Crank versus Rear Wheel HP

[icebrick]

Just out of curiosity, how much hp is lost in the power train?
-- Reference late model 240 M47 and/or auto.

[stylngle2003]

dyno yours and compare against 114hp stock at the crank :nod:

it's usually 15% or so for RWD manual, 20% rwd automatic, 10-15% fwd manual, 15-20% fwd automatic

[icebrick]

dyno yours and compare against 114hp stock at the crank :nod:

it's usually 15% or so for RWD manual,

No access to a dyno where I live.
That gives me 97 hp at the rear wheels:-( I won't be bragging about that.

[Bready]

One of my fav old artilces with related links supporting the data:

http://www.sdsefi.com/techdyno.htm

If they are to be believed (I think they make a pretty good case) 12% or less.

The 20%+ range has always made for great ego balm however : ) ...

....something the famous Capn Bondo once refered to as the "Sand in the crankcase" phenom.

The SDS page in general has a great list of Tech FAQs.

Along similar lines for calculating HP on the 1/4 mile:

http://www.sdsefi.com/techpowr.htm


JB

[Lord Tentacle]

Along similar lines for calculating HP on the 1/4 mile:

http://www.sdsefi.com/techpowr.htm
JB

hunh...
my 3600lb 945ti
which runs a 13.7 @ 101 with street tires at a flat 15psi
is suposedly making ~290hp....

it seams more of an ego boost than the 20% tranny loss

[icebrick]

One of my fav old artilces with related links supporting the data:

http://www.sdsefi.com/techdyno.htm

JB

Quote from this article
"If 25% was being lost in the drivetrain, the oil would boil in the differential housing in short order and aluminum transmission cases would fatigue and break from the temperatures ".

...........Well that sheds some light on the subject, I confess I never really stopped to think about where the loss had been siphoned off to.
I think the 1/4 mile calc. method will help get a hp number for me when I finish my mods..thanks

[MII]

The numbers above seem a little low from what I've heard in the past. Usually in manual trannies about 20% loss on RWD, 15% loss on FWD and 25% and 30% loss on AWD. The difference between an Quattro Audi and a FWD Audi feels a lot more then 10% to me.

[IceCold4x4]

while it may be say 20% for an auto tranny probably 5% or maybe even more is also related to driveshaft, ring and pinion, and tires to the road. . .

[benflynn]

call it 15%, it is dif for every single sit so..

[L8 APEKS]

One thing I learned from dyno days in my old VW's and Porsches...TIRES make a HUGE difference, not only the inflation pressure but also the model of tire.

I dyno'd one of my corrados and the owner of the dyno shop went out of his way to write down the model of tires I was on because there was very little friction at the rollers...he said it can vary by as much as 5% either way.

For comparisons sake, my coast-down and dyno on a FWD manual VW Corrado showed roughly 9.4% drivetrain friction loss.

[John V, outside agitator]

The biggest losses are in cars with HYPOID ring and pinions. This is from the large sliding component in the meshing of the 2 gears:
http://gemini.tntech.edu/~slc3675/me361/lecture/fig6_14.jpg

Spiral Bevel gears, like Porsche, VW, and Saab used have less loss, directly related to less sliding contact which is obvious in this photo:
http://gemini.tntech.edu/~slc3675/me361/lecture/fig6_12.jpg

In the old service book "MOTOR" manual, 1960 edition, I read they suggested losses in hypoid ring and pinion of a biy over 21-23%

But that was before forums on the Intra-sweb, and they were probably SAE (and that E doesn't stand for Einsteins) types.

Next biggest loss is from auto-tragic boxes especially older junk like 240s and 740s use (some of the highest end ZF and Getrag autoboxes on the snoootiest of the BIG Mercedes and BMW are within a per cent of effcient as a conventional manual box---they just cost a gazzillion Euros to make)

And gotta agree onn the tire thing.
I've worked on and driven mostly lower powed old Saab, born with only 65bhp and man there are OBVIOUSLY marked differences between tires to the point that I used to keep a "loaner set" for when customers brought in a car and I suspected during test drives that the tires were gross ones.
I'd bang the tires on when the cuastomer was there to do back to back test drives.

