Chevy 350 Dilemma

[UntrustedAlly]

I bought my 1968 GMC C2500 with a non-running Chevy 350 swapped in. The previous owner provided little information on the engine and truck, so I have figured out what I could and have done some work to the engine myself.
Engine/Truck Specs:

• ~1976 truck block, intake, heads - all stock as far as I know
• Holley 570 Street Avenger, rebuilt
• Aftermarket cam installed by previous owner, audibly bigger than stock (unknown specs)
• New Street Fire (MSD owned brand) distributor
• New plugs and wires. I don't think I've run the truck enough for the plugs to have showed fowling as I have not noticed raw fuel or buildup of any kind
• Aftermarket headers, appear to be Hooker or similar
• Engine vacuum is erratic, jumping between 8" and 16", possibly too bad to run the advance
• Compression test: 70psi across the board with the choke and throttle mistakenly completely closed - no blow-by, oil usage, or smoking, however
• Rocker press-in studs are bad: some are stripped, one is stretched. None of the rocker nuts screw in without an unreasonable amount of force.
• Rockers are in good condition, pushrods straight
• New fuel pump, intake gaskets, carb baseplate gasket
• Timing chain and sprockets gone through
• All vacuum ports plugged except for the vacuum advance
• SM465, Dana 60, 4:10 gears - 60k miles

Additional Details:
The truck starts, idles, and revs without issue. In gear 1/2 throttle+ or high RPM makes the engine stumble and sputter but I have driven up to 60mph being light on the throttle. The truck was originally a V6 so I believe in addition to the heads needing work the fuel lines might be too small. Truck constantly lunges when idling in 1st gear, no issue when throttle is applied. Cylinder #3 which somehow got 0psi compression though the cylinder's plugs are fine and the headers get just as hot as the other cylinders. I'm assuming user error on that.
I believe new or reworked heads would solve the majority of issues.

Dilemma:
My goal with this truck is to make a solid 350-400HP on 91 octane or E85. Possibly more HP in the future. I'm aiming for a fun street rod. Budget wise, would I be better off fixing and building up my current 350 or should I consider an LS swap? The engine obviously needs a lot of work but I have access to machine shops and I am willing to put in some man-hours. Budget accounting for ECU's, transmission adapters, high pressure fuel pump, etc.

[72 k15]

Not any expert,But I would take off the heads and look at the cylinders, At 70 psi has me worried that is very very low.... About the 350HP goal you could do it but your gonna need some money either way it will cost some money,If it was me I would rebuild the 350 stroke it to 383 and u should be at 400hp ish.

[Greasey Harley]

I suggest a leak down test.

[72 k15]

Originally Posted by Greasey Harley

I suggest a leak down test.

I agree

[UntrustedAlly]

Originally Posted by 72 k15

Not any expert,But I would take off the heads and look at the cylinders, At 70 psi has me worried that is very very low.... About the 350HP goal you could do it but your gonna need some money either way it will cost some money,If it was me I would rebuild the 350 stroke it to 383 and u should be at 400hp ish.

That's what I was thinking. I just found an amazing deal on rebuilt vortec heads, an intake, and a 750CFM Holley. that I'm picking up tomorrow. That should take care of the heads.

Originally Posted by Greasey Harley

I suggest a leak down test.

That's a good plan, I'll definitely test it when I get the chance.

I am not opposed to making it a 383, but what other options do I have for 400hp, taking into account the new heads and carb? Would a used turbo be a reasonable option if I did my own fabrication?

[Greasey Harley]

I misunderstood, I thought you were trying to fix the problem first.
Hell yeah, if you're just going to build a stroker motor slap some vortec heads and a good cam in it. Use quality parts and a good proven formula, you'll make 400 horsepower easy.the only substitute for cubic inches is cubic dollars!

[Greasey Harley]

Originally Posted by UntrustedAlly

That's what I was thinking. I just found an amazing deal on rebuilt vortec heads, an intake, and a 750CFM Holley. that I'm picking up tomorrow. That should take care of the heads.


That's a good plan, I'll definitely test it when I get the chance.

I am not opposed to making it a 383, but what other options do I have for 400hp, taking into account the new heads and carb? Would a used turbo be a reasonable option if I did my own fabrication?

With enough time and enough money Anything is Possible. If you're going to try to build your own Turbo System, you better have a solid plan in place before you buy a part or turn a bolt! If you just want to fix your motor, or figure out what's wrong with it, I still suggest a leak down test as your first recourse.

[UntrustedAlly]

Originally Posted by Greasey Harley

With enough time and enough money Anything is Possible. If you're going to try to build your own Turbo System, you better have a solid plan in place before you buy a part or turn a bolt! If you just want to fix your motor, or figure out what's wrong with it, I still suggest a leak down test as your first recourse.

