6.2 or 4bt in my application?

[Everhard]

Hi all, new member here, been lurking for a while reading everything on fsj's with diesels and it's where I'd like to go with jeep number 8. Specifically I'm looking for an m715. Given my shop is good for general maintenance but not full on engine swaps etc I'm hoping to find one that already has the swap done. I'm in no rush so I'll just keeping my eyes open for one.
The question is which diesel?
My usage will be as follows:
-Transport for myself to work on those days that snowmageddon is going on and the commuter car ain't gonna cut it. (I'm in the country in the snow belt in Ontario so it's pretty much a guarantee to happen a number of times in the winter)
-tow vehicle - nothing crazy normally not more than 6000-8000lbs.
I'm debating with myself which engine would be better between the 6.2 and the 4bt? At the end of the day would both tow that kind of load the same?
I plan on this being a jeep I keep for a very very long time, I've wanted one for many many years and now in at the point I can make it happen. It won't be a high mileage vehicle either I don't expect to put more than 3-5000 miles a year on it max. I'm not looking to win races just be able to pull a load without the m715 being on its knees trying to pull it. Highway use will most likely be a very very rare occurrence given where I live and where I normally travel.

If anyone has experience with both I'd be curious to hear what they say. I'm not biased towards either, I feel with proper maintenance both would be good long running engines.

Thanks,
Everhard.

[Stuka]

Honestly, if you are towing that much, you will need more than just an engine for the M715. You really want modern axles under it with disc brakes. The stock drums are pretty bad. The stock gearing, even with an over drive transmission, will limit you to about 50mph with a diesel. Having a set of modern 1 ton axles with 4.56's (Rather than 5.89's) will allow you to actually drive on a HWY without redlining the engine.

Either engine could pull that much, it just wont be very fast. But if its not long distance, or high speed, they will do it.

[Pablo]

People are pretty loyal to their engine brands. Some of the replies you get might reflect that.

GM 6.2

I have owned and driven a 6.2 and I have found them adequately reliable, but too slow to tolerate as they come stock. However, there is now a thriving aftermarket in these engines that did not exist when I drove one. Without modifications, this motor will not be able to be tuned up much power-wise. If you modify the internals, you can put a small turbo on it and wake the motor up. If you go this route I would do this, I would not try running with a normally aspirated 6.2, as my experience in a 4x4 Suburban was it was bus-like in acceleration. The later 6.5 version of this motor has more refinements. I believe it is computer infested to a larger degree, if that matters to you.

The 6.2 is easier to get emissions compliant swaps with than with a 4bt, as it was EPA rated for 1/2 tons and the 4bt is rated for 1 tons and up only. I would look into emissions laws in your neck of the woods before proceeding with either swap. The 6.2 is also more refined than a 4bt, but puts out a fair amount of indirect diesel noise itself. I don't think you can get the amount of power and reliability out of a 6.2 that you can with a 4bt for the money spent. From what I remember, the indirect design just won't take the turbo pressures. If you spend enough money, well I suppose anything is possible.

4bt

The 4bt is less refined. It is a bag of hammers, but it can be quieted down a bit if you throw cash at it (liquid filled harmonic balancer, liquid filled engine mounts, turn the RPM up a bit at idle, and if you go nuts balance the motor when rebuilt). Stock, it sounds like an old UPS or FedEx truck, as it was the motor in several of the older models of these trucks.

The 4bt is not overly impressive in stock power output (105-130 HP, torque levels are around 300+ foot pounds). It is very easy to increase power however. All you need is the right inexpensive turbo (comes stock with later 4bts), a charged air cooler if it did not come with one, and manually turning up the fuel pump to get you to an easy 200 HP / 450 foot pounds. Power levels over 250 HP may require dual turbo's, head work, and aftermarket fuel pump work. 300 HP is achievable in a daily driver. I think this motor is tougher all around than the 6.2. Its power peak is a bit lower in the RPM range and its stock power band is a bit narrower (but easy to increase by replacing the governor spring). No question in my mind that it will tow better. It is rated to go in trucks up to 20,000 pounds and several folks on 4bt have them in 8000 pound brick shaped one tons that pull the same amount of weight in the mountains.

