Yet another GMC build

[OKGMC4]

Trying to problem solve. The terminator x system requires an MAT sensor. I used the hole up top to install a Haltech sensor for 300zx. I had already tapped that hole for 1/4 npt and plugged it but the location was handy. Most that I could find were either 1/8 or 3/8. The Haltech fit perfect. Below that I had installed an aluminum “tube plug” behind the throttle plate. Since I’m going turbo the Holley system requires a GM 2.5 bar MAP sensor. It won’t fit at the rear of the intake but I was able to drill that block off plate and attach the new map sensor onto it.

On a side note I’m feeling super fortunate that I ordered all my big parts a couple years ago. I see that my Trick Turbo manifold and Huron Speed 7875 are no longer available and my Terminator X max is on a lengthy back order.

[solidaxel]

Great location, good idea thanks

[OKGMC4]

Bought a 10an swivel forever ago and it would have fit perfect if I hadn’t bolted a low mount ac bracket in the way. Extended it out with a 1/2npt close nipple and finished the turbo drain line.

[OKGMC4]

Brake lines done. Trans lines done. Had painted my calipers black then wrapped some 320 grit around bar stock and sanded the raised letters. Should look nice through the wheels and advertise that my brakes might not be original equipment.

[OKGMC4]

One thing that has been a frustration has been my side fill arrangement. The gas door is so low that you can barely squeeze the gas nozzle or it shuts off. The pipe didn’t have enough drop and the fuel backed up. Using a pop up cap, up high, should help. I’ll need to patch the gas door now.

[6DoF]

i was going to make the same mistake with the low filler, good heads up. that pop-up cap is a really nice solution.

[OKGMC4]

Originally Posted by 6DoF

i was going to make the same mistake with the low filler, good heads up. that pop-up cap is a really nice solution.

I hope it’s better, that’s why I post this stuff. Maybe it’ll help someone else. Got my 1.5” elbow from Filler Neck Supply. And added a barb so I can run a vent hose to the tank. The old cap angled close to 45 degrees and sort of kinked the hose. Hoping that with more drop and a vent it will flow enough to fill correctly. One time I actually had to leave a gas station and go across the street to fill up. The nozzles pumped so fast I gave up around $1 worth. Squeeze, click, squeeze, click. It was frustrating.

[washington blue]

I'm glad to learn about your problems with the gas fill. I was until now planning the same thing in my build, and I have been concerned about the nearly horizontal fill hose. I did not want a cap in the bed. This change you are making looks like a perfect solution for my worries. Thanks for posting this. Norm

[dsraven]

I did something like that to mine as well, a fender fill. I used a reshaped fill door from another newer vehicle and welded it into the fender making sure the door would open without hitting th box rail. then I used the filler neck from the saame vehicle as it comes with a built in vent hose connection and a screw clicker cap. not sure if it is a vented cap but that is not a problem with my system.

[HAULIN' IT]

Many years ago (late 70's to mid 80's) my dad had a '65 stepside (same bed) & he cut a hole in the back fender...right about where your tail lamp is. There was a 90* bend just like yours but turned angled back & used the end of the original neck, cap, grommet, ect. There was no trouble at all filling it. I dont know what the tank was from...could have been about anything that fit (GM). I dont know if it was because of the longer angle (not so sharp) before the bend or maybe the gas pumps didnt have as fussy of shut-offs back then? It couldnt have been at most an inch higher than yours. It was just below the bodyline & looked like it belonged there! Ironically it was Orange with a White roof. Lorne

[dsraven]

here are a few shots of mine that I dug out of the archives. I chose a round door to fit the theme of the truck better in my opinion. the filler neck bolts to the bracket inside the door area but not attached to the fender. the filler came with a mounting bracket already welded onto it so none of the plastic or light metal anti siphon internal parts get deformed or melted by the need to change something. the door hinges open towards the front so wind will not try to move it when driving

[OKGMC4]

That looks good! I used the square door cuz it was free but I agree that round looks better. I saw this one at Pigeon Forge a few years back and swore if I ever repainted I’d try it out.

