i need more power

[W_A_Watson_II]

i'll post pictures when it's done, hopefully by spring time!

Great looking forward to it. Packaging the cylinder between the differential carrier and the wheel when the drag ling is behind the axle was the challenge. When I was looking at it with a supplier, the only room was hang it down below the axle but we all know how that would survive.

[JimC]

An old post, but interesting.
I swapped a 318 into my 37 back around 1968-69.
It was a simple swap. Took about 3 days. I used a slant six bell housing and the longer transmission pilot shaft and housing from a D200. I had to relocate one transmission bolt hole in the bell housing. I used a Plymouth brake master cylinder to drive the hydraulic clutch. Mounted it backwards just outboard of the stock 37 brake cylinder so the reservoir could be filled through the stock hole in the floorboard.

Mileage increased from 11 to 13 mpg. It had substantially more umpphh than the stock six, but was still somewhat anemic. So about 1971-72, I replaced it with a big block Chevy and an SM465 transmission. That gave me adequate torque and power, but the fuel consumption dropped back to 11 mpg. Radiator remained in the stock location and cooling was sufficient.

[Vaughn2]

If your concerned about MPG, going to a V8 is going to drop MPG and if you do go with a V8, go with a 2-barrel carb, a cam for fuel efficiency helps. Changing gearing to 4.30 R&P gears or a 5 speed OD trans is best, lower engine RPM. Ray's Helitool kits for the engine swap/hanging pedals are no longer available, only Vintage Power Wagons sells the kit for the engine and hanging pedal installation. You can go with a hydraulic clutch or hydraulic throw-out bearing which I installed in my power-wagon, works good. The more power is nice and worth the conversion, and two more cylinders does suck the gas. Here is a link to my conversion so you can get an idea of what to expect. Go to page 352 and scroll through it. [https://www.dodgepowerwagon.com/pw/pw_pif.pdf]

[JimC]

"If your concerned about MPG, going to a V8 is going to drop MPG"

I did not find that to be the case.
I retained the 5.83 differentials.
When I installed a 318, mileage increased from 11 to 13 mpg.
When I switched from the 318 to a big block Chevy, mileage dropped back to the original 11 mpg.

As an aside, I did not switch to hanging pedals. I kept the original pedals for both the 318 and big block Chevy installations.

Vaughn, what engine did you install?

[Vaughn2]

It's a 1965 SBC 327, 300HP Corvette with double hump heads, 500CFM Edelbrock carb, matted to a Muncie SM420 4 speed heavy duty truck transmission. I guess unless you plan for more MPG in a conversion it becomes a hit and miss on mileage. Driving a Power-Wagon or M37 one can’t be too concerned about mileage but there are things we can do when converting to try and get the best mileage we can, if that is one of the conversion objectives. The best mileage is from a 4BT Cummins with 4.89 gears which can give around 24MPG on the road, but power will be less and most who have made this conversion have experienced heating problems climbing grades.

Since the Military NP420 mounting ears are different than the civilian NP420, when installing a 318, one will need to look for a civilian trans. from a civilian truck if you want to stay with an NP420.

[JimC]

When I installed the 318, I used a slant six bellhousing and the original mlitary transmission by relocating and tapping one hole in the bellhousing. I swapped in a a longer civilian pilot shaft and housing from a D200 to fit the bellhousing. This was almost 60 years ago, before the days of installation kits. I don't recall any particular difficulty in the installation. From memory it took about three days. The 318 was a big improvement over the 230, but still somewhat anemic.

When I switched to the big block a year or two later, I also swapped in a GMC SM465 transmission, keeping the PTO in the original position so I could continue to power the Braden LU-4 winch with it. The Chevy gave me 375 hp and a lot more rpm capability than the 318. I was running a Detroit Automotive KS-22 No Spin differential in the rear and Warn M13 lockouts in the front.

When I get through refurbing the 708, I need to redo the 37 once again. I think I'll go with a 454 or 502 this time (and yes, it does have dual headlights). Should I retain the white color, or go back to 24087?

