Ural 375D repower (1 Viewer)

[Seth S]

I figure this is the section for the crazy ideas. There is a Ural 375D thats been for sale near me for quite a while and I've lusted it after it for some time. Its completely impractical which is why I probably desire it . Vermont Unimog is the owner and importer and the back story is apparently they brought it in about 10 years ago and it was at one point rented out to the movie production company who was filming the movie "Salt" nearby in the Albany NY area. During that time the production company apparently left something on and flooded the engine with fuel and apparently destroyed the engine.

So the stock engine is a 7.0 liter Zil 375YA-V8 engine which produces a whopping 180 hp at around 3200 rpm and about 240 ft-lbs at around 1800 rpm. Top speed was a claimed 47mph and fuel economy for 47mph was claimed at about 3mpg but in reality is closer to 2 mpg from my research. The Zil 131 would be the similar but I've seen real world accounts of people getting about 6 mpg at "highway speed"...80kmh.

So Vermont Unimog is offering the truck with a repower via a Ford 7.3 powerstroke and an Allison transmission. I've done the math and I run into one major issue with any diesel conversion. The common conversions being something like a 6BT or 7.3 where both those engines seem to be most efficient at or below 2000 rpm and while capable of revving higher at a cost of efficiency.

Other numbers - (Stock config) 5 speed gearbox 5th gear ratio @.78:1
Final drive 8.9:1
Tire size 12x20 which I think is about a 44.2" diameter or a rolling circumference of 11.55 feet.

So if I have a diesel that i happiest at 2000 rpms then:

2000rpm x 1/.78 = 2564 rpm delivered to final drive
2564rpm / 8.9 = 288.1 rpm delivered to the drive wheels
288.1rpm x 11.55ft = 3327.57 ft/min
3327.57 ft/min / 5280 ft/mile = .63 miles/ min
.63 mpm x 60 min = 37.81 mph.

So with the stock axles and tires but a new engine and trans limited to 2000 rpm the max cruise would be 37 mph. to get back to a 50 mph capability there needs to be another OD box at between the rear axle and output of the transmission of 37mph/50mph = .74.

The stock gas engine would be spinning around 3200 or so rpm at the claimed top speed of 47 mph.


So this is really a long winded way of asking....assuming that a re-gearing isn't feasible for final drive ratio are there OD boxes available to increase the rpms to the rear axle...and even more realistically can a 6BT or 7.3PS even turn things with that much OD? I looked at Eaton and Tremec transmissions and the most they overdrive in their top gears is .75. I feel like you might be able to to have an electronic 2 speed box that could be shifted into for long straight stretches and maybe slowly reach and hold a speed but my gut says that any hill would kill that speed pretty fast.

Personally I'd think doing a swap to a modern gas engine would be the easiest and make the most sense. The challenge there would be finding something that makes good low end torque...or I guess choosing your transmission wisely.

Thread is worthless without photos:

took this one back in 2009 I think.

 

[Seth S]

I think the key with vehicles like this is remembering that...and accepting that they are just Turtles. They will go a lot of places that other things will never go and to do so they have an admission price which is slow speed and inefficiency. You really get an appreciation for mpg though...especially when adding 1 or two mpg doubles or triples your range

 

[Seth S]

 

[Seth S]

a fun series

 

[RockDoc]

I had (still have, but rolled) a 2003 7.3 PS with the ZF6 manual. 0.72 6th gear overdrive, diffs seemed to be geared for trailering. Pulled a cruiser on a gooseneck effortlessly at highway speed (say 2200-2400 rpm), drop to 5th (1:1) for anything steep. I think red line is in the 3300 rpm range.

Have replaced it with a 1999 7.3 PS with the auto. It's geared deeper (I'm assuming both OD and diffs) and cruises a touch under 2000 rpm I believe. Gets better mileage, but I hate the feel of the auto and the engine control programming that seems to go with it, and look forward to swapping the manual in when I get around to it.

 

[Seth S]

I was looking at the Chevy Crate motor website and I saw they had a T56 6 speed box where 6th gear was .62:1. if I ran that in my above calcs I could achieve a speed of 47 mph at 2000 rpms. So any additional revs would be icing on the cake. I also read up on the NV4500 and I think it said max GVW was 14k lbs....hence the need for a big truck gearbox.

@RockDoc thanks for the data points an personal experience on the 7.3. I have driven both an E450 box truck and an old airport bus friend had each with the 7.3 but It was long enough ago on both that I cannot remember specifics. I remember they did pretty well but the transmissions were a little strange.

 

[RockDoc]

FWIW I was out with the 7.3 auto today. Cruising at 65mph it turns 1800-1850 rpm. OD with the 4R100 appears to be 0.71:1 from a quick search.

 

[Seth S]

FWIW I was out with the 7.3 auto today. Cruising at 65mph it turns 1800-1850 rpm. OD with the 4R100 appears to be 0.71:1 from a quick search.

I think I found the correct gear ratios in the stock 5 speed box on the Ural and 5th gear was listed as .71:1 with an 8.9 final. But thats attached to the gas engine which can rev.

