numbers from chassis dyno vs. engine dyno

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hotrodhp
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numbers from chassis dyno vs. engine dyno

Postby hotrodhp » Mon Dec 08, 2008 9:46 pm

today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks

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Re: numbers from chassis dyno vs. engine dyno

Postby Jason G » Mon Dec 08, 2008 10:23 pm

hotrodhp wrote:today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks


hotrodHP,

There are a lot of factors that come into play and you can't really compare from one chassis dyno to another, but......

The first iteration of my engine was 672 HP @ 6300 RPM on what I believe to be a reasonable SF-901 engine dyno. I installed the engine in the car with an 8" converter (4400 flash), TH350, 3.5" steel driveshaft, 12-bolt w/posi and 27x9 tires DOT slicks. It put down 548 RWHP @ 6400 RPM.

The only changes were adding 3.5" exhaust, 3" mufflers, and an alternator. Everything else was as it was run on the engine dyno.

Jason G.

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Re: numbers from chassis dyno vs. engine dyno

Postby David Redszus » Mon Dec 08, 2008 11:17 pm

- knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks

That is pretty close.

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Postby andyf » Mon Dec 08, 2008 11:22 pm

The last time I did some back to back testing we had 550 hp on the engine dyno and 475 rwhp on the chassis dyno. So that is a drop of 14%. That was with a manual transmission, 3.54 gear ratio and radial tires.
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Postby 1989TransAm » Mon Dec 08, 2008 11:31 pm

A couple of weeks ago I got to witness an engine dyno and then a chasis dyno with the same motor, the same facility and the same brand of dyno's.

The motor made 525hp on the engine dyno. The motor was then installed in the car and made 425 horsepower on the chasis dyno. The transmission was a built 200-4R and non lock up converter. The car was a 1972 Corvette.
Last edited by 1989TransAm on Tue Dec 09, 2008 12:49 pm, edited 1 time in total.

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Postby hotrodhp » Tue Dec 09, 2008 12:01 am

thanks alot for the info!!

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Re: numbers from chassis dyno vs. engine dyno

Postby maxracesoftware » Tue Dec 09, 2008 1:53 am

hotrodhp wrote:today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks


i just talked with a Guy who builds 1 Cyl 4-Valve and 5-Valve ATV Drag engines
77.0 HP @ 10,500 w/27.391cid on Engine Dyno
67.0 to 69.0 HP on Chassis Dyno

this is a 4-Wheel ATV...its around 10% Loss on Chassis Dyno

for Cars basically, its somewhere between 18.0 to 22.0 % Loss on Chassis Dyno

i've seen up to 22 % Loss on 800 HP Engines
going to Chassis Dyno, some of the loss due to tire distortion
on the Rollers as to how much force you need to tie-down the tires
to the rollers, and what tire compound as to how much its trying to grow
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Postby MadBill » Tue Dec 09, 2008 7:45 am

A lot of people screw up on the conversion from chassis to engine power. Assuming a 20% loss, you do not multiply the chassis figure by 1.20, you divide it by 0.80.

e.g.; 500 HP engine dyno with 20% loss = 400 CHP x 1.20 = 480 BHP, Wrong!
400/0.80 = 500 HP. Correct!
Felix, qui potuit rerum cognscere causas.

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Postby revolutionary » Tue Dec 09, 2008 8:42 am

Similar numbers here. We ran an engine on a SF901 and made 622 then on a Mustang Chassis dyno through a TH400 and 9inch made 518 for a loss of 17%
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Postby hotrodhp » Tue Dec 09, 2008 11:17 am

great info. the test was done on a dynojet 224 LC. its a 69 camaro with a 4 speed an 9' ford with 4:30 ratio- 275/60-15 radial tires. thanks!!

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Postby W. Tripp » Tue Dec 09, 2008 12:44 pm

hotrodhp wrote:great info. the test was done on a dynojet 224 LC. its a 69 camaro with a 4 speed an 9' ford with 4:30 ratio- 275/60-15 radial tires. thanks!!


FWIW- the 9 inch Ford tends to take a couple more percent to drive than the 8.8" Ford or 12 bolt Chevy, mostly due to the outward pinion location from centerline.

Also, transaxels tend to be a bit more efficient than normal trans/diff combinations.

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dyno

Postby EthylCat » Wed Dec 10, 2008 7:44 pm

My two experiences showed more loss than most of you guys.

1. 435 hp 383 on DTS Powermark into mid 80's El Camino. Put 300 to the tire on Mustang 1100se same day, same building. TH350 trans and 9 inch rear.

2. 495 hp 460 on the same Powermark became 325 hp to the tire on the same chassis dyno.
69 Mustang w/ C6 and 9inch.

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HP-Flywheel vs. Rear Wheels

Postby GOSFAST » Wed Dec 10, 2008 8:04 pm

According to the "Vette Doctors" here on Long Island you can use a 16%/18% factor and be right on the money!

We've had the opportunity to confirm about 4 builds recently with the dyno HP and then with the chassis dyno!

The guys at the "Vette Doctors" were correct, 16%/18%.

The last one I recall was 676 on the dyno and 575 at the tires!

Thanks, Gary in N.Y.

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Postby 1989TransAm » Wed Dec 10, 2008 8:16 pm

GOFAST, are those numbers with manual or automatic transmissions?

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Postby Duner » Wed Dec 10, 2008 9:05 pm

So would an automatic putting down 625 at the rear wheels be about 750 at the flywheel then?


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