37.jpg (99.54 KiB) Viewed 17606 times

[Vaughn2]

I didn't realize a 225 slant six bellhousing bolted to a 318, and would allow the use of the Military NP420 by drilling one hole, good to know! I've thought about switching to an SM465, part availability is better and PTO's are easier to find. I need to find a PTO for the SM420 that's bi-directional for the front winch, but haven't been looking to hard. In using your stock pedals, did you retain the original brake master cylinder or go to something else? My 327 has a lot of punch, but I keep it easy since I have the off-set pumpkin in the rear, and long axle shaft. Going to the really big engines, go for a sleeper, keep the original patina, and give the kids a thrill ha, ha! Thanks Jim!

[JimC]

You also have to replace the short pilot shaft and shaft housing in the NP420 with the longer one from a D200. Keep in mind that I'm remembering stuff that I did almost 60 years ago, so it isn't as fresh in my mind as I would wish. I think I also had to machine a cylindrical 'bushing' to space the base diameter of the pilot shaft housing out to the size of the hole in the particular slant six bell housing I was using - but don't hold me to that.
I retained the stock brake master cylinder in stock location and mounted a Plymouth brake master cylinder adjacent to and outboard of it to use as a master cylinder for the hydraulic clutch. Slave cylinder mounted to the passenger side of the bellhousing. I could fill both master cylinders from the stock access cover in the floorboard. I reversed the throw of the stock clutch pedal by adding an extension roughly maybe about 4 to 8 inches long to the bottom of it below the hinge pivot. I don't remember if I clamped the extension to the pedal, or welded it. Welded, I think.
It was all an easy, reversible installation, but the 318 was a bit anemic - though much perkier than the 230. If I were to go the MoPar route again, I'd probably use a Magnum 360. However, I've been much more satisfied with the big block Chevy and SM465. A 454 has adequate but not outstanding low rpm torque (I'm currently running a 375 hp 396 - less idle torque, but outstanding at high rpm). I positioned the engine and transmission so the PTO shaft remained in the stock location and cocked the engine about the crankshaft axis slightly so that with a bit of pounding on the side of the oilpan with a big hammer, the pan cleared both the front pumpkin and the crankshaft. I've been very happy with that installation for a long time now. I cut the SM465 gear shift lever off short and ground a groove in it laterally so I could bolt on and continue to use the stock M37 gear shift lever for looks.

[JimC]

Google tells me that a 1962 slant six manual bellhousing off a 1962 crew cab W200 will NOT fit a 318 of similar vintage, so either my memory of using one has failed me, or I lucked out. Wish I had taken a photograph.

Edit- My manual shift donor bellhousing was off my 1962 Air Force Slant Six W200 Crew Cab.
Very rare and low starter location similar or identical to the one in this photo.
I converted the clutch linkage to hydraulic.
It and the 318 went back into the W200 Crew Cab when I converted the 37 to the Chevy engine.

Screenshot_20250809-160853_Samsung Internet.jpg (113.35 KiB) Viewed 17565 times

[Cal_Gary]

My memory isn't as great as my younger years either-that is why I keep a journal of all my M37 purchases and activity. Trying to convert my scribbling to a thumb drive right now takes a great amount of time since I got my M37 early in 2004. The journal has saved me a few times since I included parts numbers, etc. when I needed to reference my earlier work.
Gary

[JimC]

My clients tell me that my memory is still working. I hope it is and was happy to find that Google was wrong about the slant six bellhousing.

I got my 37 on May 28, 1962. It was my first vehicle, and my foster brother gave it to me on my 20th birthday. It was my daily driver for several years. I got my 708 ten years later.

[Vaughn2]

All great information that will help other members make choices as which way they may want to go upgrading the engine in an M37. Thanks Jim and others!

[DCook]

I have an M43 chassis with a 318 mounted in it. It was apparently driven into the shop when the body was removed. Its in Durango Colorado if someone is interested in it?

[Cal_Gary]

That shouldn't be hard to move to a new owner Dana-how about a picture?
Gary