Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

@nutcase couldn't agree more, thanks for the kind words.

I finished up running the steering shaft and as anticipated, the starter proved to be a bit tricky to work around. I tested out a few different routings but ended up running the shaft above the starter then dropping almost straight down to connect to the rack input shaft. This down-turn created a bit of a steep angle, so I ended up running a double u-joint just to be sure it turns smoothly.

It's a bit more complex than I had originally pictured in my head, but it turns as smooth as butter lock to lock and I am happy with the finished product.

I also installed a Classic Performance brake pedal bracket (P/N: 4753FBB). The fitment on this it was pretty excellent and real simple to install.

https://i.imgur.com/LfwrMU0.jpg

https://i.imgur.com/UD9WaAp.jpg

I also fabbed up a little bracket connecting the lower end of the OEM steering column to the fire wall.

https://i.imgur.com/L03284b.jpg

Overall shot of the steering column/under dash. You can see the CPP Brake Pedal Bracket installed in this one (booster isn't connected to the pedal yet).

https://i.imgur.com/VV3hfk9.jpg

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Very nice work on that column.

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Hey everyone, I was on a bit of a hiatus for the past few months, had some other life stuff going on and had to put the truck on hold, but I’m back at it now…time for some updates. Next task on the truck was to start working on some turbo airside/exhaust plumbing. Step 1 was to mount the intercooler. I picked up a Mishimoto G-Line intercooler a little while back; the plan is to make up some brackets that will mount this to the OEM radiator support.

This is also the first time I get to put my new CNC plasma table to work (a birthday present from my lovely wife – perfect timing). I started by modeling the intercooler in CAM (Fusion 360) and design some brackets around it. After some tweaking I cam up with a design I was happy with.

https://i.imgur.com/y0pQwFU.jpg

Cut the brackets out, and welded them up

https://i.imgur.com/i4DLG1s.jpg

https://i.imgur.com/jJ0Bbfb.jpg

I mounted the bracket to the radiator bracket using some aluminum standoffs and mounted the IC to the bracket with some rubber bushings. Very happy with the final product, this CNC table is my new favorite tool.

https://i.imgur.com/23rk7iT.jpg

https://i.imgur.com/DfU0LOH.jpg

https://i.imgur.com/yDjIchI.jpg

I'm thinking that i might want to make up a little air deflector for that big gap between the bottom of the IC and the apron…

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

love it! good use of "lightening" holes too haha

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Very nice work!

-Joe

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

yeah it's a racecar, I figure each one of those holes should give me a tenth in the quarter...lol

I got to work on some turbo plumbing; I used a combination of 2-1/2” and 3” stainless tubing. I started with a pile of mandrel bends and started cutting.
The early 3 bar grilles have an extra support link that connects to the frame, this was the first obstacle to deal with. After some measuring, looking, measuring and a lot more looking I started cutting. I started off with the passenger side (IC to engine).

https://i.imgur.com/YAqRHs7.jpg

https://i.imgur.com/qhjHea3.jpg

https://i.imgur.com/5iKcYNx.jpg

https://i.imgur.com/bvSagAU.jpg

The passenger side (high pressure turbo to IC) proved to be much simpler. I turned the compressor housing and it ended up beinga straight shot…blind luck on that one

https://i.imgur.com/MqGzt2L.jpg

https://i.imgur.com/OgUBPQq.jpg

Also, bit of a course change…decided to go with compounds (HX30 over an HX35). I got to work mocking up the hot pipe. The area between the exhaust manifold and inner fenders looked gigantic when there was nothing there…needless to say, space disappeared real quick when I started hanging the turbos

https://i.imgur.com/bcemelw.jpg

https://i.imgur.com/mZrIOq2.jpg

more to come…

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

That’s some awesome looking work you’re doing. Wish I had those mad skills!

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Great build. Love the attention to detail and execution!!

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Thanks for the kind words, very much appreciate it.

Finished up the cold pipe last night. I used a full-round tube donut to makeup the tight radius of the u-bend. The radius was good but tube itself was fairly out of round and didn't fit up too well to the straight tubing. Not sure if it was just the manufacturer I went with or if its a common thing to these. Kind of a pain but should be able to blend it when I finish weld it.

https://i.imgur.com/XFSiIZd.jpg

https://i.imgur.com/rNfCuCn.jpg

I have all the air-side plumbing done now. Nothing too flashy but happy with the final product.

https://i.imgur.com/t27PNkU.jpg

Now just have to put some time under the hood and burn in some finish welds…

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

I always thought there was room for a decently sized intercooler there ... thanks for proving my thoughts for me.

Fab work looks awesome! I really like those intercooler brackets. Do you have a link for the plasma tab,e you have?

Thanks!

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Yeah there is a boat load of room between the radiator and front grille in these trucks. The IC I have in there is 3" thick but you could definitely fit a much thicker/wider/taller unit.

I have a Langmuir Crossfire plasma table. I am still getting cut speeds/amperages dialed in but I am really happy with it so far, very crisp clean cuts. It is definitely not an industrial level table, but its perfect for teh weekend warriors like me.

