Diesel repower alternatives to the 4BT?

[Josh]

GM 6.2 would be another option. Especially witha turbo add on. The early 6.5 would work as well, anything prior to 94 has straight mechanical injection.

[Tanner]

GM 6.2 would be another option. Especially witha turbo add on. The early 6.5 would work as well, anything prior to 94 has straight mechanical injection.

Ummm.... yeeeeaaaahhh...

Third post down in the message.



'Tanner'

[mikkelborg]

Master Yota, that does help a lot. I'm curious, what kind of milage did you get post-swap with your old truck? My stock flathead is making about 12MPG right now, I've heard of people getting less than 6 though. My goal is to get over 20MPG and I thought diesel was the only way to go. That's why I'm looking at higher RPM diesels in an effort to keep the swap cost low by not changing too much but also improve my milage enought to actually pay for the swap in a few years (I drive the truck about 4000 miles a year). I think that means inline 4's are out because balance issues keep them from spinning up high enough for decent road speed without tons of gears, so that leaves short inline 6's, and V8's. Based on what you have said it seems like the stock drive train will hold up at higher speed. I do the proper maintenance, so I’m not worried about spinning it faster. I’ll balance my drive shafts just to be safe though, I think if I get rid of some vibration there it should make the bearings in my transfer case and axles last longer. The exhaust is a problem I haven't given much thought to yet, hmm...

I've been trying to wrap my head around the idea of doing a 6.2, I've heard so many bad things about that engine, mainly about it breaking cranks and cracking blocks, it's reputation kind of scares me. The use of a timing chain instead of gears to drive the pump and camshafts too, it just sounds too light for what I want to do. It doesn't help that my only firsthand experience with one of these motors ended in a breakdown with a cracked cylinder.

Tanner, how is the clearance on the exhaust with the 6.2? Did you have to notch the frame or do anything funny to make it fit? If I do go the 6.2 route with overdrive the redline is high enough I could get by without 4.89's for a while, but I'll be spinning it kind of fast to cruise on the highway. It would eventually need 4.89's or some nice 1100-16's.

That Mercedes 5 cylinder motor is really pretty interesting, it doesn't have much more torque than stock, but I wonder is leaving the low gearing and really winding it up would make up for the low torque rating? I wonder how long it would last being wound up to 4000 turns before shifting every time? More to think about...

Thank you,
Collin

[Master Yota]

At best, my Cdn 251 was getting about 6mpg and it didn't get that very often. With the 305 and general cruising around town, and short trips up and down the highway, I'll confidently say that I was averageing about 15-18mpg. Bare in mind I live in hilly country, and most of the speed limits around here don't exceed 50mph (80kmph for us Canadians...) While the v8 might be turning at a higher than average rpm for cruising, the 5.83's provide so much leverage that the engine dosen't need to work (read: minimal load on the engine) to move the truck around. I was using at the time a 600cfm edelbrock carb, on a stock cast iron intake, no fancy anything, not even an electronic distributor. I ran dual exhaust with one muffer under each running board. I also ran on the stock NDT tires. I also never had any issues with driveline vibration. I don't know if mine was the exception to this, or the norm, but all the shafts ran true.
The biggest issue with the stock tcase is the volume of oil that it holds, which is a little on the low side. Excessive speed causes the oil to over heat, blah, blah, blah.... Tcase tech has been beaten to death already, so I won't flog that horse somemore, a simple search here of the forum should reveal all the answers to any questions you may have about the NP200. Something you may not realize is that a 5spd trans will only lower the engine rpm, not the rpm at which the tcase turns for a given road speed. The only way to alter the tcase rpm for a given road speed is to re gear the diffs, or run taller tires.

[mikkelborg]

That actually seams like pretty respectable milage for a gasser pickup truck, much more than I would have expected. On my truck at least one of the drive shafts makes a pretty good vibration, none of my u-joints are loose, all my flange bolts are torqued properly, and it's still there when I coast at speed so it's not just engine vibration. I thought it was really weird at first, but I read somewhere that dodge never bothered to balance them at the factory and I've never found any weights affixed to them so I just believed it. It's possible I picked up some bad info somewhere though; I probably did find it on the Internet...

I've been running an agricultural grade 50 weight in my transfer case (I made sure it had all of the additives for gearboxes) and it runs cooler than it did with the 90 in it, makes a little less noise and isn't springing any leaks yet despite having the original style seals, it's been 14 months since I put the 50 in there and the level hasn't dropped even the slightest bit yet. I'm inclined to use it, and if I begin to have issues either replace it with an NP205 or do the 4.89 gears to get the driveline revs under control later.

Collin

[Lifer]

On my truck at least one of the drive shafts makes a pretty good vibration, none of my u-joints are loose, all my flange bolts are torqued properly, and it's still there when I coast at speed so it's not just engine vibration.

Even when coasting, huh? Sounds like one of two possibilities to me. You could have an unbalanced shaft but if the vibration is a relative recent development I'd be more inclined to suspect a bent shaft.

[Tanner]

From a website discussion about installing a 7.3 into a Toyota FJ-X... commenter mentions that he has installed a 7.3 into an M37, but advises against it.

"We swapped a 7.3 idi into an M37, and bottomed out the springs by the end of the first trail. We had leaf-springs made with twice as many leafs to handle the weight.

BTW, the 7.3 is HUGE. on the M37 we cut the firewall and moved it back 8 inches. We also had to raise the tunnel hump about the same amount. So half the engine is basically in the cab. It is loud and Hot, trust me on this.

