[steve25]

Use new valves, and yes they will not have the needed second groove for the factory valve stem O ring if they are SS.

This then means each valve guide too will need to be machined for a positive type seal.

This also means that the factory oil shield must be dispensed with also.

If your not looking to make and cam the motor to make over 400 Hp then I would think twice about porting these heads, especially if you have never done so before and also that you have the funds and a shop that can do a before and after flow test for you.

From flow test I have done on folks home ported heads the owners have picked up some high lift flow, but killed off a good amount of lower lift stock flow.

There’s a cut in stone golden rule to intake and exh flow numbers that goes by a percentage of the valve size used.

It is simply D x.18.

For flat out race heads it’s D x .2.

So for a 2.11” intake valve the math then tells you that up to .380” lift the flow that the cylinder revives is totally controled by the valve job applied and the 1/2” of port shape before the valve seat in the bowl and the 1/2” of chamber shape after the valve seat up to that .380” lift point .

If your running a cam of .500” lift then that’s only 30% more lift then .380”.

If you kill off 10% of the flow you had below .380” lift, yet only pick up 10% more flow up at .500” lift then you are still just about at the brake even point horse power wise because up at .500” lift the cam has less duration then at .380”.

At best with such a condition you have picked up some added port area which will make the HP numbers that the motor does produce not nose over as fast.

On the exh side we see that up to .320” lift the valve job is having the greatest effect.

This being said there is with the right grinding Burr about 10 minutes work of work that can be done to pick up some easy high lift flow.

This type of porting work along with a simple 30 degree back cut on each exh valve will fatten up the flow numbers across the whole lift range.

Exh headers will add 3 to 5% more flow above .300” lift all on there own, and this plus the exh rework above needs to be factored in to the Cam pick as to it being a duel or single pattern Cam.
If you do not know what your doing when porting and you kill off some of that stock air flow up to .380” lift , well what can I say!