Speed Governor in 2004 GM 8.1 Engine

Jackm · 06-16-2009, 01:43 AM

Does anyone know if and when Workhorse (or GM) instituted the 80 MPH limiter in the 8.1 engine? I have a 2004 W-20 and vaguely recall exceeding the 80 MPH limit. Then again, it could have been a dream. I believe that the restriction is related to the design limit of the Michelin XRV tires. I would appreciate any insight into the timing of this "feature". Thanks.

Jack

oemtech · 06-16-2009, 06:24 AM

Yes - there is a speed limit parm in the ECM. I will double check this with my source.

TrekPR · 06-16-2009, 07:19 AM

XRV tires are rated at 75mph. It is possible that Workhorse feels anyone traveling 80 plus is asking for trouble and wants to protect themselves from the lawyers.

FDchief · 06-16-2009, 08:31 AM

I find that when I travel in my RV that I tend to slow down, not speed up. I arrive relaxed and refreshed at my destination. Have you ever seen a motorhome hit something at high speed? Devastation is the word. I equate RVs to air planes, they are not designed with crash tests in mind.

edgray · 06-16-2009, 08:35 AM

Quote:

Originally Posted by Jackm

Does anyone know if and when Workhorse (or GM) instituted the 80 MPH limiter in the 8.1 engine? ................ I would appreciate any insight into the timing of this "feature". Thanks.

Jack

JACK: The fuel to the engine is cut back to idle at 80MPH. That will not necessarily control your speed if on a steep descent, but will prevent you from powering past the 80 MPH limit on level. It is tire related, as others have posted. ED

wa8yxm · 06-16-2009, 09:26 AM

The one time I hit 80 MPH I was not touching the accelerator.

I was running "With the wind" (Tail wind, directly astern, of about 100mph per the weather service) down a slight grade, in drive, no pedal pressure at all.

oemtech · 06-16-2009, 10:51 AM

According to my source

Quote:

It depends on what year, some older ones (pre 2001) and newer ones (2007 up) are set to 75mph. The rest of them are set to 80mph.

max49 · 06-16-2009, 08:20 PM

I think it's false advertising for them to claim 340 HP. 80 MPH @ 2900 RPM is not 340 HP , is it

.
I know, I know, save the lectures, this ain't no "Hot Rod" forum. But it's amazing how popular the 'Ulta Power' is even tho most people seem to claim 55 or 60 MPH is fast enough.
Sorry, I have'nt posted for a long time and felt the urge.

oemtech · 06-16-2009, 08:28 PM

340 HP is measured at the flywheel.... It's probably closer to 260 HP at the rear wheels before UltraPower..

If you want to run faster than 80 mph all you need to do is.... send me as PM for the answer.

max49 · 06-16-2009, 08:48 PM

Quote:

Originally Posted by oemtech

340 HP is measured at the flywheel.... It's probably closer to 260 HP at the rear wheels before UltraPower..

If you want to run faster than 80 mph all you need to do is.... send me as PM for the answer.

And @ 2900 RPM, how many HP is that? Maybe 190?

Jackm · 06-16-2009, 10:12 PM

Thank you for the insight. In truth, RV tires aren't designed to handle high speeds. Besides, RVs don't have the handling and braking characteristics that are required to handle high speeds. Last but not least, like the big trucks, RVs have the potential to inflict more damage on the highway than your average sedan. Add it up and you see why it probably wasn't a bad decision to put in a limiter. That being said, 75 MPH seems a bit low.

Of course Ford also has a similar "feature". Thanks again.

Jack

TrekPR · 06-17-2009, 07:33 AM

The truth of it is if your involved in an accident at 75 in anything that isn't designed for the race track your odds of walking away are slim. In a motor home everything inside becomes a missile 75 seems a bit high.