RWHP to Crank HP reduction

[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.

[Ron Sutton]

Originally Posted by 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.

We did not find it to be a fixed amount of power. We found it to be a percentage. It varied "a little" ... but otherwise it was a similar percentage throughout the power range.

In fact, if you lay our engine dyno graph over our chassis dyno graph, in the same usable RPM range (3000-7000 for us), the graph looks the same ... just lower by 18.1-18.8%.

Originally Posted by INTMD8

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.

I agree. It absolutely depends on what you do to the car, drivetrain & accessories.

Different transmission designs ... torque converter size, stall & weights (if running one) ... clutch size & weight (if running a clutch) and the ultra light option of running neither a clutch or torque converter in some cases ... will all play a role.

Pinion drop plays a role. 9" Fords use up more power than most rear ends due to a lower pinion, with more angle to the ring gear & more tooth contact (friction). That is also part of what makes the 9" strong for it's size.

Of course gear oils, bearings, no/low drag seals, micro-polishing gear surfaces ... or lack of ... play a role.

And lastly, but pretty obvious, is the weight of the entire rotating drivetrain assembly the engine has to turn.

We tested our cars just like we raced them & saw 18.1-18.8% less power than the engine dyno showed. We all know there are variations in dyno readings, but we still wanted to know with the best equipment we had available to us.

We started looking for ways to reduce the loses & unlock power ... first with our lower powered cars with spec, sealed engines. We spent a lot of money & time testing to free up speed in those cars. Angular contact bearings, ceramic ball bearings (EVERYWHERE), micro polished races, micro polished gears, no drag seals, lighter weight gear oils, etc ... dropped the loss by 2% +/- ... to 16.4-16.8%.

On track, the data acquisition showed the cars accelerated faster (predictable) ... but also carried more rolling speed after braking. :-)

The ceramic bearings cost a lot of $ ... and were worth every penny to us for our race team goals. Not only did they reduce rolling resistance & freed up power ... an added bonus was cooler running stuff (remember I said we put them everywhere) ... AND ... the bearings lasted 4-5x longer.

Later we did similar upgrades to our other race cars that had more power than they could use. Why? Because they carried more rolling speed after braking.

[69znc]

hp2 - yes I have "heard" many things but the point is not "heard" but empirical data. This I can believe in with many points of verification. Thus my post. No it does not matter the crowd you hang with if they are serious.



the dyno does matter thus the need for some structure in testing.

Ron you still have the most factual opinion with empirical data and test time.

Again I think for our cars featured here lose of low 20% is great!

[Ron Sutton]

69znc & hp2 ...

I think we're saying the same things ... 20% loss in a street car is to be expected ... give or take a little ... depending on auto or manual transmission & a few variables.

I think the newer cars in the last 10-15 years have accessories that draw less power & more efficient drivetrains. I suspect if we compared a newer Camaro, Mustang, Challenger or Corvette, we would see numbers under 20%.

Just my 2 cents.

[hp2]

Originally Posted by 69znc

hp2 - yes I have "heard" many things but the point is not "heard" but empirical data. This I can believe in with many points of verification. Thus my post. No it does not matter the crowd you hang with if they are serious.

I guess I didn't get my point across adequetly. IMO, the guys with a fist full of timeslips or a log book of info have empirical data. These guys tend to speak from data driven results. Liek you said, these are the people who are serious about their performance and how to improve it.

The guy who swears his 396 Chevelle with dual quads put down 500 horses because it would burn rubber in all four gears is at the other end of the spectrum. In my experience, these two groups typically only tolerate each other for about 90 seconds at a time before hostilities begin. They don't hang together very often, so association with one group will never get you data. Association with the others will get you as much info as you are willing to digest.