halfmoontrail

Okay, my new to me '79 Hurst/Olds came to me with a '72 350. Driver's side head is #8, but passenger side is a 7A (big A). I know they have a different combustion chamber size.

I haven't fired it up, but I plan to after I set timing and run a hot wire to the HEI distributor. The question is: How bad is this situation, will it run okay or explode, or shake apart?

I'd love to keep that engine in there as an occasionally light-duty driver if it runs okay. I'm the kind of guy who would rather put in a different complete engine (350 or 455) than change the mismatched head on a '72 350.

Thoughts?

Steve

captjim

That is an odd combo! The 7A head is off of a 307, with tiny ports and a small chamber, the 8 is off a 73-76 350 with a large chamber. If it is a 72 350, it has crappy 23 cc dish pistons, more than likely it is a 73-76 which has 14 cc pistons, that would be better. Find some older 350 heads in decent shape and bolt them on or find a lower mileage 403 and drop it in.

Just curious, how does it run now?

DoubleV

I think he means he has a 72 350 head. The side of the engine with the 8 would be stupid low on the cr not to mention the worse exhaust flow. Personally I wouldn't drive it like that. Probably will run OK but it would be very slow and maybe hard to tune.

captjim

You are probably right, i just saw the "big A" and wasn't sure. Halfmoon, is the "A" as large as the "7" or smaller and offset lower? That would jive with it being a 72, also.

halfmoontrail

Nope, it's that bad, the 7 and the A are the same size, not offset. I haven't tried to start it yet, had to fix a broken dipstick tube, a valve cover gasket on the 7A (yep, 5 holes...), vacuum hose to modulator on trans.

All I have left to do is set initial timing manually and run 12V to the cool transparent HEI dizzy and see if she'll run. I'll admit that I'm curious...

olds 307 and 403

What a horrible combo. Decent compression and horrible flow on one side, other side, low compression and fair flow. #8 heads should be easy to find in decent shape for close to free, find another to match.

Lars

Start it and if it runs smooth... run it until you can find a nice matching set of heads. Check the block stamp for the year of the 350, on the block drivers side under the head in the front.

joe_padavano

Yes it will run. It will probably even run on kerosene with that crappy CR.

captjim

Since it has a #8 head on one side, I bet it has the 73-76 block/pistons in it. Pop on some older 350 heads, a little cam, and make it a fun little driver.

joe_padavano

Unclear, as the different heads tell us that the motor has been apart at some point. Of course, the VIN derivative will tell you the year of the block and eliminate all speculation.

captjim

You are correct, but I am going to assume (dangerous, I know) that at least one of the heads is OE. But like you said, the number will confirm either way.

halfmoontrail

Haven't checked VIN derivative, but oil fill tube is straight and starts with a 2, block casting is 395558.