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Old 04-09-2004, 07:17 PM
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back cutting exhaust vavles

i read in a book you can take your valves (they used a late model 350's exhaust valves) and cut a 20 degreee back cut in them. they grinded away at the top of the valve just above where the valve seats on the head. they also ported and polished the heads, had a comp 268h cam, performer intake, q-jet, and headers and made around 330 hp. has anyone ever done a back cut on their valves, and would it help to do it on the intake valves also?

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Old 04-09-2004, 07:23 PM
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This is basically what is done when a multi-angle valve job is performed. Yes, it does help the flow and it would benefit both intake and exhaust valves.
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Old 04-09-2004, 08:12 PM
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As Oddrodder said, back-cutting valves is one the the ways to increase flow (at least a little) while doing a performance valve job. New performance valves generally don't benefit as much from this as the new valves faces are usually quite a bit narrower than a stock or used valve.
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Old 04-09-2004, 08:42 PM
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Easy to do mod that does increase the flow with only a marginal effect on durability. I use the lathe to cut them (faster) but I have even done it in a pinch with a die grinder and a drill press. I imagine you could even do them just as well with a bench grinder if you were careful, many stock valves are rough forgings so balance is not a factor. I usually do mine after I have the seats lapped so I can make sure I have enough material on the valve face, you don't want your back cut extending on to the seat or the edge will get red hot there and melt off...goodbye valve seal. If you really want to get fancy you can use a flat abrasive disc and "swirl polish" the stems.

That really makes them faster.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”

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