Tend to agree with AJ here...not quite sure where 'those' percentages come from but without a dyno slip or two I'm not buying it. Holley was making big 4-bbls in '69 and yet the six-pak was available and the 426 Hemi continued using 2x4. If the six-pak 440 wasn't making enough power then it would have been easy for Mopar to convert to 2x4 and just use the 426 parts. Conversely, if the 2x4 on the 426 wasn't working well Mopar could have made a 1x4 intake and used a 1050 3-bbl. Multiple carbs, 2, or 3 or even 6 require proper linkage/proper engagement and, especially, a decent manifold. Early 50's duals and trips had primitive manifolds (by todays standards) but they worked because the single carbs were so damned small. Now, for most engines, we have more options than we know how to deal with. Seems to me, the high cost of multiple carbs is todays limiting factor in the 'cool' department, not the high output department. .
I guess it all come down to what you want the end results to be . Are looking for more HP or something that looks bad . Multi-carbs do both if they are set up correctly . Multi carbs are much easier on fuel if they are set up on a progressive linkage . It's like a single 4 bbl , it only opens the secondaries when you want them to . The same is for multi carbs like a 2x4 or 3x2 or more carbs . Yes you will get more HP to a certain extent . Like said before , your engine is an air pump so the more that goes in must go out ant the same speed . Also multi carbs set ups are best on the top end where more fuel is needed . Just remember on thing and don't over carb your engine or you are wasting fuel and HP ! A 400 HP engine will run just as good on a 600 cfm as a 800 cfm unless you can use and burn the extra fuel that is going into your engine . I did read all the post but what size engine are you running along with cam , heads , rear end gears . This will all have to be considered when you take on multi carbs if you want your engine to run good . A small block can handle a 2x4 set up on progressive linkage with 500 cfm , but I would go bigger for the street . I am running multi carbs in a 300 HP engine and hope to have lots of get up and go when I open the outer 2 carbs up when needed ! Just my opinion ! RetroJim
With all due respect: 625 CFM four barrels were available in 1957. 950 CFM's were available in 1963. Jon.
Multi-carb setups supposedly give better fuel distribution to the cylinders, as opposed to one carb setting over the center of the engine.
ok, not sure what you're getting at here. my point was you can make the same if not more power with a single carb in a street/strip application than with a multi carb setup. years ago, this may have not been true, but it's not the case now. in his particular case where a good single carb intake is not available, then the answer is clear. but for those of us who do have that luxury, it's different. there are plenty of stupid fast cars running a single quad. if a single quad can supply enough air and fuel to meet the engine's requirements for optimum performance, then why would you need dual quads? i mean obviously if they don't make a single carb big enough for your application (and at that point you're pretty well past a typical street motor) then yeah, i can see needing multiple carbs. if your engine needs 700 cfm for optimum performance, it needs 700 cfm, regardless of how you deliver it. there are way too many factors to make a generalized statement about what size carb a car will need. not every setup is the same obviously. too small and you're not getting the proper vacuum through the carb, too big and you're washing the cylinders down with fuel. you can use the old formula of displacement x maximum rpm / 3,456 to get you in the ballpark and on most street applications, the correct SIZE carb, but additional tuning may be necessary. no out of the box, drop on carb is going to give you the best numbers it can without tuning. street cars can will do well with a smaller carb since they are not operating high in the rpm range very often, but again factors such as weight, gearing, transmission choice and so on will affect your choices. whereas on a race motor, you can throw a huge carb (or carbs if you deem it necessary) since the only concern is WOT operation.
excuse me for assuming he'd give all pertinent information in the opening post. i took it as a general question. get the rope and pitchforks.
But... most people will jet it up so it isnt lean, but then it ends up overly rich at much of your RPM range
This an actual dyno test that Rod & Custom did on one of there 327 engine builds to test retro manifolds. read the facts single 4 barrel : We swapped an Edelbrock Performer RPM intake and a Demon Carburetion 750-cfm mechanical-secondary carb with this combination the engine made 426 hp at 6,100 rpm and 400 lb-ft at 4,600 rpm. dual 4's (500cfm) : We were impressed to find that the engine made 418 hp at 6,200 rpm and 382 lb-ft at 4,700 rpm with the Edelbrock dual-quad setup, considering that the low-rise 4x2 setup doesn’t leave much real estate to optimize runner design. 3X2 : the 327 managed to generate 380 hp at 5,500 rpm and 380 lb-ft at 4,900 rpm. Edelbrock states that this manifold is good for up to around 5500 rpm, and right after the 327 crossed this threshold, the power curve leveled off. for the rest of the story http://www.rodandcustommagazine.com/techarticles/custom_327_engine/index.html .....
I'd have to disagree, at least in my case. I think the key to running two fours is to use small carbs. I use a pair of 390CFM Holleys, and once they're right, they're right. They also have unreal off-idle performance and actually get decent mileage. But you're right about one thing, they look good!
