 'er up tonight and do a run with a full tank and a "weight" of 3250lbs. I'll post the results tomorrow.

FSAEracer03

OK... get this, so I decide to try to be as accurate as possible and fill up the tank halfway last night, drive home to warm her up, and do some runs at the local spot to check the numbers.

I stop by my house, get ice packs and some cubes, throw them on the intake manifold and intercooler and hose the IC down as well. I setup the GTech for 3250lbs and head out to the flat spot. I zero it in and hit -go-. The result was a bit higher then I had expected so I repeated, this time shifting slower (as to not jar the module), only to get a similar result!

I went home, took a photo of the number, cooled down the IC and intake again and went out once more (arriving to the spot quicker), again, shifting slowly.... The total results:

1st run-- 255hp
2nd run-- 253hp
3rd run-- 261hp

hmmm

jerome951

Kevin,

Don't you work at a shop that has scales???

I know you do as I've used them. Let me know if you want me to show you how. ;-)

FWIW, my '89 weighed 3150 w/ 1/2 tank and spare (+ full cage in mine - race seats)

FSAEracer03

HAHAHAHA ouch!! yeah, I do... but to hell with the hour of setup and removal time to get an accurate (level) reading

...that cage makes a huge difference in curb weight Jer... did you have the interior gutted though?? ...have I seen your car??... have we met? lol

porshhhh951

how come mine so light then. I weighed in a 3047lbs at ennis raceway with full interior and lsd all option's...stereo ect 1/2tank of gas. My car was a ex racecar.....maybe they got rid of certain thing's and were just good about hiding it. hmmmm

TonyG

The lack of a conventional drive shaft reduces the drivetrainlosses on these cars.

Typical RWD loss calcs figure a conventional driveshaft.

944's don't have conventional driveshafts.... the shaft is a much smaller diameter.. thus the polar moment is much lower.

The difference is measurable for sure.

It's common practice, and was included as performance options on some cars, to substitute a steel driveshaft for an aluminum driveshaft on muscle cars. Example, the Chevy IROC 1LE special option Camero... (included an aluminum driveshaft).

...

Actual HP refers to uncorrected wheel HP. This uncorrected wheel HP does not take into account atmospheric conditions that can and do play a large role in performance (altitude, humidity, ambient temperatures, etc...).


The GTechPro gives "crank hp"... which is not "actual power" in the context of a dyno measurement.
...

GTEC Pro Results:





TonyG

FSAEracer03

Tony... yeah... DAMNIT!

So, uhh.... I don't know exactly how to follow that **** up. Well done! I'm jealous!... and I'll call it a night!

NZ951

Holy ****! You did an 11.6 with a 2.36 60" time at 131mph? That is awesome power. You would easily have a 10 second car with .2-3 off you 60 foot time, whicj should be achievable. You using street tires?