This is my first post here, so I'll start off with a couple of the simple things... I'm very mechanically inclined, but have a tendency to forget the correct names of things... please correct me where I am wrong.

I have an intercooled 91.5 5.9, with modest goals. This engine has the H1C on it, but I currently do not know the turbine housing size. If I remember correctly it does have the 8 blade compressor wheel.

I've got the screw turned into the collar(removed) area, and getting around 25psi of boost, but it doesn't seem to matter where I put the low boost traffic cone thingy, I still get a large cloud of smoke until I hit about 15psi, then it quickly jumps up to 25psi with a very light haze.

My goal: I would like to run somewhere around 40psi using my H1C as the big turbo, what would be a good holset from a Cummins application to use as the high pressure turbo.

What size injectors should I use to support 40psi through twins?

What controls should I consider? Is waste gate on the high pressure enough?

Is there any other considerations I should make for the engine before I push it that far? This engine has always been extremely well maintained and has 180,000kilometers on it.

I will be doing all the fabricating and installation myself, I have a friend who is a manager at the Cummins rebuild shop... thats where I got my exhaust manifold for free... hoping to get a good deal on the "right" turbo.

I mostly just "race" around in my truck, but I want it to be safe to tow some heavy loads.

Exhaust run is 5" un-muffled to a single 5" stack out the passenger side of the box.

Now here is my truck as he sits.

 

First off...



Second... Good looking truck!

I put my thoughts in red above.

Also For what the level you are looking for I think a single S300 based turbo will help alot. The turbos are the cheap part of a twins setup.

 

Thanks for the compliment!

My final power goals are around 400hp, nothing more. I want the truck to remain as reliable as possible, but with the quick spooling and EGT handling of the twins.

I also mostly just want to have compound turbos, to say I put them in there. Overkill is underrated!

Again, the psi is based off my experience and 40psi in the different vehicles I've driven seems to be about the sweet spot for my ears... I'm hoping that with twins it will produce the perfect musical note. If I have to run a little more boost to reach 400hp, that is fine...

The criteria for my truck, is for me to enjoy it as much as possible and be able to spank just about any new truck on the road, without having excessively high maintenance costs.

PDR diesel is just up the road from where I live, so I was thinking once I had what twins I was going to run sorted out, get the injectors to match to fuel level I need to keep everything happy... if the stock 91.5 injectors will do that... even better for me.

In this setup I am utilizing the factory supplied ZF-5 speed with 3.73(or whatever they actually are, but very close to this) gears. I would actually like to put some 3.31's or something in there to get better fuel mileage. This truck will haul some loads, but is mostly an empty cruiser...

I currently run mechanical boost, oil and temperature gauges. When I make the jump to twins I will drill and tap into the manifold before the turbos for EGT.

I seem to remember a diesel power article about putting studs in without removing the head... though my memory could be off. Would it be possible to install the studs one at a time bringing each one to the same torque level as the remaining bolts, then when all the bolts are replaced step up to the rated torque using the torquing pattern in the cummins manual?

Would the piston mechanical pump be sufficient for my lift pump needs? I currently still have the diaphragm pump on the engine.

Clutch is a brand new off the shelf unit for a 94+, I had the flywheel properly machined before installation... the clutch is beautiful in this truck and as it runs right now I can shift faster than I could with my Toyota Supra, my Celica or my 300zx. I can usually get back under throttle with 10-15psi of boost remaining from 22-25 on the gauge.

Exhaust is already pretty open. The current setup is a 3" downpipe to just past the adapter plate where it quickly bells out to 5" without a muffler running to a stack on the passenger side of the box. I would design a new downpipe for the twin setup.

I was really hoping to find a turbo to work with the H1C as the big turbo, to reach just the right amount of airflow for the horsepower goals of the truck and to keep both turbos happy. If the H1C simply will not do this, I would still like to run turbos from Cummins applications so I have the best chance of getting a killer deal on them... I would be buying new turbo's to keep my mind at ease.

What is the fuel pin for the VE? Is that the traffic cone looking thing for low boost fuel? I currently have a 3200 rpm governor spring.

I will be doing all of the design and fabricating work myself... math is not my strong suit, otherwise I would be trying to use some of the formulas I found for sizing compound setups. I guess I could get excel to do the heavy math lifting, still it is confusing at times. The big turbo is the easier one to calculate... total system CFM at it's pressure ratio. Figuring out the PR for the high pressure turbo is easy, but I get lost when trying to figure out how much it should flow and how much CFM the big turbo is providing...

 

your H1C will have an 18cm or 21cm exhaust housing. replace it with a 14 or 16 housing and it will spool faster. start building with that. The h1c is fairly small, and using that to spool a bigger turbo would be a good bet.

 

Would using the H1C with a smaller turbine housing require the use of a wastegate between the primary(high pressure correct?) and secondary turbo? If that is the case, would it be wiser for me to pick a turbo with an internal wastegate which would simplify the plumbing?

I think it would be really cool if it were possible to run compounds without any wastegates at all... nice simple plumbing, but I don't think that is possible.

 

It sound like you really want twins (who doesnt) but i think a good single will make the power you want pretty easily and spool much faster than your current turbo.

 

I am going to put twins on my truck. I simply want to do it with Holset turbos. The plumbing and piping will be easy to do, no matter what I end up using...

I will be restoring my truck and having twins on it will be part of that process.

I was hoping someone would have some experience with the level of performance I was looking to achieve and say "oh yeah I used such and such turbo with this and that and got this level of performance... this is how it felt"

 

That's a nice looking truck. The Cummins fits a lot better in there, than it does in my Dodge.

All the input you're getting in on track. If you're only looking for 400hp, then a single would be the way to go, a 62/65/12 would do it easy, and still spool pretty quick. If you really want twins, you could pair up your current turbo with a smaller housing and a 64/71/14 or similar. That would take you over 500hp with good fueling.

 

Im not a turbo expert but if i was going to go with only holset turbos, i would do a hx35/hx60 combo.

 

So if I were to use say a 14cm exhaust housing on my H1C, external wastegate which I've been reading may be the easier choice... I should choose between HX50,55 or 60...

I'm guessing 64/71/14 refers to compressor size, turbine size and housing volume?