Community Forums

hamguy · 01-02-2008, 01:04 PM

I too, find best MPG at 2200 RPM but I only get 62 MPH and about 6.8-7.9 MPG depending on condx.

max49 · 01-03-2008, 06:52 PM

I concur! My engine seems most comfortable @ 2200 RPM also and that's about 63MPH. I'm probably the only one here who honestly believes that I get the same mileage or better @ 65 then I do at 55 on a flat road with little or no head wind.

JWatkins · 01-03-2008, 08:42 PM

Since I am new to this MH, I am looking forward to trying the 2200/2300 RPM setting and seeing what turns out. I know a lot of engine/tranny combos have sweet spots. It appears the WH 8.1/Allison is right there at 2200.
Joe

Sidewinder · 01-04-2008, 02:51 AM

I am suprised no one has made referance to the Torque Curve of thier engine. Each engine design has a very specific curve where engine RPM and maximum Torque(horsepower) is reached. Anything below or above this RPM is wasted fuel. Most manufacturues will set a coach up with a set of gears that has the coach performing just below it's peek at aprox. 60MPH.
Check your manual and then your RPM.
Hope this helps
Ron

M&EM · 01-04-2008, 08:38 AM

Sidewinder,

I think if the coach were operated at just below the RPM where where maximum HP is shown to occur, it would put the RV well above any legal speed limit while traveling in OD.

The wind resistance alone at those speeds would destroy any chance of good miles per gallon.

I also believe the electronics would govern the max speed to somewhere around 80 mph.

Perhaps those curves you refer to represent the maximum output torque and calculated power at FULL THROTTLE versus RPM at the engine.

Sidewinder · 01-04-2008, 10:14 AM

m&em, I am not sure of your question. My 460 has a peek HP/Torque acheavment at aprox. 2200 RPM. Then the HP/T drops as RPM increases. I get more fuel burned and less power developed at anything over 2300. This is the way the engineers set-up the drive train gearing and tire size on my Bounder. Therfore my best preformance is at 2100 to 2200 RPM with will translate to aprox. 62 mph loaded with tow vehicle.
If your HP/T is set to max out at 80 MPH you best take your rig back in and have the Racing gears taken out and you may be able to pull away from a stop light.

M&EM · 01-04-2008, 10:54 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sidewinder:
I am suprised no one has made referance to the Torque Curve of thier engine. Each engine design has a very specific curve where engine RPM and maximum Torque(horsepower) is reached. Anything below or above this RPM is wasted fuel. Most manufacturues will set a coach up with a set of gears that has the coach performing just below it's peek at aprox. 60MPH.
Check your manual and then your RPM.
Hope this helps
Ron </div></BLOCKQUOTE>

Sidewinder,
See page 40 of Workhorse Gas Motor Home chassis Guide (1999-2006)

The 8.1 TQ peaks at 455 at 3200 RPM.

We all know that cruising at 60 puts us at around 2200RPM.
Almost all of us know that we don't use any where near maximum throttle when we are cruising at 60 with level road non windy conditions!

My point is that the MAXIMUM TORQUE curves don't directly apply at cruising condition.

Perhaps a curve of torque produced at a throttle opening normally used while cruising. would be what you have been referring to. I haven't seen such a curve published.

Sidewinder · 01-04-2008, 11:42 AM

M&EM, Sorry I don't have that guide. I have looked at a ton of power curves and never noted an engine of that size having to rev that high to develop 455 ft/lbs of torque. The manual that I have out for my 7.5L ford runs.
395 ft/lbs at 1500 rpm
390 ft/lbs at 1850 rpm
400 ft/lbs at 2200 rpm
Then it drops in torque at aprox. 10 ft/lbs per 100 rpm beyond that to 290 ft/lbs at 4400.
This is not the HP curve at 245hp at 3600 and climbing.
Ron