The Stovebolt Site Forums The Shop Area The HiPo Shop Engine swap for 1942 3/4 ton, suggestions wanted

I and looking for suggestions on a posible swap on my 42 Chev 3/4 ton. I have several ideas in mind and would like some input from those who have gone before.
The first is to drop a newer engine from a 54, the second is to drop in a 6 or 8 cylinder and change the 4 speed crash box. Another is to drop in a 4 cylinder Toyota diesel, and the final idea is to get a running chassis from a Toyota and drop the cab in to it. So as you see, I have several ideas and would like an idea as to what you all thought would be the most viable plan.

What you want to do first is figure out what you want from the truck, or what you want to be able to do with the truck.

I wanted an almost completely stock ’41. I like that because people look at it, ride or drive it and are either reminded of their childhood or educated a little on how far we have come with trucks in 70 years. I also like driving slower on county roads.

Almost stock to me is.

A ’53 powerglide engine because it is more dependable, but looks stock to all but a few.

A 12 volt electrical system because 6 volt parts are hard to get while on the road

A 3.38 rear gear because 42 MPH is just not quite enough.

Skinny radial tires because the look close to stock, but ride softer and don’t tend to shake the truck apart

Well I enjoy driving the truck and want a more daily driver. Up till now the stock engine has been fine, but has developed a noise in the bottom end. So I want to retain the original feel of the truck, and as you point out, 42mph is not enough. The other thing I'm looking at is price of fuel. At 1.05 a litre, or about 4bucks a gallon, it's getting more expensive to roll an inefficient engine daily.
Many of you have updated or rodded, so where better to pose the question.

A chevy 261 would be top on my list. Use the 42 bellhousing and mate a t5 transmission to that combo using an adapter. Plenty of power and fuel economy can be had. The 42 3/4 ton has a modified 1/2 ton rear. the lower gears can be swappped to 3.38 or 3.90.

In my 1940 3/4 ton gmc, I used a 302 gmc 6 cylinder with a dodge NV4500 5 speed, and a full floating 9 inch rear. I will have disc brakes front and rear, and retain the stock wheels and lug pattern.

What would be acceptable fuel economy the way you want to use the truck?

The Toyota swap is not something I've seen done so I don't have a feel for how well it would work. I was not even aware of the Toyota Diesel so that should give you an idea how helpful I could be there....

I think short of a modern EFI motor and overdrive you'll have difficulty beating 20 mpg is regular usage running gasoline.

However in my area Diesel was more expensive than gasoline last time I looked. Only if you get quite a bit better mileage without giving up something else you want does it pencil out as a better option.

The last time I penciled it (Excel worksheet) out a Diesel swap would cost enough more than my preferred gas motor that it would take 20 years before Diesel really saved me any money. That was based on my expected usage, if you are going to drive a lot more miles each year than I do, your payoff could be a lot faster.

You can accomplish what you want with what you have, or similar to, but it takes a lot of time, learning and patience.

As stated previously, be on the lookout for a 261. I've had my ears open for a couple of years and come up empty, but I live in a relatively small area. A 235 would do it too, although with a little less torque due to shorter stroke.

Get a T-5 behind it if you're not using it for heavy work, or if you are using it for work go with a SM420 or SM465 with a Gear Vendors overdrive or a Ranger overdrive.

Gear the rearend so that your're cruising about 1500-1800 rpm at your chosen freeway speed. There are many calculators available online. Remember to include your overdrive percentage.

That's all the easy stuff, mostly bolt-in. All of it commonly available.

Next is to super-tune the engine. That doesn't have to mean build a racer. The purpose is to get the fuel and timing curves where they need to be. Even a simple 1 barrel carb like a Rochester B can become somewhat complicated until you learn all its circuits and total operation. I've found B's to run very rich as delivered. This can be addressed, and fuel economy greatly improved, but there is always a tradeoff when working with a carb. As a mechanical device it is functional, but certainly not ideal. Being as how it operates off of vacuum, the more vacuum it sees, the more fuel it feeds. At the point where it needs the most fuel, it has least vacuum, and has to supply enough at that point. By that nature, they tend to feed too much fuel the rest of the time.

Electronic fuel injection, on the other hand, when functioning properly, supplies fuel based on vacuum, temperature, ignition timing, and throttle position for much more precise metering. It may not look like an original carb, (this is the HiPo shop, right?) but works infinitely more precisely.

That said, I'm pulling avg 20 mpg out of my 55 2nd 3100, 235, SM420 and 3.55 gears with 30" tall tires. I'd like a Ranger overdrive unit, but can't pull the funds at this time. I cruise down the highway at 2400 rpm, just about the top of my torque band, at about 63 mph. There isn't an orifice in my carb that hasn't been massaged. I'm also willing to accept (for now) that under very heavy load it is too lean. These carbs don't have a power valve, so whatever it is jetted at is how much fuel it gets.

There was a build on here about a year ago by drummin52, putting fuel injection on a 235. He did it all with junkyard parts if I remember right.

In the end, if you stay with a 6, you'll generally have an original look, but never a great power house. If you want gobs of torque, stick a Duramax in it.

Devin

well i am going with a 250 from a 1980 van with a 350 turbo to back the engine think that will give you good power band and highway speeds while keeping the flavor somewhat stock

I thank you all for your help. I need to do some more thinking on this and figure out what is available in my area. If any of you have links to information on your suggestions and how to go about the changes, I would appreciate it. I know if I go to a newer engine, I'll have to change mounts, maybe the rad or location of it, etc. I do use the truck to haul stuff around, just as a truck should, but for the most part, just to drive and enjoy. Thanks again

the 261 will bolt in just like the stock 216. There might be a water pump issue that needs to be resolved, but there is a kit for it. I think the main problem is relocating the water pump to center the fan in the radiator.