Have a diesel 720 that has some really weird stuff going on with the frame, truck is a loss but need a couple answers.

[Mr.Disprosium]

My buddy just got this 81 sd22 4x4 720, we were gonna turbo it but upon some inspection we found some really goofy stuff going on and have decided against it. The motor is getting swapped into a different 720. it looks like some of the suspension tabs on the front of the frame have been cut off and welded back on, the control arms are different, the right arm having like an inch of shims, the front of the truck has a 3 inch body lift and the very back has none, and it's a perfect slant all the way back. 

I've never seen a diesel 720 before so I'm not exactly sure what it should look like but there damn sure shouldn't be square tubing shittely welded to the frame for engine mounts and cut out to clear the steering shift right? Also the steering column is about 4 inches short and the whole steering column and wheel sits really far into the dash because of it, its an 81 which shouldnt have a tilt column right? This truck has a tilt column in it. Also the transmission crosmember is just a piece of channel iron shoved in the frame holding the trans up. The weirdest part is the whole cab and bed has been off the frame, rust holes patched by what seems a crackhead with fiberglass the frame and bottom of the cab rhinolined and the exterior painted pretty decently. Looks like a beautiful truck from the outside but junk once you look underneath.

[NC85ST]

I don’t remember a diesel being offered in a 4x4. I’m guessing someone swapped it in. That thing has to be pretty gutless. A 4x4 was not the fastest thing stock, with the z22 in ‘81. You’re right, it does look decent on the outside. As far as the tilt column, I don’t remember if it was offered in all 720’s, or if not, when they started. Some of those pictures do seem to have some real red neck engineering. Are you sure that trucks not from the south? Haha

[datzenmike]

North America did not get a diesel 720 4x4.

 

Tilt steering was offered about half way through the '83 model year and it would have been paired with power steering. The PS unit would fit on the end of the steering box so would have used a shorter steering column. You need a manual steering column.

 

Turbo isn't going to be much use on an 61 hp SD22. You want 35 extra stump pulling horse power and torque? throw it away and put a Z24 engine and 5 speed in it.

 

 

I'd be interested in a picture of the oil pan as it was never intended to clear the front differential.

[ggzilla]

11 minutes ago, datzenmike said:

I'd be interested in a picture of the oil pan as it was never intended to clear the front differential

Ah, i was wondering why the engine was jacked up

 

and the 3" body lift on the front only, is probably to clear the raised engine

[datzenmike]

(jesus)

[wayno]

I have had a couple SD22 powered 720 trucks, they just do not have enough power for the freeway in my opinion, I helped turbocharge one and I was not impressed with the result, it was a little faster, but not enough to suggest anyone else to do it.

 

I do not have any SD22 diesel trucks anymore, the two diesel trucks I have are both powered with SD25 diesel engines now, and they are both turbocharged also, I went from 71hp to about 120hp, I would never have a diesel engine without a turbocharger, what you have if 4wd might be good as a crawler, but not good on a freeway, it is too big and heavy for a 61hp engine, one of my friends made one into a 4wd, he drove it for a little while and then sold it.

[Mr.Disprosium]

18 hours ago, datzenmike said:

North America did not get a diesel 720 4x4.

 

Tilt steering was offered about half way through the '83 model year and it would have been paired with power steering. The PS unit would fit on the end of the steering box so would have used a shorter steering column. You need a manual steering column.

 

Turbo isn't going to be much use on an 61 hp SD22. You want 35 extra stump pulling horse power and torque? throw it away and put a Z24 engine and 5 speed in it.

 

 

I'd be interested in a picture of the oil pan as it was never intended to clear the front differential.

That makes sense on the steering column then.

 

Why can't we just make more boost? Will the sd22 not handle much before blowing up or will the injection pump not handle it, we're still thinking about swapping it into a 2wd truck and turboing it even if for minimal gains. I have a small turbo I used on my z24 for a while, made 15 psi for like a year until it leaned out and melted a piston, now I have a forged ka-e I'm about test at 29 psi in my 720.

 

I didn't realize we didn't get 4x4 diesels in north America, that definitely explains why the raised engine mounts were made to clear the diff, and the body lift only on the front to clear the hood like someone else mentioned.

[Mr.Disprosium]

17 hours ago, wayno said:

I have had a couple SD22 powered 720 trucks, they just do not have enough power for the freeway in my opinion, I helped turbocharge one and I was not impressed with the result, it was a little faster, but not enough to suggest anyone else to do it.

 

I do not have any SD22 diesel trucks anymore, the two diesel trucks I have are both powered with SD25 diesel engines now, and they are both turbocharged also, I went from 71hp to about 120hp, I would never have a diesel engine without a turbocharger, what you have if 4wd might be good as a crawler, but not good on a freeway, it is too big and heavy for a 61hp engine, one of my friends made one into a 4wd, he drove it for a little while and then sold it.

How did that sd22 do with a turbo? Do you think more boost could be safely made on a stock motor? How was tuning that naturally aspirated injection pump with boost? I think we might swap the engine and bell housing back into a 2wd truck and still turbo it.

