Engine options for the GMC

For those not regularly checking in at my build thread

http://grassrootsmotorsports.com/forum/build-projects-and-project-cars/build-thread-for-the-72-gmc-finally-thanks-john/59103/page1/

I am getting close to wrapping up the bed and rear suspension. Soon afterwards I'll begin pulling the front suspension/engine/transmission apart and getting everything ready for paint.

The engine is a stock 350. I like stock for this truck. I want everything to mostly look period correct, at least, although I plan on backdating things like the steering wheel and door panels to a previous year/generation, and I've modified subtle things like the gas tank, crossmembers, damper mounts and spring mounts, along with some minor body modifications like the gas filler relocation and the shaved drip rail. Nothing too stark from stock. If you didn't have intimate knowledge of the generation of truck, you'd look at it and think it was stock.

I even plan on a stock GMC color.

So, the engine. It's a 350, and it runs 'strong enough'. Behind it is a A-833 transmission, which is a manual 1-2-3-OD on the floor from a 6.2 diesel. Awesome transmission. At the rear is a 12 bolt with a 3.73 open differential. I know the carb needs to be rebuilt (I believe the float on the Quadrajet has sunk) and the valve seals are worn out (blue smoke at startup). I am sure once I open up the heads, I'll find the valves are sunk and the springs need to go, etc.

So a head refresh and a carb rebuild. Yeah, I know, I am solidly into "while I'm here" territory.

I am not going to go modern. A gen III/IV motor looks wrong and I'm not ready to swallow the cost anyway, even though the performance advantages are huge. I'm not even going to go Vortec heads because I can't stand looking at center bolt valve covers. I really want it to look like it went there.

SO. Technically, stock for 1972 was a 350 or a 402. I want to stay with something that will work with the current transmission/driveshaft setup, so no I6 or GMC V6 (as cool as it is). So, basically, that long windup for this extremely basic silly question, to big block or not to big block? Oh, and I have no budget for any of it. Any displacement would do.

stay sbc. going bigger power in a big block gets into bigger cubic dollars much faster. More deals to be found in sbc land, since you're stubborn about sticking with that.

Because this is GRM, someone has to suggest something off the wall What about a 379 V6? :)

You need a GMC 702 cubic inch V12. It's really the only thing that makes sense.

Seriously, stay small block. It'll be the cheapest, and easiest.

Zomby Woof wrote: You need a GMC 702 cubic inch V12. It's really the only thing that makes sense. Seriously, stay small block. It'll be the cheapest, and easiest.

Dude ever since I heard what that engine was I wanted one. But yeah, it makes no sense here.

I thought about the V12 as well, but I didn't think Tuna wanted to drive from the bed of the truck.

OK, not a single vote for the cool big block, ok ok ok. Fair enough.

Bearing in mind that I'm not trying to make huge horsepower, ans it to look quite stock, I'll probably just make sure the compression looks good and then rebuild the heads.

Staying with the small block stuff will be cheaper. I will say, though, that after going through a set of stock cast iron heads for my circle track car (because we have to use stock heads), just buy a set of ready to go aftermarket heads. By the time you have the heads machined for new style valve seals, have hardened seats put in, have valve guide inserts put in, have the heads decked, buy 16 new valves, 16 new valve springs,16 new retainers and 32 new keepers, you will have spent enough to have bought a set of nice, preassembled, basic aluminum heads.

It's not even a question, given your budgetary constraints. Check the compression, pull the heads off for a refresh, put it back together and run what you already have.

Have you priced a used Big Block that you can hear run? In my area, folks want a grand, give or take.

dinger wrote: Staying with the small block stuff will be cheaper. I will say, though, that after going through a set of stock cast iron heads for my circle track car (because we have to use stock heads), just buy a set of ready to go aftermarket heads. By the time you have the heads machined for new style valve seals, have hardened seats put in, have valve guide inserts put in, have the heads decked, buy 16 new valves, 16 new valve springs,16 new retainers and 32 new keepers, you will have spent enough to have bought a set of nice, preassembled, basic aluminum heads.

That's probably a pretty good point. I'd just go to a local machine shop and see if they have any reworked stock heads on the shelf you could buy (and turn yours in as cores).

You seem to be enjoying the body work/mods, make this fit:

Period correct, and can be had with a little over 1K ft-lb of torque @ 1300 RPM.

• Lee

I vote for the big block (454 of course, easiest to get), but it will hit the budget a bit. Especially trying to get the accessory brackets for a short water pump big block. Small block can do what you need and will at least have a chance at some decent mpgs, big block not so much. But the big block will be more fun. A good set of heads will wake up the small block. Get a decent set of aftermarket aluminum heads and paint them, most won't even notice they are beer can heads.

