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I am running 1mm larger valves with bronze guides. Intake seats are .050" and the exhaust is .080". Heads are ported to take advantage of the larger valves but is a conservative job. May lap line is not in the aluminum but at the edge of the seat insert. My intake valve guide clearance is .001" and exhaust is .0015" if I rember correctly. I had the heads off after 1500 miles for inspection and to try some new valvetrain componets. No abnormal wear was found so I am still running this setup. The engine is supercharged and makes a conservitave 553 rwhp at 6200 rpm with 13lbs of boost and no intercooler. I do attribute the ability to run this valve setup to the increased control of the tighter bronze guides. I did state above that with out the proper port work that yes just putting in larger valves would be a hinderance. I do know that my engine pales in comparison to yours and that you have a far greater wealth of knowlage than me, but I am just stating my own findings. I have attached a pic to show my valve seats. These are 97 heads.
 

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Hmmm... the valves that I just bought from xr8ted turned out to be over size valve. We measured the valve seat and the valve, and my engine builder didnt seem to think that it was going to be necessary to replace the seats.

On a slightly different but related note, is .003 clearance on the valve guides too much? 500rwhp, max, probably more like 400 most of the time.
 

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I'm not calling you out (just applying logic), but I can't see why a 5.4 could run any larger valves than a 4.6. The bore is the same and hence logic dictates that the surface area available is the same. Dont forget that the valve shrouding issue is the same problem in both as well...
I'm not calling you out (just applying logic), but I can't see why a 5.4 could run any larger valves than a 4.6. The bore is the same and hence logic dictates that the surface area available is the same. Dont forget that the valve shrouding issue is the same problem in both as well...
I don't think shourding casues a problem on pentroof combustion chambers. The vale moves away from the combustion chamber edge as it opens. This is also an advantage with Cleveland heads and others that have a canted valve.
 

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