I ran a Holley 500 on my 261, different engine, but the carb requirement is probably similar or a little less on the 261.With 68 main jets, it ran quite well,just alittle soft on low speed response and got the same gas mileage as the 500 Carter 4 bbl I had on it previously. I'm now running the rare 2305 Holley 500 cfm staged two barrel.It was originally intended for use on 2 litre racing engines, the idle circuit was way too lean, instead of drilling the idle restrictions, I used a Holley 2300 metering block, and had to increase the primary main jet to a #62 from a # 55. The 2305 staged carb power valve only feeds the primary barrel, so I plugged the other power valve channel on the 2300 metering block.Runs very well thank you, better than the properly jetted Carter 500.Restricting the power valve channel on a non staged 2300 carb will help, as at least on a 261,the old 6 doesn't seem to require as much full throttle enrichening as the 2300 was designed to provide for V-8's.A lot of guys have problems with Holleys but they are very easy to modify as compared to the Carter or Edelbrock.It's been my experience that modified 6's need carb tuning , you think it runs pretty good, a few small carb changes and it runs even better.
A Holley 500 is the front half of a 780 CFM 4bbl, 4bbls are cfm rated differently than 4 bbls,the actual conversion is around 1.4 so a 500 cfm 2bbl would be rated at around 380 cfm if it was a 4bbl.
[This message has been edited by Tony P (edited 11-22-2003).]
