Back cutting valves

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Farmallgray

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Nov 4, 2009
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I tried a search but couldn't turn anything up. From the research I have done it sounds like on a gasser that putting a 30 deg back-cut on 45 deg valves can help low lift flow. Is there any benefit to doing anything like that on an intake valve that uses a 30 deg seat? Say, maybe a 15 deg back cut?


What about putting a radius on the chamber side of the exhaust valve? I'm slightly concerned that with high EGTs that may make it more likely to burn?

Any thoughts?
 
yes it's true with diesels/anything. backcut does help airflow. i do most of the flow testing at our shop. also adding the radius will help out too. you don't need much just break the edge with a file then polish up. this, i have also seen a slight gain in cfm.
 
30 back cut would help but it won't hurt anything. You could try a different valve job but you'll need a flow bench.
 
backcut the intake 45x30x22deg and on the exhaust cut it 45x31x22. it'll flow good with those basic angles for street or competition
 
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