273 mild build-----
Carefully calculate the static compression ratio and cc the heads. My 273 had new pistons when I got it, it calculated to 7.8 to 1 compression. Pistons 45 in the hole and 65cc chambers. It had 115 cranking with a mild 216 @ .050 and 110 cl hyd.cam. I tore it down and milled the heads .032 thou and the block about .040 to get 9 to 1. I am currently running a comp 270 solid. With 224 at .050 and .468 lift before the .022 lash on a 110 cl. With lash it runs more like it has about 10 degrees less duration. Very slight lope and pulls pretty good for a little motor. And 150 cranking compression.
I've heard the Summit cams work well in the small engines.
Good example there babyblue.
The isky cam mentioned earlier has 40* o lap.
I found the isky specs=.425 lift 256* 202*@.050 [112cl but instead 108*]
required comp 9.1 .
Thing is, narrower makes more o lap, o lap helps high rpm scavenge , but theres no lift or dur to rev high.
Early lift trying for more velocity but if not timed just right or if you don't have a matched/tuned in exh system it's all kinda lost in translation I think. It reminds me of wrong combos and stingy intake tracts and how I'd sometimes just advance the hell outta the cam.
A factory 340 cam has 44* which came in a motor 57ci bigger w/advertised 10.5 [really only 9.8 or so] with way better ex manifolds, better than spitfire headers or even shorty's. IMO
The Engle cam has 30* o lap which will work real good w/fact exh manifolds or headers and still have a broad power band with plenty of vacuum and hp from the added lift, but I'm no 'expert'.
Bobby from bjr who knows all the flow characteristics of those stock heads could maybe pop in and help.