abryan

Hello...I have a 260 short block built and do not have any heads or intake...I have read the article in Hot Rod about installing 307 heads
on a 260 ...you have to notch the top of the bore to clear intake valve...has anyone ever done this before.....I have a 307 with 5A heads...
Thanks

69HO43

A lot of work for what you get- to take arguably the weakest Olds V8 on the planet and put larger heads on it that needs surgical modifications worked to fit.

It kind of reminds me of an old bit from comedienne Stephanie Hodge. She was joking about how women smoke light cigarettes because some man convinced them that it was worth sucking twice as hard for half as much.

CANADIANOLDS

What are you trying to accomplish?

you’ll probably be better off with the 307 7A peanut port high swirl heads or the stock ones if you can find them

abryan

I have a 260 already built without heads...I purchased a 307 ..I've read where you can use the 5A heads but you must notch the top of the cylinder bore...
I was hoping to find someone who has done this before...Thanks

joe_padavano

That "already built" 260 needs to be unbuilt to notch the cylinders. This is a lot of work for zero gain.

67OAI

If I read this correctly, you have a fresh built 260 short block and also have a set of 5A heads which you would like to install on it. The first thing you shall have to do is clean up the 5A heads so you don't introduce crap into your short block. Install one 5A head without a head gasket but with "checking springs" on the valves and measure the amount of lift (valve travel) before contact with the top of the cylinder on at least one each intake and exhaust valve; best to check all cylinders. If it is adequate for the camshaft you are using don't worry about it and proceed with installing the 5A cylinder heads. If you find that there is not enough valve travel for the lift of the camshaft you are using and you still wish to proceed with the 5A heads, it is time to take the short block apart and take the bare block and the cylinder head to a performance oriented automotive machine shop and explain to them what you need done. They shall most probably need to see a piston also to understand just how deep they can make the notch in the cylinder without it intruding on the top ring sealing surface in the cylinder. Probably at this point more trouble and money than it is worth. Just my two cents for ya! Good luck!

CANADIANOLDS

To tell you the truth I doubt the valve will ever lift beyond the heads deck surface if it has the stock 260 cam in it which should be around .350” max lift?

anyone know the stock lift on them?

You’ll have about .410” clearance between the valve faces and the deck with a .040 felpro gasket

the actual clearance between the 7A head face and the valves closed is .370”

olds 307 and 403

The stock 260 is just under .400" lift, slightly less duration and lift than the smog 307, 350 and 403 cam. You will be lowering compression as well with the 5A heads. Remember factory is only 7.8 to 1, you will be knocking on 7 to 1.

CANADIANOLDS

He should put a lifter in the 260 and measure lobe lift before doing anything else…you never know what cam is in it.

that way he can know for sure if he can just slap them on and run it?

abryan

Thank for the reply's ...I know the 260 is not the best engine...I am just trying to use what I already have...I wanted to talk with anyone who has done this before...Thanks...

joe_padavano

Understand, but I think what most folks are trying to tell you is this is the classic throwing good money after bad...

olds 307 and 403

Does this 260 have an overbore? How far below deck are pistons?

Tedd Thompson

Just put the 260 heads back on and drive the damn thing. It's never going to be a Hot Rod with the money you are talking about putting in to it. I've been driving under powered stuff for years, you kinda get you to it sorta....Tedd

joe_padavano

What was the old saying? "It's more fun to drive a slow car fast than a fast car slow."
Of course, it was the British sports car folks who came up with this...

Koda

I'd rebuild the 307.

joe_padavano

That was exactly my reaction when I first read this thread.

olds 307 and 403

Rebuilding the 307 isn't a bad idea, the 5A early 307's provided on par performance with any 80's carbed 5L. I ran multiple 307's, one to 450,000 km. I actually used 5A heads on an Olds 350 in two trucks, they worked great, a lot of torque, idle to the 4000ish rpm shift points. The problem with running unmilled heads is the 7 to 1 compression the 64cc 5A heads will give you on a 260, depending how far the pistons are in the hole, will determine how low. You can still make your already built 260 useable by pulling pistons and rods, notching the bores, running an upgraded cam and knocking about 10cc off the 5A heads with better exhaust will have at least the same power as a stock 307. For what, a couple of hundred dollars? Although a valve job, any worn guides replaced and a bowl hog cut won't hurt and then you will have a completely fresh motor. It will add more cost but who knows how worn your 5A heads are. You can at least add a 4 barrel intake on the 260 with the 5A heads. Judging by the last 307 build, he ended up right at 8 to 1, the milled 5A would still work fine if you decided the 260 wasn't powerful enough and you wanted to spend a few thousand to rebuild the 307. Here is a good compression ratio calculator. It looks like replacement 260 pistons have a 11.5cc dish.
https://www.summitracing.com/newsand...ion-calculator

abryan

I purchased the 260 short block already built from a machine shop.......I don't have any 260 heads or intake...I purchased a 307 for that reason...
Thank for all your reply's...