[dsraven]

mine is from my 04 envoy donor, same for the fill tube. bigger than that one probably. the envoy came basically flat so I had to reshape it.

[jaws61]

wow that is a awesome build. Love the idea of the turbo.. Going to be one fast truck!!

I've got a few question. With the 245/45R17 front and 275/40R18 tires, what is your ride height of your truck from ground to your rockers and if possible your height from the ground to the top of the chassis?

I'm going to be running a C4 flat out kit too and trying to get the ride height figured out, and trying to get it be around 4.5 inches from the ground to the rocker..

Thanks

[OKGMC4]

Originally Posted by jaws61

wow that is a awesome build. Love the idea of the turbo.. Going to be one fast truck!!

I've got a few question. With the 245/45R17 front and 275/40R18 tires, what is your ride height of your truck from ground to your rockers and if possible your height from the ground to the top of the chassis?

I'm going to be running a C4 flat out kit too and trying to get the ride height figured out, and trying to get it be around 4.5 inches from the ground to the rocker..

Thanks

I haven't put the truck on the ground with full weight since changing the frame. That also means the difference between the gm crossmember up front and the conversion to coil overs from the transverse spring on the rear, plus dialing in the engine setback. Plus, the C5 wheels were staggered but the Rocket Racing wheels are not. I'll try to attack this in parts...

Since I can't say where I'm at now I can say for sure what I knew from before. If you go back to when I first got the truck driving I had the front REAL low. The tires looked cool tucked in the front fenders but it bottomed out on bumps and the tires rubbed pretty bad when turned full lock. I raised it until the top of the tires sat just below the fender lip. Much better ride and no rubbing. That was with the factory K member and small front tires.

When I bought the Rocket wheels I got them all at 18" and run 275/40r18 front and back. Little taller in the front but top of the tire still at the fender lip. I can tell you steering and handling increased tenfold. May be that the truck is a little less tilted, or more rubber contacting the ground, or both...but night and day better.

I just went out and used a tape measure to guess, since the truck is jacked up in the air, but I don't think mine is ever lower to the ground than 7 or eight inches between the ground and the bottom of the front fender. And where you have to put the flatout crossmember you'd have to ruin the suspension geometry to get it any lower. The rear is even worse. In these trucks the C4 suspension sits considerably higher in the rear than the front. If you try to lower the rear too much it will put the half shafts in a bind. They still have to have an angle like any driveshaft. You could try smaller tires to get lower. You could Z the frame front and rear and that would get you there for sure. Then engine placement is tricky. That V8 won't nestle down in the flatout crossmember the way it will a camaro clip. And most people don't want to cut the firewall the way I have.

I like the C4 swap, but it causes as many problems as it solves. All these years I've had trouble getting mine aligned because of the rear. The fender lips hang way over the tires in the rear and most of the new alignment machines can't just push through the wheels the way they should because it hits the fender lip. Think about it, most new cars have BIG ROUND wheel openings that don't cover the tire. I'm actually thinking about either raising the rear fender lips 1.5" or converting all my wheel wells to round just so I can get aligned properly at any normal tire shop. I think C4 swaps are cost effective and get a good ride with a better brake and steering than anything from the 50's ever thought of. But it's probably never going to sit as low as or handle as well as an actual corvette. And all that's in relation to a pickup. My father-in-law has a C4 swapped 62 Vette with an LS1 6 speed that everything fits like GM designed it that way. And I'm a little jealous that mine doesn't drive like his. Go figure!

[OKGMC4]

Was too low to start with, compared to the Vette (which isn't as low as you'd think), and the last pic with the new wheels and tires

[jaws61]

Thanks for all the input for sure,
You sure did have the truck sitting low at the start with the original c4 front..

