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Old 05-21-2022, 09:08 AM
GTO-relic GTO-relic is offline
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ps- BG would adjust a carb size downward in cfm, using booster changes.
the 750 Street Demon had 4 downleg boosters
the 725 Road Demon was same dimensions, with straight boosters on secondaries blocking some flow.
their 725 could be shortened to a 625cfm with annular boosters. meaning annulars could cut 100cfm

Holley did some of the same thing, but not to such a degree, on their 750/780/800 family:

750cfm 4779 Holley DP had 4 equal venturis, 1-3/8", with downleg boosters
3310-1 vac. sec. rated 780cfm had 1/16" larger secondary venturis, i.e. 1-3/8" primary, 1-7/16" secondary, with downleg boosters, so it was a slightly "SPREADBORE" design.
4780 rated 800cfm DP also had 1-3/8" & 1-7/16" venturi combination, but the secondary downleg boosters had thinner legs than the 780 vac sec, giving it 20cfm more for 800cfm total.
3310-2 onward revisions of 3310 Holley were rated 750, they had the 1-3/8" & 1-7/16" venturi combo as well, but had straight boosters on all 4 barrels that were larger, blocking some flow, losing 30cfm, so it wasn't a 780 anymore, it became a 750.
this is why the good 3310, always was, and will be, the 3310-1. it's the one with metering blocks on both ends. you can make one by putting the front blocks on both sides. but you'd still have the straight boosters on a 3310-2 and later.

Stealth Carburetors used to sell a Holley rework, it was made on any 3310 core. they would put 2 front 3310 metering blocks on it, front and back, get rid of the rear metering plate, so it was a 4 corner idler adjustable carb, and would polish out the bores approx. .020"-.025" oversize, install (4) annular boosters, drill all 4 throttle plates with idle air bypass holes, mill the choke plate off, and scallop the entry just like an old BG Holley rework. it was sold as an 800cfm vacuum secondary carb. they gained with the scallop and bigger venturis, and lost a little with the annular boosters, and ended up around 800cfm. a carb like that with annular boosters would have electrifying throttle response though.

there's a tendency to just look at the throttle plates, when judging a Holley design...take some time, measure the venturis, and look closely at the boosters.
epiphany will strike.


Last edited by GTO-relic; 05-21-2022 at 09:17 AM.
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