chassis dyno

[astikhossw]

Can anyone tell me if a chassis dyno multply the torque of the drive train and give you the results are does it some how give you the engine results.

[Mike Taylor 3601]

It gives power @ wheels ,I know on Dynojet they have setting that after pull put car in neutral and let driveline and dyno drum coast and it calculates % driveline uses. Dynojet told me figure 25% at least. If you have reverse pattern valve body don't attempt going back to neutral.
Mike Taylor3601
I looked at your post again I may have misunderstood your question chassis dyno calculates HP by how fast you accelerate the drum thats how they measure Dynojet has 3500lbs. drum.Engine dyno has whats called torque link attachted to dyno brake which calculates TQ.torque link is stretched and calculates TQ. from amount of stretch of tq link and converts HP from that,Super Flow now calls them load cells.

[Run to Rund]

Some chassis dynos measure torque and then calculate HP. The Dynojet measures HP directly, and uses the tach pickup to convert roller speed (which calculates mph) into rpm for torque. The Dynojet can be used for coast-down HP measurements and comparisons of the drag from different things like diff designs (e.g. 12 bolt vs. 9" ford), or lubricants.

[Mike Taylor 3601]

That's what I was trying to say but you did better job.
Mike Taylor3601

[Robert Swartz]

I'm curious about this. I have always been under the impression that you can't use a chassis dyno on a car with slicks? I may be completely wrong, since drag slicks grow, they would seem to be unstable on one of these rigs. Or am I completely out in left field?

[Robert Simpson]

I would like to know how a test is conducted on a roller dyno? For example a stocker with a loose converter. How do you run a test with reading down low, 3500rpm, on up with a converter that slips and flashes, etc? The couple operators I have spoken with around here have no idea what I mean, then again they mainly run imports and manuals.

[art leong]

Originally Posted by Robert Swartz

I'm curious about this. I have always been under the impression that you can't use a chassis dyno on a car with slicks? I may be completely wrong, since drag slicks grow, they would seem to be unstable on one of these rigs. Or am I completely out in left field?

Some chassis dyno tear up soft rubber slicks.

[Chris "drooze" Wertman]

Originally Posted by astikhossw

Can anyone tell me if a chassis dyno multply the torque of the drive train and give you the results are does it some how give you the engine results.

There are many different types of "Chassis Dyno's" just like engine Dyno's

There are "Inertia" Dynos which guess at HP and Torque based on calculations of what the drum weighs or resistance and how much it takes to do that, some very accuratley

There are "Load Brake" Chassis Dyno's or Hub Dyno's that bolt to the axle like a wheel would, some are Hydraulic Load brake Dynos, just like and engine dyno, these can be "hyperaccurate" as in seeing gap changes, Dynapac is one, and if you look at their site they have a listing of places here in the states that have em, they also have other advantages. You can actually simulate a "Pass" or Full accel ramp, they are also easier on the Chassis and "Safer" do a search on youtube for "Dyno Accidents" some are funny as hell, some very very sad (in loss of iron) These are much more accurate on torque, but calculate HP based on Torque (a mathmateical equation)

There are other types as well, but those are the main 2

Dono if that helps, my limits of knowlege on Car Chassis Dyno's

[Mike Taylor 3601]

Only have used Dynojet on it you get car in hi gear or 1-1 get rpm steady as can for start RPM hand held controller gives operator green light then driver goes WOT get to upper RPM point let off throttle dynojet has airbrakes on drum that stops drum after pull.
You can start whatever RPM you want but has to be around converter stall,if you try to start below that it's just going to go straight to flash point of converter anyway.
Dynojet has knurled rollers the one I used has 48'' rollers the bigger the rollers the better the traction you get I've heard small rollers are hard to get repeatable results on,I still like engine dyno over chassis anyday,It's alot easier to get them to repeat,one reason is you eliminate a bunch of varibles getting rid of driveline and you can control your oil/water/air temps on engine dyno.
As far as numbers go the Dynojet numbers were real close to what they should've been compared to what engine did on our Superflow 901,the HP was about 25% less at the wheels than engine had on Superflow 901,the dynojet is about 275 feet from the Superflow and cell.I'm just talking about one car I know well my own.
When you start getting big #'s it starts slipping tires,had Procharged SBC was in 990's HP range @ wheels,had 10.5 X 28.5 MT's it was spitting a little rubber mist out the back,had dodge w/cummins was flat lineing TQ from 55-85 mph on graph TQ shows up to 1200lbs graph went up steeply 55 mph would flat line till about 85mph don't know how high it peaked took about 1.7 seconds to go through pull,may had traction issues,but could'nt notice them.
The main thing is don't get caught up racing dyno's,don't worry about what someone makes on another dyno,learn how fast X amountHP&TQ on dyno you are using will make your car go.
Mike Taylor 3601

[bill dedman]

My car, running a normally-aspirated VERY MILD 360 Magnum Mopar engine made 260 RWHP on a Dyno Jet dyno, with a 2.76 rear axle ratio.

If I had swapped a 4.56 gear into my car on the spot and had immediately, re-run the test, I am SURE I could have accelerated that inertia roller a lot more quickly.

Would that have altered the "reported" HP output, since it did the same amount of work more quickly?

It should have, or maybe I don't understand physics.... a definite posibility.

If NOT, then how is the Dyno Jet type of computer able to deal with this variance, and give us a legitimate HP number with both rear axle ratios?


Just askin'....