This is The Bomb ... with Turbo!

[asavage]

My dad has an 87 VW Golf with a blown TDI engine . . .

Sure it's a TDI? VW mfgrd turbo IDI and DI 1.9l engines, and I thought that the TDI (Turbo Direct Injection) was introduced in the '90s.

[Knucklehead]

After I get the tranny done and the whole thing back in I will be doing pressure checks to see how good of a fit the turbo I have is. I never did that before, and I got all my turbo sizing experience with Cummins motors since then, so now to go back and apply all the details I have learned to the first job.

Caveat stated, for your project, estimate the theoretical airflow at the most used rpm for both motors and compare the number. If they are close then the turbo will probably be just fine. I like to have it slightly undersized for quicker boost, but I have a hunch some of the modern automotive engineers think the same way, so if you go with a turbo from an application with less airflow than the SD22, it shouldn't be by much. I'm guessing that the redline on the VW is higher than the Nissan, so though the displacement is a little less the turbo would probably be perfect.

This is going to sound funny, but the first time I put my foot in it after I put the turbo on it took my breath away. Not that it is so fast, just that it felt like somebody unhooked the trailer. I couldn't get the smile off my face. It used to top out about 65 mph on a good day (bigger tires), but after the turbo it would do 85 any day. I have hauled two Harleys in the back (I have a modified bed) and once, 1700 lbs of shingles without any problem. Yea, it definitely makes a difference, and that was without turning up the smoke screw.

I'm very sorry that I can't give some solid numbers and I feel dumb for that (not even any pictures!), but when I put the turbo on in '94 I'd never done such a thing and didn't even know if it would work. It was kind of like a long trial period and I really had no idea there was anyone else in the world who would have any interest.

[EvergreenSD]

What did the turbo do to you fuel mileage numbers?
It's certainly out of my range for now but I am definitely interested in your project. Some day I would really like to turbocharge my SD22 and swap it into a 720 4X4 and put a custom flatbed on it as an all-terrain biodiesel expedition machine. Kudos and keep up the good work!

[Knucklehead]

Uh, I think it went down slightly, hard to tell because not long after I added about 350 lbs with my bed modification.

[zen]

telling you it goes down...reason ..you put your right foot down more cos it goes so good!!!(and sounds so good)

(sd33 n/a owner now converted to turbo!!.oh boy. )

[TooManyIdeas]

How many pounds of boost were you / are you running, what are you doing to compinsate for the added fuel requirements Do you think its possible to run 10+ boost

[philip]

Galen mentioned about 8 psi boost. Since the OEM compression remains unchanged (22:1), the risk of blowing head gaskets in the presence of more boost is quite real. Even the SD33T had only 7 psi boost with the same 21:1 compression.

[Knucklehead]

what are you doing to compinsate for the added fuel requirement

Unlike a gas engine, the addition of a turbo on a diesel does not create any "fuel requirements". Fuel does not burn in a diesel at a carefully metered air ratio the way it does in a gasoline engine. You can add extra air without going "lean". But you CAN go rich, which causes high exhaust gas temperatures among other negative things. So, you can add a turbo to a diesel and do nothing at all to change the fuel delivery. But if you increase IP fuel delivery to take advantage of all that extra air, the mixture will be too rich when you first put your foot down and boost has not yet built up, so, on factory turbocharged diesels, most IPs have an anaeroid valve that restricts fuel delivery until boost comes up. Kind of the opposite situation that you have with a gas engine. Sans such a valve, you just learn to put your foot into it gently.

Do you think its possible to run 10+ boost

Depends what on you mean by "possible". I think the IP will deliver enough fuel to make a correctly fitted turbo push over ten pounds, yes, though I don't know what the limit of this IP delivery is. I think Zen is probably doing around 20 when he turns it up, but that is a guess. Standard hot rodding fare for diesels is to beef up the IP, but generally that is for the guys who are looking for over 30 lbs boost. More importantly, will the piston/pin configuration be able to withstand the pressure rise in the cylinder for very long? (When I say pressure rise, I should clarify that I am referring to a higher pressure near TDC rather than a more even pressure all the way through the stroke) Will you run at 20 lbs all the way up Raton Pass? Or will it just be for getting up the freeway onramp?