That sure is some wide tires to run front end and rear, I didnt think it was possible to get that fat of a tire in the truck, I ran a 255 on the front last time and thought that was to close...

I really appreciated you did this..

"I just went out and used a tape measure to guess, since the truck is jacked up in the air, but I don't think mine is ever lower to the ground than 7 or eight inches between the ground and the bottom of the front fender. And where you have to put the flatout crossmember you'd have to ruin the suspension geometry to get it any lower. The rear is even worse." doing that and
I gotta say the truck height looks awesome, making rethink on how long to go.."

I"m not going to be running a C4 rear end in mine, going a different route, so i'll be cutting up some rear fenders by the look of it too..

I like the C4 swap, but it causes as many problems as it solves. I agree with your there for sure... But isnt building a truck all about 1 step forward on a good day...lol and 5 steps backwards,
Thanks for the pictures gives me a bunch of ideas and pointers.. so thanks.

[OKGMC4]

It’s been a long day. I think I’m completely exhausted. Ha! Wait, not funny? All the voices in my head laughed. I was originally going to go 3” since the turbo exhaust flange is 3” but I read an article that convinced me 3.5” was the way to go.

https://www.motortrend.com/how-to/mo...ust-test-tech/

You can read it or take the short version…on a Supra running 19psi of boost they baseline at 527hp. Then they swap the whole 3” exhaust for 3.5” all the way back and it makes 610hp. I refuse to go to all this trouble and expense and potentially give up 83hp because of exhaust pipe! Used a Vibrant resonator as a muffler and transitioned to oval pipe at the 90 so I could easily weld in an oval tip.

[6DoF]

100% agree with going as big as reasonable. but ppl were still laughing at my 5"

[OKGMC4]

Originally Posted by 6DoF

100% agree with going as big as reasonable. but ppl were still laughing at my 5"

At least I didn’t do like the diesel guys and have a giant stack coming out of the bed floor!

[OKGMC4]

Set the truck down and rolled it back and forth, then turned out the front and rear coils to get it down some more. Then put it down and rolled it again. It still looks high to me but I don’t have any interior or hood up front and no tailgate or fuel tank in the rear. I’m going to wait to lower it any more. Right this moment I have 8” from the ground to the bottom of the fender. Unsure but guessing another inch to get where I used to be.

[OKGMC4]

And I probably have the coolest wife ever. She had a t shirt custom made for my birthday. Of course I can’t wear it while driving the truck. That’s like wearing an AC/DC t shirt to an AC/DC concert!

[duramax55]

OKGMC4 would like to know where you got the bar insert for your hood?

[OKGMC4]

Originally Posted by duramax55

OKGMC4 would like to know where you got the bar insert for your hood?

I made templates to gauge the width and curve, had my father in law machine the bars in aluminum, then had somebody else tig weld them for me after fitting them to the supports. Built it to match the lower grill which is for 55-56 Chevy. Whole front clip is sort of a hybrid mix.

[OKGMC4]

Originally Posted by OKGMC4

I made templates to gauge the width and curve, had my father in law machine the bars in aluminum, then had somebody else tig weld them for me after fitting them to the supports. Built it to match the lower grill which is for 55-56 Chevy. Whole front clip is sort of a hybrid mix.

You know, I would like to remove that hole in the hood as an air grabber. At about 80 mph the back of the hood would shake pretty badly from the air pressure underneath. Even if I tried to block the hole it wouldn’t help the aerodynamics much. Almost wish I could find someone with a 55-56 Chevy hood to trade straight across for my gmc hood. I’ll figure something out. Still need to rework the interior, install AC, wiring , paint, blah blah blah….fuel lines are built now and I fixed some of my foot space issue. I read that bmw slightly turned the seats in the M2 because of the same limited space in the foot well. I loosened the adjustable seat bracket and swung it about 3/4” and low and behold I still feel centered on the steering wheel but my feet are more comfy in the pedal area. It’s magical.