I think the easy answer to all this is pick a modern gas engine and either adapt to the stock transmission or source one that bolts up easy and meets the physical requirements and accept what the results are.

 

[Seth S]

It took a long time but I finally found some info on the Zil 131 which internet reports from real drivers often claim about 6 mpg in real world driving....I believe the Zil has a final drive ratio of 7.34:1 which would support a diesel conversion quite easily. A transmission with an output of .75 in top gear could do 50 at 2000 rpm assuming the torque is there.

 

[Seth S]

Just for the sake of information and interesting I’ll post some more. I figured out that the Ural 4320 which was the later version. With two Diesel engine variants. One of which was a 15 Liter!!! V8....had 7.34 or close to it final drives in the axles. The axles are very similar in design to the Rockwell axles where the diff sits on top vs coming in from the side. I have yet to verify if the 4320 diffs will bolt into the 375D axles. But if they do then you’d pretty much match the zil. I believe the zil and Ural 375D both run the same 7 liter V8 gas engine. Not sure on the 5 speed trans. Still if I could get the local Ural, swap diffs, and rebuild the engine and get 5-6 mpg like the Zil I will seriously consider taking the plunge. Having an RV that like climbing river beds when there’s no road is strangely appealing

 

[Seth S]

More research to appease my psychosis. The engine bay in these things could swallow a suburban so engine options are quite abundant....my Youtube recommended videos are now populating with Russian truck engine swaps....mostly in russian. Just watched one where they put in an OM366 mercedes engine. The Om366 is a 6 liter 6 cylinder mercedes engine....looked like a beast of a motor...but similiar in size to the 6BT. The easiest swap would be a modern gas engine....either an LS or if a little older one of the big block ford engines and set it up for low end torque.


The real question is transmission. things like NV4500's are rated for a GVWR of about 14,000 lbs. I'm guessing the most economical would be a 5 speed out of a 5 ton USA military truck...think they might be Spicer. Otherwise maybe an Eaton product. Really not too well versed in the world of heavy truck transmissions.

 

[GLTHFJ60]

6BT with a RTO or something. SAE bellhousing would allow all that to bolt together.

Pirate used to be a good reference for these things, but after the redesign, most of the users in the tow rigs section (where you'd be looking) left.

 

[Seth S]

There is a russian truck military forum but there isn't much traffic and when I tried to join it a while ago it took the moderator months to grant me access so I pretty much gave up on that route. Its admittedly an obscure corner of the truck world. Perhaps theres some USA based military truck forum.

 

[wapitimud]

Lots of details in these plans. I think I agree with some of the earlier replies to accept the vehicle as built, knowing that a new engine won't solve the low gearing of that offroad truck.

They shouldn't be very expensive overseas, as there's plenty of them. Shipping to the Eastern seaboard should be cheap from European ports.

I think there's other related models that may have improvements, including a diesel engine. The Kamaz and Kraz military trucks come to mind as alternatives

 

[Seth S]

The later Ural trucks had V6 11 liter diesel or V8 15 liter diesel and lower ratio axles to compensate for the lower rev engines.

I think the most realistic and easiest driveline swap would be an American V8 and transmission out of something like a school bus or truck like an international 1600 etc. the Russian V8 gas engines aren’t so reliable. Think a US V8 with efi could make a lot of difference. Stick with old school push rod for space saving.

diesel would be great but axle ratios are too limiting. unless there is a medium size 7-9 liter out there that’s happy and efficient turning 3000 rpm

 

[wapitimud]

I question what you're trying to achieve here on this job. The original engine is gasoline? It runs, and for the few hours it'll be operated, it'll work as designed?

The block isn't cracked? there isn't a siezed crank or camshaft that can't be replaced? It wasn't hydrauliced through water in the intake? etc.

I don't see why you would modify it otherwise. Trucks closer to central europe, like the Czech Tatra, might be better quality, with more design features, and still available at a low price rather than putting money into modifying this into something it isn't.

 

[Seth S]

The engine as far as I know in this particular truck is no good. The owner is a business who imports big trucks from around the world. They have it listed for sale with a ford 7.3TD and an Allison transmission. But based on passed conversations I’ve had with them I don’t think the conversion was actually done. I’ve since emailed about the truck but haven’t heard back yet. I was researching power train swaps if I could get the truck as is for a reasonable price knowing I’d have to pull the engine.

 

[Seth S]

Also this truck is 30 miles away. Lots of other trucks in Europe for less money but a hefty shipping cost. I’d love a zil 131.

 

[wapitimud]

Also this truck is 30 miles away. Lots of other trucks in Europe for less money but a hefty shipping cost. I’d love a zil 131.

That's my point exactly. It does seem then that a pull and replace on that engine may be more reasonable than trying to repair it in-frame. I don't even know what the problem might be. The machining quality on some Soviet equipment, like Belarusian tractor engines, was very poor.

I suggest there is a wide range of simmilar or better models to choose from in Europe at a low cost. Importing them may not be that difficult if they are over 25 years old. I wonder if you could get road registration and license plates for this Zil, it seems like it might not be DOT compliant, and would never be a speedy truck.

I see a few modern Unimogs around here on the highway.