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Stock "186" heads with 1.94"/1.50" valves and no modifications whatsoever flow right around 180cfm/121cfm (at 25" of water and .485"/.450" of valve lift). A good three angle valve job, backcutting the valves and increasing valve size to 2.02"/1.60" will get you up around 206cfm/155cfm... At least according to David Vizard's testing.
Any luck with photos of your clutch assembly? I've talked to a couple of owners of original cars since that thread was active and they swear that the 11" clutch/14" flywheel was what was installed in their cars... If your 10.4"/12.75" setup was originally installed in your car, you might have a real oddball there!
Try GM performance parts--they have a complete chart for all the SB and BB Chevy heads. And I believe these heads weren't near the top, but check it out. Seems to me the Vortec and SB II heads were quite high in flow, according to GM---
:yesnod: :chevy :chevy :chevy :yesnod:
Back in the day a friend of mine ran 10.15's in a super gas Vega he built from scratch. He was young and poor and used a set of double bumps that he had heavily ported. They must have flowed good to be that fast but then again the car only weighed 2200 pounds and made up for lost power elsewhere. That's a while ago but he consistantly tells me he would have run 9.40's or better like everyone else, had he had better flowing heads and a Lenco transmission and stuff. I'm assuming you could probably get them to flow like 250 or something but that's completely a guess. Most enlarged port race heads flow close to or over 300 cfm.
Can anyone get to these charts? GM Performance Parts was rather worthless unless you know the part number as far as I could find. http://www.chevyhiperformance.com just won't open. So, if anyone else can get to these charts and email them or post them (text preferred)...
OK, my bad, got to go to Best of CHP Engine Tech, then Engines, then Cyber Flow to Go. And they don't have a listing for the 186 heads. Probably the closest is the 462 heads which ere used on 327's thru 1968.
David Vizard seems to be one of the few people still interested in testing the older original engine parts as well as the current offerings. He has put together some great books over the years and I would recommend reading ANYTHING he has written.
I went back through his book How To Build And Modify Chevrolet Small Block V8 Cylinder Heads last night (where I found the original flow numbers that I posted) to see what else I could turn up... Ran across a sidebar on page 66 that noted while the flow numbers in the book were taken at 25" of water, it was possible to convert pressure drops to allow direct comparison of flow numbers. The formula that David Vizard gave was:
[(New Pressure Drop/Old Pressure Drop)^(1/2)] x Flow at Old Pressure Drop
For example: going from measurements taken at 28" of water to 25" of water;
[(25"/28")^(1/2)] x Flow at 28"
[.8928571^(1/2)] x Flow at 28"
.9449112 x Flow at 28"
For those interested in making "apples to apples" comparisons of flow numbers taken at different pressure drops, this should be a big help.