M-725 common engine swap advice

[Joe Gamma]

A friend has offered to sell me a 725 Ambulance. I plan to use it alot (Flea markets ect) and wonder which would be the most common engine swap for reliability and power. The shock is the back is literally a mint time capsule and all original parts will be saved.

Thanks Guys..

Joe

 

[maddawg308]

My advice, the stock engine is pretty good, if it's running condition I'd keep it for originality's sake. If the stock engine is blown or missing, common replacements include the 350 Chevy, the 318 Dodge, or the 4BT/6BT Cummins diesel. I'd go with the latter myself, but all are decent replacements.

 

[Joe Gamma]

Thanks MIke..I love my Gamma Goat but the M-561 isn't the easyest to work on at times. These sound like things a mechanic (when I help him he only charges double) could do fairly easy and I could do alot myself...

Joe

 

[combat32]

300 ford and chevy straight 6 work too, a chevy 6 would probably be my choice.350 is too much horsepower with a stock drivetrain and 4bt is nice but = more money to swap.I rebuilt the Tornado in my first 715 and would never do it again, just costs too much and not worth it imho, but if you got a runnin Tornado by all means drive it as is,mine was a every day driver for a couple of years, but don't expect more than 45mph, good for me as I only commuted 5 miles each way.The Tornado drinks fuel like a 350 though

 

[DieselBob]

Something like this could be a option. Brand new for a reasonable cost compared rebuilding a tired runner. Not HP so it should be easy on the rest of the drive train and every parts house in the country has everything you could need in the way of parts. Just a thought

GM Goodwrench - 10067353 - New Chevy 350 CID, 5.7L , V8 - Universal Crate Engine, Factory Replacement for 71-85 GM Cars & Trucks

 

[NDT]

I couple of guys around here have swapped in 6.2 diesels (ex CUCV or HMMWV). Goes in as easy as a 350. Top speed would be even worse than a CUCV unless you 4L80E'd it.

 

[m16ty]

I've been planning on a engine swap for a couple of years but the old Tornado just won't die. When it's time to swap I'm planning on going with a GM engine of some sort. I had originally planned on going with a inline six but haven't ruled out a 350. I've got a 3053 deuce trans and divorced 205 waiting to go in also when the time comes.

 

[spicergear]

Anything will fit just take time to decide on transmission as that will dictate your highway rpm's more than anything else.

 

[91W350]

I used a 305 Chevy and it was plenty of power. It was not quite as thirsty as my brother's 350 swap. The 305s are still cheap, everybody wants the bigger brother.

 

[Joe Gamma]

I plan to drive it on roads more than off road and it would have to go 55 fuel economy if it exists would be nice because. Intend to drive it a bit. I guess that means a average priced engine with fair economy and power that won't smoke the drive train..

Any package come to mind?

Joe

 

[spicergear]

305, 327, 350 with later 700R4 and plan to swap out the NP200 for the NP205. Find a 37x13x16 Swamper or Bogger and run stock wheels (...awaiting the lockring nay-sayers...) and you'll prolly be pretty happy with the result. If you're not going to regear and don't want to do a spring over lift, this is larger tire, no clearance issue, upgear via tire, and somewhat down and dirty to making the truck streetable.

700R4's got a bad rap early on but later ones had the issues resolved and proved to be a good tranny. The NP200's can only take so much speed since they were M37 designed at like 40 - 45mph max. 1 in 10 will run cool at the 55 - 60mph and the other 9 will cook the seals and leak oil.

Whatever your V8 preference...just make sure to get some kind of overdrive if you want the truck at stock height. If you're in love with TH350's or TH400's or any 1:1 high gear manual... then do a spring over in the front, rear perch only shackle reversal on the rear packs and 2" tapered block and slap on 42's to make up for the no overdrive difference.

Here's a comparison that was fun in my M715 builds. Stock 5.87's, 3053 overdrive, 37x13x16 Boggers VS 6.72 geared Rockwells, same 3053 trans, 1100x20 (42x11x20) X-tra Grips. Less than 50 rpm difference at speed between these two set ups with that large gear span just because of the increased tire diameter.

