Author Topic: 1981 G30 Class C RV potential MPG  (Read 2870 times)

Offline MuddiGGEr25

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1981 G30 Class C RV potential MPG
« on: May 03, 2016, 03:28:00 PM »
Ok first off i know its a MH and i know its probably gonna get crappy MPG regardless, we just have a 2300 mile trip coming up in 5 weeks and I am trying to plan out stops for fuel since the tank only holds 33 US gallons...

Quick info on the rig
1981 25' Class C Fleetwood Tioga
454/TH400 4.10 14FF 8.75-16.5LT's
11 ish feet tall and about 7ish feet wide.

Dry weight around 7,800, GVWR 10,500 and will be pretty dang close to it when loaded for the trip.

Towing a 1988 V20 suburban 4-down weighing 5,000lbs on its own and will have a lawn tractor and its trailer in the back of it.

The 454 was cam'd, and presumably cleaned at the time based on how clean the internals are when i pulled the intake off to inspect it.

Has a double roller chain and steel top gear. Absolutely NO specs on the cam whatsoever, was built for a mudding truck so probably a RV cam grind which would be fine anyways.


Our 1977 midas class C which was almost identical in every aspect would get 12-14MPG under 60mph not towing and 10-13MPG towing another camper behind it at 55MPH or less. It actually seemed to like having the trailer back there i think due to the wind rolling off the RV down across the trailer. the only difference was the 77 had a 400ci stock, and all i did was increase the timing as far as was safe to do, and usually ran premium fuel.


Assuming a mild cam grind with peak TQ ending up somewhere near the hwy cruise speed what do ya'll think I can expect for MPG? I would assume that by having more power than stock, the throttle can be closed more and thereby decrease fuel consumption (if that is even plausible on a 454 lol)

here are my approximate RPM at each given speed on the interstate given some TC slippage

2100RPM @45 mph
2300RPM @50 mph
2500RPM @55 mph
2800RPM @60 mph

and just for the Sh*** and giggles because i wont be sustaining these speeds in a RV except to pass or merge

3000RPM @65 mph
3200RPM @70 mph
3500RPM @75 mph
3700RPM @80 mph

ANNNDDD

4200RPM @90 MPH



Ok now that the #'s are there, If i install a "econo" meter on my dash (a vacuum gauge hooked directly to the carb), From what I have read, once I reach my "crusing" speed the goal is to keep my Vac reading as high numerically as possible without losing momentum, is that correct?

Also at my peak TQ/shift point, the Vac guage will jump up just a little???

If i understand this correctly I will be adding one to the RV to avoid unnecessary fuel use on the highway.


The toad tires will be inflated to 75PSI for minimum rolling resistance.

One more thing, but not until probably next spring, Could i change the ring and pinion for example to 3.73 or 3.4X to lower the RPM once cruising, i know it would cause a little more TC slip in town but in town driving would be maybe 5% as opposed to hwy.

Other than making me a little slower off the line, I dont see how its any different than having an O/D lower my RPM on the highway to save fuel
« Last Edit: May 03, 2016, 03:32:12 PM by MuddiGGEr25 »
1988 V10 Suburban 5.7L TBI/TH350 39K on rebuild 4.10AR GM14FF/GM10SF 235/85R16 & 18.4-16.1

1988 V20 Suburban 6.2L-J/TH400 CA truck, 125K G80 14FF/ GM10 4.10AR GVWR 8,600

1977 Ford Granada ~450HP 302 2bbl/C4 27K original 2.47 215/70R14

Offline zieg85

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Re: 1981 G30 Class C RV potential MPG
« Reply #1 on: May 03, 2016, 06:02:34 PM »
6-8 mpg if you are lucky and keep it 55-60
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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