Also consider that the crankcase is also Huge. We needed to notch the side of the crankcase to clear the driveshaft.
Ford auto trannies are really long. We used a Clark 285 tranny because its a manual and its short."

'Tanner'

[Master Yota]

From a website discussion about installing a 7.3 into a Toyota FJ-X... commenter mentions that he has installed a 7.3 into an M37, but advises against it.

"We swapped a 7.3 idi into an M37, and bottomed out the springs by the end of the first trail. We had leaf-springs made with twice as many leafs to handle the weight.

BTW, the 7.3 is HUGE. on the M37 we cut the firewall and moved it back 8 inches. We also had to raise the tunnel hump about the same amount. So half the engine is basically in the cab. It is loud and Hot, trust me on this.

Also consider that the crankcase is also Huge. We needed to notch the side of the crankcase to clear the driveshaft.
Ford auto trannies are really long. We used a Clark 285 tranny because its a manual and its short."

'Tanner'

Yep - the 7.3 is a monster of an engine, weighs about 1200lbs. The Ford/IH 6.9 isn't really any smaller either. This about sums up the headaches of this swap...

[mikkelborg]

Thank you for finding that Tanner, that is much more modification than I want to take on so the 6.9 and 7.3 are out... I am not THAT crazy about those motors!

As for the shaft, it has been doing it the entire time I've owned the truck, the shafts don't show any signs of damage, but it is possible one is bent a little.

Collin

[Tanner]

Collin -

Sorry to have missed your earlier question re the 6.X GM motor swap into my truck...

My truck is currently in mid-swap mode right now, and actually on the market. Time constraints with 4 children & new job are keeping me major busy; thus, I'm putting my truck on the market.

The 6.2 fits the M37 quite well with a bit of massaging - I looked at pictures of the swap that Daniel Tibbius did on his, and also chatted with Juan Castro (on this forum??) as Juan has done two of these swaps IIRC. Motor should be raised up & tilted back slightly to allow header clearance over frame rails. Juan used the stock cast iron manifolds. I spoke with a couple aftermarket clutch companies (Ft Worth Clutch was one of them) - they can build a custom clutch disc that has the large Spicer 10-spline hub & 11"-12" GM 6.X size disc for about $125 or so; this way, you can use stock 6.X flywheel along with the Spicer 3053A OD 5-speed Deuce trans & mate the trans to engine with a GM 366 (large truck) bellhousing & adaptor plate.

Regards,

Bryan

[Tanner]

And for any swap you have in mind to pursue, realize that if you opt to use the NP200 transfer case, you'll want to keep the T-case RPM under 2500...

'Tanner'

[mikkelborg]

Bryan, Thank you for the additional info on the 6.x swap, it sounds like I could do that without much trouble if I choose. 2500 RPM seams kinda low for what I want to do, that would limit me to 45 MPH with whatever motor I use if I keep the stock gears, until I can afford to regear the axles. I think it would be more economical for me to convert to an NP205 and spin everything faster. Realistically I need the driveline to be capable of 3500 RPM to get 60MPH with stock axles. The next question is how well do stock axles hold up at those speeds, do they start to have heat issues too?

Thank you,
Collin

[Tanner]

I may have been a bit premature in posting the 2500rpm limit on the NP200 (higher shaft speeds increases fluid temps & the chance of shaft seals getting cooked) ... IIRC, that is the number I've read... somewhere. Possibly SteelSoldiers.com...

But keep in mind that other issues will play into the mix regarding road speed - tire diameter, final drive ratios at axles, overdrive transmission gear, etc. Garbee has a good calculator formula available to configure your road speed based on engine RPM/trans gear/final drive ratio/tire size/etc.

http://www.garbee.net/~cabell/equations.htm

And the torque peak on a J-code 6.2 motor is about 1800-2000 RPM; HP peaks (IIRC) at around 2400-2600; beyond that, you're wasting fuel.

'Tanner'

[Josh]

another option, if you're looking for a modest power increase,better fuel economy, lighter weight, more RPM flexibility, and durability like you can't imagine would be the....


225 slant six.

Seen em get 30+ MPG in a propperly geared dodge dart... I know, I know, a dart isnt am m37 blah blah blah. But, I think it is a good viable option. Torquey, tough, revs faster than a diesel, would fit, lighter, etc. Throw some EFI on it, I bet it would crack 20 no problem.

[mikkelborg]

Well, I've done some more research and a lot of fooling around with excel and different engine specs and torque curves and power ratings and I think I might finally be onto something. I had a hard time comparing different engines directly because they really are apples and oranges, so I decided to formulate the workable road speed and maximum force exerted by the tire on the pavement over the engines entire RPM range for each gear using published torque curves for each engine... I wound up with huge messy tables of figures and eventually distilled them down into graphs. This one in particular is interesting to me.

I used the driveline that Cabell Garbee details on his website as a standard for comparison because it it a known working solution. I compared it to an OM617a hooked up to the stock driveline. They are remarkable similar, the OM even puts a little more force on the ground at some speeds! The stock gear set even looks appropriately spaced, although a 5 speed would be nice, I would probably opt for a non-OD 5 speed. One note, I did not compensate for loses of power in the driveline which would be greater with higher shaft speeds, which the OM617a would be running, so the real life performance will probably be slightly less than the Cummins across the board. What do you guys think, would a Mercedes turbo painted OD look too weird under the hood? Externally the truck would probably stay dead stock looking, the exhaust will still dump on the passenger side and I don't think I will need to lift the front end at all if I can set up a rear sump oil pan.

Collin