Valve Shrouding Q's

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805moparkid

805moparkid

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So is there any general specs as far as a minimum valve to valve and valve to head/cylinder wall before shrouding starts to take effect?

I see pics with valves almost touching but then some say its never enough distance.

Obviously is most cases the chamber has to be corrected to the cylinder but as far as a "Theory" number.
 
i dont think thats relevant. not looking for application specific, just in general
 
As a general rule, the less the valve is shrouded the better. But i have found, that if you get real crazy with it, it can really mess up the way the air travel through the port. I only have experience with the J,X, and early emission 360 heads.

That is why i asked, as this is the only ones that i could give you more then theory on.

I guess I'm not answering you question but i don't have any cold hard fact on this. My guess is around .020 on valve to valve and as far as shrouding goes i would say .020 at .100 lift and continuously enlarging as the lift goes up.

Unfortunately you can't do that as the head gasket surface is in the way.(were talking intake valve here)
 
I think the whole valve shrouding thing is way over thought. Plenty of performance engines came from the factory with what would be considered valves that were shrouded all to hell, but they ran like gangbusters. I am sure the argument will ensue since I said it, but that's my thought.
 
Cudafever said:
As a general rule, the less the valve is shrouded the better. But i have found, that if you get real crazy with it, it can really mess up the way the air travel through the port. I only have experience with the J,X, and early emission 360 heads.

That is why i asked, as this is the only ones that i could give you more then theory on.

I guess I'm not answering you question but i don't have any cold hard fact on this. My guess is around .020 on valve to valve and as far as shrouding goes i would say .020 at .100 lift and continuously enlarging as the lift goes up.

Unfortunately you can't do that as the head gasket surface is in the way.(were talking intake valve here)
Click to expand...

sorry i didn't mean to be rude, whether you took it that way or not. thanks for those specs, gives me some reference material to start plotting!

RustyRatRod said:
I think the whole valve shrouding thing is way over thought. Plenty of performance engines came from the factory with what would be considered valves that were shrouded all to hell, but they ran like gangbusters. I am sure the argument will ensue since I said it, but that's my thought.
Click to expand...

well i think its safe to say those said engines would run harder if the shrouding was relieved and compression corrected. That said i think if a valve was big enough over the stock valve the gain in area minus the shrouded area would probably still be more giving gain.
 
805moparkid said:
why or why not? if two valves of the same size are run, one with more area shrouded over the other, the less shrouded valve should flow better, or do you not agree?
Click to expand...

Mcsa.(Minimal Cross Section Area) If it is at the valve at say .400 lift on up, then yes less shrouding is a good idea. IF the Mcsa is some were else in the port. (most likely at the ssr)well your not going to get any more air through that port by un-shrouding it.

I'm sure cleaning and smoothing will help.
 
Cudafever said:
Mcsa.(Minimal Cross Section Area) If it is at the valve at say .400 lift on up, then yes less shrouding is a good idea. IF the Mcsa is some were else in the port. (most likely at the ssr)well you not going to get any more air through that port by un-shrouding it.

I'm sure cleaning and smoothing will help.
Click to expand...

very true, if its not the smallest restriction its not going to do much! so i guess the real issues comes back to how close you can get the valves together and not hitting anything.

So .020 from margin to margin or from the edge of the seat angle to edge? also that would probably be the same to the cylinder wall?
 
I never really knew any technical numbers on this subject. Just hillbilly style engineering that made sense to me...lol.

With stock style closed chambers, I used to lay back the intake wall a little bit.....especially on overbored engines. I used the scribe method to make sure I was close to the actual bore size. How well it worked? Beats me, but i figured it couldn't hurt. I never used oversized valves big enough to get near a interference point between them, so I'm clueless there.

A example below of what looks like a pretty shrouded chamber is the "true" closed BBC. Looks a little ugly as far as what we're talking about here, but maybe looks are deceiving. Although they did lay back the plug side of the chambers on performance spec'd engines...
View attachment Chevy BB Closed.jpg

I guess the 348/409 engines below were the true idea of un-shrouding. Even though the chamber was in the cylinder and was formed mainly by angle mounting and the piston dome, the fact that the piston was away from the deck for most of the event had to alleviate any issue with shrouding i would think. Maybe on the intake cylinder wall side if a large valve was used? Although they were very large bore engines.
View attachment Chevrolet-409-head.jpg

I'm sorry I used Chebbies as a example, but since the discussion was in general terms, these were the best examples I could find.
 
