My 1980 Datsun 720 diesel dually

[wayno]

Well I drove the 720 today with a functioning intercooler, it helped slightly, not a lot, but slightly.
Basically I was able to do get 10mph more speed at the same EGT(1200 degrees), not a lot of benefit.
I am going to have to put an EGT gauge in the 521KC diesel(non turbo) and see what kind of temps it is running at, I have nothing to compare the 720 temps to, maybe the diesels all run that hot.
Funny thing is that my 521 non turbo diesel engine may be slightly slower off the line than the turbocharged 720 diesel, but it will kick this turbocharged diesels ass on the hiway, I cannot go fast up a hill because the EGTs get to hot in the 720, while the 521 diesel goes right up the hill, but I have no idea what the EGTs are on the engine, and I have to drop a gear sometimes, did i mention I hate dropping gears.
But I have to admit, the 521 diesel will go fast, but gets shitty mileage going fast(27/28mpg), as I have my foot deep into the pedal, this 720 goes 65mph using hardly any pedal at all, so it likely gets way better mileage, that's a trade off that doesn't interest me as much as being able to go up a hill/long grade without having to drop a gear.

[jayden71]

Dunno much about small (4cyl) diesels but the big ones, 6cyl 15 Liter ones dont even run that hot on flat ground. Pulling a long hill, under a load, will heat them up to 1200-1500. I think 1800 degrees is danger zone. Flat ground they are running about 600-800. The turbo is hardly working then too though.

[wayno]

I put an EGT gauge in the 521KC diesel this evening and took it for a drive, it did not run quite as hot, but it was up there also, it ran 800/900 degrees at about 70mph, but when I went up a steady grade, it just got to 1400 degrees, I then hit another grade and it repeated the 1400 degrees, but it takes me flooring it for a while to get there, and it happens slowly after 1200 degrees.
I hate to think what it reached when I drove up the grape vine north of LA, I was floored for a very long time, and the engine almost overheated, I had to let up, as the water temp was real high.
I am thinking that the guy I bought the engine from went to far with the injection pump, he had an injection service company turn up the fuel mixture, more fuel, more heat.
I am not sure what I am going to do at the moment, the intercooler really didn't help that much, I will think about it a while.

How about this goof, I drilled the head pipe for the EGT bung, then when I put the head pipe back in the truck, it interfered with the steering, so I cut the bung off and welded it shut, then re-drilled the hole and welded the fitting into the head pipe, well then it was interfering with the front mount nut for the head pipe, I got it in there, but I just could not seem to set it up in the correct place, but somehow I got it all back together and have a functioning EGT gauge, I am wondering how long it's going to be before I have issues.

[izzo]

drop a gear? From fifth to fourth, or fourth to third?

From my understanding it's not recommended going up hills in 5th gear. A lot of pressure on the bearing. 4th is a straight shot and perfect. Tho, I imagine the truck this is in will be used for work and hauling stuff so probably mean 4th to 3rd...

[wayno]

drop a gear? From fifth to fourth, or fourth to third?

From my understanding it's not recommended going up hills in 5th gear. A lot of pressure on the bearing. 4th is a straight shot and perfect. Tho, I imagine the truck this is in will be used for work and hauling stuff so probably mean 4th to 3rd...

I don't like dropping any gears on the hiway in anything, I am in 5th all the time, if it goes bad, I will put a new bearing in it, and if it explodes, I will put a new transmission in it, it's not that time consuming to do anymore, as I have done it a lot of times, thankyou very much dogleg transmissions.
It is not good to tow or haul heavy loads in 5th, but I do it everyday because I can only go so fast in the work truck on the freeway with 437 gears in the rear.
The 720 transmissions are way better than the dogleg transmissions, I have never had one of them howling in 5th, every dogleg transmission I ever owned ended with howling except for the last one in the work truck, that one locked up solid, dogleg transmissions are pieces of shit in everything except in what they were designed for, a car.

[Laecaon]

Dude.... 5th is not a towing gear, plain and simple. 4th is. 4th is the straight threw one and the one that is stronger for towing. Drop a gear!

Also, dropping a gear will raise RPMs, which in turn will get more air flow through the motor, reducing EGTs. More boost, bigger exhaust, MORE AIR FLOW!!!

