516 heads-porting/unshrouding valves

[Mark Barnes]

I know that there have been a thousand posts about 516 heads and their usefulness, or lack thereof. Fact is, that's what I have, and that's what I can currently afford. I already installed stainless Manley valves 2.14/1.81, three angle grind, new springs and retainers, etc.
Then I got educated by the guys on this site. I can handle a port/polish and gasket match, but the thing I'm unclear on is "unshrouding valves". Can anyone tell me, or point me somewhere I can actually see what exactly has to happen to "unshroud" valves? Is this something a semi talented putz like myself can tackle without ruining the existing work? Any input would be appreciated.

 

[steve340]

There are plenty of good books on the subject and SOME reasonable stuff on YouTube. A couple of old valves to protect the seats and you should be able to do a reasonable job.
Most of the mojo is in the valve pocket and the short turns. If the seats are already cut may be best to stay away from these areas.
Do not hog the ports open.

 

[wyrmrider]

do not open out to the gasket
what bore are we working with?

 

[Dodge Bros]

We pulled the 516s a week ago, I started working on them. Originally I was only planning to unshroud the intake. But the head had a burnt exh valve and one was sunk bad, so we are installing 1.81s.

Work on progress but no reason why you can’t start on your heads. I have some work next to spark plug yet.

 

[Dodge Bros]

Like Wymrider said you should match up your bore to the unshouding cuts. Pic’s are for a 4.32 bore with the block unshrouded to match.

 

[69Bee]

You open up the chamber wall to give about 0.080" to 0.100" of clearance between the valve edge and chamber wall.

 

[Mark Barnes]

do not open out to the gasket
what bore are we working with?

4.28 bore. What is the reason that I shouldn't open out to the gasket? This is all new to me.

 

[Mark Barnes]

You open up the chamber wall to give about 0.080" to 0.100" of clearance between the valve edge and chamber wall.

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Thanks for the explanation and the pics. Now I get it.
BTW, that's some impressive work.

 

[Dodge Bros]

Notice that the pics of the head 69bee posted has another angle above the spark plug than the head I am working on. If you grind up there try to keep that end matched up to the bore. Taking to much off there would be detrimental if it is like the head I am working on. I took plenty of metal off trying to drop the compression. It was more than I could remove with the fixed cutter.

 

[zyzzyx]

Mopar used to make template kits that you could fit down into the pocket. It would give you
a visual of what needed to be taken out. Good luck finding them. Maybe someone here has a set????

 

[69Bee]

Mopar used to make template kits that you could fit down into the pocket. It would give you
a visual of what needed to be taken out. Good luck finding them. Maybe someone here has a set????

I do, but am keeping them. I used them over 20 years ago, and broke thru two intake bowls to water, LOL...

 

[PRHeads]

The amount of porting should be commensurate with the overall level of the motor combo build .......and how it will be used.
In other words, Pro Stock levels of porting aren’t called for in a tow vehicle.

Depending on what the combo is, sometimes “less is more”.

Not quite enough porting almost always works better than too much porting.

 

[zyzzyx]

I'm by no means an expert, but all I can say is: Remember that air moves in a straight line unless it
is obstructed by something (Valve stem). Gasoline droplets move with the air unless the air stream
changes direction too sharply. When that happens, the droplets come out of suspension as they hit
the wall and go around the bend. Try to keep the port as smooth and straight as you can and you will
do just fine! Those of us that don't have a flow bench can do a great job.

 

[steve340]

Knock any big lumps out of the throat area under the valve head but be careful not to hit a valve seat. You want to leave a slight choke point below the valve seat so taking less is better. From what I have seen do not get carried away as PRHeads rightly points out it is easy to do too much and make the heads actually flow less.
Using a couple of old valves blend were the seats are cut in the combustion chamber to eliminate any ledges when the valves open and you are probably OK.