I'm talking what i know,.... but if it was a bone stock LA cyl head then the Biggest cfm jump is in a GOOD 3 angle valve job and bowl blending the bottom valve cut. The 70 or 75 bottom cut takes a lot of material with it, but it need to be blended into the as cast of the bowl area.

Aka the mcsa is in the bowl area. It could vary well be the case with yours as well.

Just a little food for thought.
 
Cudafever said:
I'm talking what i know,.... but if it was a bone stock LA cyl head then the Biggest cfm jump is in a GOOD 3 angle valve job and bowl blending the bottom valve cut. The 70 or 75 bottom cut takes a lot of material with it, but it need to be blended into the as cast of the bowl area.

Aka the mcsa is in the bowl area. It could vary well be the case with yours as well.

Just a little food for thought.
Click to expand...

this will be a max effort deal so it will be heavily ported. and the place i use does full radius valve jobs
 
Shrouding can be used to steer combustion gasses. Give them a swirl. There's a use for it. Of course, like anything else, too much is bad.
 
this will be a max effort deal so it will be heavily ported. and the place i use does full radius valve jobs
Click to expand...

#1 does he have a flow bench and ............
#2 don't get hung up on max ### and don't port past the cfm potential of the motor.!!!

this will only cause your car to slow down a full Sec in the 1/4 mile.

Ask me how i know:violent1:
 
Cudafever said:
#1 does he have a flow bench and ............
#2 don't get hung up on max ### and don't port past the cfm potential of the motor.!!!

this will only cause your car to slow down a full Sec in the 1/4 mile.

Ask me how i know:violent1:
Click to expand...

yes and this head cant out flow the engine...

Also a 7 axis cnc
 
Cudafever said:
As a general rule, the less the valve is shrouded the better. But i have found, that if you get real crazy with it, it can really mess up the way the air travel through the port. I only have experience with the J,X, and early emission 360 heads.

That is why i asked, as this is the only ones that i could give you more then theory on.

I guess I'm not answering you question but i don't have any cold hard fact on this. My guess is around .020 on valve to valve and as far as shrouding goes i would say .020 at .100 lift and continuously enlarging as the lift goes up.

Unfortunately you can't do that as the head gasket surface is in the way.(were talking intake valve here)
Click to expand...

With valve to chamber shrouding you need to be careful. If you unshroud near an area already boarderlining turbulence, you can push it over the edge and lose higher lift flow.
 
OldmanRick said:
I never really knew any technical numbers on this subject. Just hillbilly style engineering that made sense to me...lol.

With stock style closed chambers, I used to lay back the intake wall a little bit.....especially on overbored engines. I used the scribe method to make sure I was close to the actual bore size. How well it worked? Beats me, but i figured it couldn't hurt. I never used oversized valves big enough to get near a interference point between them, so I'm clueless there.

A example below of what looks like a pretty shrouded chamber is the "true" closed BBC. Looks a little ugly as far as what we're talking about here, but maybe looks are deceiving. Although they did lay back the plug side of the chambers on performance spec'd engines...
View attachment 1714675861

I guess the 348/409 engines below were the true idea of un-shrouding. Even though the chamber was in the cylinder and was formed mainly by angle mounting and the piston dome, the fact that the piston was away from the deck for most of the event had to alleviate any issue with shrouding i would think. Maybe on the intake cylinder wall side if a large valve was used? Although they were very large bore engines.
View attachment 1714675862

I'm sorry I used Chebbies as a example, but since the discussion was in general terms, these were the best examples I could find.
Click to expand...

The 409 heads did flow well, particular castings flowing near 270cfm.
Only thing was...the flame travel sucked, no chamber, and then again chambers can help flow to begin with. Crower made pistons to help the combustion travel, but in the end it wasn't enough.
 
Chevy replaced the closed combustion chamber BBC heads with an open chamber. We just recently experienced the same thing here with a pair of heads we had for eight months. We even destroyed one of our own heads trying to get the others to work in the upper lifts. Finally after hundreds of hours testing it came down to a discussion amongst ourselves, what is different with these compared to the heads we have that flow 20+ cfm more? The combustion chamber. Once we changed that, we found our flow. It was a combustion chamber somewhat like the closed BBC combustion chamber. We were leaving it small in an attempt to keep the compression up. Bad choice. Again I've reinforced my opinion that raising one point of compression isn't that big of a deal. Especially if your goal is pump gas.
 
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