SD25 Turbo Blues

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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dc1184
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Location: Costa Rica

#16

Post by dc1184 »

Hey, thanks for the advice and feedback elboss and ehtrain.

High RPMs could certainly be an issue, especially since I am running only a 4 speed gearbox on this old Land Rover. At 75 km/hr and higher, it's runs at high RPMs (not sure how high, no tach). At 100 km/hr, it's about at it's max RPM.

I have now mounted a garrett T3 turbo, and this time I have an EGT gauge hooked up and working. I'm only running 5lbs of boost at the moment. The VE pump and turbo wastegate could be adjusted for more boost, but I want to keep it at 5lbs for the moment.

The EGT gauge provides some extremely useful data, and my EGT temps are higher than I expected, especially when on the highway on long climbs. I can EASILY get up to 1150F or higher on long climbs if I don't consciously back way off the throttle. I mean, I have to back off the throttle about 20km/hr in order to keep temps down. It's kind of a bummer, because the motor wants to give so much more. I could easily hold 100km/hr (approx 60mph) up a long climb but my EGTs would be 1200F or higher and I don't want to push it that far based on my past issues. I live in an extremely mountaineous region, so long climbs are abundant.

On flat land, even at high RPMs, the EGTs typically stay under 1000F.

All of these initial numbers are with no load on the vehicle, but if I were pulling a trailer I would expect the EGTs would rise even faster.

Is there anything I can do to keep EGTs down other than backing way off the throttle? Intercooler? I could mount an overdrive on the gearbox, which would bring my RPMs down, especially at higher speeds, but I'm not sure if that would make a big impact on reducing EGTs?
ehtrain
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Location: regina, sk

#17

Post by ehtrain »

goes to show you how much an engine can take sometimes! it's amazing to see engineering pushed way beyond its capabilities and still live. just goes to show how resilient stuff can be at times.

well there are a few things you can do to get your egt's down.

an intercooler would be first on my list. I'm not even going to try mine without as friend with toyota surf has ran stock (no intercooler) similar to you getting 1200+ egt's on long pulls at 14psi. he now has trouble touching 1000+ with a cheap ebay intercooler. he also says it's like a whole new truck, boost lag isnt to noticeable but major power difference. he was measuring inlet temps +80 and getting +10 celcius afterward. that was with ambient temp about -10 celcius though. even for a cheap intercooler 50c temp drop would be substantial with hiegher ambient temps.

you can also try adding more boost. in theory your gaining more heat from unburnt fuel then from the intake pressure difference. but depending on volume of black smoke etc, it may make very little difference. my NA was touching 1000-1500 no problems on highway pulls. but it was dogging hard with low compression and lots of smoke.

also 1200-1500f isnt common in a engine that is being worked hard, 1600 is getting way up there. if your pedal to the floor to go as fast as you want and overdrive would likely help some as your engine is running flat out. if you are constantly running flat out, maybe drop your max rpms closer to 4000? if im not mistaken stationary motor is 3800 rpms governed (held) so if the motor can handle 3800 constantly then the 4700rpm is only for passing type situations.


also just for your own reference. as I was doing turbo map calculations and pressure/flow equations. I found a 2" pipe can flow upwards of 550 cfm (cubic feet per minute) of air. which is pretty substantial considering the sd25 even calculated at 150hp and 15psi boost would only touch 350 cfm. people on forums were posting as much 350-400hp capable on 2 in piping give or take flow restrictions (types of bends medrel or not, and how many bends) EITHER way a 2in pipe should be plenty of air flow and shouldn't be restriction. Many people choose the biggest everything they can, which is unnecessary. the larger the pipe the more you change your power curves.

in theory a smaller pipe maintains exhaust/air velocity better so would increase torque and power gains in the low end due to the PHYSICALLY smaller pipe/intercooler volumes. while a large pipe promotes more horse power with increased over all flow to higher rpms but drops of velocity and torque. As for the intercooler piping causing you grief. Personally I think smallest is best for routing and off/on boost time. any time a pipe changes size you will change velocity and volume.

I kept all my pipe 2" even the exhaust after turbo, but my intercooler is 2.5. This will hopefully put majority of intake heat into the cooler itself as it's the expansion area. If i notice high egt's on 2in exhaust I will got to 2.5 in as the pipe size after turbo will allow decreased back pressure and lower exhaust tip temps as gases have more time/area to expand.


also another good way to get your intake temps and underhood temps ( which all translate to HEAT SOAK. exhaust wrap and heat reflection/ heat shields can help. not only with on/off boost time but egt's! getting the intake air as cold as possible and keeping the exhaust as HOT as possible across the turbo is its best efficiency. the turbo temps will eventually go through the heat wrap and heat protection (heat soak). but the goal is to keep your average temps lower. instead of 100C underhood you'd rather have an average of 50c. ambient air/air flow has a large effect on this though so even just routing your intake pipes could provide a difference.
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dc1184
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#18

Post by dc1184 »

Great advice, thanks.