The guy that was going to sell me the vortec heads just offered me this deal:
79 Corvette motor bored 30 over with flat top TRW forged pistons, forged SCAT crank, and Vortec heads. 1400 miles on it $600, bolt in ready. I'm seriously considering getting that engine and selling my old one, possibly keeping the good parts from it. Would you guys say this is the best course of action?

[clay68c10]

That’s a good enough deal that I’d be sceptical. The crank would cost that much.
Any receipts?
Can you hear it run?
Can you look at the bottom end and verify it has that crank?
Check the casting numbers.
Never believe the Corvette crap unless the casting #s verify it.
If it is legit, then I say go for it.

[MARKDTN]

Originally Posted by clay68c10

....Never believe the Corvette crap unless the casting #s verify it.....

I so agree. Most mid 70s up Corvette blocks are nothing special. Base Corvette motor in '79 is the same as an Impala. Big whoop. Now if was '69 then it would matter because it would be a 4-bolt and better block. Or if it was '89 it would have Corvette-only aluminum heads but the block again is nothing special.

OP-the deal sounds too good to be true. Beware.

[biketopia]

I'd pull the pan and verify that crank is in there. If so 600 bucks is a smoking deal on that engine.

[jocko]

Yes, that's a good deal. All depends what you want. But you'd probably never get 350-400hp out of your original setup with its original 76 heads - best to move to an alternate plan if hp is your goal. Welcome to the site.

[geezer#99]

Ah!
The allure of cheap parts!
He’ll have 600 bucks!
You’ll have a block with scored walls, roached bearings and cracked heads.
Can’t pass up a deal like that!

[UntrustedAlly]

Originally Posted by geezer#99

Ah!
The allure of cheap parts!
He’ll have 600 bucks!
You’ll have a block with scored walls, roached bearings and cracked heads.
Can’t pass up a deal like that!

Originally Posted by MARKDTN

I so agree. Most mid 70s up Corvette blocks are nothing special. Base Corvette motor in '79 is the same as an Impala. Big whoop. Now if was '69 then it would matter because it would be a 4-bolt and better block. Or if it was '89 it would have Corvette-only aluminum heads but the block again is nothing special.

OP-the deal sounds too good to be true. Beware.

If the guy is telling the truth, the engine is a great deal. In South Dakota or at least the general area I am in, rebuilt engines sell cheap in my experience. Lots of old farmtrucks and especially people doing work on them. My friend got a complete, rebuilt 355, all forged for a comparable price. The engine ran hella good for a couple years before he sold it.

I am definitely aware that this sounds too good to be true, however. I'm heading to the guys shop later today and hoping we can get the engine running on the stand or at least have some of the internals or receipts shown to me. At the very least we'll pop off the valve covers and turn the crank to make sure its all together. The guy is selling a lot of various parts equally cheap so that improves my confidence. This includes a set of rebuilt vortec heads w/roller rockers, guides, seats, and springs, aswell as an intake for $300. He has the receipt for the heads, gone over by a local machine shop.
Again very cheap, but the receipt speaks for it.

Originally Posted by Coley

Sometimes these types of conversations need to be reset in order for them to move on in the correct direction....so quick recap.

You have an engine that has 70 psi compression?...what?...I don't think that would even run, so you need to recheck that.

Next up, if you do have low compression (but maybe more than 70 psi)...then its clear you aren't happy with the performance....fine, understood.

Next: .......ready?

What is the budget you have and are willing to put into this to achieve something close to 400hp?

This answer and feedback needs to come ...waaaayyyy...before how to do it.
Respectfully,

Coley

Yes, 70psi. It was consistent however, and as mentioned, with the intake almost completely closed. I was confused how it ran at all too but there's no blowby and the number seems oddly consistent. Budget is probably 2k or less. I get that's not much but appearance and ghetto-ness is no issue.

Originally Posted by geezer#99

On that note Coley, he has a lot of supporting parts already.
He just needs a good long block to use it on.
Plus the ability to lower his expectations of 400 hp. That number is doable down the road.
First you need a good sound base, second get it built, third learn to tune it and then do upgrades to achieve your hp goals.
Buying cheap unknown parts doesn’t help.
He’ll need a crate motor that runs about 2 grand to start with. Down the road a few more grand will get his hp up there.
Don’t forget the supporting cast in your 400 hp dream. You need a better converter, maybe tranny, rear gear changes, etc etc.
It all adds up!
Start simple, build it from there.

That's where I'm leaning, I'm not sure the engine itself is worth keeping but the supporting parts are good. The biggest issue I had with the engine was that it was bought not running and I had no point of reference. The balancer slipped, the timing mark was off, distributor was unmarked, carb untuned, and no history. I figured out the timing, got a free replacement balancer and crank (old one was stripped) and got the carb tuned but I'm not confident the current long block is worth keeping with the heads likely needing replacement.

