Carbie selection

[Big Rob]

Hands down, Holley 650 Double pumper, mechanical secondary's, Spread bore..... Can't go wrong.

Well yeah you can.... if running an auto without a high-stall torque converter it'll get too much fuel when you floor it and bog down. Even worse if you are running a big cam.

Otherwise, I agree it's a good choice, especially with a manual box.

[sandasharpe]

I've ran 600 holleys and rochesters on 253s and 308s on gas as others have said both are good if tuned properly I've never driven a 253 with a standard 2 barrel is there much difference

I remember getting in a new VC (Blue motor with Rochester Carb) and being impressed with how much more go it had over the red motor and returned better real world fuel economy as well. It was a big improvement over the 2 barrel

[Taily]

I remember getting in a new VC (Blue motor with Rochester Carb) and being impressed with how much more go it had over the red motor and returned better real world fuel economy as well. It was a big improvement over the 2 barrel

That is more to do with the higher airspeed through the smaller primaries in a quaddy. The quaddy on a 253 was almst overkill at WOT but the design of the carb was its saving grace. Those who tell you they wont feed a healthy stroker are yet to meet someone who can set them up well. Quaddies will flow well over 700cfm and can be easily coaxed to provide a better progressive fuel curve with a couple of small mods, especially for a stroker.

If you're in or around Sydney I can put you onto a bloke who is a guru with these carbies around the Blacktown area.

Failing that a Holley is a simpe carby you can mod/work on at home if something goes amiss but don't fall into the trap of over-carbing your engine, you'll lose airspeed through the venturies (think loss of torque) and it will rev OK but pull like a dog.

[Big Rob]

I remember getting in a new VC (Blue motor with Rochester Carb) and being impressed with how much more go it had over the red motor and returned better real world fuel economy as well. It was a big improvement over the 2 barrel

True, the 253 in my WB goes real well. I was expecting a motor swap (for the stroker I have ready) to be the 1st thing I did to the van when I got it, but it's running so well that I may leave it there until the van is done.
The 4 barrel (and whatever late model updates) makes the 253 a much better motor than the early ones.

Taily, you are 100% correct about the flow through the small primaries on the Q-jet. Most of the time it's behaving like a good 2-barrel anyway until revs and load are right for the secondaries to open. (If the Trimatic kick down coincides with the secondaries opening it really gets moving!)

[panoz78]

There's actually a formula for working out carby size
Which is Max rpm x cubic inch divided by 3456 = cfm
So a 308 x7200 /3456 =641.666cfm and @ 355ci
355 x7200/3456 =739.58 cfm
By this you can choose what size you need .a 725 cfm would be my choice .A 355 would rarely see 7200rpm and I think would be great.On a 308 would be a tad large as Taily said it would not get the air speed through the Venturi which triggers the timing of the fuel delivery on a Holley .Rochesters use vacum to meter fuel in more precisely with metering rods fine tuning the fuel in.
Carby's like qwikfuel, demon & the newer holley's have adjustable air bleed restriction to allow finer tuning of the fuel timing.This allows for the old case of over carbing of holley's as a lot of older ones don't have this feature adjustment.
Most of the demon style carbs I think you'll find they use holley parts and design for the convenience of available parts as Holley has been around for donkey's.
I personally prefer them due to being less fiddely and most adjustment are made with out pulling the thing to bits to tune.