Fuel tuning and injectors

I have an 85 and will be building my own custom twin turbo setup, however i have concerns of if the fuel system and stock injectors can hold up. Target boost will probably be around the 18-20lb range.

First how about a little history on this guy. Was my grandfathers pickup he bought off the showroom in 85 and was his baby. i inherited it in 2012 when he passed with only 70k miles on it. When i got it it was leaking oil rather profusely but me being young just ignored it and added oil regularly, that is until i stretched it a little to long and torched the #3 rod bearings and crankshaft. Upon disassembly i also found to small cracks in the head. So i junked that engine and but one off ebay from Just Japs Imports. When it showed up i assumed it was an 83 because the turbo was non-wastegated. I put on the 85's turbo and intake manifold and threw it in the pickup. Now looking at the fuel pumps i can see some differences between the two. The little guy runs great but i want to build it more because i feel the potential and uniqueness of this cool little diesel.

Now the main question is does anyone here want to help me tune this puppy up to run 18-20lbs safely on two turbos? will the factory injection pump and injectors handle that?

Thanks in advance

Go to this facebook page: https://www.facebook.com/groups/mitsu4D56NorthAmerica/

I've safely been running 15-25 lbs on the factory turbo for some time now. I did get a set of ARP stud just for peace of mind, but I'm sure that the factory bolts could hold that much boost fine. I'm my opinion the factory injectors and pump will have no problem supporting those boost numbers, you may want to consider advancing the timing on the injection pump a few degrees, it makes a pretty noticeable difference.

You will be mildly disappointed...
I am running a billet td04h-13T with a SR50 (upgraded with a billet GTX3076r wheel)
I am running 30psi, recently i started having issues with headgaskets, no issues since replacing with a MLS and ARP studs.

One thing to note, i am running the 4d56 not the d55 you have, but parts are the same

https://photos.app.goo.gl/W7Nwn6adXVJPuNmdA

Did you have to adjust any of the settings on the pump aside from advancing it? Any idea where your egts are sitting?

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Originally Posted by skullzaflare

You will be mildly disappointed...
I am running a billet td04h-13T with a SR50 (upgraded with a billet GTX3076r wheel)
I am running 30psi, recently i started having issues with headgaskets, no issues since replacing with a MLS and ARP studs.

One thing to note, i am running the 4d56 not the d55 you have, but parts are the same

https://photos.app.goo.gl/W7Nwn6adXVJPuNmdA

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How would I be disappointed? I like your set up. Instead of going with compound though I will be sitting with parallel turbos to stay inside the particular turbos I have efficiency. Looks like head studs are looking like a good idea though

As I had it set up the highest egts I saw were about 1300-1350, and that was no intercooler and a never rebuilt turbo. I recently upgraded from the factory TC05 to a Holset HE221 with an intercooler, so I'll let you know what that does for it once I get it back together

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Originally Posted by cptkill

Did you have to adjust any of the settings on the pump aside from advancing it? Any idea where your egts are sitting?

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I did not change pump timing at all. My EGT cruise interstate around 300c, heavy boost usually around 600c, extended boost around 650ish
I have a top mount intercooler which isnt very efficient, will be converting to front mount eventually

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Originally Posted by cptkill

How would I be disappointed? I like your set up. Instead of going with compound though I will be sitting with parallel turbos to stay inside the particular turbos I have efficiency. Looks like head studs are looking like a good idea though

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Just remember if you cut the exhaust in half, you will spool at half the speed. Compound was a combination of low end power (td04h-13t) to interstate power (SR50)

The sr50 also reuses the wasted fuel of the td04, i average 32mpg with this setup.

Again though i will note that i have a 4d56, so limits i have a 4k rpm limit, but i never go above 3200rpm. I know the 4d55 has 1k more rpm so that will assist you.


I say disappointed due to me dynoing several setups. I have run a td04-15t Billet along at 28-35psi, SR40 at 30psi, SR50 at 25psi, and td04h-13t with sr50 at 30psi.

td04-15t @28psi peak with 1000cc 50/50 meth/water, dynod 117rwhp/223rwtq
SR50 at 25psi (no meth anymore) made 121rwhp/217rwtq
td04h-13t with sr50 (no billet at the time) made 131rwhp/277rwtq

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Originally Posted by skullzaflare

I did not change pump timing at all. My EGT cruise interstate around 300c, heavy boost usually around 600c, extended boost around 650ish
I have a top mount intercooler which isnt very efficient, will be converting to front mount eventually

Just remember if you cut the exhaust in half, you will spool at half the speed. Compound was a combination of low end power (td04h-13t) to interstate power (SR50)

The sr50 also reuses the wasted fuel of the td04, i average 32mpg with this setup.

