final drive and rear differential different?

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Postby Conan » Thu Jan 18, 2007 11:17 am

coyoteboy wrote:Run an engine-dyno test and then a chassis dyno test on the same engine in a car.

It will still depend on the setup of the chassis dyno. They all use some sort of brakes to simulate road load and those are configurable so you won't get a 100% true figure.
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Postby coyoteboy » Thu Jan 18, 2007 12:28 pm

So long as they are calibrated correctly, which you'd hope they would be since you're paying for that service, it is irrelevant what sort of brake system is used. If they were that far off you couldnt actually ever assume you had an accurate dyno result at all and that unless all cars were tested on the same dyno you could never claim higher power than the next person. Power at the fly "measured" on a chassis dyno is pointless without the accurate drivetrain loss amount, i was talking power at the wheels btw.
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Postby Conan » Thu Jan 18, 2007 12:52 pm

coyoteboy wrote:unless all cars were tested on the same dyno you could never claim higher power than the next person

That's exactly my point, I think of dyno graphs as means to track your own progress with upgrades and tuning, not a dick-measuring event.
coyoteboy wrote:Power at the fly "measured" on a chassis dyno is pointless without the accurate drivetrain loss amount

I have access to a local chassis dyno of inertial type, i.e. no brakes, and it gives very accurate flywheel figures. I'm talking 95+% accuracy for stock cars compared to their specs (as that is the only thing you can believe).
coyoteboy wrote:i was talking power at the wheels btw.

I know, I was too. Through almost 2 years on this forum I have seen too many different chassis dyno results from people with similar mods so I'm not pulling anything from the air...
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Postby coyoteboy » Thu Jan 18, 2007 1:46 pm

Totally agree, although the only way you could guarantee your local inertial dyno was accurate is to test your car when stock (and assuming the same X% error) and then watch it rise. The OC in the UK did a dyno shootout a while ago with the north and the south at two different RRs with a control car going to both. I cant remember how far out they were but it was only a couple of HP on the control car of ~250hp.
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