4.6LPoppy

I'm going to be putting in some cams and springs soon, and want to put the larger 46.8mm stainless intake valve in my P&P PI heads. Quite a few offer them for that purpose. I've been reading on it but am still not sure if anything else is required to accomplish that but to have the intake valve seats ground and the new valves seated. My machinist says that's all that's needed, but he works on Chevys so what can he know? Anyone know? Thanks.

oxfordgt

You will need a full port job to get valves that are over 2mm bigger then stock in there. That part is easy the hard part is getting them to fit within the walls of the of the cylinder. You need to be bored.

4.6LPoppy

??? Well...they are 2.33mm over stock, or approx. 1/10". So, they will fit nicely inside the combustion chamber of the head and in the cylinder. I'm not sure what porting would accomplishother than increasing the runner volumeof the intake. Besides, I've done that. Rev, Ferrea, Sean HylandMotorsports, and others all make stainless SVOintake valve "replacements" for the stock intake valve in thestock4.6 PI head. Just wondering about seating the valve??

oxfordgt

Ill try to explain this as simple as i can. The hole that the valve seals has to be made bigger.

They will fit inside the combustion chamber no problem, the chamber is bigger then the cylinder. That is why most people that upgrade to a bigger valve already have a big bore block. You can use them but you will never be able to change out the stock cams.

4.6LPoppy

OK. I'm not trying to pick a fight here....just trying to understand. Yes. The valve seat must be made larger. My machine shop says that they can grind the seat to acommodate the new valve by just grinding the new size (46.8mm) with the stepped angles and it will seat properly with no other changes necessary to the seat or seat area. What I hear you saying is that the valve face may not clear the cylinder wall of a stock 3.55" bore when the valve is opened? And, why would I not be able to change out the stock cams? Notchallenging you...just asking. I appreciate your help. No one else has answered. Thanks.

oxfordgt

Any more lift on the cam then stock will make the valves slam into the top of the block

4.6LPoppy

Got it. Thanks.