71 GMC turbo LS build

[andrewu6]

Hey everyone,
Starting a new project, and figured it would be fun to document it for all that are interested.

Truck is a long box 71 gmc, coil spring rear, 307 4 speed. Bought it farm fresh last weekend where it had been sitting at least 15 years. truck is pretty nice overall, typical rocker and cab corner rust, but very original and complete.

Rebuilt the carb and threw some new gas in it, turns out the old 307 is super healthy, the truck ran and drove really well. The running and driving was short lived, as I have already yanked the motor and trans in preparation for some more powerful stuff



Here she is on the ride home from the farm where she sat for many years.




polished up the paint and it came out pretty nice! has some nice patina starting.



Motor and tranny yanked out, ready for a new home, if anyone is around montana and needs a good running 307 and 4 speed, Ill give ya a screamin deal!



Fabbed up some quick motor mount adapters for the LM7 (5.3 truck motor) That will be going in. Found the dimensions on the LS1 forums, these plates should set the motor in the same location as the original small block.

[andrewu6]

Suspension wise: parts on the way, will be installing this weekend
3" drop spindles, cut springs, and new shocks up front
5' drop springs, 2" block, C notch, and trackbar relocation out back

Wheels: 15x8 rally wheels all the way around for now (found them really cheap and couldn't pass it up.

Drivetrain: Parts sourced already
2001 LM7 out of a surburban, complete pullout with all computers sourced locally for $900
4l80E fresh rebuild, forward manual valve body, and a good converter (Too much money, but it should be a good time!)

Turbo setup: Probably ON3 78/75, havent decided yet, have some work to do before its ready for the turbo.

Plans for the motor are to tear it down and inspect the internals, open up all of the ring gaps for boost, headstuds with ls9 gaskets, possibly a set of 317 heads if I can find them cheap, possibly a cam LS9 most likely since it is a cheap cam for boost. LS1 style intake and fuel rails, and 80LB injectors.

Still undecided on the engine management, leaning towards a factory computer with a standalone harness, tuned with HP tuners. Have also heard good things about the Microsquirt setup for LS platform. Any advice?

I plan on working through this build fairly quickly, and will keep this thread updated as I progress. The end goal for this thing is to be low, fast, and streetable.

[skyjgmc]

good to see another Montana boy on here. love the plans you have for this truck looks like a great platform. funny I saw your ad for the 307 just a few minutes ago and thought "307 plenty of power" my 307 is on its last leg and I want LS power but have A great running 5.7 vortec to throw in for now but that 6.0 LS with everything thats for sale makes me tempted to..

good luck hope to see it someday we aint to far away. Im headed to GF tomorrow to get me some more GMC sheetmetal goodness.

[andrewu6]

Lots of progresss made this weekend. Got all the suspension installed (minus C notch) thats next weekend!

All new ball joints, control arm bushings, wheel seals, 3" drop street edge spindles, front springs cut 1.5 coils, belltech shocks up front

Rear is 5" CPP springs, 2" block, adjustable trac bar, and shock relocation.
everything installed easily, and I'm excited to get some tires for my rally's to complete the look!


Also got the LM7 and MVB 4l80e mounted using motor mount adapters that I made, and a tubular cross member I made as well. (forgot to snap pics under the truck, but will post up some later). Also, don't give me too hard of a time about the clapped out old motor mounts, I have a set of poly mounts on the way!

The motor and trans are just test fit for install, theyre both coming back out, so I can go through the motor, open up the ring gap, do the headstuds and gaskets, and reseal it! Trans is heading to the trans shop tomorrow to confirm its in good working order!



Here it is on the stockers, Still a bit high in the back, but it also has tractor tires back there that are much taller than the fronts. We will see how it sits with the right size tires and the notch installed!

Hopefully fitting a fuel cell tomorrow night to get that tank under the bed where it belongs! ordered a 380 lph AEM fuel pump, filter, and fittings so hopefully will have this fuel system built soon!

Still doing some planning on the turbo system. anyone with experience want to send me a link or tell me what size intercooler they stuffed behind the grill? I forgot to measure while I was at the shop tonight!

[andrewu6]

skyjgmc- If you need another 307 to hold ya over Ill send this one your way cheap! I was honestly surprised with how well it ran, Granted its not "fast" but I would say I was surprised with its quickness for what it was! it did great big smokey burnouts lol

[andrewu6]

Didnt make an update last week but got lots done, so lll fill everyone in.

Got the CPP notch installed, bolted in, and welded on the perimeter for peace of mind. Definitely recommend a nice air hammer for the job, makes all those rivets come out with ease. Also took out the rear two crossmembers to mount a fuel cell, thats later in the post though.



After the Notch was finished up, I mounted up a universal 20 gal fuel cell behind the rear axle. I had to trim 2 of the bed cross members as shown in the pictures below. I also removed two crossmembers behind the rear axle. I relocated one to the back of the frame and welded it in place. I mounted the cell on some 2x1, and used all thread through the two crossmembers. I brought the tank all the way up to the bed floor, and cut a hole out of the the tank fill. With the tank all the way up to the bed floor, Ill have plenty of ground clearance even with the 7" drop out back.




Also mounted an AEM 380 LPH fuel pump and inline filter on the frame rail and plumbed the feed and return lines. 1/2" ID lines from tank to pump/filter, -6 braided return line, 3/8" ID supply line from pump to motor.

[andrewu6]

Also, Finished painting the frame while I had the bed off. When I had everything done out back, I mounted up my radiator and intercooler.

Radiator: universal 31x19 double pass (same side inlet/outlet for LS) $115 on Ebay
Intercooler: Stock 1999-2003 7.3 powerstroke (perfect size, and had one laying around the shop)

Used a 4" hole saw and cut holes in the core support. Some additional trimming on the back side of the core support was necessary as you can see in the pictures, but thats no big deal. I utilized the top two mounts on the IC, and the on the bottom I mounted rubber pads on the frame. IC is mounted super stout.

the radiator fits perfectly between the intercooler Inlet/outlet. I had to relocate the stock lower radiator mounts, and the upper radiator mounts by moving them in towards each other by 1 hole, and drilling an additional hole. some minor trimming and clearancing was done on the bottom of the core support to clear the thicker core radiator, but I think it was mostly because my core support isnt the straightest.




not sure how to get my pictures to rotate, so sorry for the sideways pics!

You guys cant tell me that intercooler doesn't look bad ass! Only downside so far, is the intercooler is so big, the factory hood latch will not fit, I have an Idea to solve that problem, but do you guys have any suggestions (and Im not wanting hood pins!)

[andrewu6]

Also got a chance to tear into the LM7, Cleaned and painted the block, and regapped the top rings to .027" to keep it happy under boost. Just waiting for my studs and LS9 gaskets to show up in the mail and ill slap the motor. I plan on doing a cam, but not at this time, I've spent enough money on my budget C10 already haha!

For the turbo setup I ordered a On3 78/75, that should be showing up any day now, and Ill get the turbo setup built. More to come!