Rear wheel horsepower

[EV2RTSE]

So for 1970 we all know that a 426 Hemi was advertised to put out 425hp, a 440-6: 390, a 440-4: 375, a 383 Magnum: 335, a 340-6:290, and a 340-4: 275. Measured at the crank.

Just curious to see who has run their car on a chassis dyno and what the result was, measured at the rear wheels with full exhaust, air cleaner, and etc. With basically a stock original configuration or rebuild, more or less.

Basically wondering how much hp gets lost through the exhaust, trans, diff, etc.

Would like to hear your configuration and results, thanks.

[chargerdon]

looking forward to hearing those results.   Just remember those HP numbers back then were "gross" HP numbers.   Then in 72 they switched to NET numbers.   As an example a 318 was rated at 230 HP in 71...in 72 under the Net system only 150.   How much of that 80 hp loss loss was gross vs net...and how much of that 80 hp loss was due to switching to Unleaded gas ...  ? 

[HP2]

Yea, net rear wheel power measured by a dyno is a heart breaker. 

Where I am at, our local club had a dyno day a few years back. We had many a stock rebuilt big block knock out an amazing 200-245 horsepower. Before you say that's impossible even with the worst parasitic losses, keep in mind that I live at 6200' in elevation and those were not adjusted numbers but real world, net at the tires as they drive it in that day numbers.

[Mr Lee]

Yes but from what Ive read, gross hp is on an engine stand, without an air cleaner or an exhaust, running pumps etc which is how the cars were rated initially...  and "net", or really, "SAE Net" hp is not at the rear wheels, but rather on an engine stand WITH air filter, exhaust, running pulleys etc. 
Is this correct?   
Just to make sure we're all on the same playing field here? 


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[Mr Lee]

In any case, i ran my freshly rebuilt 383 magnum yesterday on the chassis dyno and my numbers were 232 hp and 320 ft lbs at 4,800 rpm.  I didnt want to rev much higher for fear of my tires blowing up (not being Z rated).  My speedo was at about 140 mph and i run a 3.23 rear.

My power curve was very smooth and almost flat.
I have a mild lunati cam (dont know the specs) and a .030 bore.  Otherwise stock (intake, exhaust, etc).  Holley 650 mechanical secondaries. 92 octane. 4 speed car

It was a little disappointing.  But made me think about all the heavy stuff the engine is turning btwn the crank and the wheels though, not to mention the 15x8 wheels thenselves with 255 tires.  Probably a couple hundred pounds worth of stuff.  Thats a lot.


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[Headjam]

Good discussion! I'm also curious about rebuilt stock engines being tested on an engine dyno. Do they hit or exceed the published numbers? Does a stock 383 HP meet or exceed 335 HP?

[76orangewagon]

In my last build I had a stroked 340 that made 502 hp on the engine dyno and then once the car was together it made 379 hp at the wheels on the same shops Chassis Dyno. So I lost 123 hp or roughly 24.6 %. depending on the efficiency of your driveline I've read anywhere from 15%-up to 40% can be lost. A big mechanical fan compared to an electric fan can cost you up to 20 hp.

[Mr Lee]

In my last build I had a stroked 340 that made 502 hp on the engine dyno and then once the car was together it made 379 hp at the wheels on the same shops Chassis Dyno. So I lost 123 hp or roughly 24.6 %. depending on the efficiency of your driveline I've read anywhere from 15%-up to 40% can be lost. A big mechanical fan compared to an electric fan can cost you up to 20 hp.

Interesting.  That lines up with some other examples ive seen on the web.  A loss of approx 100 hp or more is not uncommon apparently. 
Your 340 sounds like a beast [emoji106]


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[Scooter]

Best illustration on how an automatic transmission works I have ever seen...

[Mopsquad]

Also to take into consideration are the different types of chassis dynos.  Some read consistently lower numbers  (Mustang Dyno) compared to others (Dynojet).

My 5 speed '65 Mustang ran 686HP on the stand and 508 on the chassis dyno. A 26% loss.