Question on 516 big block exhaust seat diameter?

[chargerbr549]

I am looking at building a set of 516 castings so I can build a quench motor and I already have them, I have put seats in several of these heads over the years but I have always used an 1.750 od seat and the 1.74 exhaust valve as opposed to the 1.60 valve but I am thinking about going to a little bit bigger exhaust valve so I was wanting to goto a 1.810 od seat, would the bigger seat work and what about the big bump that protrudes out just under the exhaust seat area, how thick is that since I will be porting these heads as well? I work in a machine shop so the labor part won't cost me at all.

Kevin

[Challenger340]

1.81 will work, 1.85 might be better.

You mean the bump on the side of the exhaust port wall, closest to the Intake side ?

Leave the bump, it acts to shape the exiting gases over to the far side of the port. Just shape and blend.

You'll notice the 516's don't have much of a typical "short turn" in the port floor, the bump on the side basically "is" the short turn.

[chargerbr549]

Hey thanks Challenger for the info and your correct that is the bump I am talking about. I am actually looking at putting in early 70,s 455 Pontiac valves since they are basically the same length (within about .015) as stock big block valves and they have 2.11 intake head and 1.77 exhaust head plus 11/32 stems to save a little weight and maybe gain a little airflow.

Kevin

[R/T1968R/T]

 The 516 heads will not flow enough to warrant a 1.81 valve. For most motors in the 400-450HP range the 1.74 will do. the intake runner will be the restrictive factor. check out this article from Moparts.
http://www.moparts.org/Tech/Archive/bb/42.html        or this  http://www.moparts.org/Tech/Archive/bb/62.html

[Challenger340]

Just remember, how much power are you realistically trying to make ?

I tend to agree with 1968R/T here somewhat.

I know you work at a Machine Shop and the Labor price is "right", just be careful just how far you wanna get into these Heads.

A "well-built" set of 516's even with stock Valves, can probably supply sufficient air for what you wish to do ?

The Poncho BB Valves is an interesting idea, if you do go that route, I'd concentrate more on the Intake Side Flow than the Exhaust Port, and use the "hotter burn" for more Exhaust "pressure" to get it out, especially on Todays split pattern Camshafts.

Flow Benchs aren't "Dyno's", and they NEVER will be.
Guys have been falling in that hole for decades.