I have a 1982 Ford E350 Based Motorhome with carburated 460 engine. The Motorhome weighs just under 12,000 pounds fully loaded. It has a C6 automatic with a GearVendors Overdrive (22%) and 3.54:1 rear. It turn about 2,200 rpm cruising at 65 mph. It has the full complement of power accessories including power steering and A/C. I'm running an Edelbrock 1411 carb and a 2166 manifold with appropriate lack of EGR. My primary concern is fuel economy and reliable operation. The engine has 52,000 original miles on it. The torque converter is stock (~ 1700 rpm stall) and the cooling system is in good shape with a recent radiator recoring. Engine and cam are stock for 1982. Runs regular gas. Lots of it. Currently runs 8-10 mpg cruising. Future use includes significant mountain driving.

My question: What is the optimal distributor advance curve, initial timing and total advance for fuel economy with this engine? I intend to recurve the stock Duraspark distributor. Should I change the stock vacuum advance can to one with more or less vacuum advance?

Thanks for any help and insight.

 

Re in"Car"nation High Performance - Home

I have just received my dissy from Scott - great service and a very knowledgeable guy.

Hope this helps
Kiwi

 

First off 8-10 mpg with a motor home is great. My 1984 F250, 460, C6 and 4.10 gears gets 10 mpg empty and thats with a reworked Holley 1850 and a recurved distributor. It used to get 7.5 mpg before I massaged the combo.

Advance curve, Total mechanical advance should be no more than 38° and with a rig as heavy as yours, 36° would be safer. The mechanical timing should be in by about 3500. In my opinion you have to much rear gear, especially with an O/D. The engine pulls peak torque around 2600 rpm and is where best mpg is achieved.

 

Kiwi, Bear,

Thanks for your comments. It was certainly my intention to have Reincarnation recurve the distributor, but I was looking for some opinions upon which to base my request.

I agree that the gearing may be too high. For the record, at 2,200 rpm, I'm at 63.5 mph in OD and 50 mph in regular 3rd. At 2,600 rpm, the numbers are 75 mph in OD and 58.5 mph in std. A 75 mph cruising speed would be fine for over the road time, but probably bad for fuel economy pushing a brick/sail through the air. The machine was clearly built and geared for 60 mph high mileage efficiency cruise.

I've never found a BSFC (Brake specific fuel consumption) curve for the carburated 460 in stock tune, so I don't have a feeling for how peaked the torque curve is or how sharply the fuel efficiency varies. When I have this thing completed, I'll do some consumption runs looking at cruising load vs. road speed.

 

In my world you never tow in OD (toting around 12,000 pounds is just the same as towing) and my truck is rated to tow 12,000 pounds, but that is because of the 4.10 gears, air bags in the rear to compliment the 1 ton rear end and springs in the truck. But I just don't see how, even with just the 3.54 that your rig is rated for the 12,000 pound it weights, not even counting the OD which would lower the numbers. Lugging the engine is a sure way to break something. I have a 1999 Ranger and it is rated to tow 6,000 pounds but not in OD, but just in high gear, oh and it has a 3.55 rear end.

Recurving a distributor is child's play. I've done several and did the one in the 460. Getting the springs right for the correct curve is the hard part and that just means taking it apart and adjusting several times. Paying someone to do it is a waste of money.

As to fuel efficiency, with my truck at 2700 rpm you are running 57 mph and unloaded I get 9 to 10 mpg. But bump the throttle to get 60 mph and you down to 7 or 8 mpg and 65 mph gets you a whopping 6 mpg. Being retired I don't travel weekends (Friday and Monday included) and never drive over 58 mph. Putting my dual axle flatbed with 4 to 6 quads on it changes nothing. Load the camper and even at 55 mph all you get is 7.5 mpg max.