350 Olds, what to do?

[oldson]

So, I picked up a 1973 olds 350 complete including trans for a song. Wanted to build it up a little with stock parts to drop it into my 87 cutlass. Happened to find a set of rebuilt 7a heads. Now, as I'm talking with the guy, he offers me a rebuilt 1975 350, with crank and pistons. The block is bored 30 over, the crank is ground 10/10, and pistons are flat top. I was told the engine ran low 11's in the 1/4 mile and has really low hours. This was offered to me for a "I'd be stupid not to" price.

Here is my dilemma, I was playing around the compression calculator on the summit web sight, and, all things being the same, If I just drop the heads on my 73, I'll be close to 10:1 compression. If I buy the 75 block, crank and pistons, I'll be around 10.65:1 compression. (bear in mind, these are loose calculations) Now, I know there are other variables like quench, dynamic compression ratio, etc. That's getting a little to involved for me at this stage in the game. Right now, I just want to get the foundation down. I can add window dressing, in the form of degreed cams, roller rockers, performance intakes, etc., later.

What I want to know is which would be better for the pump gas we have around here? We have up to 93 octane, which I have no problem using. I just don't want to get into race gas. Changing the cam is an option, but staying stock is preferable, as I have the parts.

 

[L92 OLDS]

So, I picked up a 1973 olds 350 complete including trans for a song. Wanted to build it up a little with stock parts to drop it into my 87 cutlass. Happened to find a set of rebuilt 7a heads. Now, as I'm talking with the guy, he offers me a rebuilt 1975 350, with crank and pistons. The block is bored 30 over, the crank is ground 10/10, and pistons are flat top. I was told the engine ran low 11's in the 1/4 mile and has really low hours. This was offered to me for a "I'd be stupid not to" price

What I want to know is which would be better for the pump gas we have around here? We have up to 93 octane, which I have no problem using. I just don't want to get into race gas. Changing the cam is an option, but staying stock is preferable, as I have the parts.

I would stick with your 73 set up. Unless you have aluminum heads, anything more than 10:1 will be a challenge in my opinion. I run just over 10:1 on my 403 and with 93 octane, I still need to retard the timing more than I'd like. Pre ignition knock becomes more noticeable in hot weather unless timing is pulled back. Both 73 block and 75 blocks are about the same and have solid main webs. Are you sure your 7a heads are 1972 vintage or are they 307 heads....

 

[oldson]

Thanks Anubis! Yes, I checked the casting numbers before I handed over the cash. They are 7a's from a 1972. I have the 7A's on my current 307. Confusing, but double checked.

You also confirmed my suspicions on the 350. While it's nice that it's done, it's to much for what I want to do. Now I just hope my 73 isn't trashed and needs to much machining. Haven't broke it open yet.

 

[oldson]

This last week I broke apart the 73 350 and it's a mess. It's been sitting for quite some time and the cylinders are scored. So, I'm back to considering the rebuilt 350 or a running 350 that was given to me the other day.

Here is the recipe that I am considering for this project:
72 7a heads (rebuilt)
Stock grind W-31 cam (howards cam from competition products)
Stock intake (either A4 or Cast iron)
Stock Carb (from current 307)
Stock HEI (from current 307)
Stock exhaust manifolds (from 73 350)
And a choice of 1 of 3 blocks:
a) 1973 350 (stock 2bbl, needs rebuild)
b) 1975 350 (stock 2bbl, running last year)
c) 1975 350 (bored 30 over w/ flat top pistons)

Going for a stock look that will run on pump gas (up to 93 octane) and will pack a lot of punch. Near as I can tell, this is a close recipe for the W31 350. May not pack as much punch as the valves are smaller, but should be close.

Any thoughts would be appreciated.

 

[olds307 and 403]

Don't use the W31 cam, much better cams with more power and better manners. The stock 75 bottom end with the 7A heads and a mild cam would work, mid 8 to 1 with Felpro head gaskets or even better the .028" head gaskets Rocket Racing sells. I would only run the stock 73-76 #8 heads on the block with flat top pistons. Mill them for true 9 to 1 compression and open up the bowls and add at least a 2" valve like the W31 had or a 2.07" intake like the BBO had. The stock 1.625" valve is fine, same size as the W31, once the lip is removed under the valve, they are as good as early heads. I am running 9.5 to 1 compression with the small 204/214 cam. I also am running 1.72 to 1 true roller rockers which should in theory make the cam act slightly bigger on the duration side and gain a good amount of lift. The #6 heads have bowl, port work, 2"/1.625 valves, filled crossovers and milled to 55cc on a stock 76 block with Felpros. I have to run 91 octane, cut down the vacuum advance and run extremely cold NGK 5670-8 spark plugs to eliminate the pinging. Get a Performer RPM intake, the stock intake is OK for stock, not much else.