Turbo Diesels of todays trucks will run all day at 1200, but it is on the hot end. Quick jaunts higher are alright, but keep it brief. But believe me, there are guys who run at 1350 or even 1400 all the time...

[wayno]

Dude.... 5th is not a towing gear, plain and simple. 4th is. 4th is the straight threw one and the one that is stronger for towing. Drop a gear!

Also, dropping a gear will raise RPMs, which in turn will get more air flow through the motor, reducing EGTs. More boost, bigger exhaust, MORE AIR FLOW!!!

Turbo Diesels of todays trucks will run all day at 1200, but it is on the hot end. Quick jaunts higher are alright, but keep it brief. But believe me, there are guys who run at 1350 or even 1400 all the time...

My RPM range is kinda limited on this rig, basically it is a 1000rpm window, but it has torque, at the moment I have 370 gears in the rear, he was running 330 gears in the Volvo, so his RPMs were lower than I am turning, on this engine it seems like the more air/fuel, the hotter it gets, I have not drove it that much yet, it spends a lot of time around 1200 degrees, and if I give it the pedal, it shoots right up past 1300 degrees in the blink of an eye.
I think one of the differences here is that he kept his RPMs below 2000, while I am always above 2000RPMs, he drove like a paranoid grandpa, 55mph was about top speed for him, at that speed/rpm, I am above his redline 90 percent of the time.
He says he got 48mpg once on a trip from Portland to Tacoma and back, so he could not have had his foot into the pedal that much, I am on the search for 330 gears now.
I have been beating the shit out of transmissions now in the work truck for 20 years now, 15 years of them I have been pulling a loaded trailer, I went through 4 doglegs in 5 years, they just could not take the abuse, since I figured out the hybrid 720 5 speed, which was likely figured out about 10 years ago now, I am still working on the second hybrid, the only reason I changed out the first transmission was because it popped out of 1st gear under compression, and the second gear synchros were shot, you see when hauling around a lot of weight daily, and I make a turn onto a road that is uphill, I slam second trying to keep up my speed going up that hill, well that first transmission seen to many hills behind that L20b, now that I have the LZ23, that is not as much of an issue anymore, it has the grunt to take me up most hills in second at lower rpms.
I might go to a couple wrecking yards today, I have not been to the Sherwood yard in a long time.

[wayno]

I went to the Sherwood yard today, not much there that is worth buying at this time, the 520 there doesn't have much left, the tailgate was still there, and is better than a lot I have seen before, but it was still there for a reason, and the taillight mounts were in really good shape considering it's a 1966, but they can easily be made.
The 521 was a POS, not much more can be said about it.
There was 1 720KC, it had 370 gears in the rear, and the fuel tank was wasted
There were 3 1986 hardbodies in that yard, one of them had an HG43 positrack rearend in it.
I stopped at the Foster road PNP and took a look around, there was an old school 620 with a square headlight grill sitting in top of it, it wasn't perfect, but it was really good, it also looked to have a W53 head on it, it was a conversion, it was open from the windshield to the tailgate with a sealed canopy.
There was one 720 in that yard, and unbelievably, it had the 330 gears I was looking for, and they appeared to be good, so I bought them, I remembered why I don't go there much anymore, when I got to the counter they charged me $114.50 for that gearset, I guess I have spent my wrecking yard funds for a while, jeez that place is expensive.
I am not sure if i will put the gears in this weekend or not, maybe tomorrow morning while it is cool.

[wayno]

I installed the rearend pumpkin this evening after the tree put the truck in shadow, it didn't take as long as I thought it would.
I drove it about half an hour, twenty miles maybe, up two hills, it got to 1400 degrees both times, I also floored it on level ground, there was nothing there, so now I need to figure out if I have everything set correctly, boost and BOV are untouched by me so far, I left them the way the guy had them set up.

I think that it's just another turbo failure, sure it runs alright in the very small envelope it has, but I am thinking that it is just not getting the injection pump control range it should have, I am thinking it is either floored or not floored, and the speed is determined by how much air it is getting, that is why I can floor it on the freeway and I get nothing, it's already floored before I floor it, I also suspect that is why the EGTs are so hot, it's getting a lot of fuel/air all the time, I also believe that is why it surges when I am trying to go one speed, the fuel control rack is moving back and forth between floored and whatever position it is moving to before it goes back to floored, that vacuum control is very sensitive.
I have a VE type injection pump, I might go that direction if I cannot figure this pump control out.

