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Old 01-31-2023, 03:10 PM   #1
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3126B Turbo Upgrade

I was suffering from a few minor exhaust leaks between the manifold and head, and I was also suffering from an overboost condition that appeared to be related to the wastegate seized closed on my turbo. This necessitated pulling the turbo and exhaust manifold.

Never one to overlook an opportunity for an upgrade, I decided to upgrade my turbo while I was in there. This turbo is on the smaller side for a 330 HP 3126 (Cat uses this same turbo in 250-330 HP engines, maybe 350 HP ones as well) and also it's a 23 year old turbo that's probably closer to a 30 year old design. There have been a lot of improvements in turbo technology since then.

3126s from the factory have a standard T3 divided flange on the manifold, which gives a lot of options for turbo upgrades. I wanted to stick as close to bolt-in as possible, and not looking for any real power gains (more looking for lower EGTs and better efficiency) I decided to go with a Borg Warner S300SX-E (which is basically the new version of the S300G that my engine came with.

The turbo is essentially a bolt-in. I say essentially because it bolts up to the exhaust manifold, but it does slightly move the exhaust flange and also extends the compressor inlet about 1/2" forward on the engine (towards the rear of the bus). This resulted in me having to trim a bolt that was too long off the alternator to make the inlet elbow fit, and I'm going to have to rotate the exhaust brake to make that fit (right now the actuator is interfering slightly with the transmission dipstick tube. I had to buy a new boost elbow ($23 with clamps off Amazon) as the new turbo needs a 2.5" hose on its outlet, while the original turbo was 3". The inner diameter of the compressor outlet is the same, but the new turbo is machined down to 2.5" instead of the original turbo being as-cast at 3". Lastly, I'm also going to have to have a new hose made up for the oil supply as the new turbo doesn't have the bolt holes for the bolt-on pipe. And while I had the exhaust manifold off, I wrapped (some of) it in header wrap, to help keep some more heat in the exhaust and out of the engine bay. I had already been running a turbo wrap on the turbine housing side and bought a new one that I will put on the turbo.

I don't have the installation fully completed yet, but so far it's coming together well. I've got a long trip coming up after it's back together and I'm looking forward to seeing the results. My expectations are a bit higher boost at the same fuel flow/part throttle (full throttle will still be governed by the wastegate), lower EGTs/IATs, and hopefully a little better fuel economy related to those.

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Old 01-31-2023, 06:05 PM   #2
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Nothing insurmountable. You will provide before and after dyno runs. Right?
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Old 01-31-2023, 06:22 PM   #3
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Quote:
Originally Posted by JNSNWT View Post
Nothing insurmountable. You will provide before and after dyno runs. Right?
Before would be hard since everything is taken apart and it's starting to go back together. If you want to pay for after, I'll provide an after run, and even video it and put it on YouTube.

The goal isn't more horsepower - it's more airflow for the same fuel flow and lower EGTs that go with that, plus a more efficient turbo that should also be able to get the same airflow at a lower IAT. Plus having a functioning wastegate, that'll be nice.

And no, nothing insurmountable at all - I expected it to be a "mostly bolt-in" and that's what it's proven to be. I'd considered getting the PDI manifold but I didn't think the extra cost would be worth it for my application.
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Old 02-07-2023, 02:47 PM   #4
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I managed to get the turbo fully installed and ran the engine - it passed the leak check.

My Amazon boost elbow showed up and I got that on, and I had a new hose made up at the local hose shop. I explained the location, and they did what they often do - full overkill - and it's a hydraulic hose rated to something around 3-4k PSI and plenty high on temperature. It fits beautifully, and the factory turbo drain also fit just fine as well. I did have to enlarge the bolt holes on them slightly with a 3/8" drill bit. They were just undersized such that the new bolts didn't go through, and then everything went on just fine. I was happy that I was able to start the engine and everything worked just fine with no leaks.

The one issue that I do have right now is with the wastegate actuator. The one they sent me is about 3/4" shorter than the stock Cat wastegate actuator, which is just enough for it to hit the drain tube. This makes me really glad that I didn't install the wastegate actuator before putting the turbo in. I called the company I bought the turbo from and they're sending me a new actuator, which is also adjustable. I got the actuator off of the old turbo (and confirmed that my old wastegate was 100% seized up tighter than a drum) and I'll be able to reuse that bracket. So once I have that on, I can test drive it and we'll see how she does.

I could've waited on the start, but I also wanted to do an air system leak check, make sure that the fuel cooler I installed on the return line isn't leaking (it isn't), and make sure that there were no coolant leaks from where I installed the new thermostats (there aren't). So, the wastegate actuator and finishing up the exhaust wrap are the last things I need to do before test driving it, hopefully next week.
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Old 02-08-2023, 09:27 AM   #5
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Iím glad to hear everything is coming together and working out for you.Thanks for keeping us in the loop.
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Old 03-04-2023, 07:04 AM   #6
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I test drove the bus the other day for the first time with this new turbo as well as a number of other changes I did to the bus. One concern that I (and some people on a Cat group I'm in) had stated was the potential of a larger turbo making the bus more difficult to drive due to excessive lag. The place I bought the turbo from convinced me to go one size up on the compressor from what I had been originally intending.