Conclusion

You will want to pay serious attention to gear ratios and make sure that at your desired cruising speeds the motors RPM is at or right above the engines torque peak. Failure to get the gears right will make the swap a pig to drive and will make it get poor fuel economy and decrease longevity.

Diesels like to be driven and if you are only driving it 3000-5000 miles a year, you are likely to have fuel system issues (critters in the fuel, fuel gelling, etc). Make sure you stay on top of your fuel or you will be on the side of the road, likely with a plugged fuel filter.

Also note that anything you know about gas automatic transmission strength and longevity does not apply. Experience with a transmission taking absurd power levels behind a big block Ford or Chevy is not indicative of it being able to handle even a stock 4bt. Investigate a candidate transmissions reliability behind the diesel engines you intend to swap with before making an assumption that it will handle the power.

Either one of these motors should work for what you want to do. I would focus on pricing out the complete driveline, fuel, and brake system upgrades for both and then go with the one that makes the most economic sense. At 3000 to 5000 miles per year, I doubt you will ever wear out a healthy example of either one. Of course, for mileage that low, it may make more sense to stick with a vortec swap, as the money saved will likely buy more fuel than you will use with the thirstier Vortec over the vehicles life.

I would spend lots of time reading on 4btswaps dot com (they have a 6.2 section) and make sure you want to go down this road.

[Fleg]

The 6.2 that I had in my CUCV was a dog of a engine.

[Mr. Goatman]

Given your end usage desires I think the best (and economical) way to go would be a 6BT. Get the whole drivetrain and the axles from a Dodge truck. It will be much more enjoyable to drive highway speed with the OD tranny and the matching axles. It will be much easier to stop with the newer brakes. The engine will pull per your requirements. There are tons of available parts and aftermarket support is second to none. I currently have an Isuzu 4Bd/47RH and a 6.2/700R project in the works. I can tell you that for the money I have tied up in them, I wish I'd gone with the Cummins 5.9 (12v with 47rh)

[Gumby]

Look for a 6by from a more modern rig and take the entire thing, frame and all. Then drop the 715 on it.

[Everhard]

Thanks guys for all the replies, lots of good info. Yes, definitely will be making sure I have strong axles and disk brakes. I'm big on being able to stop. My personal preference is a manual tranny. Most (but not all) of my jeeps have been manuals, the only Jeeps I've had any problems with have had automatics!
I think I need to see if I can find a couple old running trucks with the engines in question and drive them and see how well they work to get an idea.
I'm hoping though that I'll be able to find some one that's selling an m715 that they have already converted, and then do what ever it needs to make sure it'll be up the task, and that it won't rot from around me. Speaking of which any recommendations if there's something I can coat the frame/body with to help protect it from the typical winter road salt etc? This part of the world isn't very kind to vehicles and Jeeps in particular. I want what ever I get to last me indefinitely.

E.

[Pablo]

If you are on the East coast or in the upper midwest, you can probably find someone to e-coat the frame and body when it is tore down: http://www.finishing.com/116/94.shtml . This should get the nooks and crannies covered, but it is not cheap.

The e-coaters often want to dip (chemically strip all paint, body filler, and rust) a car first, however. I would not let them do this to mine as if they mess it up you will have the acid leach out through the paint a year or two later and rust out the vehicle from the inside.

I would media blast the frame and body or bake it, make your repairs, and then have them clean the surfaces again and E-coat dip the whole thing. I cannot find someone to do this in my neck of the woods. So I am leaning towards Eastwood products over clean rust free surfaces and calling it a day. I am unsure of powdercoat or rubberized undercoats as they can trap moisture under small hairline cracks in the finish: spreading rust under what looks to be pristine surfaces. I think you are better off getting more rust where you can quickly see it and fix it then having rust that hides away under the surface where you cannot see it until it is too late.