Question on Dyno Testing

Indy SS · March 16, 2003

Anybody ever put their truck on a Chassis Dynamometer?

I had planned measuring my rear wheel hp after installing an FIPK and Gibson exhaust, but while cleaning the engine bay I found a factor sticker that said "This vehicle is equiped with an automatic transfer case. Do not test on a 2 wheel Dynamometer" in front of the batter.

Now I know the factory warning stickers usually don't lie, but I was wondering if anybody has ever ignored this (intentionally or accidentally) and what happened.

I kinda wanted to see just what my truck was putting down to the rear wheels, but now it seems that I'll not get to find out since I don't know of a local speed shop with a '4 wheel Dynamometer'.

Shaners · March 16, 2003

That might be a generic warning sticker for safety reasons. If you have the pushbutton "AutoTrac" transfer case, then it is understandable... I don't know the real reason though, unless the truck is full-time 4wd.

Talk to your local speed shop and see what they say about it...

I could see an ABS light coming on during a Dyno run, but that is about all...

WEFs99 · March 16, 2003

My truck, with Autotrac, has been on a single axle dyno with no harm done.

'02 Sierra Denali · March 16, 2003

I've had my '99 Z71 on a Dynojet a few times. Never had a problem with it other than the speed limiter kicking in.

99silveradoz71 · March 17, 2003

We've got the single wheel dyno here in Ohio for the emissions testing and I posed this question either here or on another forum previously. My understanding is that it's a cya sticker so someone doesn't try to put it on the dyno while in 4wd or auto. I think in 2wd you will have no issues at all. Mine went on it for the testing and had no problems.

CapnDean · March 17, 2003

Okay yall...help out an old timer here....The only kind of 4WD I have ever had is the kind where you had to get your knees dirty locking in the hubs.

That being said: Automatic Xfer case to me means that it is CONCEIVABLE that the truck could 'think' it was losing traction while on the dyno....as a result it could automatically engage the front end.

Is that the deal here? Or is (as said before) the General covering his liability suit a$$ against the truck launching off the dyno?

CapnDean

Shaners · March 17, 2003

Okay yall...help out an old timer here....The only kind of 4WD I have ever had is the kind where you had to get your knees dirty locking in the hubs.

That being said: Automatic Xfer case to me means that it is CONCEIVABLE that the truck could 'think' it was losing traction while on the dyno....as a result it could automatically engage the front end.

Is that the deal here? Or is (as said before) the General covering his liability suit a$$ against the truck launching off the dyno?

CapnDean

Certainly if the truck was in the "auto" position, the front axle would kick in. If the 2 High light was on the transfer case should not overide this command and should only apply power to the rear wheels.

cyrylyn · March 17, 2003

I just gained access to somewhat free dyno's.. and then I noticed that warning.. if worse comes to worse, I'll put the front on jackstands

Indy SS · March 17, 2003

Thanks for all the replies.

After seeing how many have put their trucks on a 2 wheel dyno (assuming at least half of them are 4x4s), I have to think the warning IS a CYA for the Auto 4x4 pushbutton transmissions.

My Speed Shop dyno guy is pretty with it, I'll go ahead and ask his views on the subject. Then I'll let 'er rip! :thumb:

99silveradoz71 · March 17, 2003

if worse comes to worse, I'll put the front on jackstands

Buehler?...Buehler?...

CapnDean · March 21, 2003

Didn't Ferris try that on a Ferrari?

MarkD · March 21, 2003

Didn't Ferris try that on a Ferrari?

I believe that is why the sticker is there. If the auto transfer case were to suddenly apply power to the front...uh oh!

Something else... our auto transfer cases are are actuated via vacuum or electricity. If for any reason that "communication" was disrupted (like say a 6000 rpm dyno run with wheels turning 125 mph) the consequences would resemble Baghdad right now.