Engine dyno vs Chassis dyno
 

Anybody know the % loss in hp/trq numbers when the same motor is taken off the engine dyno and then ran in a car on the chassis dyno? Have seen a couple of ASCS motors with chassis dyno numbers, and wondering what that would relate to when the same motor would be on the stand.
Thanks for any knowledgeable information one may have or experienced.
Rob

Re: Engine dyno vs Chassis dyno
 

Re: Engine dyno vs Chassis dyno
 

Standard factors for engine power losses through the drivetrain (15-17 percent for manual transmissions and 20-25 percent for automatics are figures accepted by most tuners)

Thank you both, but I am wondering if it is less considering it is a direct drive application - no transmission ... ?

Thank you both, but I am wondering if it is less considering it is a direct drive application - no transmission ... ?

Re: Engine dyno vs Chassis dyno
 

A motor on engine dyno hooked to the end of the crankshaft shows 500 HP
Same engine would show approximately 420 HP on a chassis dyno (using 16% loss factor) With manual transmission

With that in mind, a 603+Hp ascs motor on chassis dyno. would equate to approximately 718hp on the std dyno.

With no transmission they’re obviously no. Losses there but my guess is the quick change rear end would be more of a loss than a conventional rear…. I’d think something in the line of 10% would be close. From a very reputable hands on source the nascar teams strive for 1% loss at the wheels….. if it’s more they find out why

A direct drive situation, like a sprint car, is going to have considerably less loss of horsepower than a street car or drag car (which is what the blog is talking about). Through a standard transmission AND a differential, you’ll have slippage at the clutch as well as frictional losses in the gearbox and differential. With no clutch and no additional rotating gearing to deal with in a manual transmission, your drivetrain frictional losses will be limited to your quick change and your birdcage bearings. I don’t know specific figures, but I would be surprised if the losses were greater than 10%.

All that being said, none of that horsepower, at the crank or at the rear wheels, means anything if you don’t get it in the ground, and in dirt racing, that’s the proverbial $64,000 question.

As said above all the horsepower in the world does not mean a thing if it can’t be hooked up…. Probably something more important than all out horsepower is the drive ability of a motor. Especially on dirt. If the power hits hard making it hard to hook up there is a good chance the guy with 50-75 less horsepower is going to drive past

Parallel axis gears, such as transmissions, rob far less power than perpendicular axis axis gears, such as rear ends and steering boxes. The lack of a transmission is beneficial in terms of overall car weight and driveline packaging. Getting rid of the clutch and flywheel gets rid of rotating weight which is a big advantage in accelerating and slowing down the driveline, but doesn't have a big influence on steady state power. Driveshaft alignment will also have an effect on rear wheel power, and any difference in tire circumference will show up as a power loss. The general rule of thumb I learned is that any gear set that changes the direction of power (ie rear end, steering box) is going to cost you 15%. Then add on losses from there.

Very good points, but for my purpose, not as relevant. I don’t discount the application of power to the ground and am very aware. But for this exercise I wanted some sort of % of loss when comparing supposedly like motors. The 10% number sounds a little more valid. Was hoping to be lucky enough that someone had both for the same motor.
Thanks to everyone!

Re: Engine dyno vs Chassis dyno
 

Call Engler, great guy, does many dyno tunes and he will be straight with you.

Please report back here if you do.

My feeling is that 10% is a touch high and that it will be more of a fixed number than a percentage anyway.

I know that like in street car drag race stuff for a given driveline combo the hp loss will be almost identical whether it's 600hp NA or 1000hp turbo'd.

The friction generated between gears is a function of the force on the face of the gear tooth times the friction of the surface. Therefore, the higher force pushing on the gears, which goes hand and hand with more power, results in more frictional losses. To test this, drive your pickup around the block for 10 minutes at 25 mph, then measure the temp of the rear end. Let it cool (if it even got warm)and then get on the highway and stand on the gas for 10 minutes. Check the temp again. The higher temp indicates that more energy was lost when operating at higher horsepower.

You might be able to strain gage a shaft that you could use in both applications, run it with the dyno, then with the car, and compare the data.

Re: Engine dyno vs Chassis dyno
 

7% for a sprint car

That depends on the calibration of the dynos being compared. I was wondering the exact same thing bout 10 years ago. Sooo we ran a decent 410 (GB engine) on an engine Dyno made as expected around 830 peak. Then with a quickness pulled it out. Put it in a car and chassis Dyno tested about 2 hours later. It made 787 so about 5%.
Having said all that I’ve never seen a Dyno sheet win any races.

I was told by Tim Engler to multiply his chassis Dyno HP result by 1.07 (7%) to get engine Dyno HP result.