ok, 302 vs 308

[streetdak]

Anyone know the differences between these 2 swirly heads?

I just purchased some 308's off of moparts, going to be doing the porting work with a friend of mine who has more porting and machine experience.

I know the 308's come with 1.88 valves and were on mostly 360's , but does anyone know the combustion chamber size and any difference of the 302's?

 

[EL5DEMON340]

don't know the size, but the 302 are 318 heads with poor flow on bigger small blocks. the 308's are the best flowing SB heads pre magnum, exhaust is what shines, but have them checked for cracks before you do work on them, they often have cracks.

 

[72bluNblu]

There are a few differences-

The 308's are for 360's. They have the larger 360 ports, and they are open chamber heads. 65cc chambers normally, but up to 72cc's depending on the casting. They have 1.88/1.60 valves.

The 302's were for 318's. They have the smaller 318 ports, but they are closed chamber heads! Typically around 62cc's, but anywhere from 58-65 cc's depending on the casting. They use the smaller 318 valves too, 1.78/1.50.

I had a set of 308's ported myself, final numbers showed them flowing 264 cfm at .500". The 308's really shine on the exhaust side though compared to the earlier J and X heads, since they use the W2 style port. Both the 302's and 308's have hardened seats, and both tend to crack between the valves (possibly because of the hardening process).

I don't know how the stock 302's compare to other stock 318 heads though. Stock 308's are pretty comparable to X and J heads with matching valve sizes. Most of the numbers I've seen show them flowing better on the exhaust side, but giving up just a touch on the intake side to the X and J's.

 

[moper]

72s pretty close, except with regard to chamber size.
302s are closed chamber, around 63ccs, small valves, 318 ports.
308s are open chamber, closer to 74ccs factory, 1.88/1.60 valves, same basic port and chamber as all X,J,915, 587 heads but a much better exh port (like a magnum more than LA head exh port). IMO, the 308/587 heads are the best factory iron heads to work with.

 

[streetdak]

well you guys are definitely making me feel good about my purchase. I read something on the 302's that seem to be negative. Is there truth to a rumor about them running air/fuel lean>>

 

[Prine]

I have known about the 302/308/587's for quite some time......guess thats why I have 2 sets of 302's, 2 sets of 308's and a set of 587's.

Everyone covered all the relevant info, so I will leave it alone....just wanted to add my .02.

 

[72bluNblu]

72s pretty close, except with regard to chamber size.
302s are closed chamber, around 63ccs, small valves, 318 ports.
308s are open chamber, closer to 74ccs factory, 1.88/1.60 valves, same basic port and chamber as all X,J,915, 587 heads but a much better exh port (like a magnum more than LA head exh port). IMO, the 308/587 heads are the best factory iron heads to work with.

Everything that I've seen on the 308's says the factory spec chamber size is 65 cc's. Obviously, all the open chamber heads have been known to vary quite a bit, and a lot of them are usually closer to the 72cc mark.

But the set of 308's I had reworked for my 340 started at 65cc's on the nose, and they appeared to be uncut before I got them.