Looking at what turbos people put on 6.7L Cummins engines in Rams (which make more power, but at the end of the day an engine is an air pump) made me figure this would be fine from the 7.2L of the 3126. In the end, this proved to be true. While the lag is slightly more perceptible vs. the stock turbo right off the line (maybe...), the end result is that this is obviously a better turbo. On the initial test drive it appeared my induction air temps were about 20 degrees cooler than I would've expected with the old turbo.

I hear the turbo a lot more than I did before with the old one, and it seems like it's boosting more for the same fuel flow, which is the goal. This lowers EGTs, and I'd say 50-100F is what I've observed so far, although the next trip will tell more about the total behavior, including at altitude.

The turbo I picked was a Borg Warner S300SX-E, specifically an S363, with a wastegated 0.80 AR housing. The next size up would be an S366, and from this initial test drive my thought is that I probably could've gone up to the S366 to get a little more airflow/boost at the expense of a hair more lag, but still acceptable. But I'll reserve full judgement until I put some more miles on it.

The only issue I'm having so far is that the engine is still suffering from an overboost condition and hiccups. This isn't entirely surprising, though. The wastegate on the old turbo was completely seized, so I essentially had an unwastegated turbine housing sized small enough that it needed a wastegate. The new wastegate actuator I adjusted for the arm to be the same length as the stock wastegate actuator arm, but it's still a new actuator and thus probably has a different spring in it. It ended up being easier to adjust with it installed than I was expecting, so I turned it back a turn, and will see how it does on the next drive, and can adjust further if needed.

I definitely feel like this has more top end power, and I expect it does and will have better fuel economy. Even though fuel flow isn't increasing, this makes sense. The air should be cooler (that's good and probably does make the computer add a bit of fuel from that alone) and also being a larger turbo, I'm sure the exhaust backpressure is lower, which also reduces pumping losses and makes more power.

I'll report more after I put more miles on it and take the next trip.
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Old Yesterday, 06:35 AM   #7
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We just got back from an 11 day, 3500 mile trip. Going out west so we ended up at a max of 7,000 ft elevation. The turbo got a good workout and I had a good opportunity to explore its performance.

I'm very happy with the overall performance. No doubt, my induction air temps are generally around 20F cooler than they were before. EGTs are roughly 50-100F cooler in cruise (depends on the point), although at full power they tend to be around the same. A little more turbo lag off idle at elevation, but none that's noticeable at lower altitudes. The cooler IATs I think play into better overall cooling since the intercooler isn't pre-heating the air as much before it goes through the radiator. I attribute most of that lower IAT to the turbo itself being more efficient, and the lower EGTs to the slightly larger compressor section feeding more air in, running the engine a bit leaner for the same fuel flow.

Power improvement? I do feel like it's improved some, but based entirely on the butt-o-meter and no dyno results. Logically, it would make sense for there to be some power improvement as the new turbo should be significantly less of an exhaust restriction vs. the old one (I have a video up comparing the two, and the size of the turbine outlet is obviously larger).

If your 3126 needs a new turbo, I can definitely recommend this one. And if your diesel in general needs a new turbo, an upgrade seems worthwhile.
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Old Today, 10:51 AM   #8
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Thanks for the update! I really enjoy going along for the ride without having to get my hands dirty lol
I didn’t see any before/ after boost pressure numbers. Can you share those numbers with us?
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Old Today, 12:27 PM   #9
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Quote:
Originally Posted by JNSNWT View Post
Thanks for the update! I really enjoy going along for the ride without having to get my hands dirty lol
I didnít see any before/ after boost pressure numbers. Can you share those numbers with us?
Glad you like the updates

I don't post many pictures on here since most of my photo documentation is on the YouTube videos, you can check those out for more fun.

The Cat ECU can only display up to 32 psi boost. I get my boost reading from my BlueFire (through the ECU). The fuel cutoff is around 44 psi. With the old turbo I was hitting the fuel cutoff anytime I got it to full throttle. Keep in mind the wastegate was seized, so it was just making boost until it either didn't have enough exhaust to keep spinning the compressor, or the fuel cut off and thus reduced the exhaust flow. With the new turbo it did that at first, and now I've got it to where it's right around 31 psi.

I'm honestly not sure what the stock boost should've been. I've heard 25-30 psi numbers for 330 HP but I can't find a spec. One thing to remember with diesels is that boost matters, but it's not necessarily the same as with a gasoline engine since diesels run lean and more boost can just mean running leaner (which isn't a bad thing).
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