Against our better judgment, we put a big turbo from an early '90s Cummins diesel on our Lemons Dart. We threw all this together in a hurry for a race in November and are well aware that the entire setup is sub-optimal. Now we have time to make it better, and one of the first decisions we need to make is if we stick with this turbo or find something smaller. As such, I'm here to ask what we can do to make our current engine/turbo setup work better (spool up faster, and/or make more NA power down low) without spending a lot more money. If that's just not feasible, I'll be looking for input on what (smaller and/or more modern) turbo to look for.

The turbo is a Holset WH1C. Very similar to an HX35, but with a slightly larger compressor inducer (small side) and a convenient V-band mounted compressor housing. The dimensions I'm finding are as follows:
56 mm inducer/83 mm exducer on compressor wheel
70 mm inducer/60 mm exducer on turbine wheel
12 cm exhaust housing with integral wastegate and T3 flange

Current engine is a stock 225 bottom end with a shaved head and 1.70/1.44 valves with 8.6 SCR. Stock '71+ camshaft installed at ~107° ICL. Doing some rough math with the advertised duration (244°), the duration I measured at 0.050" (198°), and a hot valve lash of 0.010", I get an intake closing point somewhere in the neighborhood of 44° ABDC and a 7.8 DCR.

The turbo is mounted on a homemade "up-pipe" manifold with twin 2" runners leading from dual Dutra Duals to a T3-style flange. We tried to make the runners equal-length, but didn't do so well. From the turbine exit, it's a 3" pipe through a big Thrush muffler all the way to a side exit. The up-pipe is wrapped, but the manifolds, turbo, and downpipe are not.

On the intake side, we have a 4-barrel Holley of unknown type, with mechanical secondary linkage but no secondary accelerator pump. The primary side has been modified for boost but the secondary side has not (yet). The secondaries are currently wired shut because they haven't been tuned properly, but we do have a Percy dial-a-jet to make that process easier. We raced with it as a 2-barrel. We also have a big damn intercooler in front of the radiator, and I think all the cold-side piping is 3".

On track, the engine was a total dog until the boost came on (probably due to the late cam timing). We might be seeing positive manifold pressure by 3500 RPM, but it's not making more than a couple psi until over 4000. By 4500, we're seeing ~10 psi (which is more than we actually want, but we need to play with the wastegate some more), at which point it hauls ass and will continue to scream until things start to break. We'd like to keep the redline around 5000 RPM (endurance racer). With our 904, shifting into 3rd at 5000 drops the RPMs down to ~3400. We have 3.55 rear gears now, but we may eventually be changing to 3.23 or so. Once we get all this stuff set up better, I expect with the added power we'll be getting above 5000 at the end of the longer straights in 3rd.

The new engine I'm planning to build will use 7" 198 rods with dished 2.2 turbo pistons. Target SCR will be about the same (8.6) with a new head that isn't shaved, also cut for 1.70/1.44 valves. Maybe with a well-built long-rod block I could get comfortable with a slightly higher redline. We'd like to limit the boost to 7-8 psi until we have the whole system proved out, at which point we'd slowly dial it up to 10 psi.

So... ideas to help the turbo spool faster:
-Better flowing head. The current head has some mild port/bowl work done, but it could be better. I need to build a new lower-compression head for the long rod block anyway.
-Better flowing up-pipe. Our current one isn't bad, but we may have added an unnecessary amount of pipe in our attempt to keep the runners equal length (which is probably not necessary at all). We could also start with a bare flange at the head and fabricate a one-piece exhaust manifold to go straight to the turbo, but this would be a lot more work.
-Keeping more heat in the exhaust (wrapping or coating the Dutra manifolds, wrapping the up-pipe better, adding a blanket to the turbo itself)
-Tuning the primaries on the carb to not be pig rich all the time
-Setting up the secondaries for boost and actually using them
-More optimal camshaft profile and/or timing. I realize this is the last piece of the puzzle, but I'd like to get the new short block built and in the car by the end of January.

After typing all that out, I think there's plenty we can do before we give up on this turbo. What do y'all think?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I'm trying a similar-sized turbo (Garrett GT4082) on my 225, and it's making even less boost so far. I am hoping the problem I had with the valvetrain turns out to be the problem - I'll keep you posted on what I try on my build. Does this turbo have a divided housing by any chance?

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Matt Cramer
1966 Dodge Dart turbo / EFI project

The beauty of Holset turbos is they are quite modular. Many different configurations can be made by swapping components.
It would definitely spool up faster with a 9cm turbine housing. You should be able to find one for pennies. That housing would have been (I think) original on early Dodge/Cummins with automatic transmission. If I remember correctly the turbo on such a truck would be called HX30.

