1 barrel, 2 barrel, 4 barrels, more...?

[ratonabike]

ok so i chanced upon a cool looking alcohol single-barrel carb, made my ProSystemsRacing... and i began to wonder why we have 4-barrel carbs... i mean, ok, i understand having a primary and secondary setup for the street, a primary venturi to handle low rpm running, and a secondary for WOT... but why the 4-barrels??? why not just two big venturis?? why not just a slick high performance 2-barrel carb? is it simply a matter of packaging, like in cylinder combustion chambers, where more valves can equal more area in a given (circular) space? in other words, 4-valves can cover more area than 2-valves in the same circular area (or better yet, 5 valves can equal more area)? i think i may have just answered that myself, but idk... what do u think? or even, on another idea, why not just forget about the primary/secondary idea... and just use a huge single barrel like the ProSystemsRacing carb for the street... if it meters well from idle to WOT, why extra venturis? just seems to simplify the carb so much... reminds me of a FI setup.. interesting to note that it has one large venturi, but it looks like two boosters/jet groups... sort of like a 2 barrel/1 barrel combo... and the bars going across reminds me of NO2 spray bars... are those the 'boosters'??? this is a gorgeous carb

[RichSchmidt]

A single large throttle makes part throttle transition tuning a nightmare.Even on a full out drag car you need some way to drive the engine at part throttle,maybe in the burnout,maybe thru the pits,but either way you need a small amount of throttle opening and a fairly tuneable transistion circuit.One large throttle opening does have more area for the given space then 4 smaller ones.The reason why multi valve engines make more power is because the smaller valves reash peak flow at a lower lift,so the valves can be controlled easier which allows for higher rpm potential.Otherwise,a single 4 inch pipe has about 7 times the flow of dual 2 inch pipes,and has about 40 percent more area then 4 2 inch pipes.The Pro systems carb is all about maximum throttle area.Since most of the engines we run can be run with nearly no airflow restriction whatsoever thru a single 4 barrel carb,there is no advantage to this system.This carb is designed for 800 plus cubic inch engines being run with a single carb manifold.A pair of these could be used on the now near 1000 cubic inch engines that are being developed for pro street,pro mod ect.

In the case of a traditional carb,you typically need .25" of pressure drop thru the booster to initiate the movement of fuel.This varies depending on where the booster is placed,how it is shaped and how much air bleed correction you are using,but this is pretty much the standard.Carbs are rated for flow at 1.5 inch pressure drop thru the venturi,but most racers running over a short powerband will upsize the carb until they get about .4 or .5 inches of drop at peak airflow.This is about the standard for getting maximum fuel flow out of the booster with slight variations for the above mentioned adjustments.In the case of this carb,you could never reach .5" pressure drop until you were moving enough air to make 1500 hp.You couldnt move enough air to create .2 inch drop unless you were making 750 hp at that point.How many engines so we play with that start making hp at 900 hp at just above idle and peak out at about 1500 hp.basically you would need some kind of circuit that just dumped fuel whenever the engine was running at a state of making less then about 650hp.

This carb is designed for 900 plus cube engines making in excess of 1500 hp and not needing any part throttle driveabilty.Anything less then that and it will be a pig.

[RichSchmidt]

One way to improve slightly on that carb would be to use a 4 barrel base with taper openings both above and below,and only about 3/4 of an inch of area where the throttle plates would seal.Have a progressive linkage,put idle circuits and idle trasfer slots on at least one end of it,and it might almost be driveable.At WOT,you would still need some way to force feed fuel thru those spray bars since there is no way they would ever pull fuel.Even on big booster would be a bit of a stretch.In the case of alchol,you need a lot of fuel and minimum atomization since if too much of the large volume of fuel were to evaporate it would take up too much space in the induction charge and hurt power.You need a lot of compression and latent heat in the heads and pistons to make that work,and it would be a pig on a cold engine or one with insufficient cylinder pressure at low engine speeds.I would run that setup with 4 small barrels,with the above mentioned idle transistion circuits,then use some type of barrel valve metered injectors to feed the main circuit.If you made the 4 barrel base plate tapederd top and bottom kind of like a 2 way super sucker carb spacer it wouldnt really hurt flow,and would give a lot more driveabilty to that combo.You could add one additional curcuit,You could run a true intermidiate circuit with draft tube type tubes used to initiate some flow,kind of like the intermidate circuit on a dominator.Place the 3rd circuit over the throttle plates and eliminate all or most of the transfer slots,and up the accelerate pump discharge a slight bit.

[ratonabike]

rich that's one of the best reads, thanks for sharing your in-depth knowledge... of course it just reminds me how much of an 'amateur' i am, and how little i know.... it's amazing i can make anything run... thanks for reminding me how much of a loser i am... lol

[ratonabike]

and reading your post again it made me wonder why we don't have a 6 barrel carb... er, well, i guess that was the triple deuce setup... ok how about 8? so, the smaller the venturi allows a higher velocity of air, allowing gas to be sucked out more easily at lower flow rates (more sensitivity)(?) then why not use even smaller venturis? i guess it's because we only need so much at part throttle to work smoothly (and not stall)... guess that was the idea on the triple deuce setup (3x2), which i think is 2 barrels for part throttle and 4 extra ones at full throttle..... how 'bout a 3 barrel carb? 2 small primaries, and 1 huge secondary (a variation of the idea on the quadrajet i guess)

[RichSchmidt]

Actually Holley mad a 3 barrel like you descibed.They made it back arond 1970.It ever really caught on.I think shortly before the dominator was created,the 3 barrel as a way to increase thottle area on a conventional square bore manifold.the secondary side was one big oval opening.

[ratonabike]

u got me looking for pics of it now....

found one! but it still has two boosters, jets, etc.... it just has the two venturis meeting in one oval one, almost no difference from a common 4-barrel.... except maybe harder to meter i guess, with more volume of air (fuel)