Which motor to swap in...

[jollygreen6x6]

Alrighty, first off, I know this is for my 5-ton, but this seems to be a more appropriate place to pose my question.
Anyway, I am looking to do a motor swap in my M-54. Right now, it has the Continental R6602 gasser. If you looked in the 5-ton forum, you would know that I am in the process of introducing a 13-speed to my 5-ton, and replacing the old five speed. However, I have just now come across two opportunities. I can buy either a Cummins 250 or a 6-71 Detroit. The Deroit apparently runs good, and the Cummins needs injector lines, but should run. The Cummins is in an old Reo tractor and I can get it for $700. The Detroit is in a GMC cabover tractor that I believe I can get for less than $1000. I would like one of these to replace my 602. Before I make a decision on which one, I need to know several things.
1. What is the displacement of each engine? I think the Cummins is 855 ci?
2. What is the average torque for each engine? The horsepower for the 250 should be around (ta-da) 250, and the Detroit says 229 in the cab.
3. What is relative fuel economy for each engine?
4. Finally, which motor would be best for the truck in your personal opinion? It will be in my M-54 mated to an Eaton-Fuller 13 speed, and the truck would, in the future, have have a wrecker boom/crane, a snowplow in winter, and most likely be used to haul whatever crap out of whatever field/swamp/river/mudhole/gravel pit/etc I need.
They would both have their advantages. The 250 WILL fit in that some 5-tons had them, and the 6-71's revving capability would be fun with the low gears. I am already biased towards the 6-71 because my Grandpa worked for Detroit Diesel for 47 years. But seriously, what do you guys think?
6-71?
250?
Leave the 602 where it is?
Come on... Y'all er smart... do some thinkin'(It's good for ya...)

 

[Desert Rat]

Chuck,
Having driven and turned wrenches on both, I'd go with the 250 for several practical reasons. First is parts by far. Any International, Freightliner, Kenworth or other truck shop will have those parts in stock most anywhere in the country. Second those cussed Detroits leak like a stuck pig. It's difficult in certain areas of the heads and pan to see if you have a serious problem or not. Cummins are tight engines. I had an '88 3406 with a 13 over that would out run most anything, especially the tire caps. I also had an '87 with a Cummins 350 with a 13 over that was a tight driveline. I put almost 1 million miles on the '88. I also had a '94 with the same 3406 and 13 over. Loved it. Mom had two Detroits in her fleet and neither were worth scrap metal value. Every six months or so they were in the shop being worked on for something pricey. I looked at her experience and stayed away from Detriots. I understand sentimental value. However, to me it's not worth anything if it's a junk motor. The world I came from (trucking) Owner / Operators would stay away from the Detroits because they were not reliable power. I know the 6-71s leaked horribly. Beyond that I don't know. I'd buy a Cummins before a 6-71 for the reason I know I can trust a Cummins to do what I want it to and parts are plentiful and cheap. I can major a Cummins for much less than I can buy a used Detriot (including labor).

I hope this helps.

 

[Recovry4x4]

If you go with the cummins don't forget to factor in the length. The 800 series which have the NHC-250 have longer front sheet metal to accomodate the length. FYI!

 

[Desert Rat]

That's true. I forgot that.

 

[jollygreen6x6]

How about driving experience from a 6-71? As can be guessed, this is not a long-distance hauler nor is it going to be much of a road truck. It's main job is to go into some mudhole, drag something out, and take it somewhere simply because it's already attached. That's why I'm curious. I can guess from reading that the Cummins wins hands-down in a road truck, but I'm looking at off-highway useability.

 

[Desert Rat]

My vote goes to Cummins again. They make a very reliable motor for any application.

 

[ken]

As far as displacement goes 6-71 stands for 6 cylinder, 71 cubic inch displacement. So a 6-71 is 426 cubic inches. The 2 stroke DD is going to rap out much faster than the cummalong. (more deiseribale when busting mud holes) Now only being a 426 CID doesen't count because it's a 2 stroke =852cid in a 4 stroke. In my opinion the cumy will outlast the DD by far. But if you're only using the truck for a toy you proballly won't be putting a lot of hours on it. If the DD doesen't leak oil then one of two things are wrong. The oil pump quit, or it's out of oil. (helps a lot fighting rust) I've ran a few 6-71's in firetrucks and stationary pumps. Bieing 2 strokes they are more simplistic than the cummy. But my decision maker would be, Witch one is lighter? My m35 has seen it's fair share of mud holes. And it goes down like a rock in a lake. The m54 has a pound or two on the m35 so keeping the front axle up is a big factor. Let us know what you decide. BTW the DD uses the same oil and fuel filters as the multi-fuels. That's why our filters are so common. Good luck!!!

