Although almost everyone in the motorhome market is tremendously attracted to diesel power, before launching into a diesel repower, it may not be a bad idea to ask yourself why. There are advantages to both types of power, diesel, and gas. Let's compare the advantages of each: Gas:
- Lower capital expense
- Greater Availability
- Greater, Less Expensive Service Accessibility
- Greater, Less Expensive Parts Accessibility
- Greater User Servicability
- Wider power band - Fewer gear ratios required
- Will contend with lower final gearing
- Less Noise and Pollution
- Better Efficiency
- Less Expensive Fuel
- Longer lasting between overhauls
The greater expenses involved with diesel power are ironed out over higher mileages, but if you plan on less than 2-3,000 miles/yr of use from your new conversion, it may pay to consider gas power. Furthermore, if you're planning on chucking the 4 or 5-speed Spicer manual gearbox, remember that its 5th is an overdrive gear. So, if you replace it with an automatic of some type (Allison preferred, but the HD light truck automatics seem to handle the job), you'll need to re-gear the rear axle if you can't find a relatively rare OD transmission. So, while shopping around for a new power combo, look at both possibilities - you may end up choosing gas!
Finding New Power
The choices are buying a new "crate" engine and transmission from the dealer, finding a "rebuildable" or "good condition" combination from a wrecking yard, or buying and do-it-yourself wrecking a suitable donor. The latter can be a wrecked larger motorhome, a medium truck, or a school bus. The last choice is a good one, since school districts often dispose of school buses in astonishingly good condition for equally astonishingly low prices. In any of these DIY wrecking situations, there will be a multitude of parts you can use as well as the engine and transmission. If you have the space, this is the best choice by far, in this writer's opinion. However you chose to do it, here is a listing of gas engines up to 1980 - this data is hardly up-to-date, but gas engine technology having changed little for this type of engine, can still be helpful. (An exception is efi - Electronic Fuel Injection. A tremendous advantage, fi you can find it, get it!) Look also for heavy-duty automatic transmissions attached, such as the HD Chrysler Torqflyte often found behind bigblocks such as the 440 in Motorhome apps, the GMC Turbo- Hydramatic (400 Turbo), and the HD Ford C3 in HD pickups and up to 2-ton light trucks. Look also for Allison Transmissions, which will have an SAE1 or SAE2 Bolt pattern, for which adapters can be had for the major gas bigblocks. Schoolbusses will be found almost exclusively to be using Allisons, if they're automatic at all. This older list includes only carbureted engines, efi (electronic fuel injection) is a great improvement which should be considered carefully for the extra efficiency involved. The main thing to remember is that you want a "Big Block" or at least "Truck Application" engine. Higher-revving but lower torque car engines can look better on the HP charts, but don't really make the grade (literally!) on the long pulls for which truck app engines are designed.
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