I have blown holes in pistons with too much boost and too much compression (on a Cummins, but that was at 17:1, 25 lbs boost, and that took a few years of over the road use to be fair). A crack starts at the pin bore and works its way up to the rings. And please note that this can happen without any of your gauges ever going into the red. The pin diameter on the Nissan is not very big and I can see the same thing happening. If I didn't care at all about fuel mileage and wanted only power, I would have built this engine with bigger pins and lower compression, but then, why don't I just slap in a v8?

There are some charts that show what boost creates what pressure rise, and what pressure rise can be withstood by what SD engine configuration for what time period..., but we just started working on them. Until Zen or I start blowing things up, we won't know for sure exactly what the limits of the N/A SD motors are. There is a legend that factory SD25t motors exist, and that would obviously be the source for some details, but I've never seen or heard of anyone with one nor seen specs. The next best thing is the factory SD33t. The compression ratio is not much different between the turbo models and the N/A models, and Zen has mentioned that guys with SD33t motors are breaking parts, but we don't know all the details.

Let's recap. My stock pistons worked fine for years at 7 lbs boost, no increase in fuel delivery. SD33t owners have broken parts, conditions unknown. Proceed with caution Will Robinson.

[philip]

Unlike a gas engine, the addition of a turbo on a diesel does not create any "fuel requirements". Fuel does not burn in a diesel at a carefully metered air ratio the way it does in a gasoline engine. You can add extra air without going "lean". But you CAN go rich, which causes high exhaust gas temperatures among other negative things. So, you can add a turbo to a diesel and do nothing at all to change the fuel delivery. But if you increase IP fuel delivery to take advantage of all that extra air, the mixture will be too rich when you first put your foot down and boost has not yet built up, so, on factory turbocharged diesels, most IPs have an anaeroid valve that restricts fuel delivery until boost comes up. Kind of the opposite situation that you have with a gas engine. Sans such a valve, you just learn to put your foot into it gently.

SNIP

I have blown holes in pistons with too much boost and too much compression (on a Cummins, but that was at 17:1, 25 lbs boost, and that took a few years of over the road use to be fair). A crack starts at the pin bore and works its way up to the rings. And please note that this can happen without any of your gauges ever going into the red. The pin diameter on the Nissan is not very big and I can see the same thing happening.

SNIP

Until Zen or I start blowing things up, we won't know for sure exactly what the limits of the N/A SD motors are. There is a legend that factory SD25t motors exist, and that would obviously be the source for some details, but I've never seen or heard of anyone with one nor seen specs. The next best thing is the factory SD33t. The compression ratio is not much different between the turbo models and the N/A models, and Zen has mentioned that guys with SD33t motors are breaking parts, but we don't know all the details.

Let's recap. My stock pistons worked fine for years at 7 lbs boost, no increase in fuel delivery. SD33t owners have broken parts, conditions unknown. Proceed with caution Will Robinson.

Soooo ... you're confirming that without anaeroid circuitry and with IP pump delivery optimized for maximum boost pressure, nearly all other times of less boost will result in ... shall I say ... "smokey exhaust" to some degree.

At the other end ... if IP pump delivery (again, no anaeroid circuitry) is optimized for only a couple of pounds boost then ... at times of maximum boost the excess air will ensure more complete fuel oxidation.

With boost comes an increase in dynamic compression. Now with the new cam profile you have (intake valves closing closer to BDC than with the OEM cam), this too will contribute to some degree in raising dynamic compression.

[Knucklehead]

Bingo.

One time, after I had blown a Cummins (and then limped it bobtail for ten miles) and had it rebuilt, the throttle response was nearly gone. I mean the thing had no power, like I was only stepping down 1/4 on the pedal, and it was really bad when it was cold. Instead of 30 lbs boost it was maxing at 12, and instead of 300 lbs of fuel pressure there was about 70. Absolutely gutless. Turns out that flying parts in the exhaust had damaged the turbo, which in turn pumped a lot of oil into the intake. The oil went through the tube from the manifold to the anaeroid and filled up the airspace on one side of the diaphragm. The mechanic had forgotten to clean it out, which in effect, left the pump in a low delivery, or N/A mode.