[DRIVEN]

Man, I'd love to find a set of 3.30 or 3.54 gears.

[wayno]

Man, I'd love to find a set of 3.30 or 3.54 gears.

I seen a set of 437 and 370 gears, wasn't that many 720s out there at this time.
I think I was real lucky that I got that set of 330 gears, I mean one truck in the yard and it had what I needed, I have only seen a handfull of 330 gearsets ever.

[wayno]

I have been thinking about this a while now, at the moment I believe that the injection pump is floored most the time on the hiway, and that is why when I floor it, it acts weird, I think what is happening is that the injection pump is floored and what determines the speed is how much air it is getting, and the reason I think this is this below.

I will start by describing how the SD series inline injection pump works, it is controlled by vacuum and a venturi in the what I will call a carb, when the carb butterfly is closed there is a vacuum created on the intake manifold side of the carb, when this vacuum is happening the venturi creates a lot of vacuum that pulls the injection pump to the idle position, so when I give it a little pedal to speed up, less vacuum is created, so the injection pump gives the engine a little more fuel, if I were to floor it, no vacuum is created, so the injection pump is floored, I hope everyone understands this now.
So when Larry put the turbocharger on this engine he left the carb stock, so any boost is pressure on the turbo side of the carb, to keep this pressure from keeping the injection pump floored because no vacuum can be created if the turbo side of the carb is pressurized, a BOV(blow off valve) was put between the carb and turbo, the idea is that when I let off the pedal enough vacuum will be created on the intake manifold side of the carb to open the BOV to dump all the pressure in front of the carb and then it will create enough vacuum to pull the injection pump to the idle position.
The issue here is that when I am driving down the freeway I am at 5psi boost, and basically this is enough pressure to neutralize the venturi no matter what position the carb butterfly is except for closed, when closed it opens the BOV and and dumps all the boost, then the venturi creates enough vacuum to pull the injection pump back to idle, so basically when I give it any pedal at hiway speeds, the injection pump gets floored except when I am barely touching the pedal, I believe that this is why it surges when I am trying to go an even speed, the injection pump rack just moves back and forth depending on all the factors pushing/pulling on it, the boost trys to floor it and it picks up speed, and then I let off just a tiny little bit and it dumps the boost and the injection pump rack moves towards the idle position and then it starts all over again, there is no middle place to go for an even rpm, either there is boost or vacuum.
This scenario above is why I think it runs so hot, the injection pump is floored a lot, and when I give it air it heats up very fast, this is also why there is nothing there when I floor it, the injection pump rack is already floored, I am just giving it more air when I give more pedal, but I am not giving it any more fuel.
Larry has put this together in such a way that it doesn't blow black smoke which is amazing in itself, because it should blow black smoke, somehow it doesn't, but it does get hot very fast, and when I say hot, I mean the EGT(exhaust gas temperature) gets to 1400 degrees just getting onto the freeway, on any up grade/hill that I have to go up, and what literature I have read doesn't give me any kind of guide written in stone on when I will melt the tops of my pistons, or when the vanes on the turbo will melt.
they do say that anything above 1400 degrees you are living of borrowed time and will eventually lose in the end.
This is the link I got this temp. number from.
http://bankspower.com/techarticles/show ... -important

I am wondering if there is any valve out there that will dampen the rack control, I don't know what kind of psi numbers that the venturi creates, I do not have a meter to measure it.
Also there are 2 hoses going to the injection pump, one goes to one side of the diaphragm, the other hose goes to the other side of the diaphragm, so in theory I could use pressure to control the rack instead of vacuum.

Anyone have any thoughts?

[Laecaon]

Wayno, which style of injection pump is on the sd25? Is it bosche?

[wayno]

Wayno, which style of injection pump is on the sd25? Is it bosche?

All the early/mid 80s injection pumps are inline in the USA, they are Diesel KIKI, licensed by Bosch.
I have 3 SD25 engines with inline pumps, I had a SD22 shipped from Australia with a VE type injection pump, if I cannot get this inline setup to work, I will likely put the VE type pump on this engine, but I would rather get what I have to work if possible.

It's all about the turbo pressurizing the venturi, I wonder if there is a way of metering the injection pump rack in front of the turbo without using a butterfly/venturi combination, just using a venturi, but I think the BOV will screw it up.