I say the SBC. I have a 454 in my ski boat and I think I can see the gas gauge go down while idleing around the lake. It will be much cheaper and easier th use what you have. The already done complete heads probably make sense for time and budget.

if it was my truck:

ring and bearing job on the bottom end if its not requiring machine work. take the heads, and scrap them. buy the cheapest set of aluminum heads you can find. put stock valve covers back on them after painting them orange. mild cam. spreadbore intake (aluminum), rebuild quadrajet, recurve timing as necessary. paint it all chevy orange with a stock air cleaner, grind off the logos from the aftermarket parts, and no one will be the wiser.

more power/tourque, more economy, and stock appearing. run 2 1/4 headpipes from the rams horns, into a good y-pipe, and 3 inch single after that.

michael

Dusterbd13 wrote: if it was my truck: ring and bearing job on the bottom end if its not requiring machine work. take the heads, and scrap them. buy the cheapest set of aluminum heads you can find. put stock valve covers back on them after painting them orange. mild cam. spreadbore intake (aluminum), rebuild quadrajet, recurve timing as necessary. paint it all chevy orange with a stock air cleaner, grind off the logos from the aftermarket parts, and no one will be the wiser. more power/tourque, more economy, and stock appearing. run 2 1/4 headpipes from the rams horns, into a good y-pipe, and 3 inch single after that. michael

I am here, minus the re-ring and bearing pending compression results. I may also go different than the stock air cleaner, it's ugly.

Thinking the EQ CH350F heads would be a great choice.

If you have to buy a carb, manifold and headers anyway, a junkyard 4.8l and the MSD ignition box will cost about the same as a gasket set and going through the heads on your sbc. Aftermarket valve covers and moving the coils the firewall or back of the manifold go a long way toward making the motor look more correct.

It's a lot of performance to leave on the table. Same kind of goes for the vortec heads, they make center bolt to perimeter bolt valve cover adapters for exactly this scenario.

I thought that the straight six (and some 4s) had the same bolt pattern and bolted up to the same transmission as the v8? Around here there are always some late 70s straight six motors from Novas and such available for peanuts, to the point that I find myself at the Clifford page all too often.

On a budget though used SBC parts are going to be the ticket. With that transmission I would build for torque and not rpms, since the gear spread is so wide and you won't be able to keep it in a peaky power band.

oldopelguy wrote: If you have to buy a carb, manifold and headers anyway, a junkyard 4.8l and the MSD ignition box will cost about the same as a gasket set and going through the heads on your sbc. Aftermarket valve covers and moving the coils the firewall or back of the manifold go a long way toward making the motor look more correct. It's a lot of performance to leave on the table. Same kind of goes for the vortec heads, they make center bolt to perimeter bolt valve cover adapters for exactly this scenario. I thought that the straight six (and some 4s) had the same bolt pattern and bolted up to the same transmission as the v8? Around here there are always some late 70s straight six motors from Novas and such available for peanuts, to the point that I find myself at the Clifford page all too often. On a budget though used SBC parts are going to be the ticket. With that transmission I would build for torque and not rpms, since the gear spread is so wide and you won't be able to keep it in a peaky power band.

No to the 4.8. It would look wrong and I'd be giving up some displacement. Plus, it's a large expense. Also, the ram horns won't fit the gen III.

Anyway, the heads I mentioned are Vortec in port and chamber but old style in valve cover and intake. That's cool. Those valve cover adapters are stupid expensive. Modern performance in an iron casting that looks original.

I'm not buying a new carb, remember, just rebuilding the quadrajet. And absolutely no MSD boxes sitting under the hood. EDIT: oh, and no headers either. Just the ram horns.

tuna55 wrote: OK, not a single vote for the cool big block, ok ok ok. Fair enough. Bearing in mind that I'm not trying to make huge horsepower, ans it to look quite stock, I'll probably just make sure the compression looks good and then rebuild the heads.

Big blocks do have a bit more cruise night glory (and some really screwball port design), but a BBC seems to be the wrong tool for the job. Some sort of "big block" from another GM division, or even a Cadillac 500, would raise the cool factor even more, but still, doesn't seem to match the goals here. How about a Pontiac SOHC six?

Seriously, I'd just freshen up the motor you've got. It's not like you encountered a terminal problem with the engine like what prompted me to put a 4.8 in my truck - and the swap has been pretty involved.

In reply to MadScientistMatt:

Do BOP bellhousings for a big retainer OD 833 exist? If not he'd have to have a BOP bell or his bearing retainer modified.