The Stovebolt Site Forums The Shop Area Engine Shop Big block V6

Well, Lately I've had some cool ideas floating around my head. The newest one involves the gmc V6s. I guess my first question is has anyone ever souped them up, like a race motor?
I've been thinking about aquiring one to tool around with but I was thinking why not take some parts from the BBC v8 and put them to use in a v6.
First off I thought of pistons. Get a set of some flattops or high compression pistons that are at least bigger than 4.25 (depending on which v6 you've got.) Get the shorter(heightwise) pistons so you can use the longest rods possible. Better rod/stroke ration, lighter pistons, etc. Then maybe get the block and crank lightened up a little bit. So you could spin up faster, and not have a sub 850 pound engine. But the actual cool idea floating in my "head" is that. Heads.
I was wondering if it would be possible to modify the cylinder heads from a Big block chevy (cut 1 cylinder off each one.) and create your own sort of hybrid head. Like the inline-6s where they cut a cylinder off 2 separate heads and weld them together. I'm just wondering if the big block chevy heads would be close enough to fit, or if they're too small/big/something.
But you see. Now if that were possible, my next idea would be Multi port fuel injection. Take the ECU off of another 6 cyl (4.3 or something) or get a megasquirt. custom build a sheetmetal intake manifold, like a cool high rise or X-flow or something that looks awesome then drill holes at each port for injectors. Get a high energy ignition of some sort. I mean, really whatever all you would need with this engine. Just go all out.

Well you know, I wonder if any big block heads would fit. I think it would almost be cool if the mopar ones were similar enough to be modified to fit just so you could have a hemi v-6 big-block.
If I had a choice I'd probably do that sort of set up with either the 351 or the 401. I would definately want to try and lighten up the engine block though. when your engine is almost half a ton, there may be some weight issues.
I guess you could call it another quest to be different.

To add a bit to this, Well, I guess if one were to go to such lengths, you might as well turbo it or supercharge it. You know?

those engines are simply too heavy built to get any RPM out of them, repair parts are tough to find sometimes let alone performance stuff-get a 350 ta soup up

The big 6's were very good at what they were designed to do- - - - -deliver stump-pulling torque at low to medium RPM for a long time. Hotrodding one would be an exercise in frustration. For the same reasons, you won't see any Clydesdales or mules running in the Kentucky Derby.

I worked at an automotive machine shop where we tried to keep some of the older big sixes rebuilt for a few companies with GMC medium-duty trucks still in service. Any attempt to mix & match parts, particularly pistons, rods, and crankshafts, was a disaster. Apparently, there was a lot of custom balancing done at the factory, and even reboring an engine necessitated very precise piston weight matching to keep the engine from shaking itself apart. High RPM would be the death of one of those engines in very short order.
Jerry

[QUOTE]The big 6's were very good at what they were designed to do- - - - -deliver stump-pulling torque at low to medium RPM for a long time. Hotrodding one would be an exercise in frustration. For the same reasons, you won't see any Clydesdales or mules running in the Kentucky Derby.[/ QUOTE]

Hey, now that is a great analogy!

I know it's a bit late, but thought I'd throw in a GMC plug here... I got a GMC because of the dual headlights, and didn't care about the engine, as I figured a vortec headed 327 or 350 would be what I'd swap in. Then I got to tinkering with the 305, added HEI, and Holley carb, and I really started liking these engines. They are designed for low rpm torque mainly, but you can do some custom work to them to make a good hot rod. Tuneup and basic parts are available, although more specific stuff may need to be ordered. There are a handful of places that still make internal engine parts for them, so there isn't a terrible shortage of that stuff.

As far as a hot rod... a 351 or 401 would make a really unique hot rod engine, but would take a bit more work than just bolting on tons of readily available parts to a an sbc V8.

First off, deck the block and/or mill the heads to bring the stock compression up to 9:1. Secondly, get a carb adapter to ditch the stromberg and bolt on a 500cfm Holley or better. You'll benefit from opening up the intake manifold wiht a die grinder to the size of the Mr Gasket Adapter.
Get a 78-79 Buick Even-Fire 3.8L V6 HEI distributor, and have a spacer machined to fit the larger GMC block hole, and transfer the GMC distributor gear onto it. Upgrade to 8mm plug wires and plugs to a split fire or E3 or whatever.
If you want to go all out, the 80/81+ Buick 3.8L HEI distributors that came on computer controlled carb cars can be used to retrofit some GM TBI fuel injection!
very important thing here - most models of the big V6's did not have a harmonic balancer, as they were never intended to reach the rpm range where one would be beneficial. You might want to look into what it'd take to retrofit one, especially if you do the following...

You can get custom cam profiles ground for these engines (no one makes aftermarket spec cams anymore for them). There's a few good grinds some of the guys have tried on the 60-66 GMC Group.
Here's a dyno simulation, based on a 401 with 401 Magnum heads, decked or milled to 9.0:1, and magnum exhaust:
401: Intake duration = 257 degrees, exhaust duration = 263 degrees, both measured at "seat-to-seat." Valve lift = 0.500", centerline angle = 112 degrees, no advance or retard. Carburetion = 700-725 cfm max, no more power with a larger
carburetor. Magnum intake, heads and exhaust, through the mufflers. Peak torque forcast as 502 lbs / ft @ 2500 rpms, peak hp forecast as 386 hp @ 4500 rpms. 450 lbs or more torque forecast from 1500-4500 rpms. Can your clutch handle it....?

I would have your machinist do some mild porting to the heads, and polishing, as well as very intricate balancing and blueprinting. The balance will be crucial if using a custom cam grind and winding it out.

Also, the whole front cover (water pump housing/timing cover) is a big cast iron piece. If using the bigger V6's (401, maybe 351 has it also?), the front cover is really heavy duty and weighs a TON. The 305 front cover is a much lighter casting and will drop A LOT of weight...
401's turn up all the time from fire trucks, big busses, motorhomes, and RV's, as well as big GMC trucks. If you can get a 401 Magnum or even a 351E (Magnum heads and intake, not as good of exhaust manifolds I think), you could make a cool hot rod out of it. If going for power, I'd just go all out and get the 401 or maybe a 432 if you found one. With as big as the 478 pistons are, I'd forget trying to spin that thing fast.

Also if you found a 379 crank ( or engine - a stroked 351), that would make a good size also, but the 379's never came with the Magnum top end parts. The 432 did have all the Magnum parts. Both these variations came along later in the late 60's and 70's.

Here's more:
http://autos.groups.yahoo.com/group/6066_GMC_Truck/message/10534
http://autos.groups.yahoo.com/group/6066_GMC_Truck/message/9644

I can't give any more detail than the following. My Dad who was in the auto parts business in the 50s, told me of roadster that was running around San Jose, CA. This roadster had a blown GMC V6. It was owned by the Long family that ran a Shell service station. Wish I had more information.

Larry

Why not start with the V-12?

Same level of ingenuity and persistance with twice the spark plugs.

Got this on other posts, but thought you might enjoy it!
http://www.rodbods.com.au/V12.htm