Breazlan

iTrader: (1)

What is considered shrouded or unshrouded in a valve to chamber relationship? Is there a formula you use when taking measurements? How are measurements taken?

rx7speed

if you have looked at a combustion chamber with the valves in there you should see that there in the depression that makes up the combustion chamber where the valves sit. around the valves you have quite a bit of open space but usually part of the valves sit right on the wall of the combustion chamber also.

so even when the valve opens up since the wall of the combustion chambe ris right there it's not able to really let any air through there.
what valve unshroading is is taking that part of the combustion chamber and remove some of it so this way you have more open area around the valve so it is able to breath a little better.


one downside in doing it though is since you are removing material from the combustion chamber your effective compression ratio goes down a little as well

as far as forumula I don't know of any myself but hopefully a few of the others here might be able to help you with that

Sonix

iTrader: (1)

there is no real "measurement", like grind for 10 mins and remove 1cc
that would be tough to calculate...

When you're done unshrouding, put plexi or something on it, fill it with liquid and measure the liquid.. that's the common way to cc a combustion chamber...
do a search for a more descriptive.... description

Breazlan

iTrader: (1)

Sorry, I will clarify to put this on track. Main question is: What is considered shrouded? ex: A 1.94" valve has a radius of .97" and should have a clearance radius of x.xx" I would like to measure my heads and see where I am at and if larger valves will cause a shrouded condition. People say this is shrouded and that is shrouded, how do they know? I am assuming when they say this they mean big negative effect.

Another issue:
I see sometimes the comment, "A 1.94" is already shrouded so going to a larger valve does not help." As it has been explained here, a portion is shrouded. Would the unshrouded area increase in flow with the larger valve? The shrouded area shouldn't matter much with the larger valve as it is already cut off. Would this be a correct comparison: A larger valve can flow more than a smaller valve, both unshrouded; a larger valve can flow more than a smaller valve, both shrouded.

8Mike9

Standard Abrasives website mentions 3/16th clearance, but not to infringe out of the bore.

IIRC, FBird88 (I believe) did post a formula, but I never saved the thread ID.

Sonix

iTrader: (1)

chances are, F-bird88 knows more about this... and if you're really lucky he'll post up a nice little paint picture showing how a larger valve does have more flow area on the inside area, but also that more area is now shrouded, *minimizing the gain*...


So yea, larger valves are always better, but the shrouding makes it not really worth buying the bigger valves for the small gain...

Just to get as much info as possible here to help the most:
What heads?
What valves were you considering? 1.94? larger?
What kind of powerband were you looking for? full out race-high rpm? just around town?
budget?
just if you wanted more help with your application...