unshrouded valves=more cfms?

JL Builders

JL Builders

On a quest for more power
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Apr 25, 2011
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Anyone know/experienced any increase in flow through the head if the valves are flush to the surface of the head. Or will it not direct the flow of air down.

Assuming there is plenty of piston to valve clearance also.

I have a ported head and oversized valves. I am also wondering with larger valves will the cylinder wall shroud the valve in a bad way. If the valves at flush to the head.

Thanks
 
well, I partially unshrouded the intakes on my engine...not sure what it did...

also, you could unshroud the cylinder...just dont remove any material below where the top ring would seat...
 
JL Builders said:
Anyone know/experienced any increase in flow through the head if the valves are flush to the surface of the head. Or will it not direct the flow of air down.

Assuming there is plenty of piston to valve clearance also.

I have a ported head and oversized valves. I am also wondering with larger valves will the cylinder wall shroud the valve in a bad way. If the valves at flush to the head.

Thanks
Click to expand...

I'm curious as well. If you have the clearance and wouldn't need flycuts, why not, right?
 
.060" from the cylinder wall, anything less and you will cause some restriction.

What do we mean by "flush with the head"?
 
why not go this route for more cmf and better flow?

dimples_3.jpg

valve2.jpg
 
Impressive. I'd love to watch the machine that makes it that way.
 
those are sexy. was always curious why everyone polishes there port job
 
joelc79 said:
I think it would be cheaper to flip the tow mirrors up to gain the 1-2 hp over the entire power curve...duh


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Click to expand...

Lol that and the dimple port job is hp over a maxed ported polished setup. If you want more hp than the next guy you have to think outside the box. 20hp in a prostock car is HUGE

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That's old tech already. We had guys doing that along with the insides of the intake 10 years ago. I gonged one guy after I told him several months before to not bring that stuff back. He showed up at the next traveling race and I teched him after his heat race that he won by 3/4 of a lap. Told him to "NOT come out for the feature with that intake, I don't care if your daddy sponsors the track. If you do and you finish in the top 5 you will get dq'd." He won by half a lap..............then he lost.........then he had a tantrum and threw the intake at me. Then he came at me............Then he lost his dignity and his father apolologized for his sons behavior and thanked me for not hurting him badly.....lol
 
Watching this, I was wondering the same thing. I had to have the valves in my new head sunk in quite a bit cause I don't want to cut pistons (needed more PTV clearance). Maybe it will hamper the flow some but its a street motor and I'm not trying to make eleventy billon hp.
 
I've been told more than once that getting the valves further into the combustion chamber (decking the head) will be beneficial.
 
Ah good ole port roughing...an attempt to create a boundary layer between the fluid flow and wall to lower shear stress. Those valves were from a motocross application. 1 hp is a lot on a 40hp 250cc.

However the general consensus is that unshrouding the valves will definitely give you some CFM but I always heard you should do it by "chamfering" (for lack of better word) around the valves rather than surfacing the entire head. The lenahan sponsor guy that always gets in fights with people can tell you all about it...
 
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