Recap:
We've determined that my current engine needs a lot of work, likely not worth keeping unless I am willing to put in a lot of work.
I am looking at a 355 this afternoon that supposedly has forged internals and vortec heads. 4 bolt main. Should be able to get 350hp with a cam.
The best history I have of my current engine is that the truck was bought built and was running 2+ years prior to my ownership, as confirmed by several people in the area who knew the owner. Owner also said the truck used to run very strong for whatever that's worth.
If I was to guess based on the history and issues, I think the cam put in was too big for the springs, the engine was overrevved, and the valvetrain damaged. If not the valvetrain, I'd guess a fuel issue.

Thanks for the replies guys!

[Daves70]

That 79 Corvette motor with flat tops and vortec heads sounds like an ok deal. But... flat tops and vortec heads may have too much compression for pump gas. Kinda depends on the cam if you will get away with it. It's something to look into.

[Coley]

Sometimes these types of conversations need to be reset in order for them to move on in the correct direction....so quick recap.

You have an engine that has 70 psi compression?...what?...I don't think that would even run, so you need to recheck that.

Next up, if you do have low compression (but maybe more than 70 psi)...then its clear you aren't happy with the performance....fine, understood.

Next: .......ready?

What is the budget you have and are willing to put into this to achieve something close to 400hp?

This answer and feedback needs to come ...waaaayyyy...before how to do it.
Respectfully,

Coley

[geezer#99]

On that note Coley, he has a lot of supporting parts already.
He just needs a good long block to use it on.
Plus the ability to lower his expectations of 400 hp. That number is doable down the road.
First you need a good sound base, second get it built, third learn to tune it and then do upgrades to achieve your hp goals.
Buying cheap unknown parts doesn’t help.
He’ll need a crate motor that runs about 2 grand to start with. Down the road a few more grand will get his hp up there.
Don’t forget the supporting cast in your 400 hp dream. You need a better converter, maybe tranny, rear gear changes, etc etc.
It all adds up!
Start simple, build it from there.

[GASoline71]

To make 1hp per cubic inch in a 350 is pretty easy. Only thing I ever did to the stock 350 bottom ends is put stronger rod bolts in the big ends of the rods. The stock crank and rods will handle it, and you can use hyperuetectic pistons to save some coin. All the reast is EZPZ...

Gary

[UntrustedAlly]

Well I'm buying the engine Tuesday. Turns out, the previous owner has all of the receipts and we went through the engine with a bore scope. The engine is flawless.
Specs:
Ported and built vortec heads, decked engine block, Holley 800 DP, TRW forged pistons, forged SCAT 383 stroker crank, forged SCAT rods, stage 4 clutch, racing valve covers, new points system and wires. All of the work was done at a professional machine shop. EST 450hp
Price: $600
Goal met I guess. I almost feel like I'm ripping the guy off.

[clay68c10]

Go get a lottery ticket, you are lucky.
That will be a fun runner!
Enjoy buying rear tires often.

[UntrustedAlly]

Originally Posted by clay68c10

Go get a lottery ticket, you are lucky.
That will be a fun runner!
Enjoy buying rear tires often.

Haha I guess so.
Now I'll have to find an LSD or locker of some kind to get rid of the one wheel peel

[biketopia]

Damn, that's a SMOKING deal!!! I need something like that badly for my camaro. Looked at one this weekend they guy said had a stroker crank and world heads etc etc...but couldn't prove any of it. Everything sounds nasty open header in small closed garage. He also was asking $3k

[72bowtiestepper]

With so many guys switching over to the LS engines, I would think the older SBC engines would be plentiful & getting cheaper to buy used. Parts are also cheaper & can be found everywhere.

[biketopia]

Originally Posted by 72bowtiestepper

With so many guys switching over to the LS engines, I would think the older SBC engines would be plentiful & getting cheaper to buy used. Parts are also cheaper & can be found everywhere.

You would think but from what I've been seeing is the guys getting rid of the SBC to go LS think that they can sell their SBC set up and get into the LS world for a NET zero in the bank account. I've met sooo many people whos old, open header, sbc, with no paper work, that they built in grandpas garage with Tony, you know Tony, the carb guy in town is worth 4k. Occasionally you find someone like OP found though and you get lucky as hell.

[UntrustedAlly]

I think I found out what was wrong with my truck engine. We took it apart and found out the cam is an Elgin E1213-P. The intake spec is 244° at .050", far too big for the 570 carb. This explains most of the issues I think, the vacuum, compressor reading, etc. Everything inside the engine was in great shape, and the engine is bored 30 over.