Nothing beats hands on experience! I don't want to put people crook.
I have only delt with Holdens and Valiants. The 500 cfm 2300 I have is just a throttle body on a propane car, so that doesn't count as a sucessful petrol 250 with a 2-BBL Holley.
My friend, a died in the wool Holden man, ran a 650 cfm 4MV Q'jet on a Cain manifold on his HZ 3.3, and it was passable, but had a stock cam.
I
have heard that Holleys are touchy with respect to total cam duration. Apparently there is physically less venturi in a Holley, rather than, say, a Rochestor 2-Jet (not Varajet). Some people have said the 350 and 500's are not compatible with durations of over 280 degrees. My thinking is that its a fuel standoff problem, or a lack of hi velocity air mixture flow on overlap. There is no room to fix this on an Aussie 2V, unless you make a bonnet bulge for a spacer. My XE onlt has 188mm from the manifold to the base of the bonnet. Nearly all of it is taken up by the 84 mm carb and 12 mm adaptor I have; the rest is 74 mm deep air cleaner, and stupid blo**y 28 mm bump where the gas goes in, and where the mixture is adjusted. 2V's on XY/XA's run a 39 mm deep air cleaner, and no space for an adapter.
Question 1. What sort of problems does over carbing with a cammed 250 2V seem to cause?
When Danny, my old neighbour, had his 265 Hemi, he found the 500 was nice on that engine, but the ex 1966 390 LTD Autolite was better. But the 500 had no problems, and he ran an E38 spec cam.
Question 2. Not an issue because of a bigger engine? 272 degrees not too much to create a propblem?
Street Machine did a very public engine build on a 3300 XT5 with YT alloy head engine in 2001. Its rear wheel horses were 152 net with a trimatic. Drive train losses are around 1.3 for a corrected dyno to corrected net flywheel horsepower. They were forking out 200 net flywheel horses, and uesd a 500 cfm 4412 Holley and a cam. There was no reported problem with pig rooting, but they were doing dyno runs, no driveablity.
Question 3. Have you found it to be a driveability issue with cammed 250 2v's, or is it worse than that?
Oh yeah, question 4, what is Schjeldahls' compression calculator. Is that the really good little number they use in the Tech section, or is it somwhere else?