Again though i will note that i have a 4d56, so limits i have a 4k rpm limit, but i never go above 3200rpm. I know the 4d55 has 1k more rpm so that will assist you.


I say disappointed due to me dynoing several setups. I have run a td04-15t Billet along at 28-35psi, SR40 at 30psi, SR50 at 25psi, and td04h-13t with sr50 at 30psi.

td04-15t @28psi peak with 1000cc 50/50 meth/water, dynod 117rwhp/223rwtq
SR50 at 25psi (no meth anymore) made 121rwhp/217rwtq
td04h-13t with sr50 (no billet at the time) made 131rwhp/277rwtq

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Thanks for all the info. The reason I'm doing parallel is also because the two turbos I'm going to try this with are a little smaller than the stock one but much more efficient, so spooling them shouldn't be much of a problem. I'm also thinking with some pump mods like timing and such I'll be able to get more out of it but damn you've got to love that torque these little guys make. If it doesn't make the power at least it will look and sound cool lol.

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Originally Posted by cptkill

Thanks for all the info. The reason I'm doing parallel is also because the two turbos I'm going to try this with are a little smaller than the stock one but much more efficient, so spooling them shouldn't be much of a problem. I'm also thinking with some pump mods like timing and such I'll be able to get more out of it but damn you've got to love that torque these little guys make. If it doesn't make the power at least it will look and sound cool lol.

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Seeings as the stock turbo doesnt flow enough to keep up with the engine, id be worried about going smaller even if running 2 lol.

Side note, i did not do any mods to my pump or injectors aside from adjusting fuel

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Originally Posted by skullzaflare

Seeings as the stock turbo doesnt flow enough to keep up with the engine, id be worried about going smaller even if running 2 lol.

Side note, i did not do any mods to my pump or injectors aside from adjusting fuel

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You think they would restrict the exhaust to much?

Anyone know if there is a performance difference between the 83 and 84 injection pump or injectors? I see some physical differences in the pumps but don't know if that transfers to any performance changes.

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Originally Posted by cptkill

You think they would restrict the exhaust to much?

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The stock td04 is overly restrictive on the d56, only .2l more and same compression but 1k less RPM. You would want a little bigger to allow the higher RPM, if single turbo i would probably look for a td05h size. 2 td04 would probably be fine.
Intake wise, the 9b doesnt put out enough air to make the 2.5 happy, 30psi stopped in its tracks at like 2500rpm. 15t was better though took 35psi for 3300rpm though. But again im talking about single turbos on the 2.5

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Originally Posted by cptkill

Anyone know if there is a performance difference between the 83 and 84 injection pump or injectors? I see some physical differences in the pumps but don't know if that transfers to any performance changes.

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Only thing i know on the 4d55 was there is one year with one off smaller threading injectors so they wont fit anything else.
You can use a 4d56 pump and injectors as long as you dont have that 83 head lol. Dont know if there is any help from it though

Are you guys upsizing the exhaust diameter off the impellor housing as well? That should help getting the boost to kick in. I'm not into the diesels but I don't think it's worth the extra coin adding a second turbo and the manifold mods it would take to glue it all together. The engine bay will be getting cosy as well.

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Originally Posted by geezer101

Are you guys upsizing the exhaust diameter off the impellor housing as well? That should help getting the boost to kick in. I'm not into the diesels but I don't think it's worth the extra coin adding a second turbo and the manifold mods it would take to glue it all together. The engine bay will be getting cosy as well.

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up sizing the exhaust housing or turbine would slow the spool. On diesel you do not want to lose to much exhaust gas velocity from exhaust port to turbine due to gases being much cooler than gasoline.
Thats why you normally dont port the exhaust ports/manifold on a diesel unless you have a lot more things going to it lol.

Also i agree, gluing the 2nd turbo on the back of my small turbo wasnt really worth the work/money, but i did gain 5rwhp and 75rwtq lol. Also cleaned up the exhaust, added a few mpg, and gave me some interstate power back

Extra torque and improved mpg was a good trade off. As for the exhaust, I actually meant the exhaust plumbing not the housing on the turbo. Last thing you'd wanna do is add lag.

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Originally Posted by skullzaflare

up sizing the exhaust housing or turbine would slow the spool. On diesel you do not want to lose to much exhaust gas velocity from exhaust port to turbine due to gases being much cooler than gasoline.
Thats why you normally dont port the exhaust ports/manifold on a diesel unless you have a lot more things going to it lol.

