H1C and WH1C
The 1st Cummins powered Dodge pickups ('89-'93) used a Holset H1C turbocharger. This turbocharger had no wastegate! Because of this it was outfitted with a large 18cm or a 21cm (depending on model year) twin scroll turbine housing. The large housing was Cummins' way of preventing over boost. I would not recommended this turbocharger for most 2.3 applications, as the turbine housing is simply too large for at least 99% of us.
Starting for the '94 model year the H1C was fitted with an internal wastegate, thus the birth of the WH1C (a "W" in any Holset model number designates that the turbocharger has an internal gate). Due to the addition of this wastegate they no longer required the overly large turbine housing to control boost levels, and they were fitted with a more reasonable 12cm housing. This turbine housing remained twin scroll like the earlier H1C. The WH1C is actually very similar to the early HX35, including being outfitted with an identical wastegate actuator mount, but sporting a slightly different method of holding the compressor housing to the back pate. This turbocharger should be viewed as the equivalent to the early HX35W for aftermarket purposes, except for the fact that compressor housing upgrades are not as readily available (which will never be a problem for at least 99% of us). The WH1C can often be picked up cheaper than the HX35W, due to the popularity of the HX35 in the Honda and DSM crowds, and the lack of knowledge of the WH1C's existence and similarities. Just the other day a WH1C sold on ebay for less than $130!
H1Cs and WH1Cs have the compressor housing clamped to the back plate (WH1C shown - notice that you can see the wastegate actuator hanging off to the side of the turbocharger, located at the bottom of the pic):
I stole these photos from the ebay auction I just referenced. It gives better shots of the wastegate actuator, and a good eye will notice the T-bolt clamp around the compressor housing:
HX35W
The WH1C was not a very common turbocharger to be found, and only appeared early in the '94 model year during the transition to the 2nd generation Dodge Ram, most of which were fitted with an HX35W. The early HX35W was packaged with the '94 - '98 12v Cummins powered Rams. It can be identified by its black compressor housing, as well as the wastegate actuator that hangs off to the side underneath (in the same fashion as the WH1C). This WGA configuration makes for some clearance problems in XRs with the motor mount and/or fender, but can be worked around. I would not pass up a good deal on an HX35W or WH1C because of this. Contrary to the later HX35W, the early compressor wheel has 8 blades (as opposed to 7), and is SLIGHTLY larger. This does not make the early one more desirable, as the difference in size is negligible. Possibly the only up-side of this turbocharger over the later one is the fact that you can reclock the compressor housing without having to figure out a new mounting system for the WGA.
Pic of an early HX35W. Thanks to Colin for the 1st one.
Factory black compressor housing:
HX35W that someone painted, but it does a good job of showing the layout of the WGA:
The later HX35W has a slightly smaller 7 blade compressor wheel, and a silver compressor housing, and can be found on '98 - '02 24v Cummins powered Rams ('01 and '02 automatic transmission equipped trucks were equipped with the HY35W, which I will cover later). As stated before, this smaller HX35W is NOT any less desirable. The wastegate actuator is mounted to the compressor housing, not on a separate bracket underneath. This makes for a more compact design, however also prevents one from maintaining use of the internal wastegate while reclocking the compressor housing.
Pics of a late HX35W:
All HX35s have a snap ring that holds the compressor housing to the back plate, similar to what is pictured below:
The HX35W is the most common Holset on the market, since the most trucks got it. From the factory they have a twin scroll 12cm turbine housing, just like the WH1C, although upgrades up to 21cm are available. There are also compressor housing upgrades. Once again, 99% of us 2.3 guys will never exceed the abilities of the factory housings, so chances are you won't have to do this. HX35s are available (notice the absence of the "W", meaning that this is not an internally gated turbocharger), but not very common to be found. If you HAVE to have one, you might look on various heavy equipment, or speak with your Cummins dealer, as they have acquired Holset and are in the process of changing the name to Cummins Turbo Technologies.
For best results, use a HX35W with a custom twin scroll header. This takes the divided turbine inlet, and pairs the exhaust pulses in each side in the firing order to GREATLY decrease spool up time (more info and real world numbers can be found on Turboford). It is not recommended that you use the internal wastegate, as it only dumps one side of the split turbine housing, which does not control boost very well. Also the factory WGAs are set at VERY high boost (over 20psi), which is not what most of us want as our bare minimum boost level! If you MUST use the internal gate there is a Volvo WGA that can be adapted to the late HX35W, and more information about this can be found on Turboford also.
HY35W
The HY35W can be found on '01 and '02 Rams with an automatic transmission. The HY35W has a small 9cm SINGLE scroll turbine housing. If you want to control boost with an internal WGA then I would recommend finding an HY35W. The 9cm turbine housing may be a bit small for some who plan on running bigger power numbers. You can see in the pics below how much smaller the turbine housing is in comparison with the 12cm one found on the HX35:
HE351
The HE351 can be found on '03 and newer 5.9 Cummins Diesels in Dodge Rams. The HE351 has the same size compressor housing as the HX35W, although the forward facing elbow is molded in as part of the compressor housing. The turbine housing is a single scroll inlet and the outlet is 4", unlike the previous Holset model turbochargers that have an outlet of approximately 3". I cannot find any data regarding the size of the turbine housing on the HE351.
In the pics below, the HE351 is the big one, sitting next to a stock Volvo turbocharger:
The '07+ 6.7 Cummins has a VGT turbocharger (I believe this one also wears the HE351 badge). VGT stands for Variable Geometry Turbine, and requires no wastegate! It is controlled with a variable electronic solenoid that moves a mechanical arm. The mechanical arm then moves vanes within the turbine housing to change the direction of the exhaust flow through the turbine wheel. This allows one turbine housing to have quick spooling characteristics at low RPM, but also allows the same turbine housing to have high flowing characteristics at high RPM. The minute that someone adds code to Megasquirt to get it to control one of these devices is the minute that I will ditch the twin scroll header that I am building and buy one of these turbochargers!
Pictured below is the VGT turbocharger. Mounted to the side you can see the electronic solenoid with the actuator arm sticking out of it. The arm works in a similar way to the wastegate actuators that we are all familiar with, but is electronically actuated and moves the vanes rather than opens a gate.
All Holsets equipped in Dodge trucks come from the factory with a silencer ring, at Chrysler's request. This is in the compressor inlet and looks like a velocity stack, and seems like it would act like one as well, but the Holset engineers insist that is purely for noise reduction and suits no performance purpose what-so-ever! With the silencer ring removed and a cone filter on my truck I found that the screaming of the turbo (I found out when I did this that turbos this size don't sing... they literally SCREAM!) even tends to drown out the noise of the diesel engine! I'm just looking forward to seeing how mine other Holset will sound on my XR!
Once again, the silencer ring can be found in the inlet of the compressor housing and is held in by a small snap ring. Anyone one with a small flat screwdriver and the mechanical skills of a monkey should have no problems removing it.
Holset with silencer ring (notice you can see the snap ring with angled cut ends... this is a good place to start with your screwdriver):
Same Holset after silencer ring has been removed:
Whew, that was a lot of typing! Anyway, let me know if there's anything that I should go into more depth on. This obviously isn't all the information available, but should assist one in deciding what Holset is right for them, and aide them when it comes to tracking it down.
