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GMx turbo upgrades for towing heavy, worth it?

Will L.

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Boulder City Nv
You have an hx35 sitting around....
want to run the gm instead because of....

Dude- we know you can fabricate. You know how to cut plate steel and weld the drain bib on for free for the drain. Lil chunk of pipe, with pie cuts from the bandsaw, and some welding and you’ll have the exhaust done and turbo mounted in a few hours. Probably have the Supply hose Fittings in a shelf in that work trailer, if not they’re at the shop where they make hydraulic hoses like your oil hose- which would surprise me if you dont have a hose crimper in that trailer too.

I have cousins on the other side of the lake from you btw. They move around- lehi to payson areas, cant remember where at right now. There is exactly 87 men in that whole part of the state that cant make something from nothing themselves. 86 are dead and 1 is a rumor. At least that’s what they tell me!
 

red

stubborn Texan displaced to Utah
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Eagle Mountain, Utah
You have an hx35 sitting around....
want to run the gm instead because of....

Dude- we know you can fabricate. You know how to cut plate steel and weld the drain bib on for free for the drain. Lil chunk of pipe, with pie cuts from the bandsaw, and some welding and you’ll have the exhaust done and turbo mounted in a few hours. Probably have the Supply hose Fittings in a shelf in that work trailer, if not they’re at the shop where they make hydraulic hoses like your oil hose- which would surprise me if you dont have a hose crimper in that trailer too.

I have cousins on the other side of the lake from you btw. They move around- lehi to payson areas, cant remember where at right now. There is exactly 87 men in that whole part of the state that cant make something from nothing themselves. 86 are dead and 1 is a rumor. At least that’s what they tell me!
Hahaha you're right I can, just being lazy with the fab stuff because the 3500hd is the daily/only driving truck right now and have other priorities first. Got back from an interview on friday, might be going back to work in the Texas oilfield again this summer (fingers crossed) which would be great for the income, but puts towrig reliability and getting the trailer ready for a long trip first.
 

WarWagon

Well it hits on 7 of 8...
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AZ
@red You did ask and not only was the answer "NO!!!" but thrown some better options out there for you. With a transmission that won't allow you to stay over 2000 RPM for any shift IMO the HX40II is also a bad choice. Very slight difference in lower spool RPM that was hard to notice with an auto.

If you got an afternoon with nothing better to do take @Paveltolz up on his offer and try it out. The exhaust housing mods can help vs. just a wheel. Anything to get the backpressure down is a major improvement esp. if it gets the load off the cooling system and power robbing cooling fan. Exhaust restrictions via backpressure add serious heat to an engine.

Again a wheel alone on the compressor side is a BFD when the problem is the exhaust side. Compare the size of the problem area exhaust housing and that should explain a lot.

ATT, HX40II in random eBay who knows config, and GM3 scrapmetal.

largemedsmall.jpg

It was one of the original testers for the ATT that noted the CAC added to "lag". With the ATT you are literally in NA mode below a specific RPM and ANY restriction is just that till it reaches an RPM when it can light off. You got enough RPM (say 2500) there is no lag. You go from 0 PSI to 15+ PSI faster than your foot can hit the floor. At the same RPM a GM3 goes from a parasitic 6 PSI to 14 and CHOKES... (Hell a 2008 Duramax will seriously lag it's modern turbo if you get on it, off it, and then floor it.)

1000 TO 8000' Altitude would run the GM3 up 2 PSI. So "boost creep" is a real concern esp. when running the GMx to and past their choke point. We had to set the turbomaster on the GM3 at 12 PSI at 1000' to keep it from going over 14PSI at 8000'. It started life out in 1992/1993 designed for 6 PSI...
 

Twisted Steel Performance

Anything worth doing is worth overdoing.
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You know these are economy motors, if you keep your speed & rpm's low a gm turbo will do, you know the draw backs and for a budget trip it will work, it's when you push it out of it's comfort zone you get in trouble...