 

[bcowanwheels]

I,VE DONE ABOUT ALL THE ENGINE SWAPS YOU CAN DO AND IF IT WAS ME I,D GO THIS OUTE AS ITS THE BEST BANG FOR THE BUCK.
1. 4.56 GEARS
37" TALL TIRES
AND SMALL BLOCK CHEVY, ALL BONE STOCK !!!!!!!
GM Goodwrench - 10067353 - New Chevy 350 CID, 5.7L , V8 - Universal Crate Engine, Factory Replacement for 71-85 GM Cars & Trucks

P/S SPICER GEAR HAS GREAT IDEAS ALSO !!!!!!!

 

[Tanner]

I'll add that the Spicer 3053A 5-speed would be a nice swap with a small-block Chevy, or maybe it's bastard offspring 4.3 Chevy V6 instead - AND note that GM Goodwrench engines give you a 12 month / 12k mile warranty when installed in 'non-cataloged applications', which mean if the chassis is not a GM chassis, you get a Parts Only warranty.

'Tanner'

 

[Tanner]

I couple of guys around here have swapped in 6.2 diesels (ex CUCV or HMMWV). Goes in as easy as a 350. Top speed would be even worse than a CUCV unless you 4L80E'd it.

OR if you use an over-driven 5-speed manual & 38"-40" diameter tires... keep the NP at 2500rpm or less & it'll be fine.

'Tanner'

 

[Wolf.Dose]

Excuse me, the interior of the NP200 was used already with the 6x6 Dodge (WC 61, WC 62) in WWII in the later series. It was originally desigened for some 300 lbsft torque. The M37 Series and the M715 Series were in the range of these torque specs, for transfers usually were designed with a safety factor of 1.5 or higher. Thats why it works (on the limits). Transfer oil should be changed any 6000 mile if you drive longer distances instead short distances which is covered the 12000 miles given in the manual. This is the experiance from some 91200 miles with my M715 since 1982.
Wolf

 

[Joe Gamma]

Whew there is a lot of engines that can fit with the apprpriate tranny..now here is the dark question...oh and thanks guys you are quite the 715/725 community...

I rumble around in my 561 with its standard shift but my friend at eight years old had his left arm paralized on the operating table because of a stroke...is there any automatic trasmission sutibule for the 725...if not well he will take it well but begged me to ask...

Thanks again...

Joe C

 

[Tanner]

The aforementioned slushboxes can be installed behind the Inline 6's/V6's/V8's, but MAY require moving transfer case rearward if engine/transmission combo is long in combined length. Which in turn could require new/modified driveshafts. There has been talk on various forums in regards to using a Mercedes OM617 turbodiesel 5-cylinder engine in conjunction with the Mercedes 4 speed automatic transmission & swapping this into an M37, but it may work on a M715 as an option. You won't get anywhere quickly, but it might be fun.

Regardless of engine/trans combo used, you're going to definitely want to have an over-driven top gear with those stock M715 diff ratios...

'Tanner'

 

[odiegreen]

I swapped in a 350. Novac makes some very nice moter mounts for our trucks. I found a donor rig (89 suburban) and used everything power brakes, steering column, 350,turbo400,208 gear box and drive shafts. I also used chevy one ton axles. My fuel millage is not good 9 mpg, but im running 4.56 gears and 49" swampers. Good luck with the hunt.

 

[Capt Pat]

As you've seen its pretty much what ever your pocket book will take when it comes to swaps on the 725. A friend of mine in Hastings, Mich. has never found an M-725 he wanted to leave stock, even asked me to let him do a swap on one of mine. (like I need a 725 that does in excess of 70 MPH....) His first was a small block that won him a prize from some radio station and he later bought it back, the next one, a "daily driver" has a 454 Chevy and auto transmission and made it from Hasting to Tobyanna in about 12 hours. He never changed the speedometer, and said that the needle went on around to PER on the Miles Per Hour written on the bottom of it... I asked him if he didn't mean PURR.
But it seems its all up to you and your buddies mechanical abilities and what the pocketbook will take. Some of these 'beasties' actually had a plate in the bellhousing that would take the AMC 360 engine or there abouts as is. But I've not seen that swap.

 

[spicergear]

Maybe my next one I'll try a juiced up Goat 3-53 for that dare to be different thing...