Holset Turbo Install FAQ, and Holset Info w/ Maps

The Holset Turbocharger FAQ
By: Roastin300

This FAQ is provided to help with the installation of a Holset turbocharger from the Dodge Cummins turbo diesel trucks. While each turbocharger can be fitted, this particular install is an HX35 model turbo from the 5 speed Cummins.

Why choose a Holset turbo you say? Well, there are many good reasons. Some include their very low cost used, comparable specs to the Garrett aftermarket high performance turbos (in fact, Holset started out making outright Garrett knock-offs), they are easy to come by online used and still in good working condition, most have T3-compatible turbine housing flanges, and some have internal wastegates.

First, lets take a look at some of the different models of Holset turbochargers that can be obtained, and their specs in comparison to a Garrett turbo:

HY35 – Came on the Automatic 5.9L Dodge Cummins. Turbine housing roughly has a .55 A/R and a T3 stage 3 turbine wheel. The compressor housing is about .60 A/R and the compressor wheel flow is .46 kg/s, which converts to 60.8 lbs/min.

HX35 – Came in the 5 speed 5.9L Dodge Cummins Turbo Diesel. Very similar to the HY35, has the same turbine and compressor wheels but utilizes roughly a .80 A/R turbine housing and a .70 A/R Compressor housing. Also flows 60.8 lbs/min.

HX40 – Came in the 8.3L Dodge Turbo Diesel motors. Everything on this turbo is much larger, the turbine housing is a 1.00 A/R+ and the turbine wheel is approximately a P trim in garret specs. The compressor housing is approximately a .70 A/R and the compressor wheel flows .53 kg/s, which converts to 70.1 lbs/min.

HX50/55 – Enormous, never seen one in person but the compressor wheel flows .75 kg/s which converts to 99 lb/min.

H1C – Came on the much older Dodge Cummins. Very similar to the HX35 but flows slightly less and is said to spool a little slower due to older and less efficient technology.

H1E – Comparable to the HX40 specs, but the older version just like the H1C is to the HX35.

This information I have given is not exact, however, it is composed of good approximations from my research I have done along with a margin of error for unit conversion.

Choosing Your Holset:

Selecting the “right” model from these turbos to fit on a Z31 300ZX’s VG30ET engine is fairly simple.The HY35 will support about 400RWHP, will spool very fast, nearly as fast as a stock T3. I am currently running the HX35 and it will support roughly 450RWHP, and my spool time is around 3600-3800 full 18lbs boost. This is comparable to the spool you would expect from a Garrett “stage 3” turbine and a large T4 compressor, and the same performance, but at a fraction of the cost. I used to run a HX40 in the past, but I didn’t get full 18lbs of boost until around 4300RPM, making for a very short power-band. Because of its larger sized turbine and housing, the HX40 should support 550RWHP+.

I don’t recommend the H1C or H1E because they are outdated and harder to find anyway; the HX50/55 is just stupid-huge for our 3.0 Liter V6 and would be a very poor investment (unless you plan to spool it with gobs of nitrous).

Installation:

To fit a HX35 into a Z31 300ZX, a few relatively minor modifications must be done to the turbo and oil delivery system. Let’s look at the mechanical side of it:

The compressor housing needs modification. You need to grind down the V-band outlet on the 2.5” compressor outlet. This needs to be done so a normal 2.5” silicone coupling can be slid over it and clamped. This picture kind of shows it, you will fully understand what I mean when it comes time and you have the turbo in front of you.



Some Holset models have two studs and four holes for the turbine housing inlet flange, instead of the “usual” 4 holes with 4 studs on the manifold. You can simply drill the studs out of the turbine housing with a clearance hole large enough for the studs on your manifold to clear.

Next is the wastegate actuator. The stock Holset wastegate actuator should not be used as it is designed to run a lot more boost and will probably not fit well if at all with the turbocharger mounted. Almost any internal wastegate actuator from another car can be used because they all work in the same way. I chose to use a Ford 2.3 Liter turbo actuator diaphragm. I cut the rod and welded in an adjustable end to adjust my preload on the actuator’s internal spring. It will also need a new bracket to hold the actuator itself physically to the compressor housing. I was able to cut, bend and drill the stock Ford bracket to work. As you can see the actuator rod is pretty short and I bolted it to one of the threaded holes on the turbine housing that the original unit bolted to.



The next part is much harder and requires some real fabrication skills. You need to make either a downpipe adaptor to the stock downpipe or aftermarket exhaust made to fit the stock turbo exhaust elbow’s 3-bolt flange. Another solution is to make a completely new custom downpipe. I chose to make an adaptor; here are a few pictures of it. First I made the flange to fit the turbine outlet.



Then I used the 3” mandrel bent pipe I purchased online to mate up with my 3” downpipe. I bought a 3 bolt universal 3” flange and welded it at the bottom to bolt to the downpipe. You can also see that I took the extra time to weld in a smoother transition for the wastegate opening rather than going straight into the flange and intersecting with the turbine exhaust flow. In theory this should give slightly better flow and more precise boost control.









Here are the pictures with the turbo installed:







Now as far as the oil system, the stock oil return works perfectly on the HX35. Mine is different because I have a N/A oil pan with a fitting welded on it. But I know it will work for a fact because I had this setup with a stock turbo, and when I swapped my HX35 in the oil return lined up and sealed perfectly.

The oil feed line must be swapped as the oil inlet on the Holset turbos are threaded and need a fitting. I purchased a stainless steel –4 AN line with an adaptor fitting to go from the block to the line, and bought a fitting that screwed into the holset turbo inlet and had the –4 AN fitting on the other end, presto, a great oil feed setup! The fitting size for the holset's oil inlet is 12mmx1.5, the oil feed hole from the vg30 block is 12mmx1.25

For the intake before the compressor you can go many routes from a pipe motor mount setup, a new motor mount to route big 4” piping to it, the sky is the limit. If you have a MAP sensor with a speed-density system like myself, I run a little butterfly filter right on the compressor inlet with no extra piping to deal with!

You will need to rotate the center section and compressor housing as needed to fit right in the vehicle to line up the compressor outlet, oil feed and oil return. This is called “clocking” the turbo and is fairly easy to do with it test-fitted in place.

That’s it; happy hunting for a used Holset!