My 78’ Pontiac GP/SJ 454 build

[bracketchev1221]

How’s it going fellas, it’s been a while and thought I would give a update on my car..
I managed to swing The cash for a built 700R4 and also a pair of pro comp aluminum big block GM cylinder heads.
Their rectangle port, 02.25 intake & 01.88 exhaust valves. Their set up for hydraulic flat tappet but was thinking about going with a roller assembly?
I’m kinda at a cross roads so to speak. I’m not too Up with big blocks, we always rebuilt small blocks when we were younger because they were cheaper.
I’m really trying to figure out what cam I need to make around 500-550 hp out of a stock 1979 (454) truck motor? I was told also I need longer push rods for the heads I have?
I’m not to sure about that, the guy I got them heads from told me that. He also said I needed longer head bolts on one side of each head which he gave me the ARP longer bolts.

I took the heads to the machine shop and they replaced two intake valve seats on one head and one intake valve seat in the other.
they also resurfaced them for me and checked my valve spring pressures and wrote them down on on tags wired to each head.

Longer pushrods and head bolts are pretty common. The heads usually have a raised exhaust port and use them in the 4 holes at the ports. A hydraulic roller is a good idea but you may struggle getting the compression up with big chamber heads.

 

[78BB-Pontiac]

Longer pushrods and head bolts are pretty common. The heads usually have a raised exhaust port and use them in the 4 holes at the ports. A hydraulic roller is a good idea but you may struggle getting the compression up with big chamber heads.

The guy I got them from had these heads on a 496 running 9.5/1 compression and was a roller motor.
He said it dyno at 638hp and was in his mud truck.

 

[MrSony]

Just caught this thread now. That GP is sharp.

 

[78BB-Pontiac]

Just caught this thread now. That GP is sharp.

Thank You! I consider myself lucky to Find and have it. I also believe I’ll be a good caretaker for that car.
It’s very clean and I will put as much money into it as it needs to be a real head turner. This past summer every time I took it out on Friday nights to the North St.Paul car show. I get people always stopping to ask about it. Usually wanting to know if it’s for sale.
I just tell them I think my oldest son will get it some day! Till then, I’ll just keep putting money into it.

 

[bracketchev1221]

The guy I got them from had these heads on a 496 running 9.5/1 compression and was a roller motor.
He said it dyno at 638hp and was in his mud truck.

I think the 79 truck motors struggled to get past 8:1 compression with big chamber heads. 9.5-10:1 is mot likely a piston change. Did he happen to say what the intake runner size is?

 

[454GrandPrix]

I’m really trying to figure out what cam I need to make around 500-550 hp out of a stock 1979 (454) truck motor?

The good news is, you won't need much camshaft (by big block standards, anyway) to hit this goal. A cam with an intake duration in the 224-230 range @ .050" can easily give you over 400 crank horsepower even with low compression and peanut port heads, and will push you over 500 crank horsepower with higher flowing aftermarket heads. The Comp Cams XE268H is one example of an appropriate camshaft for this result, though there are many others.

As just one example, here you can see how Super Chevy built a wrecking yard Gen-IV 454 removed from a one-ton truck. They retained the entire stock bottom end--cast crank, forged rods and cast pistons. After disassembly and a thorough cleaning, they reassembled the engine and re-used all the stock bearings--only a new set of rings was installed. Topped with a Summit cam kit (0.540 lift, 238/248 duration) and Pro Comp aluminum heads, the engine produced 565hp and 532 lb-ft of torque on their engine dyno.

 

[DJHull]

Hello Gbody fans. I’m pretty new to this sight but thought now is a good time as any to start a build thread on my recently purchased 78’ Pontiac GP/SJ. I’m sitting up in a crane at work and the roll mill is down, I get pretty board.
From what I can tell it’s been here in Minnesota since around 2009 and is a original Idaho car. The previous owner passed away and was sold by one of his sons.
The car is rust free and came with a 1979’ 454 truck motor installed. The internals are stock and has a bunch of new aftermarket parts under the hood.

Holley strip dominator high rise intake.
Edelbrock 750 carburetor.
Billet distributor.
Aluminum four core radiator. 170* thermostat.
Dual electric fan set up.
Chrome 150 alternator.
Polished aluminum water pump.
Summit electric fuel pump.
Oversized front coil springs.
Oversized front sway bar.
New rear coil springs
Dual Flow masters.

That’s about it that the car came with. I have since had to strip the underside of roof from surface rust and coat with POR-15 rust preventive coating. I also put a sound barrier on to of that.
I have a headliner coming any day now from stock Interiors.
I also wanted to tint the back and side quarter windows. My back window had the defrost lines in glass but found a old Gbody cutlass at you pull our parts in Rosemount, Minnesota that had good Clear back glass I got for $22.
My car was a landau roof car but luckily the previous owner had both back quarter Window interior panels from a non-landau car sitting in the trunk. I don’t plan on putting a landau roof back on it.
When I got the car I noticed it had two small patches of surface rust inside trunk on both sides just behind the inner wheel well.
I have since sandblasted both spots and coated with POR-15. Real happy it was only surface rust and didn’t eat metal!
Another nice thing about this car, it has all its trim except the side panel trim which I wouldn’t put back on anyway.
This car has a 700R4 that I plan on changing to a 4L60E or 4L80E. The car has a 10 bolt 411 in rear that will need to be a 12 bolt. I also plan on aluminum heads and bigger cam in the 454. It’s not near where it needs to be at the moment! Any suggestions are more than welcome!
These first pics are from the day I picked the car up in a snow bank I had to shovel myself before the flatbed driver showed up. The car sat all winter and fired right up.View attachment 114389View attachment 114390View attachment 114391View attachment 114392View attachment 114393View attachment 114394

Car looks much better uncovered with snow. Welcome aboard and good luck with your build!

 

[78BB-Pontiac]

Car looks much better uncovered with snow. Welcome aboard and good luck with your build!

Thank You! I really like the car, apparently other people do as well. Every time I take it out people are asking me about it. Usually it ends with is it for sale? Nope!
I was lucky to find a car so clean. Nice too not have to deal with any rust and concentrate on motor, drivetrain and suspention.

 

[78BB-Pontiac]

I think the 79 truck motors struggled to get past 8:1 compression with big chamber heads. 9.5-10:1 is mot likely a piston change. Did he happen to say what the intake runner size is?

To answer your question on the aluminum big block heads I got for my 454. They have 135cc intake runners, 120cc combustion. 2.25 intake and 1.88 exhaust valves.

 

[78BB-Pontiac]

I think the 79 truck motors struggled to get past 8:1 compression with big chamber heads. 9.5-10:1 is mot likely a piston change. Did he happen to say what the intake runner size is?

They also have Manly severe duty valves + .200 length.