I wasn't trying to start something, I was asking because at one time, Carter had a CFM chart that you could put in your cubic inches, 454, and your estimated rpm limits, 4500-5500, and it gave me 650 cfm. All my gearhead buddies told me it was too small a carb for a big block. All except my friend Mike Norris, who said the same thing Carter said, that the engine will only use whatever air it needs. His example was a 327 with a 1000cfm carb on top. Sure, you could lean it down enough to make the engine run, but if the 327 only needs 650, the rest is wasted, and you are only making comprimises with the big carb. I DO know, I have two 650 Triumph flat track bikes, one a Thunderbird, (single carb) the other a Bonnieville (Dual carb). The single carb bike makes more usable torque down low, and the dual carb bike likes to rev. I guess where I'm going with this is I believe my 454 is just fine with a 650 AFB on top, but at the same time, if I could afford a three deuce setup, I'd have it!
Wow, I didn't realize the big ones were that early. Were they not widely available or just in low demand due to the popularity of multicarb? I still believe that many of the multicarb applications in the muscle era were more about marketing than anything, but that's just an opinon. Good facts, thanks for adding them.
If all you care about is absolute top end horsepower at wide open throttle, then more carb flow area is always better. But with less rpm, and less throttle, the airspeed through a really large carb can fall to the point that it will not atomise fuel as well, and can become more difficult to tune. You might start to get stubborn flat spots and hesitations that can be difficult to diagnose and. It may run super rich in other places, all of which is never good. A vehicle that has flat spots, hesitations, and is really difficult to drive will not be as much fun, or as fast (or economical) as something else that has been properly sorted out and correctly tuned. It probably does not really matter that much if you run a single or multiple carbs, as there is such a vast range of sizes and styles available to choose from. Either can be made to work. My own choice would be a single carb, simply because you need to change less parts to alter the tune. If there is a fault, or something needs to be changed, and you run multiple carbs, usually every carb need the same amount work doing to it. If you are into quickly trying things, multiple carbs can quickly become a nightmare. These days I never bother with carbs a all. EFI works so much better, and I can change anything I like, and put it back again, in a few seconds with a few computer keyboard strokes.
yes and the camshaft duration determines the peak RPM range engine size does matter but you could run a 600 on a stock big block as well as a stock small block? so my money goes on the camshaft being the most important, but not only factor. not being a prick, but just making a point
From the factory, the Buick 364 nailhead used a 575 cfm Carter AFB carb, the 401/425 used a 625 cfm AFB, and the factory dual quad setups used two 625 cfm AFB carbs. Nailheads generally like bigger carbs. I've even heard of guys running dual 750 cfm AFB's on them.
9 times out of ten, an engine will drop power when converted from a good 4 barrel/intake to any type of multicarb- unless your talking about a very wicked race engine. Hotrod magazine did an issue with all the favorite manifolds and carbs on a gen I small chevy and the single 4 beat them all. but multicarbs look good......
The carburetor manufacturers would build what was desired by the auto manufacturers. An example of this would be the fact that Carter, Rochester, and Stromberg ALL introduced 4-barrel carbs in the 1952 model year. Many car enthusiasts are either unaware, or forget that industry used some huge (many over 2000 CID, a few over 5000 CID) IC engines. Carburetors had to be produced for these engines. True, most were low RPM engines (all were low RPM compared to modern V-8's); but still carburetors were needed. I have some examples of marine and military 2-barrels that flowed over 900 CFM (on the 2-barrel scale) as early as the late 1920's and early 1930's. I also have a prototype two-barrel (never produced) that would flow more than 1200 CFM (on the 2-barrel scale). The automotive engineers WERE AWARE of these units. And I personally share your opinion about marketing being the main factor for several (but certainly not all) of the factory multiple carb setups. Jon.
I would agree with your first paragraph virtually always on tripower, but only because of carburetor/manifold selection on dual fours. Our dual fours go the other way! As to the Hot Rod article, when younger, I bought and read many of the auto magazines as they came out. I have a complete set of Road & Track, and most of the early Motor Trend. I gave all the Hot Rod mags away after reading the article recommending the "hot" setup for the 270 HP Corvette was to replace the vacuum piston springs carefully selected and calibrated by the Carter and Chevrolet engineers with those from Paper-Mate pens acquired from the local five and dime. Probably a poor financial decision on my part as the first year of Hot Rod is bringing some serious money on Ebay. And I had them all. But after that article, I had no desire to keep them in my reference library. Jon.
the way i understood all of this arguement is that whatever you use for an intake/fuel delivery system, all its real intent is to keep up with the engine at its intended performance level. carbs and intake alone will not make any more power for the same engine with the same cam/heads/compression by itself. think of the engine as being your constant with a particular cam it makes "x" horsepower and torque @ whatever rpm. what the intake and fuel delivery end has to be designed to do is provide sufficient fuel/air ratio to match. that is all. dont go over and dont go under. thats why some engines suck on bottom end and perform well on top end and vice versa. just swapping intakes and carbs does not always mean more power. guys will tell you that swapping a 2 bbl to a 4 is always a 1st, but in all reality the performance gains are negligible and really the most of what they have done is just made the engine a little tighter by replacing a few gaskets with fresh ones. in short what determines power more than anything is the cam. performance gains come from there first and foremost. everything else is to support it. this includes spark events, fuel delivery, bottom end support, cylinder head work (both compression and charging) and so on. to make real power for what you what you need to do, realistically it has to be a total package.
This is just a guess.....I'd say on a typical hi-perf motor..... 10.5 compression, good factory cam and heads...... probably in the area of 25 hp, but getting up to fine tuned pro stock motor, I'll bet you're in the area of 200-300 HP there. To maximize multi carbs combo, the total package needs to compliment every component
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