30 degree intake seat angle on a SBC???? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-01-2005, 05:45 AM
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30 degree intake seat angle on a SBC????

Has anyone here done some real world testing using 30 degree intake valve seat angles on a small block chev? I know Vizard did some impressive work with the bigblock heads years ago and also shows the flow potential at lower lifts in one of his books. I'll be building a grunt motor for my offroad truck down the road and have been toying with the idea of setting up the intakes with a 30 degree seat angle, 15 degree top cut, and a small 45 degree throa cut below the seat tapering to 60 into the bowl. Just wondering if anyone here has been down this road already. With a short cam it sounds like there's power to be had if the valve is unshrouded enough. Bob

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Old 12-01-2005, 08:06 AM
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This would be a good project for someone with a flow bench and/or an engine dyno. Personally, I think that if it made a useful difference someone would be marketing the 30 degree valves. A quick check in Ferrea and Manley shows no 30 degree valves for the BBC or SBC. BTW, I personally think David Vizard is a legend in his own mind and is seriously over-rated as an engine guru.

tom
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Old 12-01-2005, 02:11 PM
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The only gains are in the low lift ranges so that probably explains why Manley and Ferrea don't market them since there probably isn't much low rpm racing going on. I don't know if Vizard is overrated or not but either who.... has anyone done any real world testing? Back ttt. Bob
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Old 06-20-2006, 01:22 PM
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30 degree valve seat

Bob,
I am currently investigating this scenario. With a mild cam there may be some significant advantages since the crossover point is usually around .300"-.400" valve lift.
What this means is that you may be able to get more power from a stock type motor and maintain decent fuel economy by keeping the stock cam.

Working on a set of 305 heads now that will be going on a 327 sometime this summer.
If interested, AMC wrote an SAE paper in the early 70's comparing the flow differences between 30 and 45 degree seat angles.

Another thing to consider is that the 30 degree seat may help prevent exhaust seat recession on some of the older heads that relied on lead in the fuel.

NR-Paul
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Old 06-20-2006, 07:51 PM
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Cool! Let us know how the little mouse runs. Using the 305 heads and small combustion chambers you should be able to unshroud the valves and still keep the chamber small. Some of the 262, 267, and 305 heads were only 52cc's I opened up a set of these and ended up with 64 when I was done. Interesting stuff. Bob
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Old 06-20-2006, 11:48 PM
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Vizard has info on SBC 30* intake seats in this book: http://www.aptfast.com/APT_Parts/Boo.../B-93_info.htm
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