[chrisp]

Chassis dyno vs engine dyno , how much is lost to the rear wheels on chassis dyno vs engine dyno . Torque & HP.

[Steve C.]

If interested there is lot's of opinions on 'Google' regarding Chassis dyno Confusion....

http://www.badasscars.com/index.cfm/...d=64/prd64.htm

http://www.onallcylinders.com/2012/0...u-should-know/


Also what type of chassis dyno makes a difference. And a discussion here:

https://forums.maxperformanceinc.com...t=chassis+dyno

https://forums.maxperformanceinc.com...t=chassis+dyno


.

[Stan Weiss]

Originally Posted by chrisp

Chassis dyno vs engine dyno , how much is lost to the rear wheels on chassis dyno vs engine dyno . Torque & HP.

My very first question is manual or automatic trans?

Stan

[Trevor78]

How long is this piece of imaginary string I'm not holding? Without any details you can't even guess approximates.

[chrisp]

461 muncie S-60 rear 354 gears chassis #s @ rear wheels 424HP & 484TQ.

[Stan Weiss]

A WAG 500 HP and 570 Torque

Stan

[Lee]

Look at the two sets of dyno graphs I've attached.

Same car, same tune, same everything - except torque converters.

The first graph has two different converters I was testing. The second graph is another converter, but with a lock-up feature and the test was ran with the converter locked.

The locked converter test is more similar to testing a car with a manual transmission.

I had another instance to test a motor on an engine dyno, and it made ~550hp at the flywheel. In the car, different headers, full exhaust, air cleaner in place, it put 426 to the wheels on a DynoJet.

Recently, I tested my friend's TOTALLY stock '79 Trans Am, 403 2.73 gears, 27,xxx miles. It was rated at 180 or 185hp, which I always assumed to be flywheel (since chassis dynos didn't really exist at the time). On our DynoJet, it put 178 to the wheels. That was through the crappy old pellet catalytic converter.

SOOOO many variables. Like Stan stated, a Wild @$$ Guess is about as good as you can do.

About as accurate as I can state is the RWHP will be about 20% lower than flywheel - but with a +/- range of up to 18% (2% to 38% of flywheel).

[Scott Stoneburg]

Just for comparison, on an engine Dyno my combo made 794hp and 697 lbft. Tq.
The mph and ET from the track shows
728.62 flywheel HP and 655.76 rear wheel HP.
Your HP computed from your vehicle MPH is 754.50 flywheel HP and 679.05 rear wheel HP.
from the Wallace Calculators. I know it's not engine to chassis Dyno. But is a comparison on how much I may be losing through the trans/rear and exhaust.

[steve25]

The chassis dyno's don't just see the losses from trans, rear and maybe Exh , but they also see the losses from the mass of your rotating rear tires and that can be a good added percentage of loss when your spinning up a big pair of slicks that can hook up 600 plus hp .

I have never looked to see if anyone has done such, but I would love to see a back to back chassis dyno test of a car with street tires and then a 11 or 14" wide set of slicks.

[Bill S]

There is also the Dynatrac hub dyno, rear wheels removed with adapter bolted to the axle flange.

My 2004 LS1 GTO did 428rwhp/402 rwtq. Being a stick shift, I am guessing around 15 percent drivetrain loss putting it about 500 flywheel hp. I plan to have my '67 455 Firebird out on this dyno someday.

[Skip Fix]

i had one chassis dyno gut tell me convertors do make a big difference and slicks that grow also do compared to a radial slick/DOT tire.

I would think gear ratio would affect it as it multiplies torque at the tires.

My auto 2004 GTO stock LS1 made 274 on one chassis dyno and 282 on the other one at the shop, factory rated 350 hp.

[Stan Weiss]

From my understand of how the chassis dyno and math works. Different rear gear ratios should not change the readings.

Stan

[Lee]

On the chassis dyno, I've tested in 2nd gear then in 3rd gear (automatics) and there was very little difference in power readings. So very minimal change with different rear gears.

[Tom Vaught]

Originally Posted by Lee

Recently, I tested my friend's TOTALLY stock '79 Trans Am, 403 2.73 gears, 27,xxx miles. It was rated at 180 or 185hp, which I always assumed to be flywheel (since chassis dynos didn't really exist at the time). On our DynoJet, it put 178 to the wheels. That was through the crappy old pellet catalytic converter.

About as accurate as I can state is the RWHP will be about 20% lower than flywheel - but with a +/- range of up to 18% (2% to 38% of flywheel).

Clayton Chassis Twin Roll Dynos have been around from the early 1960s, not 1979. (think Dyno Jet, etc).

Your 18% Trans/Chassis/Tire loss number is "SPOT ON" vs what Ford has used for many years (and verified yearly on the Company Test Tracks).

Tom V.

[Lee]

Originally Posted by Tom Vaught

Clayton Chassis Twin Roll Dynos have been around from the early 1960s, not 1979. (think Dyno Jet, etc).

True, I knew the OEMs had methods of testing. But the general public didn't really have access to them. I know it was in the 90's before I knew of any place where I could use a chassis dyno.

Then it was love at first sight!

[GTO JONES]

I ran mine on a chassis dyno a few months ago and got 516 hp and 543 tq