[6x400gmc]

First off, Hi! My name is Britt, and I live in the Houston, Texas area. I've browsed on and off on this site for years, but finally got around to joining and posting. I've been involved with Pontiac's one way or another since I was a kid. We ( read: my dad ) drove and raced Pontiac's on both the dirt and strip back in Louisiana, and I helped build and maintain the power plants. They're great engines, which is why when I bought this truck, the SBC 350 had to go. Maybe I'll turn it into a garden planter or something. This was my fifth "solo" build, and though that went painlessly - I really didn't know what to expect when I went to do the transplant.

This is my write up. Enjoy.
---------------------------
A few months ago I bought my wife an 82 GMC with what we thought was a 305. The truck came with a 2bbl, and what turned out to be a 145 horse 350. I'm not too big on chevy engines, so I immediately started looking for a Pontiac block to put together. We used to race Pontiacs on the strip and dirt, so I'm intimately familiar with them, inside and out. While looking for an engine, I did manage to swap the dismal 2bbl for a proper 4bbl and Q-Jet.


Long story short I found a 74 Pontiac out of a Firebird, and started the swap today. Here are the pics.



This is the 350 chebby while still in the truck. Its ratty looking.




This is the 400. Its .030 over with 4X's, and an 067 cam. I was running low on funds so I had to go with the cheapie 4 tube Summit headers.



After pulling the 350, I set the engines up side by side. I knew the Pontiac block was physically larger, but I'd never had two blocks together for comparison. The 400 makes that sbc look like a Briggs and Stratton.



This is my Flintstone impression. I didn't get far.



I expected the header installation to go very, very badly - as they do in 2nd Gen. Firebirds. It wasn't quite as bad, I had to install them from the bottom, with the engine elevated about 6 inches off of the mounts. I got all the bolts in, sat the engine in the mounts, and everything cleared. Speaking of mounts, I used the stock Chevy mounts with the Firebird's brackets. It fit like a glove.




As the 400 used the same mounts it wound sitting fore/aft in about the same place. I didn't have a BOP bell housing transmission available, so I bought an adapter plate from TCI for cheap. Its 1/8" steel with dual bolt patterns, and supposedly is rated to 600 ft/lbs of torque. I used the supplied bolts and washers to space out the converter, adjusted the trans mount ( I did not have to move the cross member ), and that was it. I didn't even unbolt the drive shaft. Soon after finishing this off, it started pouring.

Next Day.



After everything dried out, I started fiddling around with wiring, hoses, and such. I had to fabricate/modify the battery tray, and remount it on the left wheel well. The backwards Chevy's have EVERYTHING on the right.

The only real problem I ran into, and is yet unresolved, was the column shift linkage. I managed to bend the rod and clear the headers, but the arm that it connects to ( which connects to the trans ) hits the collector while in drive. That means I cannot shift into 2 or 1. Just P R N D, and then it hits. I'll fix that later, or go with a floor mounted shifter with cable.

http://www.youtube.com/watch?v=LMggCM71q5w

I got her fueled and watered, and around 2pm today I lit her off. Open header, 'cause I don't have the exhaust fabricated as of yet. It ran fine. Link above.



This is the truck. I bought this for a couple thou from a Mexican bodyshop in Pasadena. I call this the "Ghetto" truck because of the paint job, and the wheels that it used to have. ( 295/50's on wire wheels ). I sold those off, and bought these stockers ( minus trim rings and painted RED ) with brand new tires. It also came with a front end off of a 91 Suburban, but it was a total hack job. The headlights didn't work, and it was all attached with wood screws. I'm in the process of converting back to the origional headlight/grill configuration. So its all mix matched color wise, but the body is rust free and straight. I figure I can paint it later.

Well, that's it. I haven't driven it yet, so I can't give you a "seat of the pants" opinion yet. All I've got in the truck is a 10-bolt open rear with 3.23's.

Thanks for reading,




Britt

[SergeF]

Nice and clean installation. I had the same problem with a column shift linkage in mine truck. I didn't want a taco shifter so I went with lokar adjustible rod. I can shift in all gears. It was cheap about $40. Summit stock it. Good luck.

[Pontiac guy]

Very nice job!! I had a 81 Chevy that I put a 400 Pontiac in. It was a great truck until the body just fell apart. I had to put a Pontiac emblem on the front grill got a lot of questions about that.

Vince

[pontiac6269]

Thats a nice looking truck.

Originally Posted by Pontiac guy

I had to put a Pontiac emblem on the front grill got a lot of questions about that.

Vince

Like this.