Also i agree, gluing the 2nd turbo on the back of my small turbo wasnt really worth the work/money, but i did gain 5rwhp and 75rwtq lol. Also cleaned up the exhaust, added a few mpg, and gave me some interstate power back

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Those gains are worth it in my book. Out of curiosity how much did you end up spending?

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Originally Posted by cptkill

Those gains are worth it in my book. Out of curiosity how much did you end up spending?

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Kind of hard to add up since most parts i already had lol.
So the bigger sr50 turbo i had purchased and ran as a single, it was $400 used. The GTX3076 billet wheel i installed was $125.
The smaller turbo i purchased for this project but also ran single of, td04h-13t with billet wheel was $320. (was cartridge only since i already had the non billet version)

Think i have ~100 in the flanges and schedule40 piping. I welded everything myself, another 70 or so for the couplers to connect the turbos. Maybe 30 in all for the extra oil feed/return fittings.

My airbox was added after the twin turbo, was only $20 at junkyard.

Turbo choices will change pricing

This will be a well used thread. Good collection of information. If I ever make it out to West Virginia, I will make the extra effort to come see Skullzaflare's turbo set up. Hopefully by then you'll have the intercooler updated.

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Originally Posted by Uncle Spence

This will be a well used thread. Good collection of information. If I ever make it out to West Virginia, I will make the extra effort to come see Skullzaflare's turbo set up. Hopefully by then you'll have the intercooler updated.

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At this point its mostly sitting, a few weeks ago i picked up a cheap 1.8 miata, and of course a week later turbo'd it. So i have been putting my money in that right now lol.

I have the plastic front bumper, my plan is to put an intercooler in the gap below the tag mount (wv no front tag) but have yet to find a good option for it. Will also be having a friend cut/weld the intake manifold to have a 2.25 or 2.5" plenum vs the stock 1.25" lol

Assuming i still have it, i do have it posted up for sale lol. Best offer so far is a supercharged 1999 328i (though i only consider it for trade then sell lol)

Anyone a guru on squeezing more juice from these injection pumps without changing the timing? I want to do that eventually but I really don't want to do all the work of disassembling it right now lol. (unless im overthinking how to do it)

im running 30psi on 2 turbos, and you dont think im getting more out of a stock pump? lol

On the back of the pump there is a flathead bolt (also 8mm) with a 13mm nut on it, adjust that IN to add TOTAL fuel, note that your idle will also go up with that screw. There is a point where you can no longer adjust your idle down to compensate for adding the fuel there.

On top if you remove the 4 bolts on the boost compensator. under the cap you will find a rubber diaphram. Pull the assembly straight out, noting the exact heading.
You will see on the shaft attached that there is a shiny line, this is where it was riding for added fuel per PSI. Turn it to the deepest/sharpest ramp for the most fuel added per PSI.

ALSO, there is a star there you will see the big gear while the diaphram is out. Lefty loosey righty tighty. As you loosen it, it "weakens" the spring pressure making 1psi move the plunger more. So if stock is 1:1, as you loosen it you will move to 1:1.5 to 1:2 etc (loosen adds more fuel per psi)

Obviously do not go overboard, excessive black smoke cools the internal cylinder losing power

Quote:

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Originally Posted by skullzaflare

im running 30psi on 2 turbos, and you dont think im getting more out of a stock pump? lol

On the back of the pump there is a flathead bolt (also 8mm) with a 13mm nut on it, adjust that IN to add TOTAL fuel, note that your idle will also go up with that screw. There is a point where you can no longer adjust your idle down to compensate for adding the fuel there.

On top if you remove the 4 bolts on the boost compensator. under the cap you will find a rubber diaphram. Pull the assembly straight out, noting the exact heading.
You will see on the shaft attached that there is a shiny line, this is where it was riding for added fuel per PSI. Turn it to the deepest/sharpest ramp for the most fuel added per PSI.

ALSO, there is a star there you will see the big gear while the diaphram is out. Lefty loosey righty tighty. As you loosen it, it "weakens" the spring pressure making 1psi move the plunger more. So if stock is 1:1, as you loosen it you will move to 1:1.5 to 1:2 etc (loosen adds more fuel per psi)

Obviously do not go overboard, excessive black smoke cools the internal cylinder losing power

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Haha I had assumed you had tweaked with the pump but since you didn't mention it directly I thought I'd just ask outright. Thanks for that info though, that should help quite a bit. I've already messed with the total fuel screw on the back a little but haven't messed with the others. Currently I have the stock turbo running about 14lbs which I think is as much as the manifold pressure release deal will allow it to do. I have a manifold off an '83 that I'm going to modify for the twins that doesn't have that so should be good there. After all this talk I'm getting pretty anxious to get it going haha