So my vote is drive it like it was designed to be driven and know the speeds it will work safely and save things for later...
 

GM Guy

Manual Trans. 2WD Enthusiast
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NW Kansas and SC Idaho
Love that grade braking coming into SLC on I80. ;) NV4500 in 4th, a/c on, and the GM turbo will choke down 20K... lol

Basically drive with a tender foot and an eagle eye on the temps, and a guy can keep it alive. Dont be afraid to throw the 4 ways on and get down to 1st gear if you have to to keep temps in check.

No $ for upgrades sucks. Hang in there!

If you have any issues between there and TX, give a message and I can try and help.
 

quadstar87

Quadstar Tuning LLC
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PA
We actually have a GM8 installed on our 94 right now with a pressure ratio logger on it, however, it's gross winter and we only drove it once on the last nice day we had. Not because we want to run the turbo, but because we got a better data logger than we used to have and want to save the data to our toolbox.

Stock turbos work ok at low boost. Even when we add the wicked wheel, you want to keep the boost lower, say 12psi, to enjoy the gains a wicked wheel provides. If you turn it up more, you are still just pushing it past where it's efficient and going backwards. Say you have a stock 4911 pump or a DS4 that's not tuned, this might be the route you want to go and not modify your truck too much.

In other words, if you have enough fuel to warrant more airflow and try to accommodate that with a GMx turbo, it's not going to be a great fit.

There isn't a "one turbo fits all" solution for every single situation, especially manual trans trucks.

The s54 is a hx35. It's just not an off the shelf turbo. He uses a combination of genuine holset parts to build a turbo to better fit the 6.5.

The 12cm is a little small for the 6.5. And the s54 uses a larger a/r turbine housing because of that. But with a manual trans and heavy towing. A slightly tight turbine housing will help with low end spooling. Either turbo should be great for a 6.5 used for towing. I personally have not ran a s54 so I cant comment on how it does with a nv4500. But the hx35 off the cummins does a great job for a cheap off the shelf upgrade.
The HX35 is definitely one of the most popular budget swaps and that's why we support DIY swaps with install kits and parts needed outside of just selling our full turbo kit. We call the HX35 a budget kit because it's definitely better than stock but you still see a 2:1 drive pressure ratio if you push it. Here's a log from some auto trans 3rd gear pulls on a P400 with a 14cm HX35 that had the gate set at 15psi. (Auto spikes a a lot faster due to unlocked TCC)
HX35_Pressure_Ratio.png
 

WarWagon

Well it hits on 7 of 8...
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AZ
You know these are economy motors, if you keep your speed & rpm's low a gm turbo will do, you know the draw backs and for a budget trip it will work, it's when you push it out of it's comfort zone you get in trouble...

So my vote is drive it like it was designed to be driven and know the speeds it will work safely and save things for later...
It's simply the wrong turbo and powertrain combination including the rear end ratio for a HD truck asked to tow. Maybe in the flatlands at 55 MPH. The speed limit here is 75 MPH and it gets fatiguing getting passed by everything esp. the trailer sway from big rigs passing. With 4.10's and the auto 2200 RPM is about 62 MPH: WOT and that's all the GM3 got on the constant slight grade into Phx from the west and any slight headwind I recall fighting as well. That's with the TCC override lock up switch thrown. It's worse unlocked.

With his lower gearing the RPM's are going to be higher. Utah has 80 MPH speed limit zones that exceed the speed rating on most ST trailer tires and the speed rating on some 19.5" tires. So yeah not going to stay with traffic regardless. A 10 MPH difference from the speed of traffic is rough. 20 MPH slower than traffic IMO gets to be dangerous as you make even the slow vehicles pass you ...

@GM Guy It would be interesting to know the RPM ranges you are using with the MT's. Specific to the RPM drops between the gears.

