I'm asking about the ones you typically see at car shows. A friend of mine was telling me they will have one at an upcoming car show soon and I was curious how accurate they were. Thanks

All dyno's whether mobile or otherwise are only as accurate as the operator wants them to be, an inherant flaw with chassis dyno's. I've seen the same car run up to 30RWHP different with no other changes just going from dyno house to another (both claimed to be 100% accurate).

I had problems with the one at the Wildwood car show. It couldnt get a good reading cause my plug wires were too big. Now please, you own a DYNO, and you dont have a clamp big enough for performance wires?!?!? it went from 290 hp...to 357hp to 410hp at the wheels. So i dont know what was up...
Ed

Interesting!!!, so you don't really know if your reading is accurate or not!

A hydraulic load cell or eddy-current dyno (Dynapack, Superflo, etc) are typically more accurate than inertia dynos (Dynojet).

With the Dynapack, you have the VERY nice advantage of being able to program in RPM rates and hold the car at a steady load; great for tuning. It's much more time consuming to set up though as you have to take your wheels off and bolt the car onto the dyno. With the drum dynos all you do is pull on and strap the car down.

Dynojets tend to read a little high, Mustang dynos seems to be 20-30hp lower, and Dynapacks seem to be one of the best when it comes to repeatability but they read on the "low" side (I think most people say "low" because they don't want to say "accurate", which takes away from their bragging rights.)

As usual with any dyno, the operator can make the printout say whatever you want by fudging correction factors and/or initial dyno calibration.

However, using the same dyno/operator will help to validate and give you hard numbers for incremental changes to your combo. Jumping from dyno to dyno isn't a good idea if you are verifying combination changes simply because you won't know if the HP jump (or loss) is due to your change or simply variances between each dyno.

Troy

Thanks Gokou- I bet it's a dynojet type. That's the only type I have ever seen at car shows.

JimChevy, heres the link to the old post about my dyno run.
http://www.chevelles.com/forums/showthread.php?t=90178

Thanks for the link. Nice Nova!