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Old 01-19-2020, 09:56 AM   #1
Craig CT
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Default valve question

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Old 01-19-2020, 11:03 AM   #2
JWL
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Default Re: valve question

The valve stem does not influence ramp speed or duration. Those changes must be imparted at the cam lobe.
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Old 01-19-2020, 04:52 PM   #3
Ol' Ron
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Default Re: valve question

Using a split guid ans early valves in an 8BA engine cam be done. However this lwould lead to more oil seeping into the combustion chamber thru the valve stem. Bad Idea.
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Old 01-19-2020, 06:18 PM   #4
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Default Re: valve question

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The mushroom valves have less diameter and split guides. Has anyone used them on an 8BA performance cam to affect ramp speed, duration or anything else. Thanks in advance, Craig.
I have never done it that way but you definitely could do it to increase port flow
only. In the olden days 1.625 head diameter mushroom stem valves were available. They came with the head undercut, the port exposed part of stem reduced diameter and polished for lighter weight and improved flow.
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Old 01-19-2020, 08:05 PM   #5
Bored&Stroked
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Default Re: valve question

I'm not a big fan of the split guides - due to the larger opportunity for movement/slop in the guide bore and around the stem - as well as side-to-side misalignment on the stems, etc.. I used to run custom 5/16 valves in my race flatheads (with split guides) - and they well Hell on the stems.

But, if one is looking for optimal port flow, one could just sleeve the late 49-53 guides for 5/16 or 8mm stems - such that you can run valves with smaller stems. Of course you'd probably also have other "features" on your custom valves - to provide less restriction in the port and deliver better flow (especially at low lift).

But that whole discussion heads down the path of high-end race modifications . . . which we could ponder until the cows come home! LOL
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Old 01-19-2020, 11:12 PM   #6
Craig CT
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Default Re: valve question

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The mushroom valves have less diameter and split guides. Has anyone used them on an 8BA performance cam to affect ramp speed, duration or anything else. Thanks in advance, Craig.
Hello again; I cited the lesser diameter stem and split guides as the known weak points. It's the much wider stem base that will be affected differently by the ramp and will keep the valve open longer
at the top of the lobe than the 8BA valve.
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Old 01-19-2020, 11:21 PM   #7
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Default Re: valve question

The cam does not ride on the valve tip, as noted above by JWL.
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Old 01-19-2020, 11:25 PM   #8
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Default Re: valve question

Quote:
Originally Posted by Craig CT View Post
Hello again; I cited the lesser diameter stem and split guides as the known weak points. It's the much wider stem base that will be affected differently by the ramp and will keep the valve open longer
at the top of the lobe than the 8BA valve.
Actually, no! Valve stem width has nothing to with the cam lobe ramps. It is the bottom of the lifter (Ford called them "pushrods") that contacts the cam lobe. All flathead lifters have the same dimensions, whether mushroom valve stems or not!
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Old 01-19-2020, 11:48 PM   #9
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Default Re: valve question

Know Craig, I think he was talking about a stock engine. However, I usually cut the stems down on SbC valves when I undercut the bottoms
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