725 big block dodge swap?

[loosewrenchcowboy]

my 725 came with nothing forward of the firewall. i have mostof it now, except the spring hangers/mounts(they were torched off ), fenders, and a motor/trans. i have a 413/727 that i would like to use. can someone tell me the length of the original motor/trans-fan to trans output? and i assume a small drive shaft was used between the original trans and np200? i don't think the 413/727 is gonna fit.
thanks

 

[sermis]

If you can't get an answer here go over to www.M715zone.com

 

[gimpyrobb]

Just move the T-case back some. That way you will have equal length driveshafts.

 

[Elwenil]

I'm pretty sure the RB block swap has been done before. It might be tight around the manifolds, but my 318 fit with ease so a big block shouldn't be a huge hassle. Might have to modify the firewall a bit.

 

[sermis]

Barrman is running a 396 w/NV4500. That combo is long.

 

[Barrman]

I have a stock engine/transmission here in my class. The front of the stock water pump to the rear of the stock yoke on the back of the transmission is 59 inches.

My NV4500/396 is about 60 inches if I remember it right. I have the Mini in the class today and can't measure it.

 

[loosewrenchcowboy]

THANKS EVERYBODY! the combo i have is about 64 inches long, so i dont think its gonna fit without moving the t-case. RRRRRRR. nothing is easy, LOL. the manifolds should fit, they point straight down(its a motorhome drivetrain) . case in point: the trans on my m-135 died on me a few years ago, and i needed a dependable auto tranny, so i swapped a 350 chevy/th400 into it. then i needed a 2 speed transfer case. but the gmc axles are reverse rotation requiring an axle swap too. rockwell steer axles front and rear(i dropped one of the rears and lifted it 14 inches too, then added 16x20, that needed custom 6 lug rims). then hydro assist steer in the front. and now all i need is full hydro rear steer, oh boy, LOL. could have bought a house!! may the O.D.G. gods help me i've lost it. lol

 

[Elwenil]

Remember that you can cut a few inches out of the intermediate shaft between the transmission and transfer case to gain a few inches. I would go ahead and swap to a NP205 transfer case while you are at it though. The NP200 is a crappy case for daily use.

 

[loosewrenchcowboy]

Elwenil-whats wrong with the np200? i was planning on swapping one into my m-135(currently using a np205-kinda small, but i had it sitting around-took 4 hrs to install). in regards to the length: water pump to output flange on the 413/727 is about 65 inches. and it looks like the core support to transfer case flange is about 67 inches. i don't think i can shorten it that much, lol. looks like i will have to move the t-case back enough for equal length drive shafts, make a new intermediate shaft, and rework the t-case linkage. doesn't look to hard, but so much for a quick, cheap, easy build. i guess its cheaper than buying and rebuilding a stock motor and trans.

 

[sermis]

NP200 heat at road speed. Under 50mph it is good to go if you can live with the whiiiiine.

 

[OPCOM]

a 413 CID engine should make that truck fly!

 

[Elwenil]

Like Sermis said, the NP200 is an old case that was not designed to cope with todays highway speeds. Prolonged use over 50 MPH has been known to overheat them to the point of cooking all the fluid out of them. A NP205 is a much better case.

On the drivetrain length, just find a 2WD short shaft 727 to mount behind the 413, or better yet, snatch up a 727 and mated NP205 out of a 80s model 3/4 or 1 ton Dodge Ram and swap the tailshaft and housing over into the big block 727 case. Another option would be to use a NP435 4 speed with a 205, but the price of a big block truck bellhousing is steep. I used a Lakewood safety bellhousing and didn't look back.

 

[loosewrenchcowboy]

Elwenil- i measured my motorhome trans(it has the drum parking brake and a flat faced flange output: ie-studs) against a regular 727 2 wheel drive truck/passenger car trans and the motorhome version is about 8 inches shorter. My buddies at the local trans shop said that i have the shortest version 727 that dodge made. i have no idea, but they should. the 727 motorhome trans is 30 inches long, bellhousing to brake drum face. the tailshaft housing is 13 3/4 long. for comparison a th400 fixed yoke trans is 31 inches, bellhousing to center of ujoint flange. i guess i'll have to finish mounting the sheetmetal(core support and wheelwells) before i will know for sure what i need to do. remember, i have no idea where anything goes as this is my first 5/4 and it was bare frame forward of the firewall. i just thought somebody would have done this swap before and have 1st hand knowledge what needed to be done. thanks again for all who have replied. this is by far the most usefull and partcipated site i've ever been on. thanks to everybody!

 

[loosewrenchcowboy]

does anybody have a bad frame that might be interested in selling/cutting off both ends of the front leaf spring perches?

 

[gimpyrobb]

Well, the radiator sits where the Front frame has the diagonal braces. So I would wait till the motor/trans is in to put the sheet metal back on.

 

[Elwenil]

That trans is a short version. Some RVs had it, some didn't. There is one shorter 727 that was put in aircraft tugs with a slant six but they are a bit unusual to find. I agree that you should at least mock up the sheet metal in place to get an idea of what space you have to deal with. The odd core support and the way the firewall wraps around the back of a inline 6 can be a pain to deal with. I had to do a little moving around to get my 318 to fit behind the radiator. If I were to do a big block, I think I'd plan on using a electric pusher fan on the outside of the radiator. It might not look stock but it will gain you a few inches.

 

[loosewrenchcowboy]

well good things come to those that wait. case in point-i just scored a 4bt turbo. after i scrapped out the machine it was in my total cost was less than $300. now for a tranny adapter/trans, starter, power steering bracket/pump. anybody know the difference between a 4bt automotive and a 4bt industrial? i hear they have minor differences.

 

[sermis]

Not sure on the 4BT but on other motors, Perkins, Heracles, etc. the injector pump and injectors have to be changed for it to have RPM's for the road.
Make sure you use an overdrive trans or your top speed will ba about 50mph.

 

[Barrman]

Besides what Sermis pointed out, there might be a mount for an air compressor on the front of the engine as well. If you have it, might as well track down a compressor so you have On Board Air.

 

[gun512]

As far as i know the only differnce between the automotive and industrial 4bt was usually the bellhousing they used depending on what type of equipment it was used for. But they have the same mounting points as a 6bt. same block just 2 cyl's shorter.