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Larger valves and porting questions

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eeyore
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Larger valves and porting questions

Post #1 by eeyore » Thu Jan 08, 2009 10:10 pm

I have a question on larger valves and porting. It seems to me, that it would be wise to do the porting before machining for the larger valves to prevent damage to the new seats. However isn't there going to be a big step at some point after machining for larger valves? I realize they can/should machine beyond the seat angle with a steeper angle cutter (3 angle valve job), but won't there still be a step at some point where the machining stops? Also don't you want to unshroud the new larger valves in the chamber? Can all this be estimated carefully? Do you do some before and some after? If you do some after, what is a good way to protect the newly machined seats?
Dave

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Post #2 by Harte3 » Thu Jan 08, 2009 10:31 pm

Sounds like a question to pose to a machinist.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

eeyore
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Post #3 by eeyore » Thu Jan 08, 2009 10:41 pm

Yeah, I suppose your right, but I'm not really to that point yet and don't want to ask alot of questions at a local shop and then say "OK when I do this in a year or so I'll let you know." Right now I'm half curious and half advance planning.
Dave

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Post #4 by Harte3 » Thu Jan 08, 2009 11:12 pm

Posing the questions is part of the advance planning. Go ahead and ask. Most those people are glad to share their expertise especially if it will mean a future customer.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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Post #5 by CNC-Dude » Fri Jan 09, 2009 1:03 am

When hand porting instead of CNC porting, you would take an old pair of valves and insert them into the head to protect the seats after the valve job is done as you grind in the chamber area! As far as grinding in the bowl area, you usually cut that area oversize with a bowl cutter in a machine and not by hand when the valve job is done as well as unshrouding the valve seat area in the chamber,and then carefully touch and blend the port and bowl transition area with a die grinder....Its good to see that your are thinking to enlarge the bowl area with the installation of larger valves. Many people install larger valves and don't do anything to the bowl area, which defeats the purpose of installing larger valves to begin with. Good luck and show us your progress as it develops!

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Post #6 by rbohm » Fri Jan 09, 2009 10:18 am

8) cnc dude is right, in the old days before cnc machined heads, we would rough cut for the larger valves, do all the bowl work, then the ports, then blend everything together, then finish the valve seats. this way any damage to the seats is taken care of in the final finishing.
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