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Prepping Valves for Performance

by Mike Holler

Bob O'Neill is rebuilding an engine for his 1986 Daytona C/S, and Allpar is covering the progress along the way. In this segment, Bob gets his valves tweaked for a bit more zip and sip (performance and economy). The importance of the valves from a performance standpoint cannot be over-emphasized. All of the air and fuel going into the engine has to go past the intake valve, and all of the exhaust leaving the engine has to push past the exhaust valve. "Tharz performance in them thar valves!"

valves.jpg


Before starting on any machining operations, all of the valves are cleaned up on the wire wheel side of the bench grinder. Intake valves usually have a little carbon build up, and the exhaust valves will be caked with a tan substance that someday might prove to cause cancer in lab mice in California.

Both intake and exhaust valves are going to require a face lift. After a hundred thousand or more miles, the face will pit and/or distort. Refacing the valves restores a concentric and square surface for the valve to seal against the valve seat. Most exhaust valves will benefit from a back-cut. The particular exhaust valves I am using in Bob's head are of a tulip design and need no back cutting.

grinding-valve.jpg


The valves are chucked up in the valve grinder and ground at 45 degrees. A typical valve will require 2 or 3 passes to clean up the face. Each pass will shave only 0.0005" or so from the valve. Taking light cuts allows the minimum amount of material to be removed to restore a square face. As more of the valve is ground (or worn) away, the valve will sit deeper into the seat. This reduces compression, but more importantly, it also changes the flow characteristics of the valve curtain. It never changes it for the better, either.

polishing.jpg


After cleaning and refacing, the exhaust valves get chucked up in the drill press with the speed cranked up to "stand back kids, I think she's gonna blow!" The entire valve gets polished with a progression of abrasions. Starting with a medium grit emory cloth, the stem, back, face, and combustion chamber side get polished as well as possible. After a hefty pass with the emory cloth, a medium Scotchbrite takes a turn. The clean-up work is performed with a fine Scotchbrite pad. The end result is a mirror-finish that will resist carbon build-up on the head, and reduce friction and wear on the stem.

powre-ringz.jpg


Intake valves will get a similar treatment, except the backs of the valves won't need attention here. The combustion chamber side is polished to reduce chamber carbon deposits, and the stems get a low-friction polish. Afterwards, I chuck the intake valves in the lathe and add Powre Ringz. Using a Dremel tool with a cutting disc, grooves get cut into the back sides of the intake valves.

powre-valve.jpg
"Why do such an idiotic thing?!?!?!?" you ask? All of the fuel entering the engine will bounce off the intake valve. It is rather hot since it just came out of a combustion cycle. The air will take the short-cut across the seat, and the heavier fuel elements in the intake charge will centrifugally slam against the back of the valve. These Powre Ringz will increase the surface area of the intake valve helping to vaporize more of the fuel. Some of the fuel droplets will hit the ridge of one of these Ringz and bounce off in several dozen smaller sized droplets. Some of the liquids will actually hit the valve and stick, radially thin out, then vaporize into the incoming air stream. Bottom line is liquid fuel doesn't burn, and Powre Ringz will promote better vaporization.

The valves are now ready to be reinstalled in the head. These tricks can be used on practically any head. I've mimicked these same techniques on older V-8 heads, newer 16-V heads, and everything in between. The engine is less prone to detonate, and the fuel economy increases. That's what it's all about.


We strive for accuracy but we are not necessarily experts or authorities on the subject. Neither the author nor Allpar.com / Allpar, LLC may be held responsible for the use of the information or advice, implied or otherwise, on this site. This page is offered "as is" and without warranties. By reading further, you release the author and Allpar, LLC from any liability.


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