'72 RV 413 engine questions

[Garys1969RR]

413 std bore = 4.18"
426 std bore = 4.25"
440 std bore = 4.34"

Max Wedge blocks were notched to clear 1.88" exhaust valve

I think the 440 has a 4.320 bore size, and the 400 block has the largest bore at 4.340. I built my 451 at .035 oversize, which brought the 400 block to a 4.375" bore.

 

[mopar 3 B]

My 413 had the stock 2.08/1.74 valves that came in the 915 head. Highest lift cam I ever used was a Racer Brown mushroom lifter cam with .690" max lift. I believe the 413 block had a .060 Overbore, making it in reality a 426. Bore size of 4.25", same as a stock 383. I never had any valve to cyl bore clearance problems, although I do recall grinding a small area at the top of the block to help airflow into the cylinder.

Why would you grind the top of the block to improve air flow?

 

[Cornpatch MO]

Why would you grind the top of the block to improve air flow?

Well, I guess in a round about way it would. They cut a notch in the block deck , at the edge of the bore to clear the huge valves and high lift cam that were with the Max Wedge heads-engines. Anyways that is what I was told............................MO

 

[mopar 3 B]

Valve clearancing allows larger valves but it is still the head that increases flow.

 

[Cornpatch MO]

Valve clearancing allows larger valves but it is still the head that increases flow.

Guess it depends on how you look at it. The Max wedge heads were designed to flow a great amount, and needed the clearance for larger valves and more cam lift. You are right in thinking that taking off the heads, grinding on the deck surface , and putting the same head back on, with no other changes, will not help head flow, and probably harm performance due to increasing combustion cc's. But, there is always room for doubt ! .............................MO

 

[Garys1969RR]

Why would you grind the top of the block to improve air flow?

If you bolt a head without valves onto a bare block, you can see that the combustion chamber near the intake and ex valves may in some cases be larger than the cyl bore. This is especially true if the combustion chamber has been opened up to gasket size in this area. (Relieved) So the incoming airflow already has a narrow area to go between the edge of the valve and chamber wall. Then if it also hits a small flat area at the top of the block, that impedes it even more. This restriction is more pronounced on a 413 with a 4.19 bore size than a 400 block with a 4.340 bore. The 400 block bored .035 O Size may not need any grinding at all, since at 4.375" it will be almost as big as a 4.4" gasket. You can also lay a head gasket on the deck, and see the opened up area near the valves.

 

[mopar 3 B]

This is called valve clearancing. Just make sure not to get into top ring travel and leave plenty of material to control combustion burn.