Holley makes a 350 and 500 cfm 2 bbl, 325 cfm are available bit expensive (center carb for 6 packs) 350 cfm and some tuning should work out. Squirrels suggestion is a good one, why not use a factory 2bbl carb?
After studying the issue it's clear that many if not most install a carburetor way too big for their application. Drag racers running WOT need big, thirsty carbs. Most people don't. OEM carbs may seem small but - when using the CFM calculator plug in the typical highway cruising RPM at say 65 mph with a 75% efficiency, instead of the maximum RPM (how long do you stay at max RPM?) Odds are, now it will closely match the stock size unit! Surprise. Smaller carbs have crisp throttle response and smoother idle, and better performance.
I am putting this on a 3.0 ford that was not designed for a carb only efi. I built my own intake and a distributor.
The same body carb can actually be had in 280, 300 and 600 CFM annular discharge (no boosters in the throat) if you know where to look and Doherty was selling one that was 325 a few years back as well. The CFM is measured in Cubic Dollars. If you must have the Holley the 350 CFM model will probably work best on your 3 liter motor. I am sure that you are aware that the autolite carb is available and is also a good match for the motor. Something that we should all bear in mind is that a 500 CFM 2 bbl is a lot more carb than a 500 CFM 4 bbl as far as your engine is concerned. it is 500 CFM all at once as opposed to 250 CFM+/- to start with then the next 250 coming in at a later date. The truth be told a 500 CFM 2 bbl is more carb than a 5 liter motor really needs until it gets revved up.
How big is the intake that you have to fill up with air/fuel A weber progressive 2 bbl may be a good choice.
Hmmmmn I just happen to have one of those and need steel so bad I can taste it. LOL Saltflats brings up a good point here, intake plenum needs to be taken into consideration when choosing a carb. Let me give you an example from the real world (actually the beaner world). I have a 355 that ran real good on a stock spreadbore intake that I modified the plenum on and a 600 CFM Holley. I switched to a Holley Contender intake and Holley recommends 700 CFM (min) for this intake. Phttttt what do they know they only manufacture it right. The motor didn't fall on its face but it was clearly not making as much zot with the same 600 Holley that I took off my scab intake, so we switched it to a larger carb, now the plenum is full and it is happy as a duck again.
You can get a simple Weber to Holley adapter for cheap, if your manifold is already set up that way.. If you are super-cheap, you can roll down to your local VW house get a used Weber 32/36, and re-jet it.
Single progressive carbs tend to have fuel distribution issues on V type engines. Earlier carburetted 3 liter Ford V6 used a 40DFA Weber. 40mmm throttle plates and NON progressive. However they are /were a troublesome carb. The body is often warped mostly due to ham fisted mechanics/owners over-tightening . I would look at a 38DGAS or 38 DGES ( Weber), they are another non progressive carb which is still available new . They are very efficient and tuneable , all fuel circuits are adjustable with replaceable jets etc. You cant easily compare 2bbls with 4 bbls by the CFM rating .....Holley two barrels are rated at a twice the depression that they rate the 4bbls. This doesn't relate to twice the real cfm . Two barrels are rated at 40.6 inches of H20 whereas the four barrels are rated at 20.3. The difference is about 40% for the same rating carburetor. A 500 2bbl is actually 1/2 of a 750 double pumper.
You say that in a confrontational manner so I say to you present evidence to the contrary. I am an authorised Weber distributor, (since 1977) Weber recommends a synchronus carb in this situation, for this reason. That is why both versions of the earlier Ford V6 engines were fitted with the synchronus carbs from the factory. Ford used a 28/36 progressive carb on the V4s in the 2000E corsair and many of them came unstuck with valve , head gasket and overheating issues on two cylinders. Even when they went to triple two bbl carbs o the Cologne V6 they used DCNFs (synchronus) carbs. More modern V6s and even lower horsepower V8s used synchronus 2 bbl carbs...I won't say exclusively because I don't know of every engine that ever existed, but I have never seen a factory setup using a progressive 2bbl carb on a V engine. ( other than the V4 I mentioned) In the late 80s and early 90s Chevy had a 2throat Throttle body injector on nearly every V engine....still synchronus ( on a single shaft in fact). However my own evidence comes from 40 years of dyno work with egt guages and spark plug pyrometers, where I have had to try and tune many home brew concoctions and found that there are issues when using progressive 2 bbl carbs on these engines.