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

outstanding!

where is that intake pipe running off to?

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

hey man
grate work and fabrication on this truck
one question two turbos ok quite normal on modern diesel engines.
I know a big and a smal one to have boost over the hole rpm range.
So you use either the mal one or the big one
But in your configuration they are one after the other, why? And how do they work? Just doubel the boost?
so long
Arnd

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Joedoh: the U-shaped pipe that i think you're referring to connects the outlet of the atmospheric turbo to the inlet of the high pressure turbo. I descired this in a bit more detail below.

For this build I decided to go with a compound turbo setup. In most simple terms (and forgive me if I’m going too basic), a compound turbo system combines two different sized turbos (one smaller, one larger), arranged in series to provide a more balanced power curve across the RPM range. Essentially you are combining the quick spooling characteristic of the smaller turbo with the high RPM, big power capabilities of the larger turbo.

Now, to get a little more in to the arrangement of this setup: The smaller turbo is called the high pressure or secondary turbo; the turbine is connected directly to the exhaust manifold and the compressor discharges directly to the intercooler. It is the first to spool up and provides power off idle in the lower RPM range. The larger turbo is called the low pressure, atmospheric or primary turbo; the turbine is connected to the turbine outlet of the smaller turbo and the compressor discharges to the inlet of the smaller turbo’s compressor. By connecting the turbos in series, you are able to reduce the work done by each individual turbo and in doing so increase the output efficiency. Plumbing the turbos in series also allows for a greatly reduced drive to boost pressure ratio (ideal is 1:1).

To visualize how this works in the real world; when you get on the throttle, the small turbo will quickly spool up and provide a quick punch of power right off the line. As the RPM increases and the smaller turbo starts to come out of its efficiency range, the larger turbo begins to light off and take over, continuing to provide power through the higher RPM ranges.

For my setup, I am using an HX30W as a secondary turbo (connected to the exhaust manifold) and an HX35W for the atmospheric turbo (located below the HX30W, kind of hard to see in the pictures). I will post up some better pictures of my turbo setup this week when I take them apart to finish weld everything.

I found this graphic someone else made up (not my work) that illustrates the setup pretty well.

https://i.imgur.com/9h7538p.jpg

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

I was able to put a few hours in the shop this week and finish welded some of the stainless. Nothing too pretty but it should do the job. It’s about a 15’ weld…looks good from about 15 feet away lol. On to some pictures.

I used a spare regulator I had laying around and put together a little argon purge rig.

https://i.imgur.com/AbyTzHj.jpg


Final product, definitely need some more practice with my tig machine…go easy on me

https://i.imgur.com/He1Gq9m.jpg

https://i.imgur.com/fPnMe71.jpg

https://i.imgur.com/AAiSCZh.jpg

https://i.imgur.com/Rj2lyh6.jpg

https://i.imgur.com/PQVEndZ.jpg

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Quick update to the build; I popped the cab off and mocked up the exhaust (without a lift I figured getting the cab out of the way this was the easiest way to go). The piping is all 3” 304 SS, I threw in a few bellows-type flex joints and found some pretty trick weld-in hangers. Getting over and around the frame in the rear was a bit tricky, but nothing a few pie cuts can’t fix.

https://i.imgur.com/IJBXAEc.jpg

https://i.imgur.com/8A3w6SY.jpg

I upsized the tip to 4”, added a few more pie cuts and cut in a teardrop tip. Pretty happy with how it came out.

https://i.imgur.com/lNmGKyI.jpg

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

While I had the cab off I also put the transmission shift kit together. The transmission is a ’94 Chrysler 47RH and the shift kit is from Lokar. The shifter mechanism is pretty excellent; it indexes very smoothly and is really tight. The one complaint I did have was in the rod connecting the shifter arm to the shifter linkage. The rod was ¼-28 threaded rod and was a bit flimsy. My installation required bending it slightly (per the instruction manual) to allow it to clear the casing. That caused the rod to flex when shifting, causing a jerky-rough feel. The solution was relatively simple: I grabbed a piece of brakeline and used it to sleeve the threaded rod. It was simple and drastically stiffened the linkage.

I also picked up a Kick-Down Cable kit from Lokar. This installation was very simple and again, the kit itself was pretty high quality.

Now, on to the pics.

https://i.imgur.com/MzKY5Xg.jpg

https://i.imgur.com/uSVkxjY.jpg

https://i.imgur.com/B4oyhYH.jpg

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Nice work.

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Wow that is awesome. Maybe ill do something like this after my 70, if I ever finish it hah

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

:metal:

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Good call on adding brake line to stiffen up the shift linkage. I will have to remember that as I have a similar set up.

Thanks
Marc

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Nice work. Great fab skills. Steve

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

I'd like a look at the inside of the tubing on those purged welds.

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

Thanks for the kind words everyone, i haven't been able to put much shop time in lately, having a newborn in the house really makes time fly right on by.

This gives me some motivation to get out there and get some work done, updates to follow!!

Re: ’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air
 

such a cool build. lovin the progress bud