1971 GMC Donald

[cornerstone]

Man I'm diggin' this truck! What kind of power do you think it'll have with your current plan?

[mxerhale]

Well, that depends on how brave I get! It has Snake Eater 100lb injectors and I'm almost setup to run E85 in it now, with that in mind I should be 700-800hp. That would be with 20lbs or so of boost and a lot of tuning and some good air (a rare commodity in Utah!), but driving it around on 4-5lbs of boost in hot weather like I have been for about a month it definitely seems doable. It's pretty damn fun already!

[mxerhale]

I'm sure that I have skipped around the order of the build a little, mostly because it took over 2 years to get through and the old memory isn't what it used to be!

Having thrown out that disclaimer, I shall continue on. Here are some shots of radiator mounting tabs that I made and the one-off aluminum intercooler bracket that a friend of mine did for me. Then I moved on to 2 things that I had been working on in my brain for close to a year, a fuel filler door and a battery bracket. I have to admit (without hurting my shoulder from patting myself on the back too much...) that they turned out just about how I imagined they would and seem to work almost perfectly. So far.

The door took some serious time with a Dremel and oodles of little cutoff wheels to cut out and then some trial and error coming up with a hinge setup that was robust enough. I also borrowed the Harbor Freight spot welder from a friend and spent some hours getting everything just so with the hinge mounting and the $3 Home Depot push button magnet lock.

The battery mount was a bit easier after I mounted the bed and found one on Ebay that would tuck the battery up far enough for my liking. I didn't really want it in the bed, that looks a bit tacky to me, but I wanted it as far back as possible for some traction.

[mxerhale]

And more

[hewittca]

I really like your fuel filler door. I need to do something similar on my truck and have envisioned it looking just like yours. I'm just wondering, how on earth did you cut those radiused corners! My biggest concern it making nice clean cuts since I want everything to sit flush and use original metal like yours.

[mxerhale]

I tossed around the idea of using a jigsaw or sawzall to cut it out, but eventually settled on a Dremel with a 90 degree adapter after many discussions with my metal working friends. I had my doubts having never actually used one and only owned one because I had inherited it when my mom passed away. At least 3 people specifically said the Dremel was the only way.

I used the red tupperware lid that you see in one of the pictures as my template. It took me quite a few hours laying in the bed and about 47 of those cute little 1" cutoff wheels! You just have to be very careful slowly carving at the metal on the radiuses.

[mxerhale]

At this point I finally got to test fire the engine, and after a few foolish snafus, at one point the Holley software somehow reordered the firing order to go 1-2-3-4-5-6-7-8, it made a few spectacular backfires before I decided something serious was amiss! Once it fired though, it ran perfect! No smoke, clatter, no fireworks, it was quite a relief to hear nothing but the purr through the 18" dump pipe.

Here are some shots of the clearance between the fans and the hot side crossover pipe and the Amazon budget heat wrap and turbo blanket that the entire hot side was covered in to keep underhood temperatures down.

[coldrider]

Sweet truck, its going to absolutely haul at 20psi and E85! Time for some tires.. and maybe bigger brakes

[mxerhale]

Thanks coldrider and yes indeed it's going to need some bigger tires and brakes! I had a friend stumble onto a set of FREE 295/50 15 tires on old chrome wheels. Those things look absolutely monstrous next to the 215/60s that I'm currently running.

As for brakes, eventually I will get some Wilwoods up front and swap the drums for disc in the rear, but that budget thing keeps getting in my way...

I told my son that I wanted it to be just fast enough to scare me.

[mxerhale]

Now that I had the engine running and enough of the wiring to get it to move under it's own power I needed something connecting the trans to the rear end and someway to change gears.

After pricing some local places I found a place in Idaho called Full Torque Driveshafts that were willing to build what I needed, a 3.5" diameter exceptionally long shaft that would hold up to my dreams of 800hp! They got it done in 5 days and shipped in a giant box right to my door step this aluminum beauty. It has 1350 joints on both ends so I changed the pinion yoke to a heavy duty 1350 unit to match. I was a bit nervous getting some basic measurements and sending a bunch of money to these guys that were relatively new to the business, but it fits absolutely perfectly.

Next up finding a shifter for a 4L80E was a bit of a challenge, mostly because I didn't want to have to buy different plates and brackets on top of the big $$$ that the shifter itself was going to cost. I ended up with a TCI Diablo and a DIY riser to get it up high enough to where I can easily reach it with my seatbelt on. It comes with about a hundred extra brackets, plates, and doodads to fit seemingly just about any sort of transmission made. Brilliant!

[indymachinist]

Nice to see another LS turbo!

[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.

[mxerhale]

Now that the truck was moving under its own power I started to work on some of the small things needed to make it driveable.

First up was the blinkers, one front and the opposite side back worked when you flipped them on and the brake lights didn't function at all! We surmised that it was a grounding issue and after multiple tries figured out that it was actually grounding out in the column blinker switch. It wasn't my favorite part of working on the truck, but so far they have worked flawlessly since the replacement switch went in.

My VS Racing turbo kit came with a 50mm BOV and flange which would require some aluminum welding, I am not the guy for that job, however a friend of mine at work has a welding business on the side and he is the guy. I think it turned out absolutely beautiful.

My good friend of 20+ years was driving home from work one day and spotted some wheels and tires in a front yard sitting as if they were for sale. He stopped and asked what they fit and how much were they asking for these big fatties and the owner said that he simply wanted them gone, for free! I now have 4 295/50-15s on big older chrome wheels, luckily looks are not my real concern. These things look like steamrollers compared to the puny 215/60-15s that were on it and so far I only have them on the rear and haven't tried fitting them on the front yet.

Look at all that ground clearance!

[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.

[mxerhale]

Latest update here:

Other than a slight oil leak, that I'm pretty sure came from an inadequate breather/catch can setup, the truck is still everything that I hoped for when I started planning it. It handles and drives extremely good which is probably a combination of the Ride Tech springs, outboard shock placement on the rearend, and the caster mod I did on the front control arms.

I have the Terminator set up for boost vs speed along with a boost control dial that adds or subtracts duty cycle to the MAC valve. It took quite a bit of testing to find some numbers that work but it has helped immensely with ramping the boost in gradually and helping with traction.

I finally got the additional wiring installed last week to get my 2 pin alternator charging normally and to enable running E85. Setting up the 1D tables only took 2 tries to get it right, but I splashed in 4 gallons and mixed it with some 93 octane that was in the tank for the initial test run and was pleasantly surprised how easy it turned out! Sensor was reading dead on 10% with the 93 octane and jumped up to 32% when i mixed it and two test hits showed that it was adding fuel all of the time and also adding timing and AFR when the boost went over 1psi. All of this stuff I learned from watching and reading Matt Happel stuff from his Sloppy Mechanics content, the guy's a genius!

[68Gold/white]

I've read here about several folks running manual disc brake setups, and liking them. Obviously 71's and 72's had manual disc brakes.

The factory disc setup works well enough for me, I don't plan to change anything else concerning the brakes, when I get my 67 and 68 converted. I plan to use ALL factory parts on mine.

Carry on!!!

[mxerhale]

I really like the feel of mine and the Wilwood master cylinder is the only aftermarket part in the system.