Don't use manifold design issues as an excuse to badmouth carburetors. If you are experiencing uneven AF mixtures between cylinder then you have a poorly designed manifold. I have spent thousands of hours tuning, backed by petabytes of telemetry data. Send me a manifold and I will spin-up a VM with as many cores, and as much memory as it takes to model it at all flow rates, with every carburetor combination, and I will show you EXACTLY where the defects are.
You sir are absolutely correct, the 500 CFM 2bbl will not bog the mill. Certainly 350 CFM is not more than *250 (500/2) on any given Sunday. *for the insanely ignorant that would be if and only of the 4 bbl carb is a square bore and can actually be divided by 2, a spread bore would be less initially. Oh and not to take the Gimps side here just for information, fuel distribution is a direct cause of plenum and runner design, not the carb. If both barrels are dumping into the same plenum the plenum does not care which side the air is coming from. As long as you are keeping the plenum full of air/fuel mix it is going to distribute the same. Which is why you choose a carb sized to the plenum not to the engine. *Granted cubic inch displacement, as well as cam profile and head flow rates ( the list is actually longer than this) must also be taken into consideration but to overly simplify it for people who are not tuners (present company included) big plenum big carb is the order of the day if one wants to maintain manifold efficiency. For the intents of this discussion a carb is nothing more than a metering body. *this is where real world application takes control and number fly pretty much right out the window, as a problem solver myself I do understand simple math I will give you this, an equation is a starting place but the solution is just a suggestion when it comes to tuning. This is why tuners get paid, if it were all up to empirical data alone anyone with a computer could be a tuner.
The OP asked for a carb recommendation, I did not piss in your pocket , I gave my opinion. Actually I don't care what you can do with a manifold, if you are so clever why don't you just go out and design and build a line of perfect manifolds ? You will be rich and famous and will blow the rest of the worlds manufacturers out of the water, every racer and rodder will beat a path to your door , money in hand . As far as tuning goes , yeah I have done a bit myself, now and then. From Formula 1 ... (early days, carburetted cars) and Fuel dragsters ( still happening) to vintage bangers and kids ministocks .... not all of them carburetted obviously . I have worked on fuel systems development for two motor vehicle manufacturers , and designed and built, calibrated and tuned the entire fuel system ( injection) for a world championship winner ... I don't sit here to blow my own trumpet though, I only gave an opnion to try and assist somebody. I guess Weber has found that manufacturers often design manifolds to suit many other factors than pure fuel distribution, (packaging, body design and placement of other ancillaries etc ) if they were all perfect for all situations then there would be no need for any aftermarket manifolds, many of which are just as inefficient as the originals.... I was not commenting on any of this , it was not part of the original question. I have some records but probably don't have petabytes of telemetry , data was not easily recorded in that manner in the early days of my career working in fuel systems and carburettor development. Whatever you say , in the real world where people make their own manifolds ( as in this case ) I have found that indeed fuel distribution problems show their ugly head, and that a synchronus carb will most times work better . Often those manifolds are actually a dual plane fuel injection manifold with a carb plate welded on top( with some runners completly divorced from others)and that is a large part of where the issues lie . I did not badmouth any carburettor or carburettors in general, I offered my opinion about one over another for what I understood was a homemade manifold.
All intake manifolds that move both fuel and air are inherently imperfect, due construction constraints, and targeted useage. The only ones come close are IR, and those are still a compromise. Want perfect? EFI is as close as you can get.
lots of posts to say about 350 cfm would be a good guess and I would like to see what kind of a setup you came up with for an intake the 3.0 in my truck made more power than i exspected I think it would make a nice light car engine
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