mid '80s heads.... 2 questions

[ragtopfury]

So Jake took the rebuilt 28 years ago and never fired up 318 apart today just to make sure nothing took built a nest in any of the cylinders while it sat forever under the workbench....

We have 2 choices for heads on a stock bottom end 1984 318.... The 318 heads that belong on it.... and a set of barely used mid 80's 360 heads... Both sets of heads have the smog holes under the exhaust ports...

What size tap and pipe plug do I need to run in those little holes?

If I use the 360 heads, will I be taking power away?

Neither sets of heads have been milled beyond a very minimum just to true up the surfaces..... We are installing a repro stock spec mopar 340 cam and an old Edelbrock streetmaster intake I've had lying around for 3 decades (i'm getting old...lol)

 

[Robbie2734]

What do you intend to use the motor for? The 360 heads will lose some of the bottom end.

 

[toolmanmike]

We will need the casting numbers to be sure but the 360 heads had bigger valves. The original heads should have a casting number ending in #302. I didn't think the 302's came out untill 85 though. tmm

 

[72bluNblu]

1/4" is what you want to tap those smog holes too.

When I did it on my 302 heads I just ran the appropriate drill bit for a 1/4" tap in to clean up the holes, then tapped them about half way. The drill might not even be necessary on all the holes, they're about the right size for a 1/4" tap already. Then you just loctite some allen set screws in there. If you don't thread them all the way in they can't advance to the chambers, and with the loctite they shouldn't back out.

302's didn't come out 'til '85, so those probably aren't 302 heads. The issue with the 360 heads will be getting any compression out of them. Those chambers will be big, and with a stock bottom end and stock 360 chambers you're compression ratio will end up around 7:1 unless you mill the crap out of the 360 heads.

 

[toolmanmike]

The closed chambered heads are the desirable ones. The ones with the heart shaped combustion chambers. The open chambers will loose too much compression like Blunblu said. Here's what the closed chamber heads look like:

 

[ragtopfury]

Casting number is 4027163... Going in Jake's 65 B'cuda just to get him on the road with a fresh and reliable mill that cost me almost nothing - gaskets/cam are the only expense in it... He can build a screaming small block later in life when he's older...lol

To be honest, I don't know what the chamber looks like on the 360 heads - they are in the shed and I haven't dug them out yet.

 

[Dodge33]

It seem's like the last 1983-84 318 truck motor we had.......I think it
had 576 head's on it, might have been 516's, not really sure guy's.

 

[Abodybomber]

Stay 318s,Streetmasters work better with smaller ,high velocity heads.Did a similar build,on a 307 Chev. Torque up the wazoo,got 18 m.p.g. In a full size 1/2 ton 2wd truck,no less. Nice combo.

 

[ragtopfury]

So the 318 heads are the pick.... I knew the 360's would lose a little, but sounds like they would create quite a dog off the line... I'm not building the rookie a rocket, but it does need to get out of it's own way....

Thanks FABO!!!