[philip]

Bingo.

One time, after I had blown a Cummins (and then limped it bobtail for ten miles) and had it rebuilt, the throttle response was nearly gone. I mean the thing had no power, like I was only stepping down 1/4 on the pedal, and it was really bad when it was cold. Instead of 30 lbs boost it was maxing at 12, and instead of 300 lbs of fuel pressure there was about 70. Absolutely gutless. Turns out that flying parts in the exhaust had damaged the turbo, which in turn pumped a lot of oil into the intake. The oil went through the tube from the manifold to the anaeroid and filled up the airspace on one side of the diaphragm. The mechanic had forgotten to clean it out, which in effect, left the pump in a low delivery, or N/A mode.

Ok, I spy two issues:

1) the low boost was caused by schrapnel damage to the turbo turbine.
2) lubricant froze the anaeroid valve in NA mode.

Is on-boost fuel enrichment accomplished only by modulating fuel pump pressure on the Cummins? 70-300 psi is quite a range by SD standards.

[Knucklehead]

The turbo damage was the source of the oil that clogged up the anaeroid. After the engine AND turbo were rebuilt, boost was low because the clogged anaeroid was restricting fuel delivery.

Is on-boost fuel enrichment accomplished only by modulating fuel pump pressure on the Cummins? 70-300 psi is quite a range by SD standards.

Yes, but a Cummins system is very different from the Bosch system. On a Cummins (at least the ones I know) the IP is only a pump, not a timer as well. All it does is provide variable flow to the injector, which fills to a volume determined by the pressure provided by the pump. The injector is then actuated by a lobe on the camshaft just like the valves are. It is what is known as a single rail system. I put the gauge on myself, and it is nice to be able to see what the IP is doing. I would like to be able to do the same with the Nissan, but am not sure how to do it at the moment, if it can be done at all.

[philip]

After the engine AND turbo were rebuilt, boost was low because the clogged anaeroid was restricting fuel delivery.

Question. I got my mind around the aneroid reaction to rising boost pressure but ... I don't understand in the Cummins the idea of how the aneroid stuck in the Natually Aspirated postion would severely limit boost. Help me out here.

[Knucklehead]

Sorry, I had a problem getting a replacement Athlon CPU. What a bunch of crap, get a new CPU and you have to get a new motherboard AND a new case, AND a new power supply! Now I'm pickin' the computer junkyards too!

Aneroid restricts fuel delivery, and not just for Cummins. If you only put your foot halfway down, you only get half boost, right? The aneroid doesn't do anything that you can't do with your foot, it just does it automatically. It's not a must have on a diesel turbo system if you learn how to put your foot into it gently by watching the pyro. I wouldn't want to sell such a system to the idiot public though.

I perceive that your question is deeper than that Grasshopper. You want to know how does the system make any boost at all if it needs boost to make boost. No? That's what I wanted to know and I didn't get it until recently when I figured out that the turbo will make a certain amount of boost, such as on my SD, with no increase in fuel at all. So, there's the initial boost to get the circle started.

[philip]

SNIP I perceive that your question is deeper than that Grasshopper. You want to know how does the system make any boost at all if it needs boost to make boost. No?

Well ... having dwelled on the subject a bit further, let me bounce this off you.

In Cummins (and nearly all other diesels), there is no air throttling so ... boost creation cycle begins by increasing the fuel delivery (engine load). A broad appreciation minus some details.

With the SD's and their pneumatic governors, were you to set the air throttle at ... 1500 rpm under no load ... that a nominal level of boost would be generated. From this base & were one able to now control separately the rack position from the air throttle position, one could increase boost pressure by simply increasing fuel delivery while leaving the air throttle undisturbed ... up to a point (sooty exhaust).

WuddjaThink?