I will get an intercooler on there, and probably start with 2" or 2.5" pipe. I took a long drive today, and when my EGTs got over 1100F I backed off the throttle and tried to keep it always under 1050F or so. Am I correct in assuming that prolonged driving at EGTs at 1050 or 1100 is going to cause damage, most likely to the head?

One other thing I noticed today. I have the valve cover breather line (the one that's normally connected from the valve cover to the air intake manifold) as a free breather line. Currently the hose is just connected from the valve cover and runs freely down below the engine. There are a few oil drips from this hose that I notice on the ground after running at high rpms. I was under the vehicle today and noticed gases coming out of this hose at idle. If I put my finger on the hose and block the gases from escaping, pressure builds up, when I remove my finger it releases gases with pressure. Is this something to be concerned about, or normal behavior for these engines? Should I connect this to the air intake at some point?

Thanks again.
Cheers!
ehtrain
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Location: regina, sk

#19

Post by ehtrain »

well I cant say for sure for 1100F how long it would take since mine isn't working lol. but I would think yes if you held it there for an hour or 2 it would probably do something. in longevity. I don't think it would WRECK it or do immediate damage but it's probably not great for it haha. There's always some room to play with temps I don't think these things are that delicate lol.

personally what id expect are 900-1000F cruising. 1100F might be getting abit high. steel glows around 1200F if someone wants to correct me? so to me that's a safe limit haha. maybe someone else wants to chime in also?

that breather tube is for escaping crank case gases. On a gas motor this would be your PVC (positive crank vent) tube. Since these motors were designed with water proofing in mind I believe that's why nissan routed the vent tube back into the air stream. it is normal for a diesel to have some gases coming out of it as there is high tendancy for blow-by gases with such high compression. so what you should be seeing is unburnt/escaped combustion gases mixed with some oil splash from the crank spinning. The gases can be reburnt is why nissan routed them back inside. this keeps the truck, engine bay cleaner too. newer diesel stuff would add an EGR (exhaust gas recirculation) system into it also. but that stuff causes lots of problems typically.

I also noticed some oil drip from the tube. this is generally considered normal on other diesel stuff up here. if you look at the way the vent tube is assembled the air box and tube curves up to the valve cover is designed to be sort of a baffle and knock out the heavy oil particles from the air. it clearly doesn't work perfect but diesel oil is dirty and full of contaminants mixed with lots of blow-by just being a diesel. I wouldn't think you should see more then a few drops of oil here and there.

if you didn't already know diesel oil is very heavy with additives for anti-foaming, detergents, and acid. I don't remember off hand which but as the moisture mixes with the oil, unburnt fuel and carbon the oil actually turns acidic. This is why your supposed to wear gloves handling diesel stuff as the acid is able to penetrate your skin. I hate the way my hands feel after I spill old diesel oil. It softens my skin right up and leaves them sorta clamy lol

when I get my stuff back together I will be re-routing the vent line pre turbo, and adding a catch can or adding in a large "T" with a loop in the hose to hopefully catch the heavy oil and still have a drain... while not making my turbo and everything after all nasty.

they say your supposed to clean your intercooler/wash it out every year and inspect it. so... im ok with that as I like doing fluid changes and maintenace.... when my stuff is actually working of course haha
ehtrain
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Location: regina, sk

#20

Post by ehtrain »

hey i remembered you said you were putting in one aftermarket pistone with 3 other oem ones right? maybe you want to read my last post of my swap.

figured out the aftermarket piston is significantly shorter then the oem one to allow for maching of the block. So if your running 3 oem pistons and 1 aftermarket you may have low compression in what ever cylinder the aftermarket one is in. maybe even 80psi lower or more like I was.
ehtrain
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#21

Post by ehtrain »

the VE injection pump you have. are those easy to come by for these engines down there? I wouldn't mind a working spare
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dc1184
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#22

Post by dc1184 »

quick update, I shortened the wastegate lever as much as possible and it definitely brought down my EGTs. If I pinch off the pressure line to the wastegate, or simply disconnect it and plug it, maybe it will give the engine more air yet??

I should have an intercooler installed in the next couple of weeks. Once I have everything set up, I'll take some photos and post them up here.

I didn't know about non-oem pistons being shorter. I will have a compression test done to see if there is any issue. I'm a little bit suspicious, because it seems to be lacking a little bit of torque since the rebuild.

The VE pumps are easy to get here, probably $250 for a used one. They are sold "as is", you might get lucky or you might get one that needs to be rebuilt. I bought a used one years ago, and it worked fine.
ehtrain
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Joined: 12 years ago
Location: regina, sk

#23

Post by ehtrain »

lets see those pictures!! haha

if im not mistake shortening the wastegate rod should increase boost pressure. do you have a boost gauge? also if you close off the waste gate hose you would effectively do the same thing by not allowing the wastegate to actuate it would run all the boost it could.

well i may be interested in the near future in a used sd25 ve injection pump for a throw together build. I would wonder what shipping would cost to canada?
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dc1184
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#24

Post by dc1184 »

ok, performed the compression test today. All 4 cylinders were in the same range 350-370psi. I'm not sure if that is good or bad, maybe someone can shed some light here.

