1971 GMC Donald

[mxerhale]

We are a rare breed, aren't we? I've been a truck guy my whole life, the faster the better!

[mxerhale]

Now after a few trips up and down my 70 foot driveway, I made the executive decision that the 4" straight pipe was going to be too obnoxious for real world driving. I went on the hunt for a cheap slender muffler that I could tuck somewhere under the bed out of the way. I ended up finding a cheap 24" long 4" straight through muffler from Summit for $60 along with a couple bends to complete the exhaust far enough back to dump over the axle.

I envisioned the finished exhaust routing following the frame rail as it bends up over the axle similar to how a motocross or sport bike would look. The muffler had to take a few whacks with a large hammer to maintain some clearance with the frame as well as the straight portion getting some where it goes under the rear cab mount and past the cab sheet metal. The muffler was money well spent, it definitely quieted the engine to a very tolerable level to the point where you can have a conversation with someone while driving around.

[mxerhale]

Not sure that I ever mentioned a few oddball things that I did during the build, so here goes:

Mounted a CPP 1 1/4" front sway bar and stole another member's idea (can't remember who) to flip the rear shock mounts and flatten them out to mount those shocks on the outside of the frame, both of these mods seem to really help this old truck handle way better than I remember!

I installed Ride Tech street grip lowering springs on both ends along with some CPP lowering spindles up front and custom machined blocks in the rear. There are a few little odds and ends that a couple friends of mine custom machined for me along the way, like a one off ignition bezel.

I didn't touch the internals of the front calipers, tie rod ends, or rear differential, they are all original and work fantastic. I did replace the trailing arm and panhard bar bushings along with new ball joints, front wheel bearings, rotors and lower control arm shafts.

The cab had a CB radio antenna hole poked right through the center of the roof, so rather than filling it, I had my son 3D print me a fake shark fin antenna.

The rear passenger side of the bed where the taillight mounts had been hit and bent a little and instead of trying to pull it out, I used a heat
gun to mold a new lens to match the curve.

[hewittca]

I'm circling back and catching up on build threads that I am following. I realized I missed your last updates, and that you haven't updated in a few months. I hope that you're able to keep making progress! I really like those fat tires you put on the rear. I am actually looking at putting the same size tire on the rear of mine, so it's nice to see one installed for reference. I'm hoping I can tuck it inside the fender, but it looks close to not making it on yours. Hows your tire to fender clearance? And do you know the backspace of those wheels?

[mxerhale]

I did get pretty sidetracked with a family emergency, but things have calmed down again now.

Those tires are absolutely as far out as I think they can be without hitting, but I've put at least 200 miles on them without a problem. Unfortunately I can't remember the back spacing so I'll have to pull one off and measure it before saying. There's definitely room under the truck because it has about 2" of clearance on the inner side still!

Now, as for progress, I need to look back at my last posts and see if I've really done much more work. I have driven it a lot, probably 10 times to work and multiple trips around town. I've spent a lot of time learning how to tune the Terminator X Max and have it running really good almost everywhere. It's been in 97 degree traffic jams and on the other side of the spectrum has seen 9lbs boost a couple times. I am going to build a tune that is boost by MPH this winter and make it a little more controllable. It's as fun to drive as I ever imagined it would be, but it'll spin the tires and get a little sideways at 50MPH if I jump on the throttle. That's not a bad thing, but sometimes I want it to just hook and feel that acceleration.

[PowerdbyChevy79]

Subscribed...

[mxerhale]

Thought of a few things as I was laying under the truck adjusting my trailing arm mounts up a spot because I felt a slight shudder at about 85MPH the last time I drove it to work and it seems as though the driveline angle is a little different now that the suspension has completely settled. Anywho...

I did get a new steering wheel finally and put it on over the Xmas break along with a new heater control panel that my good buddy custom made me.

Also pulled a plug after my 9psi hit to see how things were looking in there.

Hewittca, I didn't pull the wheel off, but i did see that the back side of the wheel is almost perfectly flush with the drum brake backing plate and I'd guesstimate the backspacing pretty close to 4" on those rear wheels.

[hewittca]

Originally Posted by mxerhale

Hewittca, I didn't pull the wheel off, but i did see that the back side of the wheel is almost perfectly flush with the drum brake backing plate and I'd guesstimate the backspacing pretty close to 4" on those rear wheels.

Awesome, thanks for checking!

[mxerhale]

I'm not sure if I mentioned somewhere earlier that I put in a 3 port Mac valve and an electronic boost controller that would hopefully allow me to adjust boost on the fly. After doing a bunch of data logs I decided to do some back to back tests and found out quickly the boost controller was doing nothing! Lots of more reading online and looking at Holley schematics helped me figure out where I went wrong and now it functions great. I can turn it down to about 4.5 psi and have still not gotten brave enough (nor had the need for!) anything over 9 psi. I typically keep it between 5 and 7.5 psi for just driving around in case I need a little passing power. I have it setup as boost by MPH in the Terminator X software and that seems to make it much more civilized.

Another thing that I haven't mentioned is my heater setup. I'm not a big fan of cold weather or being cold, but my 4" exhaust made me delete the original heater box so I got creative and installed a smaller one in the cab behind the glove box. My friend built me a little PWM controller so that the blower motor is essentially controlled by a rheostat and I ran some Amazon hoses to the defrost vents and one extra vent dumps on the foot well of the passenger side.

Last but not least, my friend finally found me an honest to goodness GMC front bumper! It came off of a Carryall and it has the perfect patina to match my truck.