 

[Dodge Bros]

My original suggestion from the thread a few weeks ago to unshroud the valves was really more directed as a method for lowering the SCR to run a 262 Voodoo cam. Plus some relatively easy hp might be found. If this is a pump gas engine and the rotating assembly, pistons, heads, and cam are a done deal, unshrouding is probably your last shot when it is already 10 or better on the SCR. Our 516s have had a fair share of porting done using a flow bench. They are for a higher hp build. Stockish 516 port with big valve the unshrouding might not be holding the flow back that much. Kind of anyone’s guess. With the small cam and stock ports it may not wake it up a lot. Could even hurt it some at the level of my pics. FWIW, At least it will have a better shot running pump gas.

 

[wyrmrider]

why not go out to the gasket?
first the gasket needs some support
and the incoming air does not like to hit the topof the bore
some heads overhang the bore anyhow
there you van chamfer the topof the block but too near the ring travel like a 413 max wedge
exhaust does not matter
just a little bit helps
if the block is appart you can bolt on the head and scribe the bore on the head
to do the block deck make a hook scribe
lcky for me a 413 stainless truck gasket works out perfect- just sit it o the block and scribe
I keep a set of steel shims around 361 truck etc

no templets for 516 and they port different than 915s

 

[Mark Barnes]

In my search for information I found this, if anyone needs them. Don't know how much help they'll be.
https://www.bigblockmopar.nl/tech/mopar-porting-templates-rb-la-magnum-heads/

http://victorylibrary.com/mopar/chamber-tech-c.htm

 

[Dodge Bros]

The 516s have a sharper short side radius than the other heads. MP templates were meant for taller short turns.

It is not unusual to hit a water jacket porting on the exhaust trying to open them up to what is normal porting on the later heads.

I would clean casting flashes up on the intake. Blend the bowl cuts into the port on the intake.

On the exhaust blend the bowl into the port, remove flashing, then straighten the port where the ceiling radius ends and exits into the ceiling of the exhaust port exit.

If it is helpful I can post some port pictures of the heads I have. They flowed 235-240 with the 2.08 intakes. Nothing spectacular. Hoping to get them up in the mid 250s when done.

My brother and I were talking about these 516s and he was kind of annoyed that I unshrouded the exhaust valve. I did it more to see if there are ways to wake these heads up and make the combustion chamber heart shaped in the process. I doubt I gained anything. Still working on it. More out of a fun challenge than necessity.

Unshrouding I would focus on working on removing metal from areas that are inside the bore diameter first. I was trying to stay 1/8” from the head gasket sealing surface. Remove what you can to unshroud inside the bore, then remove the extra to gain some cc’s to drop the compression some. My head had a lot of extra metal up next to the spark plug for finding some cc’s. It would be helpful to bolt a head on and take a sharpe to mark the bore pattern on your head like what wrymrider mentioned. Good comments.

 

[Mark Barnes]

The 516s have a sharper short side radius than the other heads. MP templates were meant for taller short turns.

It is not unusual to hit a water jacket porting on the exhaust trying to open them up to what is normal porting on the later heads.

I would clean casting flashes up on the intake. Blend the bowl cuts into the port on the intake.

On the exhaust blend the bowl into the port, remove flashing, then straighten the port where the ceiling radius ends and exits into the ceiling of the exhaust port exit.

If it is helpful I can post some port pictures of the heads I have. They flowed 235-240 with the 2.08 intakes. Nothing spectacular. Hoping to get them up in the mid 250s when done.

My brother and I were talking about these 516s and he was kind of annoyed that I unshrouded the exhaust valve. I did it more to see if there are ways to wake these heads up and make the combustion chamber heart shaped in the process. I doubt I gained anything. Still working on it. More out of a fun challenge than necessity.

Unshrouding I would focus on working on removing metal from areas that are inside the bore diameter first. I was trying to stay 1/8” from the head gasket sealing surface. Remove what you can to unshroud inside the bore, then remove the extra to gain some cc’s to drop the compression some. My head had a lot of extra metal up next to the spark plug for finding some cc’s. It would be helpful to bolt a head on and take a sharpe to mark the bore pattern on your head like what wrymrider mentioned. Good comments.

I'd love to see any pictures you have. I think I'm beginning to see what everyone is talking about....

 

[Mark Barnes]

You open up the chamber wall to give about 0.080" to 0.100" of clearance between the valve edge and chamber wall.

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Any pics that show what you did UNDER the valves?