[ElliotV]

I don't know much about the sd series deisels but I know on other diesels when you are boosting them such as the om617 or the 4bd1t you need larger injector "plungers" or "elements" to push more fuel into the engine to really take advantage of the boost and turn up the fuel much. I don't think there is much aftermarket support for the sd22 or sd25 diesel engine and is why you don't see many people messing with them when there are much more easily available and more supported engine options out there that can get more bang for your buck. 

[ggzilla]

5 hours ago, Mr.Disprosium said:

How did that sd22 do with a turbo?

 

wayneo commented on that:

22 hours ago, wayno said:

I helped turbocharge one and I was not impressed with the result, it was a little faster, but not enough to suggest anyone else to do it.

 

On the other hand, wayneo also said:

22 hours ago, wayno said:

the two diesel trucks I have are both powered with SD25 diesel engines now, and they are both turbocharged also, I went from 71hp to about 120hp, I would never have a diesel engine without a turbocharger

That is a significant power boost! It seem the key factor is the newer, larger SD25

[wayno]

OK, I tried different turbochargers on my SD25 engines, and it was pure luck that the first turbocharger I found was the best by a significant amount, I based my opinion on owning a 720 with a Z24 engine and my 1969 Datsun 521 kingcab SD25 diesel, these both had about the same amount of power entering the freeway, but after 70mph my 1969 Datsun 521 kingcab SD25 with turbocharger would keep picking up speed till redline(4000rpm), with 3.3 gears in the rear using P195 tires that was just over 100mph.

 

The turbocharger I found that day in the wrecking yard was a used 1986 Subaru XT turbocharger, it's a low RPM gas turbocharger, I have thought about this a lot, this turbo was made for a 1800cc engine, diesel engines move air only so fast, this combo a 2500cc/1800cc turbo worked out great, and the result is awesome, I get it up to speed(70mph) and let off and I barely have to touch the pedal, I get 30mpg going 75mph, I expect if I could go/drive 55mph I would get over 40mpg, the trouble is anything above 2300rmps and I have to start  pushing the pedal farther down, at 2500rpms the speed I am going is how ever deep I put my foot into the pedal.

 

I also have a 1980 Datsun 720 with an SD25 diesel engine, the turbocharger is from something else and I do not remember what anymore(German car), the injection pump was messed with by someone else I bought everything from, this truck is a torque monster, it will tow another 720 diesel truck behind it without an issue, it will also do a 100mph, the thing is it does not have a sweet spot, where the pedal is, is how fast you are going, I do not know what fuel mileage it gets because I did not drive it enough after getting the 521 SD25 diesel truck going to find out, I have to get the 720 SD25 diesel going, if I let  off the pedal I have to press the pedal where it was before to keep it moving that fast, the 1980 Datsun 720 SD25 diesel engine starts the easiest no matter how long it sits in my driveway, it just starts at even 40 something degrees without smoking much at all, my 521 SD25 Turbocharged diesel smokes a lot when it finally starts, but it is the one I want to drive.

 

The friend I helped install a turbocharger on his SD22 engine did not get the dramatic result I got on my SD25 engine, it was a small turbocharger(1600cc gas engine???), he drove it for a while and had an issue and removed it, he said it had a little more power, but not enough for me to suggest others to chase this option.

 

I have to mention this, the SD22 pistons are not made for turbos(not turbo pistons) like the SD25 engines came with, the SD33 diesel engine SD22 pistons did have turbo pistons in certain vehicles(I believe they are special pistons) made with a special injection pump made for a turbocharger, I have never personally seen one of these special injection pumps, I turbocharge my engines a much simpler way.

 

OK, let's talk about boost, I have seen up to 20psi boost in both my engines, but after around 7psi to 10psi it does not pull any harder, for this reason my 1969 Datsun 521 kingcab SD25 engine does not see more than 7psi anymore as that is the one I drive, after 7 or 8 years being turbocharged it is smoking a little now, it  might be smoke from too much diesel getting in the engine, I changed my exhaust pipe from to the rear to the driver's side where I can see it, it might not be smoking any more than it did before as my tailgate was always turning black with diesel soot, but if the soot was from too much PSI I wanted to save the engine from the high PSI boost, I do have an idea on how to control how much fuel it gets with a valve on the fly, but that is another adventure in the future.

 

The way I deal with the engine being controlled the way it is controlled(inline injection pump) is to make sure both sides of the diaphram in the injection pump see the same boost, doing this cancels the boost factor out and the venturi works properly in the carb looking thing(throttle body??) that controls the fuel mixture, the Nissan Diesel forum guys did not believe how I did it, I had to draw a picture of how I piped everything before they believed me.

 

I likely have forgotten stuff now as I have gotten older, I expect there is a ratio(sweet spot) I found purely by luck when I found that first turbocharger in the wrecking yard, a turbo guy could likely find that ratio with the info I have given you in this reply for the SD22, I have this modified turbocharger with a larger vane(boost side vane) and a rebuilt SD22, I just never got around to testing it out, I only want to drive my 1969 Datsun 521 kingcab SD25 turbo powered truck.

 

The red one.

 

 

The engine compartment.

 

 

The 720 engine compartment that has an intercooler.

 

 

 

Edited May 5, 2025 by wayno