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3/8” vs 11/32” valve stem

3K views 13 replies 10 participants last post by  454chevy 
#1 ·
A street car with a 500 hp big block application that will see 6000 rpm max, would the extra expense going from 3/8” to 11/32” valve stems be worth it?
Details of heads. 781 heads, installing Manley stainless 2.19-1.88 valves with mild bowl blend, .600” max on cam lift.
Would I need the street flow or race flow series of valves?
 
#5 ·
Those valves are too big for OEM oval's, you should use some SBC intakes (2.125"/2.150") and some Mopar exhausts (1.810"). Both are 343" stems and add about 4 or 5 CFM flow by design!

Thanks, Gary in N.Y.

P.S. I would also recommend against Manley valves and get some nice Ferrea's instead. On a side note, Manley just sold out I believe?
 
#6 ·
I just went thru this myself...see my other 820 head thread. It was another $400 to go the 11/32 route. My rpm range is probably 6000 maybe 6200...I went 2.19 and left the 1.72 sized exhaust. Can’t see needing a ton of flow for not alot of rpm. Very easy to get too much wrapped up in these compared to getting a decent set of aluminum....
 
#8 ·
It's not so much of a which is better it's a matter of what's lighter. At 6K I don't think there would be much of a benefit but let's say you go to 6500 and higher now add those little grams that each component weighs and multiply them by 6500 rpm and that will tell you what what's better. Lighter internal engine components rpm quicker which translates to a better ET and MPH. Ran some 215's last year with 3/8" 2.19 and 1.88 valves and at 6K the engine was happy but to get it to spin 6500 then engine needed different springs and titanium retainers to get there without valve float.
 
#9 ·
Like bill said, if you have to do all the work anyway then go 11/32. Otherwise I wouldn’t worry about it. I’ve run 3/8 stem valve motors to 7200 with steel retainers and good springs.
 
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