RWHP to Crank HP reduction

[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.

[DTM Racing]

Don't get to wrapped up on peak numbers. Average HP/TQ numbers over the operating RPM is much more important.

[V8TV]

We tested a 1970 Buick 455 on an engine dyno several years ago, and then dropped it in a 1970 GS ragtop with an M22 4-speed and chassis dyno tested it. If I recall, we lost 17.5% at the wheels.

[Ron Sutton]

Originally Posted by V8TV

We tested a 1970 Buick 455 on an engine dyno several years ago, and then dropped it in a 1970 GS ragtop with an M22 4-speed and chassis dyno tested it. If I recall, we lost 17.5% at the wheels.

Kevin, do you recall what rear end was in the car?

[Ron Sutton]

Originally Posted by DTM Racing

Don't get to wrapped up on peak numbers. Average HP/TQ numbers over the operating RPM is much more important.

I completely agree. We were looking for total power "under the curve" ... meaning within the usable rpm range that race car was running in. Peak numbers are just to brag about.

[69znc]

I agree the power curve is the holy grail! But I think the urban rumors about the 10% loss have a real stickiness with no empirical evidence. Ron your testing is exactly what I have found in all the research and studies I have found conducted by various magazines and by individuals posted in forums.

Specifically I was thinking of street legal cars so I think that Ron's reduction of 18% in a race car set up supports my belied 18.5 with PS, AC..... is realistic. I think the low 20's is more realistic for someone who is not overall anal about minimizing the reduction (sorry some self reflection there!)

Scott thank you for your insight. I was not trying to figure out what race teams and cars can do. Really just for the types of cars people on this site talk about and own. NASCAR, Indy, Grand Prix, NHRA are in a different world!!

[INTMD8]

It can't be a fixed percentage. It would be a fixed amount of HP loss plus a percentage variable.

For instance, double or triple the RWHP and you didn't double/triple the drivetrain loss.

What trans? Converter locked or unlocked? fluids up to temp? Same exact exhaust and induction system? What type of rearend? Do you have air in the tires? What is the gearing? Same rate of acceleration on both dyno's or is one inertia? Etc/etc...

I've seen some cars go from a manual trans to an auto with a very loose converter and "lose" 80 rwhp.

I'll just leave it as, too many variables. Depending on the car and the sum of it's parts there will be a huge spread in realized loss to the tires.

[Rybar]

I just quickly skimmed the thread, but did anyone mention what type of chassis dyno here? Mustang and Dynojets read differently.

I think theres about a 10% difference between the two. (Dynojet's reading higher that is)