Chris33ad

Guys....my '81 928 is the 240 RWHP. What is that compared to say a small block chev or ford? I know it's rear wheel horses but what's the comparison between that and say a 300 hp vintage corvette with a 327?
I also have an '80 euro 300 hp. How much horespower is that compared to a vintage 300 hp 327 corvette. (That's just an example). American cars are rated at flywheel, correct? So what would my 2 928's rate at flywheel ????? (both stock unaltered motors).

Hilton

928's are rated in engine horsepower by the factory. So your hp is directly comparable to a 300hp corvette - i.e. your 300hp euro should have the same power output as measured at the flywheel as the corvette engine does at its flywheel.

There is a subtle difference between DIN and SAE standards for horsepower, but its not much, and of course its made fuzzier by the fact that drivetrain differences will affect how the power translates to the wheels and actual speed/acceleration, not to mention 30 years of use

danglerb

Different era's also had more flexibility on what the manufacturer could claim, flywheel could be a bare motor with no accessories like alternator etc., or even be from "selected" test motors, not general production.

81 Euro is pretty much the same as US 78/79 since in the same location both would be able to run the same cat or no cat exhaust.

rgs944

Then you add in brake HP which I believe is no parasidic loss at all and that makes it even more fuzzy. Bottom line is the only good measure of HP is at the wheels, after paracidics's are accounted for and any drive line loss. So when someone tells you they have 400 HP and you believe them, then just deduct 15 to 20% for driveline loss and that will be pretty close to their rwhp. The newer the car the more efficient they llikely get the power through the driveline.

17prospective buyer

They used alot of trickery with dyno'ing them back then. They put headers, ITB's on motors that would never have any of that in stock form. I have an engine building handbook that explains the old power ratings system and how it was abused to underrate or overrate power (depending on which era you're talking about )

Imo000

Is this '81 a Euro?

VT928

As for the compairing cars between eras there are major differences, back in the sixties US manufactures ratings were gross hp. In the early eighties the ratings were net hp. The compairison is even more difficult between eras due to factories "playing with the numbers" for several reasons, like insurance costs, competition class (dragrace), marketing, and in GM's case silly rules about max hp per vehicle size. The mighty L88 427 was rated @430 hp and when dynoed in a car it produced 375 or so.

My 1980 Euro S produced high of 283 hp on the dyno. I did three pulls the lowest reading was 279hp. the car was rated at 300 hp from the factory and is stock except for the exhaust.

Paul

1980 Euro S Red/Blk Lea

RKD in OKC

Most all manufaturers quote crank hp of their motors in their specifications.

If you dynoed your 81 and got 240 hp that is usually stated in rwhp. Some dynos you can leave in gear without throttle when spinning down and it will calculate the drive line drag or loss for a more accurate picture of crank hp.

If you want to calculation the loss backwards you would divide the rwhp by 100 minus the % loss divided by 100. Example for 15%: 240/0.85 = 282 crank hp, and for 20%: 300 crank hp.

If Paul'a car dynoed an average of 281rwhp and the factory stated crank hp is 300hp then his driveline loss is 300/(300-281)= 15.8%

17prospective buyer

VT928 just summarized that part of the book for you.

rgs944

Even after getting an accurate reading on a dyno of rwhp that still can not account for the big kickers of aerodynamics and weight, which both make huge variations in a cars performance. 0-60 maybe not a big deal on aerodynamics but if you are making runs from 80-140 mph, the pointed nose of a shark will do nicely even when compared to a lot of new cars today.
After this whole disussion we can then start taliking about whether HP or Torque is more important to a cars performance.

Ducman82

And then there is the difference between inertia and steady state dynos.... :-(

Chris33ad

has anyone dyno'd a 240 rwhp horse car? If that's like 15-20% off then my '81 euro would only have the power of a ford 302 2V

Tom. M

81 Ljet should have 220 crank hp.... We've dyno'd them and they are between 160 and 170 rwhp....depending on 5sp or auto... torque is around 200 to 210 ft-lbs.

The 4.7 liter 83/84 US Ljet is rated 236 crank HP... and dynos between 180 and 200 rwhp.. torque around 240ish ft-lbs.

5 liter 32V 85/86 LH/EZF rated at 288 crank hp...dynos between 260 to 270 rwhp...and same torque..

5 liter 32V 87 and up LH/EZK rated at 316 crank..dynos between 270 to 290 rwhp and same torque.

5 liter 32V GT engine rated at 326 hp crank...dynos about 285 to 295 rwhp and same torque but peak is at 4500rpm

5.4 liter 32V GTS engine rated at 345hp crank...dynos about 295 to 305 rwhp and 340 to 350 ft-lbs...


BTW..we've dyno'd a few Euro motors..both 4.7 Kjet rated at 300 crank hp and the 4.7 LH..rated at 310 crank hp... but haven't seen decent numbers out of these (not sure why..bad dyno, weak engines?? don't really know)

Assuming stock engines (no mods) average mileage on dynojet etc.... All are SAE corrected numbers...and based on our PacNW 928 dyno days we held quite regularly back in the day....

Chris33ad

Tom-thanks for that info. I gotta save that. So my '81 euro 4.5 is only about as fast as a 69 mustang 302 which is rated 225 hp

Tom. M

A 81 Euro 4.5 K-jet is factory rated 230 crank....so likely right around 180 to 190 rwhp....

Fast is a relative term...take it to the drag strip..you'd likely run a 15.5 to 16 sec quarter.....

But with a 928....the race starts at 100....run 80 to 140 and you'll beat most anything domestic and do it in style at 120 all day long