Careful the 4 way flashers don't trigger the trailer brakes. :facepalm: We have used 4 Low on some grades to keep temps in check before a cooling system upgrade. The OEM 6 blade fan didn't get removed fast enough...
 

red

stubborn Texan displaced to Utah
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Eagle Mountain, Utah
It's simply the wrong turbo and powertrain combination including the rear end ratio for a HD truck asked to tow. Maybe in the flatlands at 55 MPH. The speed limit here is 75 MPH and it gets fatiguing getting passed by everything esp. the trailer sway from big rigs passing. With 4.10's and the auto 2200 RPM is about 62 MPH: WOT and that's all the GM3 got on the constant slight grade into Phx from the west and any slight headwind I recall fighting as well. That's with the TCC override lock up switch thrown. It's worse unlocked.

With his lower gearing the RPM's are going to be higher. Utah has 80 MPH speed limit zones that exceed the speed rating on most ST trailer tires and the speed rating on some 19.5" tires. So yeah not going to stay with traffic regardless. A 10 MPH difference from the speed of traffic is rough. 20 MPH slower than traffic IMO gets to be dangerous as you make even the slow vehicles pass you ...

@GM Guy It would be interesting to know the RPM ranges you are using with the MT's. Specific to the RPM drops between the gears.

Careful the 4 way flashers don't trigger the trailer brakes. :facepalm: We have used 4 Low on some grades to keep temps in check before a cooling system upgrade. The OEM 6 blade fan didn't get removed fast enough...
Yea, I'd love to be down around 2000-2200rpm cruising at 70, but WW is right. With 225/70/19.5"s (32"s), 5.13 gears and .75od from the trans 60mph puts the truck at 2450rpm. Eventually will regear so towing at 70mph will be good but that won't happen until after the engine gets some performance work (turbo). Other than the FRB-5 fuel pump and the exhaust cut after the downpipe it's stock, no tune ds4 pump with GM5 turbo.

Nice thing with the HD's is the better airflow up front, don't overheat as easily as the lighter trucks.


We actually have a GM8 installed on our 94 right now with a pressure ratio logger on it, however, it's gross winter and we only drove it once on the last nice day we had. Not because we want to run the turbo, but because we got a better data logger than we used to have and want to save the data to our toolbox.

Stock turbos work ok at low boost. Even when we add the wicked wheel, you want to keep the boost lower, say 12psi, to enjoy the gains a wicked wheel provides. If you turn it up more, you are still just pushing it past where it's efficient and going backwards. Say you have a stock 4911 pump or a DS4 that's not tuned, this might be the route you want to go and not modify your truck too much.

In other words, if you have enough fuel to warrant more airflow and try to accommodate that with a GMx turbo, it's not going to be a great fit.

There isn't a "one turbo fits all" solution for every single situation, especially manual trans trucks.



The HX35 is definitely one of the most popular budget swaps and that's why we support DIY swaps with install kits and parts needed outside of just selling our full turbo kit. We call the HX35 a budget kit because it's definitely better than stock but you still see a 2:1 drive pressure ratio if you push it. Here's a log from some auto trans 3rd gear pulls on a P400 with a 14cm HX35 that had the gate set at 15psi. (Auto spikes a a lot faster due to unlocked TCC)
View attachment 59493

For a manual trans heavy towing application (15-26k combined weight) does the hx35, 54, or 60 perform better in your testing?
 

94DieselSub

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Reno, NV
@quadstar
Looking at the various HX35 maps, 15psi is in the first 20% of the map(s) efficiency island. IE, way down in the high 70's/80% range.

Driving the HX35 turbine harder seems to improves the efficiency data points. It would seem as though the drive pressure curve would plateau-off through the meat of the compressor curve (20-35psi).

The Cummins HX35's were optimized for a 20-35psi wastegate. Too high for many 6.5's to achieve any longevity.

Looking at the discharge port following the turbine wheel on a HX35, that dimension is rather small! Even with the wastegate flap wide open, the combined cross-sectional area looks to equate to a 2.25" tube. Regardless of turbine housing size, that seems like a choke-point for 6.5L of displacement.

Although, I do still plan to run one myself.
 
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