 

[lacoda56]

I'm no Detroit fan, but one thing in its favor in this application would be the 13 speed. You can't lug a detroit as you'd need to do with the 5 speed, so I guess it comes down to personal preference. Just my two cents worth.

 

[Recovry4x4]

Brief instructions on driving any truck with a 2 stroke Detroit.
1) Open door
2) Put hand in door jamb
3) Slam door on hand

You are now ready to drive your Detroit powered machine. As long as you drive it like ya stole it and run it everywhere WOT, it will perform. In the right hand they can be made to make gobs of horsepower. Warning though, they are stinky and LOUD!

 

[Desert Rat]

Kenny,
Once again you're on the bullseye! Eloquent way of putting it!

 

[cranetruck]

Would that be your right hand or your left hand...Sir!

 

[jollygreen6x6]

Alright. Information is sufficient. Both motors can do what I need. By the way, it's a Cummins 220, not 250. It will probably come down to which truck costs more. By the way, does anyone know about the torque capabilities of a 6-71? I assume it's not very high because it's two stroke.

 

[ken]

The toruqe #'s depend on the Hp rating. You can crank up the fuel rate on these engines for more power.
If i rember right the 229 hp setting gives you 475 Ftlbs at 1900rpm's. But i'm not 100% sure it's been 5 years since we had a 6-71.

 

[Trango]

You guys should be figuring in the length of your trannies when contemplating engine swaps, BTW. The deuce tranny is VERY short, and from what I have heard, it's all too easy to kill that tranny with a little bumped up power - I've heard of sheared Woodruff keys as well as destroyed bearings.

Also, I'd advise to choose something with AT LEAST a .75 OD, otherwise you're right back to where you started - which is, running out of gear on the flats. This holds even for 11x20 tires.

Not to say that I'm anything of an authority on this or anything.... but if you do the math, you'll want to get closer to that golden 2000 RPM cruising speed... which you'll find ever more impossible to do with anything but the lowest OD's available.

Bob

 

[jollygreen6x6]

Turning up fuel on a Detroit... What kind of power gains could I hope to expect from this situation? Also, could someone give me a general torque comparison between a Cummins 220 and a 6-71?
Also, someone told me that a 6-71's peak RPM was like 1700. I know this is crap, but what kind of rev's would I be looking at with this motor?

 

[JasonS]

From a 1971 motors manual:

plain 6-71 has 219 HP at 2100 and 574ftlb at 1600 no load governed speed is 2150

the 6-71T (turbo?) has 236 HP at 2100 and 630ftlb.

I've read that it is dangerous to go above 250HP because you can't get the heat out. No experience, though.



Assuming that you have a NH-220:

naturally aspirated 743 cu in, 220 HP at 2100.



If it were me, I'd get a cummins n14 from a cabover semi. Around here that would cost ~$1200. Parts are common and relatively cheap.

 

[Elwenil]

According to : http://www.adieselengine.com/

The 6-71 Detroit is 238 HP and a rated RPM of 2100. It also weighs 2200 lbs.

The Cummins 220, I think is a NH-220. Appearently it's an old engine, and info is hard to find. I found one bit of info that its 150HP at 1800 RPM and it's a 4 cyl engine. This may or may not be the engine you are looking at, but it was a common engine in agricultural vehicles and marine applications as well as gensets. I would think the RPM range and output would not be suitable for a large truck if this is indeed a NH-220. That's about all I can find...

 

[Trango]

Ok! So look, guys, you have these engines that can't even hit a stock LDT redline. If you intend to have any speed at all with these things, you have to look for something that has at least 2500 redline.

I'm totally not trying to preach, but the limited top speed was such a downer for me. I couldn't imagine having all that horsepower but not be able to go over 55.

Bob

 

[jollygreen6x6]

The Cummins 220 is turbocharged. I was told it was an I-6, but I may be wrong. I haven't actually looked at the Cummins.The more you guy's talk, the more I want the 6-71. I know either motor will be better than the 602, but, like I said, the deciding factor will probably be the price of the trucks. I can get the Cummins in an old Reo for $700, and I am unsure about the Detroit. I hope it's about the same or lower, because if it's much higher, I will have to drop hopes of the Detroit.

 

[red devils dude]

give your locel big rig transmission dealer a call they can get used and remanufactured transmission's for anything
with just about any ratio you want may be a lot of money or it may not.