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.

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)

Depends on the crowd you hang with. I've heard 10% losses from some the same crew spouting off 3/4 race cam like its still relevant. Other guys who deal with more practical methods such as e.t. and m.p.h. have usually been in the 20% range because they see the results of their installations and are trying to figure out ways to minimize it.

We used a Superflow chassis dyno for all of our tests.

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%.



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.

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!

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.

Thanks for the great insight Ron. :thumbsup:

Since this is a pro touring website I'll chime in with my results from a pro touring car. :poke:

I had the engine dynoed and then a chassis dyno. It worked out to 16% hp loss and 15% torque loss. Big block chevy, tko 600, 3.5" aluminum driveshaft, and 12 bolt with 33 spline axles.

There is only one way to figure it out. Do as I just said...

Hey Todd thanks for sharing.

Was the 15% torque loss at peak torque? and if yes, what rpm? Was the 16% HP loss at peak HP? and if yes, what rpm?