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Discussion Starter #1
I want to know about small blocks but I almost assume its close to the same percentage on any bore?

I think I read 53% a while back but I dont remember.
also, does the amount of valves have an effect on this number? seems like airspeed would be higher though 2 small holes vs. 1 big one

anyone have any thoughts? anyone have any links to similar info?
 

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I want to know about small blocks but I almost assume its close to the same percentage on any bore?

I think I read 53% a while back but I dont remember.
also, does the amount of valves have an effect on this number? seems like airspeed would be higher though 2 small holes vs. 1 big one

anyone have any thoughts? anyone have any links to similar info?
I've never used a "guide" like that to determine valve size, .. while it can be useful
for your average project, .. more in depth projects require much more then just one simple number.

Valve size in the most important decision you'll make in an engine.
It's tied to port area, air speed, valve lift, curtain area, cfm demand, rpm, valve location
in the bore / shrouding, .. there's just not one simple "number"

curtis
 

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I want to know about small blocks but I almost assume its close to the same percentage on any bore?

I think I read 53% a while back but I dont remember.
also, does the amount of valves have an effect on this number? seems like airspeed would be higher though 2 small holes vs. 1 big one

anyone have any thoughts? anyone have any links to similar info?
Depends as a Hemi can use a bigger valve to bore than a true wedge head even optimized and a rotated valve and canted valve like an SB2 etc. can use a little more than a true wedge heads as well but not what Hemi could in general.
 

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Someone smarter than me would have to tell you but to start you can see how far the intake valve is off the cylinder and how far the exhaust valve is off the cylinder and what the valve spacing is and go from there.

On a Ford you can move the heads a little to the exhaust side and then you have less shrouding on the intake valve. You might be able to run a larger intake valve possibly or you could reduce the exhaust a lil to make more room etc. Sometimes you can move the head up the bore as well as angle milling it and a million other things.

Unfortunately most real cylinder head pros are not in the habit of telling their secrets as that's how they make a living and it's also years or testing and testing on their end which is worth a lot to just tell someone because they asked.

Maybe some others will chime in and maybe not but I think 52% is pretty close in general on a good wedge head but some people run less and some more. It all depends.
 

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I always heard 50, 51% or a bit more, like everyone stated it's is the placment of the valve in regard to cyl wall/shrouding. But to the guy who said yu shouldn't expect an honest answer from someone regardless of who they are I believe you are living on the wrong planet. Sure theirs motives, but, anyway, I guess we all can't be engine specialist or head porters:D Question > then what is the purpose of these forums? And by the way don't mind my spelling and overall poor grammar.
 

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Depends...
 

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Yeah I have seen over 53% on a Wedge head that was a good running head and made great power and on others that big was a lil too far and they went backward on the dyno and track.

On a Hemi style with the valve in the middle of the bore you might have over 55% in some apps for sure.

Also depends on if you have .500 lift or 1.000 lift and what rpm and stroke you are trying to feed.
 

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I always heard 50, 51% or a bit more, like everyone stated it's is the placment of the valve in regard to cyl wall/shrouding. But to the guy who said yu shouldn't expect an honest answer from someone regardless of who they are I believe you are living on the wrong planet. Sure theirs motives, but, anyway, I guess we all can't be engine specialist or head porters:D Question > then what is the purpose of these forums? And by the way don't mind my spelling and overall poor grammar.
The purpose of these forums is just what is happening. But remember any info you get for free is not necesarily worth much more. I posted trends in what heads look like in the racing arena from what I have seen but someone like Curtis Boggs has seen a lot more. He also gets paid to make heads perform better than they usually come from the foundry. There are a lot of secrets and know how in really making cylinder heads haul ass so I am just saying don't expect that for free. Sometimes though people are nice on forums and quite a lot of info is passed on for free. That's the good part!
 

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Discussion Starter #11
I thought it was a generic question really. I think there is probably ALOT more to it than valve size...
 

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As has been mentioned in several posts, there is no magic formula for determining the correct valve size to use in a specific bore diameter. There are many variables that enter into head/combustion chamber/valve size/valve placement/etc. issues.
The degree that the valves are canted, chamber roof design, piston crown/dome design and spark plug location are some of the parameters that will affect valve size and placement.
 

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There is one secret I've alwyas kept pretty tight but I'll go ahead and finally share it here. Regardless of the cylinder head design, I try to always have a Minimum of 1 intake valve per bore. Now please don't go telling everyone that secret or I'll be out of work.
 

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Oddly enough the EMC stuff has run some HUGE valves in the bore size... 2.19" @ 4.00" bore seems common.... granted they are usually canted valve or hemi engines but that is almost 55%! I don't agree with that, but they are winning doing this.

Also think about the angle of the port, does it point towards the bore wall or into the chamber or at the plug? Valve size can also be used to direct where you want the charge to go into the bore.

Bret
 
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