The oem headgasket hasn't leaked at all since the install, the non-oem one was nothing but problems.

since shortening the wastegate on the turbo, effectively providing more air to the engine, I cannot overheat it whatsoever. The turbo maxes out around 8psi, and even up long climbs my EGTs stay under 1025F. Shortening the wastegate was extremely helpful for keeping my EGTs down.

I have an appointment set for next week to install the intercooler. once it's in, i'll post some pics of the old girl.
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asavage
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#25

Post by asavage »

dc1184 wrote:ok, performed the compression test today. All 4 cylinders were in the same range 350-370psi.
It's not good. See this post for details, but in summary:

My 1982 720 SD22's numbers were:

No. 1 = 470
No. 2 = 445
No. 3 = 420
No. 4 = 440

My generic SD-series manual lists:

Standard = 427
Minimum = 356
Max difference between high/low = 43

Your 350 PSI is below the service minimum, and from my experience it can be very hard to start a diesel whose compression is down at 350, if it's cold.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
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dc1184
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Location: Costa Rica

#26

Post by dc1184 »

thanks alot for the info, very helpful.

it's interesting to note that it is not hard to start, even after it's been sitting all night. I do live in a tropical climate, so it's probably in the low 60s at night. No real cold weather here.

It does use some oil, maybe a quart and a half every 3,000 miles.

Also, I checked the compression through the glow plug hole and followed the instructions that came with the compression tester. "crank over the engine 8 times, with open throttle, and record the compression reading." Does this sound about right?

Is it possible to identify the culprit of the low compression with some further investigation? Rings? Valves? Valve seals?
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asavage
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#27

Post by asavage »

Yes, your "cold" and my "cold" are different. May I suggest that you update your Profile to include your location? That can be very helpful.

"Cold" to me means in the 40°'s or colder. It can be difficult to start a diesel with compression around 350 PSI if the engine's temp is in the 40's.

For an SD, 1.5 quarts in 3000 miles is not too bad.

The instructions you got with your compression tester are fine.

SD's are not noted for problems with valves sealing. Cracked heads, yes, but not valve issues. You can set the valve clearances and possibly pick up those readings a bit, but my gut feeling, based on user experiences here and my own, is that the bore wear is a problem, the ring lands are carboned up and preventing the rings from moving out against bore walls effectively, possibly ring land wear: piston/ring/bore issues.

Some people like to try various fix-in-a-bottle types of things, and Seafoam's products are often mentioned. I feel that you probably aren't going to see much or any improvement from these, but it's worth a try.

If you're not having problems related to hard starting or oil consumption, perhaps you should ignore those numbers.

Your EGT is great.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
elboss
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#28

Post by elboss »

sorry for ansking here, what is the part. number of Bosch VE pump for sd22? thanks!
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dc1184
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Location: Costa Rica

#29

Post by dc1184 »

Hey Al, thanks for the info. I guess I have nothing to lose by trying one of those fix-in-a-bottle solutions.

It's a bummer, because in January I had the whole engine apart (after cracking a piston). it's got a new piston, I was told the other 3 were fine, and new rings on all 4 pistons (hasting). The bores were checked by a third-world machine shop, and checked out fine according to them. Plus the head is brand new with two brand new valves. The new head was blank, so the rest of the assembly came from the old head.

I was expecting much higher compression readings myself. Maybe, for some reason, the rings didn't seat correctly.

The quality of workmanship here, across the board in all disciplines, is extremely sub-standard so who the heck knows.

Since I'm not having major issues, I'll probably just drive it for a while and see how it goes. During certain moments while driving, usually climbing a hill on the freeway, I can notice a slight lack of compression. Not much, but just enough to take notice.

Elboss, sorry but I don't know the part number for the VE pump. I can send you the numbers off the housing of my SD25 VE pump if you'd like. i don't think the SD25 VE pump works on the SD22 though.
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asavage
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#30

Post by asavage »

elboss wrote:sorry for ansking here, what is the part. number of Bosch VE pump for sd22? thanks!
TTBOMY, there is not VE-type IP for the SD22, only the SD23 & SD25.

For the SD22, the Inline pump:

16700-36W03 (FED.T.REG+FED.K/CAB+FED.T.LONG).SD22

16700-37W04 (CAL.T.REG+CAL.K/CAB+CAL.T.LONG).SD22

(click on image for larger)

Image

For the SD25, the FAST's picture shows an Inline pump, but the part No's different:

16700-64W01 (CAL.T.REG+CAL.K/CAB+CAL.T.LONG).SD25

I can't find an illustration or part No. for the VE-style IP, but that may be because my version of FAST may only show USA-imported Nissans.

If you want to do very much parts lookup, consider installing Nissan FAST parts system on your Windoze computer. Instructions on how are here.

For the SD25 with VE IP, both ehtrain and plenzen have them. Maybe one of them can pipe up, get out an inspection mirror & a flashlight, and find you the pump No.

Image
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
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