Where can I get info on how to do porting? Duke, you give the impression it is fairly easy and worth the effort. Is it effective to do on a 230hp? It seems like it would probably help it a lot.
Paul
Paul
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Re: C1 pocket porting and port matching
Try This.
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Re: C1 pocket porting and port matching
Paul,
This link will show you the "bible" of small block Chevy head porting. CAREFULLY follow Mr. Vizard's procedure for measurable improvement.
Joe
http://www.amazon.com/Chevrolet-Small-Block-CylindComment
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C1 pocket porting and port matching
Just what I was after. Can't wait to start. ThanksComment
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Re: C1 pocket porting and port matching
Vizard and "How to Hot Rod your SB Chevy" are the two best sources that I know of. They deal with later big port heads, but this is not a deal buster.
The 283 heads suffer from the same basic problem - that annular ridge just above of the valve seats. It should be ground down so the top of the seat blends smoothly into the as cast portion of the port. But don't grind too much off the short side radius. This is a common mistake. Just grind enough to elimiate the ridge and get as large a radius smooth curve as possible.
At the head-inlet manifold interface, make sure that the head port wall does not overhang the inlet manifold port wall. This will require the most grinding in the corners. Similar on the exhaust side - grind the exhaust manifold flanges as required so they don't overhang the exhaust port opening in the head.
This operation is the best single modification you can make to any OE engine. It will improve top end power and extend the peak power bandwidth without any effect on idle quality or low end torque. That's because it improves the flow efficiencies of the ports without increasing velocity due to greater port volume.
Ultimately the inlet and exhaust flow path efficiencies limit power output, and the biggest "problem" are those annular ridges above the valve seats.
It would be great if you have your heads flow test before and after the rework.
I've never been able to model the 283 heads for my engine simulation programs because I've never found any flow data for both OE and massaged 283 heads.
Having good flow data is how I was able to optimize the valve timing for 461 and later big port heads, which ultimately lead to the "Special 300 HP" camshaft that is unlike any OE or aftermarket camshaft.
I could do the same for the 283 if I had good head flow data.
Otherwise use the 3896929 (or follow on 14088839 GM replacement) to replace the obsolete OE 3733431 camshaft.
DukeComment
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C1 pocket porting and port matching
Well Duke I just checked into getting the heads flow tested and I will do it. I will get them in today or tomorrow and after doing the work have them re-tested. I assume having one chamber (ex & in) is sufficient? Is there anything I should request or will they give me all the pertinent data you need?
PaulComment
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C1 pocket porting and port matching
Duke I have located two books on Hot Rodding your SBC, one is by Jim Richadson and the other is by Bill Fisher & Bud Waar. Which are you referring to?Comment
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Re: C1 pocket porting and port matching
That's great! First make sure that you understand what depression is used in the flow test and it should be clearly stated on the data sheet. The defacto standard is 28" H2O, but some use 25". It doesn't make any difference because either can be easily converted to the other, but request 28". The critical thing to understand is that if the test depression is not stated the data has no context and is absolutely worthless.
Just one inlet and exhaust needs to be tested. Clean up the valves and ports of their worst deposits, but they don't have to be squeaky clean - just representative of a new OE setup without significant deposit buildup.
Request the tests be done at the following valve lifts, in inches: .050, .100, .200, .300, .400, and .500 Actual valve lift on the engine with the 929 cam is only about .400 when you take into account actual rocker ratio, and no OE cam (and few aftermarket cams) lift the valve beyond .450", but it's common to quote max flow at .500". However, flow typically does not increase much beyond valve lift equal to one quarter of valve diameter, because this is the lift where the valve opening "curtain area" is equal to valve head diameter, and at this lift the valve no longer represents a significant restriction.
After you finish massaging the heads and (hopefully) finish it off with a three angle valve seat and a top cut off the valves to eliminate the overhang, have the heads tested again at the same depression and same lifts.
Ignore any advice you read about shortening or "blending" the valve guide boss. It's not worth the loss of structural support. Just knock down any severe casting flash around the guides and in the center portion of the port between the valve pocket and manifold interface work. It's actually advantageous on a carbureted road engine to have the as cast wall roughness because it helps break up the laminar boundary layer, which is where most friction occurs, which also helps break up liquid fuel on the wall and get it into the bulk airstream where it will vaporize. In other words the ports don't have to be polished and the finished job doesn't have to look "pretty". That's just cosmetics.
DukeComment
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Re: C1 pocket porting and port matching
My copy of "How to Hot Rod Small Block Chevys" was published by HP Books in 1976 and the authors are Bill Fisher and Bob Waer.
This version has some Chevrolet drawings that are also in the early versions of The Chevrolet Power Manual, which give good guidance, and it also has a very good drawing of the multiangle valve seat scheme, which I highly recommend you follow.
DukeComment
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C1 pocket porting and port matching
Duke the heads are finished and have 3angle grind. In fact they are installed. My son installed them not realizing you could not port and match with them on the block. I will take them off. The flow test I assume will show improvement over stock heads due to the 3 angle but I hope that can be compensated for.
PaulComment
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