Toying with idea of replacing 318 poly, that needs replacing, like idea of putting in a mild slant 6, but, but, but, it's a dump truck, but want to convert it to a wrecker, it's a 1961 d300, has granny 4 speed, and geared low. Was thinking the 6 would be a great motor for mileage, especially with all idle time, but am I'm I expecting too much? The hiway and interstates may be pushing limits? Opinions?

Welcome here!

Using a slant for a wrecker on today's roads, I'd think would depend on your expectations.
I don't think it would be an ideal choice for a working wrecker frequently found on the interstate. I'd be looking for more cubes, or a diesel swap.
For infrequent trips at 55 or less, or as a personal tool, it may be OK. It's not going to be able to keep up with the big dogs, but with patience, should be able to do the job.

CJ

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Part of Tyrde-Browne Racing

Semi afraid of that, approx 10 major hiways / interstates within 30 mins, 5 are within 10 miles. I know would warm the slant 6 up, but mildly, water/methanol injection to keep hard running in check so no possibility of detonation, but want extremely reliable, great gas mileage, I'm not a fan of any diesel. I thought mild cam, 4bbl using Holley Economaster, vintage carb, shaved head, header, I built many engines for mileage, but nothing like this project.

Chrysler built 6 ton dump trucks in the 60s powered by the slant six, but they got away with it by using four speed transmissions, two speed rear axles, and a top speed of around 50 MPH. As already stated, if you intend to use this truck on modern roads and actually haul things with it, you are better off getting a more powerful engine that can keep up with traffic with lower driveline gearing.

I'd say probably yes. Once you start talking Heavy wrecker and low gearing and warmed over slant 6, you are not going to get any kind of great mileage. Maybe in a D100 ( which I have) yes you can get really decent mileage and have a nice running truck, But adding a bunch of weight and low gears hurts everything.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I understand. I owned a few wood trucks,plus 2 roll backs long ago, plus drove a rollback for few years, never saw over 10 mpg 6-8mpg with small blocks, big blocks, even a 78 Dodge with 318, was wondering if could push closer to 12mpg? Plus idle savings? I was guessing running at least 1k miles a week, if save 2-4 mpg, with price of gas, could be big savings? Plus only behing seat tank, my old 60 Ford had behind seat tank, barely got 120 miles per tank, I know aux tank probably will be necessary? But not ran tows I. Over decade, but now want to get back into it, plus hate my job. Lol

I own truck, also have 3 wrecker boom assemblies, but will need to pull dump bed off. Already has PTO, so could use hydraulic winch, or go electric. But will need engine, plus minor fixing up. I tried to upload pic, said my Pic is too large, no idea how to down size Pic.

I am a slant-six-guy,
But I would definitely rebuild and keep the 318 Poly, those are really cool motors.
And if I could not do that get a modern Hemi out of a Dodge truck. Conversation kits to carburate those are available.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

After having several 318 poly motors in my life, not a big fan of, too hard to get parts for, so if need simple seal or gasket. Maybe get lucky, or wait several days to get, or maybe have to order online, so definitely want engine I can find most parts for easily, not researched newer Hemis, but I'm very old school, so simple, basic, but total reliable, plus mileage

'too hard to get parts for,'

you do realize that slants have not been sold in vehicles for over 30 years.

Any serious slant guy is going to keep a stash of head gaskets, water / oil pumps and gaskets / ignition and fuel system parts within arms reach.
As the truck you are working with has some age, it seems that it would be wise for you to do the same with brake and steering and suspension parts.
Having a set of Poly parts and gaskets tucked away under the work bench may simplify your life.

If you are serious about needing good fuel milage and reliability in a vehicle that will weigh north of 5000 lbs empty, a Cummins 6B would be a much better solution than a slant.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Why? I have traveled in over half the US by Harley, wouldn't hesitate to go anywhere, whether my 1973, 1961, or 1942, only have few minor spare parts, can get anything within 1 week. Yes I'm a qualified mechanic, built those bikes from scratch, I plan to go over truck. But not worried on age of engine, no interest in diesel, figure cost of ownership, mileage, repairs, per every 10k miles, gas will always be close, and 1 major diesel repair, it loses, versus a rebuilt gas engine, especially since I can do all repairs myself. Even use friends machine shop for boring, balancing crank, valve work, or even simple rebuilding heads

I like the slant. But if you want a ruggedly reliable engine with decent fuel economy and the ability to propel a tow truck then the cummins 12/24 valve swap is a much better choice. It will get you better fuel efficiency AND ability to pull when needed. The slant will likely be cheaper (but then again so would a more modern 5.2/5.9 magnum swap) compared to a the diesel swap, but you would get much less out of it.

Well, we're back to square one. The slant will move the truck, and with expectations set, you can pull quite a load. Perhaps not at "freeway" speeds.
I have a buddy that has a 1946 International wrecker. It's got a five speed with a splitter rotated by a 586 CI Six. Nasty torque monster. He tops out in the mid-single digit mpg. I think the governor pops in around 3k. He does not take it out on the freeway. It's a private use type of wrecker. It's got the market cornered on cool though! I don't think he would want to insure it for commercial use, like his dump truck. He doesn't carry those on his Over-the-road business. He has them on his farm account IIRC. He scored his 4700 dump from a GC that got tired of carrying insurance on it, and it was a bunch newer. 80's? Those all look the same to me.

CJ

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Part of Tyrde-Browne Racing

Can't beat the Slant for simplicity and it seems you really want to try it, so why the heck not. I'd get the AEM water/meth injection kit to stave off any preignition under heavy load. Don't expect to tow at high speed. We can help you build a good torque motor.

Are you good with pump premium gas, or will you require running on 87 octane?

Lou

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