[Laecaon]

Look at the vw diesels, as they came in both turbo and non turbo. There is something called a LDA on the injection pump of the turbo ones...

[wayno]

Look at the vw diesels, as they came in both turbo and non turbo. There is something called a LDA on the injection pump of the turbo ones...

I don't know anything about the VW stuff, but I do know that only Nissan put inline pumps on their SD engines in the US, while every where else they seemed to get the VE type pump like the VWs, even the Dodge and Ford diesels use the type of fuel delivery as the VE pump, that is why it's a bitch to put a turbo on these inline pumps, the vacuum fuel control creates issues.
This engine I have actually runs fairly good except for the heat it creates, and the lack of power on the hiway.
I have thought about trying to use a model airplane engine carb on these engines, bear with me while I explain, you see the vacuum created while the engine runs pulls the injection pump back to idle, so when the engine is not running or when I am trying to start it, the injection pump is floored, but the moment the engine starts it gets pulled back to the idle position from the vacuum created, meaning the engine don't rev when starting it because vacuum is created fast, so I thought about using the vacuum pump for the brake booster to pull the injection pump to idle, then put a "T" on the vacuum line very close to the injection pump, the top of the "T" would have the model plane carb, the side of the "T" would go to the vacuum source, the idea is that when one gave it the pedal, like any other carb the butterfly would open, when it is open, vacuum is lost, and the injection pump would give the engine more fuel, I think this would actually work except for one thing, lost vacuum would make the power brake booster malfunction, and when one stepped on the brakes, would that effect the throttle?
I have lots of ideas, I just hoped this was the engine that worked as Larry did it different than anyone else, but I think this one is just another fail, but I have not given up yet.

[Laecaon]

I specifically mentioned the LDA so you could do some research... not get focused on the VE IPs...

you need a boost compensator. It will limit your fuel until you make enough boost to burn the fuel. Which also implies you need to turn up the boost.

Here is a Diesel Kiki pump for SD33. Notice the Boost compensator on it.

[wayno]

I specifically mentioned the LDA so you could do some research... not get focused on the VE IPs...

you need a boost compensator. It will limit your fuel until you make enough boost to burn the fuel. Which also implies you need to turn up the boost.

Here is a Diesel Kiki pump for SD33. Notice the Boost compensator on it.

OK, that pump is metered by a control lever, not vacuum, it is an inline pump that has been modified to be controlled by cable, I also have a pump something like that, mine was made for a boat, generator, water pump, something that is meant for a steady rpm, but I could rig a pedal to it, the reason I don't is because of the lever being throttle control and fuel cutoff, 0 is the off position, and 10 is floored, so everytime you let off the pedal it would die unless you made some kind of bump stop to keep it from returning to the stop position, I suppose I could use some kind of solenoid that when the key is in the on position it would keep it from shutting down and control the idle, but I have not given up on this setup yet.
I suppose that modified is not a proper description, it was made to be controlled by a throttle cable connected to a pedal.
This is the inline pump I have that I bought on ebay a while back.

The reason I don't just change over to one of the other injection pumps I have is because they are all made for the SD22 engine, I only have the vacuum controlled types for the SD25 engines I have, so I will likely have to take them in to a diesel service place and have them adjusted for the SD25, it seems like it costs at least $250.00 to get them to do anything on one of these pumps, so I avoid going there until I have to.
I have 2 VE type injection pumps, one is for an automotive application, and I think it is just about wore out, the other is for a forklift I believe, so I will need to take it in and have the govener adjusted for something higher than 2800rpms, both are for SD22s.
One thing that needs to be noted is that unlike a gas engine, the diesel can run on less fuel, it doesn't get all hot from running lean, it just has less power, more fuel, more power, at least to the point when you have to ram more air in it also, otherwise it will just be to rich and blow black smoke all the time.

[wayno]

I guess it's always going to be something, now the truck isn't charging, I suspect it has had this issue the whole time, but it has been so sunny out that I could not see that the light was on.
After getting all that intercooler piping in and working, it's going to have to be removed just to get the alt. out, stuff doesn't seem to be going my way right now, I am thinking about just leaving it till after Blue Lake, I will just give it a full charge, and then take an extra battery with me just in case.

[DRIVEN]

Never ends.