Last year I purchased a 1982 Ford E350 24' Born Free Motorhome with 45,000 miles. The previous owner had added a Gear Vendors Overdrive to the C6 automatic. At that point the rear had the stock 3.73:1 gears. Within a year, he re-geared to a Dana 70 with 4.56:1 gears. Frankly, with the stock Motorcraft carb and full smog system, it ran poorly and often stopped on hot days on busy inclines with vapor lock. The fuel economy ranged from 6-8 mpg.
For some time I searched the web as well as this site and the 460Ford site for any and all information about the horsepower and torque curves. I was also on a hunt for any info on how the increase the fuel efficiency of this powertrain. The Born Free specs indicate that the Motorhome weighs in at 14,000 fully loaded. But neither Ford or the RV manufacturer gives any info about the torque curve or even the engine torque rating.
After studying the forums for advice I made some choices and made a few modifications. I thought I'd post them here under the assumption that others are out there with similar frustrating experiences.
By way of modifications, I replaced the Motorcraft carb and stock cast iron intake with Edelbrock components including the 1411 carburetor (750 cfm as recommended by the Edelbrock engineers) and the 2166 intake manifold, thereby deleting the EGR system. I sent the distributor to Scott at Reclamation for recurving, added a Crane Hi-6S ignition to the Duraspark 2 system, switched to Iridium plugs, added Accel ignition wires, included a fuel pressure regulator and finally added a 3" exhaust from the exhaust manifolds through the muffler and on to the tailpipe. This included the y-pipe connector. I toyed with adding headers and full dual exhausts, but this motorhome holding tank configuration blocks any reasonable exhaust path on the driver's side of the vehicle. I used a Flo-Pro 4115 muffler with 3" inlet and outlet. I did not change the stock cam or the timing gear as access was just too intimidating with the van configuration.
I also added a Compucruise fuel economy gauge, a vacuum gauge and a tachometer. As a final step, I took the package to Superior Automotive in Placentia, CA to DynoTune the result. With the Dyno run (Dynojet Research in ground Chassis Dyno), I was surprised to learn that the air/fuel ratio was dead-on over the full rpm range tested (2,750 to 4,750 rpm). Despite the negative comments on this forum about Edelbrock carbs, I mounted this one box-stock as per the directions, fully expecting to have to rejet on the dyno.
The results: Max Torque was 280 # ft. at 3,450 rpm. Dynojet Chassis horsepower measured was 203 HP at 4,500 rpm, for a net at the flywheel of 286 HP inferred. I won't try to post the curve graphic here, but the numbers follow:
Inspecting the plotted curve, the torque rises linearly from 2750 to the max at 3400. There is a flat plateau from 3400 to 3850, at which point the torque decreases linearly to 4675 rpm. Measurements of engine rpm vs. real road velocity show that the engine torque max occurs at a real road speed of 71 mph in overdrive. This shows that the slippage of the C6 torque converter is just under 10%. Current average fuel economy is 10 mpg. Interestingly, there is a small peak of an additional 10% torque riding on the rising side of the torque curve at 3125 rpm which corresponds to 65 mph road speed.
For the final details, the tires are 8.75-16.5, and dyno measurements were taken at 84 degrees F, 29.93 in-Hg and humidity at 27%.
Should have addressed that. The 1982 E350 Cutaway on which the Motorhome is built does not require a catalytic converter but is subject to smog inspection biannually here in CA. Because of the complexity of the stock (and other) engine installation the visual inspection just verifies that various smog components are present. Then smog certification requires the standard dyno emissions testing. As currently configured and tested here, the engine is cleaner on all measured species than the smog certification test level. In fact, the engine emission is cleaner than the nominal baseline values for the 1982 460. This vehicle was not certified for sale in CA as new. Purchasers of Ford E350 Vans in CA did not have a choice of the 460 engine. This vehicle was certified for sale in Iowa as a 49 state vehicle and legally imported into the Peoples Republic of California in 1983. It was configured as a Dual Fuel (LPG and Gasoline) vehicle and I am returning it to that setup. Now, however, I will use the IMPCO Commander O2 sensor controlled system for better economy and lower emissions than the original version.
In the 70's the cam was retarded on the 460 to meet emissions. It made less emissions, but also less fuel economy and less power.
On a friend's 86 E350 we advanced the cam, if I remember it was 2°. This raised the fuel economy towing his large trailer from 5 to 6 MPG. That's a 20% improvement. The truck was never on a dyno, but it had noticeably more power, too.
Very true. I wanted to at least go to a pre-71 timing gear or even replace the cam with a RV torquer but the access to the engine is a real downer. I had also been told that the stock Ford cam used in the RV designated engines was specced for lower rpm torque. Doesn't appear to be the case though. I've seen 1982 RV brochures that suggest torque levels of 350+ #ft at 2400 rpm! Haven't seen anything like it.