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 Post subject: sbc ex valve
 Post Posted: Sun Sep 02, 2012 6:43 pm 
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Joined: Sat Jul 14, 2012 11:39 am
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is the main purpose for a radius on the face to margin supposed to tighten the cone on the port side of the valve, if so what have the porters working on the 23* sbc ex port find works better, .018 or .032, or is it totally dependent on the proximity of the edge of the valve to chamber distance., so far my testing on a small port vortec bowtie show the .018 is better, but visually i dont know what the radius is doing, thanks- tom


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 Post subject: Re: sbc ex valve
 Post Posted: Sun Sep 02, 2012 11:07 pm 
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I think it helps the exhaust move from the center area of the valve head around the radius and into the main stream. I guess that is the same as tightening the flow cone. Don't know for sure but it does usually help some and I like it for other reasons too.

- it also can help the intake flow (yes, when done to the exhaust) a little at certain lifts
- removes a sharp edge in the chamber that is also very hot

I don't cut a specific radius, I put mine in the lathe and use a file and sandpaper to make a nice smooth generous radius.

Rick


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 Post subject: Re: sbc ex valve
 Post Posted: Mon Sep 03, 2012 7:17 am 
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Just how much does a back cut help flow Rick??

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 Post subject: Re: sbc ex valve
 Post Posted: Mon Sep 03, 2012 9:57 am 
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Beretta wrote:
Just how much does a back cut help flow Rick??

I don't like to use back-cuts on the exhaust. They help reverse flow more than forward flow, especially at low lift . Back-cut on the intake I do normally use. They can help flow up to .400 and maybe .500 lift in some cases. Usually a few cfm gain.

Rick


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 Post subject: Re: sbc ex valve
 Post Posted: Mon Sep 03, 2012 10:17 am 
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what do you make of this, extensive testing with the same spvb port 1.6 valve relatively small throat <1.375> with valves ranging from nailhead 9* 3/8 to 25*1/2 radius in 3* increments the 25* was the best, @ .1 it was close but from.2-.4 the 25 was better from6-13 cfm, but if you look at the profile it dosent make sense, the 25 has so much more material on the stem side it looks like its blocking the port compared to the 9*nailhead, these were all tested at 44", anyone no whats going on, i hate to order the 25* because of the weight and dish factor but 13cfm at low lift is signifigant- all valves similar seats-margins and no b/c


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 Post subject: Re: sbc ex valve
 Post Posted: Mon Sep 03, 2012 1:22 pm 
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zums wrote:
what do you make of this, extensive testing with the same spvb port 1.6 valve relatively small throat <1.375> with valves ranging from nailhead 9* 3/8 to 25*1/2 radius in 3* increments the 25* was the best, @ .1 it was close but from.2-.4 the 25 was better from6-13 cfm, but if you look at the profile it dosent make sense, the 25 has so much more material on the stem side it looks like its blocking the port compared to the 9*nailhead, these were all tested at 44", anyone no whats going on, i hate to order the 25* because of the weight and dish factor but 13cfm at low lift is signifigant- all valves similar seats-margins and no b/c

What you are talking about is called a tulip valve. The tulip valve is like an airfoil shape on the back side of the valve preventing turbulence/eddy currents behind the valve.

I wouldn't want to use a SS tulip valve unless it's on a low rpm with a little cam because of the weight. When it's titanium then it makes sense. I especially like them on high port exhaust like 18º/15º heads where the port is very straight up and no sharp turn. The tulip shape will help the port flow up into the tall port.

Rick


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