There is a wide variety of turbine housings, compressor housings, turbine wheels and compressor wheels that will fit your HX35 core.

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--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

I think Procycle has got it. Best to get a smaller turbo housing. Headwork, optimal mixture under no/low boost, and wrapping to retain heat will make some substantial difference, but likely not huge. Cam lift might help, but more duration will likely make the boost threshold go UP. Pulling the cam timing back to 102 or so CL might also help.

Lou

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Home of Slant6-powered fun machines since 1988

From what I've been able to find the 12 cm turbine housing is the smallest OE part for the WH1C/HX35. Some second generation automatic trucks got a smaller HY35 turbo with a 9 cm turbine housing. There were smaller housings made by Bullseye Power to fit Holset turbos, but they use a Mitsubishi inlet. Banks has a smaller turbine housing, but it's $700.

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Joshua

Josh said what I was just about to. I can't find references to the HX30 used on a Dodge truck. This link gives a breakdown of turbos used on Dodge Ram diesels, but I can't speak to its accuracy. I have seen other forums talking about the H1C being used prior to the WH1C, though. Unfortunately it has an even bigger turbine wheel and housing. Is there any chance I could use the turbine housing from an HX30 or HY35?

Matt, the WH1C has a divided turbine housing. I wonder if we'd see better performance with our up-pipe fully divided all the way to the turbine mounting flange.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

This is interesting. This guy is selling a "genuine Holset" 10 cm housing that supposedly fits all H1C and HX35 turbines found in 89-02 Dodge trucks. He says it will not fit an HY35, so that probably answers part of my above question.
Of course I wonder what the original application was...

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Yes, I should have said HY35 instead of HX30. The 30 came on the 4 cylinder Cummins.
I'm 90% sure the 9cm housing will swap over. Probably have to swap the turbine wheel as well which would also help it spool better..

It would be worth posting a few questions at one of the diesel truck forums. Diesel performance guys know their turbos, especially Holsets.

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--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

The WH1C and HX35 use a bolt on turbine housing and the HY35 is V-band attachment so no joy there. The 5.9 Cummins was co-developed with Case for agricultural equipment. It has industrial uses as well. If I were looking for a 10 cm housing I would look at pumps and generators. Honestly a Chinese turbo in the right size is probably faster and easier.

And taking full advantage of the divided turbine housing will help spool times.

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Joshua

I'll keep looking for smaller exhaust housings, but I think a generally smaller turbo is probably in our future. That being said, Bob and I talked it over, and for our next race in late March, we want to focus on getting everything else set up right (cooling, fuel delivery, ignition...) before we change anything with the turbo. Basically get the car to where it can actually stay on track with what we have before we spend more money. See my recent post in the "Event Calendar" section for all the gory details of our November race. We also have issues with the transmission and rear brakes to sort out.

So my plan for now is to get this engine built so we can drive the car again, make sure our new block isn't running at nuclear temps, and spend some time tuning the carburetor better (including setting up the secondaries). I'll spend more time porting the new head this time, and also look at adding a small plate to our up-pipe exit to keep the flow separated all the way to the turbo mounting flange. We also have some work to do on ignition and boost control, but I think that'll be on Bob's list.

That brings me to the camshaft question. OCG regrinds are cheap, so I don't mind getting a core ground for this setup and then changing it out if we switch turbos in a year or so. The general wisdom for turbo cams seems to be that you want more LSA (say 112-114 for a slant) to minimize overlap for a given duration (unless you're running an efficient modern turbo with a backpressure/boost ratio <1, which we aren't). That being said, I'm wondering how much LSA we really need. Is there a decent middle ground between optimizing pre-spool performance with boost that maxes out at 8-10 psi? I know too much duration can hurt low-end power (and this engine's SCR isn't far from stock). If I want enough low-end torque to get the car moving into the boost zone without a lot of overlap, should I stick with a shorter duration that doesn't require as much LSA?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Reliability is always an asset. Once you get control over the ignition timing and dial in the carb it should behave much better off boost.

You have the right idea on the amount of overlap you can tolerate. With the late arrival of boost and the massive power increase under boost I'm thinking that your pressure ratios are probably pretty good, but you need instrumentation to know.