What I did for a battery tray was find a chevy diesel powered truck at a salvage yard as they have a battery tray on both sides.

[Jeff Walker]

Yep, nothing like putting a Pontiac in a GM pickup to make a truck out of them. I got two like that! A 400 powered 78 Chevy 4X4 and 455 power 86 GMC 2WD Suburban.

[Pontiac guy]

Originally Posted by pontiac6269

Thats a nice looking truck.


Like this.

What I did for a battery tray was find a chevy diesel powered truck at a salvage yard as they have a battery tray on both sides.

exactly like that!!! in the center and then put PONTIAC on the flat middle bar of the grill

[poison heart]

Nice!

[se428bandit]

That is a very nice looking truck.

[Pontiacmuscle]

Sounds Great! Nice looking truck!

[4dblnkldude]

Nothin' is better than that!!!!!!

[Overkillphil]

Great choice that 067 cam for great torque across the board! Nice project, thanks for sharing.

[Donovan]

Thanks for sharing Britt. This is a great swap.

[triathlonx13]

Awesome !!!!!!!!!!!!!!!!!!!1

.

[Overkillphil]

You may give that Pontiac engine asthma with that dinky air cleaner though.

[6x400gmc]

Just an update after about 5000 miles on the engine.

The truck runs better than I ever could have expected. Makes enough power to suit me, and gets 15.5mpg on the highway. I ran into oil filter clearance problems with the headers and switched to the caddy filter. I still can't shift past Drive due to the header on the left side, but I have a BOP TH400 that I'm going to install in place of the Chevy TH350 and I'll throw in a cable operated floor shifter along with.

Even with the stock three row Chevy Radiator, the 400 barely creeps above 195 while sitting dead still in Houston Traffic on a typical summer day. I drove her to south Louisiana last month ( 350 mile round trip ) and back for a job, with no problems what so ever. I never thought I would have gotten the gas mileage that I did, especially with 3.73's, no overdrive, and no functional lockup on the converter. I ran 65 the whole way and back, and the motor never broke a sweat.

It's awesome! I'd get up and drive this truck to California and back without a worry.

Also worth noting is that I'm running 3" exhaust from the headers to Moroso spiralflow racing mufflers. They're not as loud as you would think, and they have an awesome tone. The bed acts as a huge resonance chamber, so the sound is pretty thick and boomy.

Now - yesterday I picked up a running Y4 block 455 and transmission... What to do, what to do? Shall I leave the 400 in place?

Britt

[poison heart]

Damn that's bad ass!

I want to put those mufflers on my truck

[tharkun8]

Been looking for this type of information and thought Id bring this thread back up..

I just bought a 1970 GMC C2500 with the SBC 350.. the engine has some issues and
seems pretty underpowered.... Im thinking of swapping in a spare 64 389 that
I have laying around ..

1. Will the motor mounts you describe ( stock chevy with FB brackets) work
on the older style blocks with the 2 holes or only work on later blocks with 3 ?
I cant seem to find a quick answer from someone who would know..

The rest seems pretty straightforward.. some wiring changes and a tranny
adapter from Bop block to bowtie trans.. etc..

Thanks for any info..

John



,,

[Goatracer1]

I installed a 455 Pontiac in my 1963 Chevy PU which I believe has the same basic frame as your 1970. I used the brackets that attach to the top of the frame rail and the front cross member and have the motor mounts on them from a late 1970s- early 1980s Chevy pu.. I bolted the Pontiac engine's steel motor mount to the lower Chevy rubber mount and set the engine in the frame. I drilled holes where the metal bracket rested on the top of the frame rail and on the cross member. Thatsall it took to install the engine. The PS hoses bolted up and stock exhaust manifolds cleared. Everything else was minor.

[tharkun8]

Originally Posted by Goatracer1

I installed a 455 Pontiac in my 1963 Chevy PU which I believe has the same basic frame as your 1970. I used the brackets that attach to the top of the frame rail and the front cross member and have the motor mounts on them from a late 1970s- early 1980s Chevy pu.. I bolted the Pontiac engine's steel motor mount to the lower Chevy rubber mount and set the engine in the frame. I drilled holes where the metal bracket rested on the top of the frame rail and on the cross member. Thatsall it took to install the engine. The PS hoses bolted up and stock exhaust manifolds cleared. Everything else was minor.

Thanks Goat..

Would you happen to have pics of the setup ? I can understand where
you are going .. just having trouble picturing it in my head..

So I would need the 80 Chev mounts .. the existing truck brackets and ???

Thanks again..

John

[Lee]

I talked with Britt. It was too long ago, and he doesn't remember the details other than what is above.