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Well, I am at that stage of my project where I am attacking my heads to rebuild. I bought this set of heads earlier this year from a guy that had them on his LS6 chevelle, and he found the correct heads, so they came off a running engine and were in good shape. I pulled the valves, and carefully beaded them over the weekend, to see what I had. They have original GM cast iron guides, never replaced (can still see the off center on some stem holes in the tops of the guides since GM jig bored the guides in place). Some of the valves have been replaced before, some haven't. There is some stem/guide wear, but nothing excessive, but the valves are history so I don't care about them. The seats have some pitting and need cutting, but are not sunk and have not been changed yet to hard seat inserts, it has the original 2.19/1/72 combination. I was thinking of using GM's valves from the performance parts catalog, the intakes are still available, but the exhausts are only in 1.88 as far as I can tell. The 1.72's look small...I am wondering if I should convert to 1.88 and install hard seats in the exhausts while I am at it, and blend the bowls in the process. I did this once on some 1063 heads, and it seemed to work fine, but I am not sure if the casting thickness was comprmised around the water jacket. Also, as I recall, this may not be the hot ticket due to valve flow shrouding around the chamber in the pocket area due to the closed chamber design. So, if I stay with 1.72 exhausts, what brand and style (Manley has street, race, pro flo, etc). Thoughts on grind style are appreciated, I assume a 3 angle job is desired, but I want a wide enough seat to allow longevity and valve cooling. Also, I was thinking of installing hardened exhaust seats in the process, but I suppose for typical use this is not necessary given all the posts about seat erosion only being an issue on engines run hard. The heads have never been milled, I can still see the factory broach marks in a few areas after beading, but, they need to have a clean up pass now to get rid of minor pitting etc. One head appears to have some pitting in the quench area that may not surface out, maybe from preignition, not sure, but none of it is in the sealing area. I suspect this is not a problem. For guide work, which way would you go, the K-Line thin bronze sleeves or a larger thick sleeve? I would leave the iron guides in place, I don't want to disturb the sealing to the jackets or the valve geometry of the original machining. I am not using this engine for racing, but I want to do the best I can with the buildup. Thx for any advice guys!...Craig
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Re: Reworking advice on my 66 - 858 heads
Another thought - seems like many of the aftermarket valve makers harp on the necked down stems for flow, frankly, it seems so small and slight I am wondering if there is that much benefit or if this is more kid hype for summit. I have noticed that GM valves have a more gradual transition tulip under the head, to bend the gas flow smoothly. Most of the aftermarket stuff has a far more abrupt tulip under the head, and while this would open the passage more, I am wondering it it acually causes more turbulance than the GM valves. Decisisons decisions....oh, bu the way, that quench area erosion comment I made in my first post was on one cylinder only, number 3 or 6, depending on the side of the engine the head came off, maybe that cylinder was lean...Craig. -
Re: Reworking advice on my 66 - 858 heads
go with F/M- TRW valves as they should be the same as the GM ones. the larger exhaust will make more power with a open exhaust but for street engine with stock exhaust manifolds it is a waste of time and money.it will helps if you are going to a larger displacement like 454/502. a 20 degree back angle to narrow the seat on the valve helps low lift flow and is worth while doing. for street engines i like the CI valve guide inserts for wear over bronze as the bronze seems to wear the stems faster than CI. roller rockers are the best answer to prevent guide wear. i also do not like positive valve seals on street engines unless you run a 3/8" reamer thru the exhaust ones because they are too tight a fit to allow enought oil to the stem/guide interface. this is all JMHOComment
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