RWHP to Crank HP reduction

[Ron Sutton]

We have had all of our race car engines on the dyno ... and then the whole car on a quality Superflow chassis/wheel dyno over the last 8 years.

This is around 35-40 cars & engines ... some with manual trans & 9" Fords & some with direct drive & quick change rear ends.

For all the "standard" drivetrains, we measured 18.1-18.8% difference (loss) from the engine dyno.

For cars we reduced the parasitic losses in ... with REM polished gears, ceramic bearings, no drag seals, lightened gears, etc ... we saw 16.4-16.8% difference (loss) from the engine dyno.

But we never lightened up parts that would have reduced the reliability, like driveshafts, u-joints, etc. More could be gained, but the risk wasn't worth it to us.

[Che70velle]

We lightened driveshafts, and lost power due to shaft flex causing harmonics.

[Flash68]

Originally Posted by 69znc

Not trying to compare auto vs manual. I was only trying to understand the urban legend of 10-15% lose for manual. Can not find any facts to back this up and I think the low 20's is more realistic. I cannot even find an empirically supported 12 - 18%. The best is 18.5 with a lot of transmission work and very light axles. All the rest are the 20's.....

Sorry, I missed that in your first post.

Just for a reference, when I was in the Porsche world for a couple years. Engine to chassis dyno conversions were routinely in the 12-15% range.

I have read about sub 10% losses for NASCAR... any truth to it, Che70velle?

[Ron in SoCal]

I have read there is also dimishing returns at higher horsepower engines. In other words, 15% (or so) at 550 - 650 hp, maybe a percent or two less over 750.

I have never seen proof of this theory though.

[Ron Sutton]

That's interesting Scott.

For our race teams, not finishing races due to parts failure was unacceptable.


So we went the other direction. Stronger driveshafts (3"), bigger u-joints (1350's not 1310's or 1330's), nothing "borderline".

[Ron Sutton]

I forgot ... we did run some powerglide automatics for 1 season & did chassis dyno test them.

These ran NO converter, nor clutch, so they were light & designed to lock the gearsets hard. With only 2 light gear sets & nothing else they used less power than typical automatics.

The numbers were 19.1-19.4% difference (loss) from the engine dyno.

But, I don't think we can compare these #'s to the automatics in street cars, even well built pro touring cars.

[Che70velle]

Originally Posted by Ron Sutton

That's interesting Scott.

For our race teams, not finishing races due to parts failure was unacceptable.


So we went the other direction. Stronger driveshafts (3"), bigger u-joints (1350's not 1310's or 1330's), nothing "borderline".

We found this during testing on dynos, not on the track. Same philosophy here.

[Che70velle]

Originally Posted by Flash68

Sorry, I missed that in your first post.

Just for a reference, when I was in the Porsche world for a couple years. Engine to chassis dyno conversions were routinely in the 12-15% range.

I have read about sub 10% losses for NASCAR... any truth to it, Che70velle?

Actually yes, there are those types of numbers out there, but again, this technology does not apply AT ALL to anything that you'll see on here, which is why I spoke about "real world" experience. The money going into drivetrain testing is in the millions of dollars, in the NASCAR world.
I worked for a firm that built cup engines, but also did testing on things such as lightweight reciprocating assemblies vs. lap times, which would take months to complete, and cost several million dollars also...The results would surprise you. We were involved in early development of many things that most people would call BS on. Some stuff I can talk about, some stuff I can't.
The owner of this firm is a dear friend of mine. He was behind Cale Yarborough at the Daytona 500 in the late 70's, when Cale blew up. No big deal, until you find out he broke 8 rods...carbon fiber rods. This was Late 70's! Totally off topic, but true.

[badmatt]

Originally Posted by Che70velle

Actually yes, there are those types of numbers out there, but again, this technology does not apply AT ALL to anything that you'll see on here, which is why I spoke about "real world" experience. The money going into drivetrain testing is in the millions of dollars, in the NASCAR world.
I worked for a firm that built cup engines, but also did testing on things such as lightweight reciprocating assemblies vs. lap times, which would take months to complete, and cost several million dollars also...The results would surprise you. We were involved in early development of many things that most people would call BS on. Some stuff I can talk about, some stuff I can't.
The owner of this firm is a dear friend of mine. He was behind Cale Yarborough at the Daytona 500 in the late 70's, when Cale blew up. No big deal, until you find out he broke 8 rods...carbon fiber rods. This was Late 70's! Totally off topic, but true.

What CAN you talk about? me and Dave will blow up your PM box soon.

[BBC71Nova]

Peter, this is easy. Surely NRE did an engine dyno. So just strap your ride down to a chassis dyno and let us know the result .

Seriously though I've put some thought into this lately as well. Primarily because I can't figure out why the LS setups put down so much rwhp compared to some pretty strong big block combos. I would generally think flywheel hp was flywheel hp regardless of it being LS, BBC or even a Ferd FE .

However, I then read a few examples where some solid 600+hp BBC builds were only getting high 400/low 500 rwhp numbers. That would support the closer to 20% drivetrain loss figure.

On the other hand, it seems fairly common/easy to get 500 rwhp out of an LS3. I know they are efficient and all but geez. Similar rwhp and 100 less cubes???? I also can't see a basic LS3 putting out 600 flywheel HP to start with.

That just doesn't seem to add up so I gotta think drivetrain differences maybe. Most certainly any BBC rwhp number you'll find is likely through an auto trans so that may explain some of it.