And even ordinary non-fanatical drivers could notice the differences.
And not JUST inflation.

[Bready]

I think the larger point being made is that chasis dyno's being used as a means for accuratley determining HP and related loss via drivetrain etc are woefully inadequate; as a result the 20%+ numbers of loss are suspect.


hunh...
my 3600lb 945ti
which runs a 13.7 @ 101 with street tires at a flat 15psi
is suposedly making ~290hp....

Using a different online calculator ( http://www.dragtimes.com/horsepower-et-trap-speed-calculator.php ) I come up with 283HP .

Still pretty high not sure the formula itself is flawed - sure the numbers are right?

At 1 bar I would think you'd be around 235hp?

...and don't call me hun unless you're from Baltimore.

JB

[mymomswagon]

Does having a open rear car effect the results when using a chassis dyno due to tire spin? When my brother had his truck on the dyno it showed a hp number that wasn't accurate by any means. His truck has a severe traction issue when street driving and i was just wondering if that might have been the problem on the dyno?
joshA

[towerymt]

Does having a open rear car effect the results when using a chassis dyno due to tire spin? When my brother had his truck on the dyno it showed a hp number that wasn't accurate by any means. His truck has a severe traction issue when street driving and i was just wondering if that might have been the problem on the dyno?
joshA
Unless his truck has enough torque to spin the tires from a roll in 4th gear, traction on the dyno probably wasn't an issue.

[L8 APEKS]

hunh...
my 3600lb 945ti
which runs a 13.7 @ 101 with street tires at a flat 15psi
is suposedly making ~290hp....

it seams more of an ego boost than the 20% tranny loss

Curb weight on a 1991 940 Turbo wagon according to Volvo is 3,135 lbs.

I'm gonna go out on a limb and guess the driver doesn't weight 465 lbs?

If not, you're a bit under 3,600 lbs. ;)

Plugging new numbers into the HP calculator, you get numbers that are much closer to accurate based on your mods...assuming a driver weight of 200 lbs, your car is making closer to 262hp at the crank.

[TerribleOne]

200hp in a 3000 lb. car?
3022

[L8 APEKS]

200hp in a 3000 lb. car?

...needs moar turbo boostification. :nod:

What mods / boost pressure on that dyno you posted?

[TerribleOne]

Man.. I dont remember. It was two years ago..

[isaac]

hunh...
my 3600lb 945ti
which runs a 13.7 @ 101 with street tires at a flat 15psi
is suposedly making ~290hp....

it seams more of an ego boost than the 20% tranny loss

Most of that ego boost would stem from inflating the car's actual weight by 400lbs.

[towerymt]

Most of that ego boost would stem from inflating the car's actual weight by 400lbs.
Probably stereo & stuff adding weight.

However, it doesn't much matter seeing as how the ET calculators need my car to be roughly 2600lbs to make the numbers work. That's not too far off...but who is driving the car? At 2800lb I have 130whp. 16.06@83.7 dyno'd 122whp.

The first link with the formula gives 134whp at 2800lbs. 2600lbs gives 124whp.

If the weight is a little high, the horsepower is going to be way off.

[Bready]

Probably stereo & stuff adding weight.

However, it doesn't much matter seeing as how the ET calculators need my car to be roughly 2600lbs to make the numbers work. That's not too far off...but who is driving the car? At 2800lb I have 130whp. 16.06@83.7 dyno'd 122whp.

The first link with the formula gives 134whp at 2800lbs. 2600lbs gives 124whp.

If the weight is a little high, the horsepower is going to be way off.

Well with that low of horsepower I would dyno the car after your thanksgiving meal for a true ego boost.....

....hehehehe.


JB