Jweast

I was wondering if anyone knew what the "max" you can port 305 cylinder heads too, is it 1.94 or can i go as big as 2.00 or 2.02. essentially going to 350 performance heads.
Thank you


JWeast

ljnowell

Porting has nothing to do with vavle size. Porting is the removal of material behind the valves and in the runners to increase air flow.

Jweast

I apologize i'm new to the whole altering cylinder heads project. But, can I increase the valve size to 2.02 or 2.00 without causing any clearance issues.

Thank you

JWeast

GuitarJunki17

iTrader: (1)

No, you cannot alter the valve sizes without getting extensive machine work done to get the valves to seal. All you can really port away (as stated before) the runners before the valves. It's alot more precise than you may think, it's not just about taking as much material off as you can. You may end up doing more harm than good. I suggest you read up on this http://www.sa-motorsports.com/portdiy/diyport.pdf as you need proper tools, and know how as to what you are doing here.

ME Leigh

Yes you can increase the valve size to 2.02. You just have to take them to a machine shop to get the seat cut for the larger valves. Then you will want to deshroud the valves. Meaning you will want to grind some material out of the combustion chamber to improve airflow.

F-BIRD'88

You can fit a 2.02" valve in a 305 head but its not nessessary. A 1.94" valve works better in this head overall because the 2.02 is too shrouded by the compact combustion chamber wall next to the valve edge.
Unless you deshroud the chamber to allow the 2.02" valve to breathe, the 1.94" valve is better.

Both valves require this deshrouding but the 2.02 requires more to get proper flow clearance. i feel it weakens the casting and adds no advantage on this head.

You can achive all the flow and power you'll need using a 1.94" valve in 305 heads.
I've achieved over 240cfm with no epoxy or welding. thats more than a vortec head flows. thats more than a edelbrock rpm head flows.

For a 350 project using 305 heads, fully port them and install new 1.94x 1.60" valves. Do all the porting first, drill and pin the rocker studs.( roll pins) If you want to run 1.6 rockers lengthen the push rod slot in the head with a 5/16" rat tail file in a drill. Do not make the slot wider just longer towards the rocker stud. Then drop them off at the machine shop so they can do a new valve job for then new larger valves.
use Lunati #73943 springs. $60. Stock retainers and have the guides machined for high lift and new seals. the spring seat diameter is fine for Lunati #73943 springs.
Each exhaust spring seat will need a .105" stack of spring shims to allow eliminating the exhaust rotators and get equal spring installed height. (1.70" to 1.75"is good)
You'll need 8 each of .015"+.030+ .060" spring shims.
The machine shop can supply these.

If you *fully port* these heads using 1.94x 1.60" valves you'll likely end up with just over 230cfm in and 180cfm exhaust. this is enough to make 430+hp on a 350 using and good powerfull cam and intake and headers with 10:1 compression. easy 12's. There are many good books By Lingenfelter and David Vizard on porting SBC heads and lots of advice and pics on this forum.