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Joshua

Frank, you can get an adjustable boost controller for under 100 bucks easy. They are simply a needle valve that is inserted with tubing between the wastegate and your boost reference point. Crap, I just realized this only works with an external wastegate and I can't remember if you have one of those or not. I would really attack your cooling issues first. Might need to add an engine oil cooler to your list. Endurance racing with a turbo engine requires excellent cooling capability. Hood louvers/openings can be very effective, but need to be in the right places and the right sizes. I saw that you already have gone in that direction, but I would encourage you to do some more reading up on them. I can't think of the excellent source I stumbled upon earlier this year, dangit. Anyhow, I would advise you to focus on the cooling issues to start with. You can have the best fine-tuned turbo/carb setup in existence, but it would be useless if you overheat quickly.

Brian

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Flyin' Brian

74 Duster, 225, rear-mounted blow through turbo at 12psi boost, street/strip car
"Sixy Beast"

We did add an oil cooler, but it only cools the oil in the external loop that goes to the turbo. Not sure how effective it is because we haven't hooked up an oil temp sensor yet. We have more work to do on airflow, for sure. When we added the intercooler, we had to cut some pieces out of the core support that were never patched back up. We'll be closing up those holes and prettying up the quick and dirty mods to the valence panel, with eventual plans to add an air dam/scoop down low. That being said, this block always ran a little hot even NA at stock compression, and when we tested the water pump flow we got somewhat alarming results. The new block we're building has been acid cleaned, and it'll have a new water pump with some more attention paid to the installed impeller spacing as detailed in Doug's book.

This turbo has an internal wastegate. I'm a little worried it might not be big enough, considering the size of the turbo and the relatively low level of boost we're trying to maintain compared to the OEM use, but we need to do some more testing and see. We didn't get the chance to make many adjustments at the last race.

So for the camshaft, does anyone have a recommended grind? My knowledge on this is marginal, and I don't want to reinvent the wheel. Should I go with something like OCG 1947I and 2106E at 112-114 LSA (which Lou recommended a long time ago)? Just stick with the stock 71+ cam and advance it to ~103 ICL vs. the ~107 we used before?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

No Im not dead. Frank if you need to contact me about what I still know, by all means, I poured a lot of research into your setup lol.
So from memory:

The carb is a holley 450 mechanical secondary. I fought trying to fuel under boost and not so i went mechanical so i knew fuel would flow when i needed it. I added the percy adjust a jet so i could just change it on the fly. Kind of like a mechanical power valve if you will.

The WH1C has a 12cm housing and when I looked to get boost sooner, on the forums there is a 9cm housing that you can get. Also looked into diverter valve to channel exhaust to one side or other. Small side on spool and then it flips to larger side. Google fu will turn up what i mean. Also, i did have it apart at one time and drilled the internal wastegate hole through the divider so to bleed exhaust from both sides of the divided housing. Playing with the wastegate can and will run below 10psi, i ordered that wastegate and started at i think 5-7 and then ended up around 10#

Also, you can look into an 80’s toronado hei module. Normal hei has 4 pins but the 80’s torn has 5. This 5th pin, when grounded will pull 5* timing. It helped with atartimg but in your case can help with boost. Shaker223 said somewhere to never run more than 18* timing. So i set mine up to run 21* max. Then added the hobbs pressure switch into the mix. When it seen 5# of boost it would close and ground the hei module to back me up to 18* timing total.

I cant remember all that i sent with you as ive cleaned out a lot of parts and as i said, my son has taken it over for hos first vehicle. He just got his license a few days ago as a matter of fact. Hes still sad he didnt get to keep the turbo setup lmao.

Not sure you still have my number or email but shoot me an email if you wish. shawn_pohlman@yahoo.com

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225, Offenhauser, Holley 350, A833OD, 3:55, GM HEI,99 Durango starter
BOOSTED! WH1C, BIG FMIC, 10#
Operation Noble Eagle 03-05
Operation Iraqi Freedom 05-07
Operation Enduring Freedom 12- 13

Well, to make a long story short we gave up on carburetion and are now running MPFI with a microsquirt controlling both fuel and spark. I'm going to make a longer post in the Events Section forum with more details about our race last weekend, but the car is running great now. I'm sure there's still a bit of turbo lag, but it's so small I can't notice it. We also advanced the camshaft a few degrees which probably helped the engine's low-speed performance.

Still having issues with boost control, though. We ordered a different wastegate actuator with a lighter spring, but we still can't control boost down to 5-6 psi. With a well-tuned microsquirt we were actually still hitting 20 psi on full-throttle dyno pulls. I needed to limit myself to half throttle or less to keep the boost gauge at 5 psi on long straights. Tried to drill out the holes in the exhaust housing a little more, but it didn't seem to make much difference. I'm surprised to hear that you drilled the internal hole in the divider; I figured a divided housing would've had a hole there from the factory! Maybe we should try drilling those holes out even more before we switch to an external wastegate.

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing