2x4s to a single 4 barrel ?

[wannadrag]

Thinking of maybe pulling the dual 4 setup and going the single route.Performer RPM with a eddy 800 AVS.Thoughts?Engine is a 10.1 engine with some port work and a 590 lift solid cam.Runs very good as is and will sit and idle all day with no load up,but i am lucky if i get 5 miles to the gal.I guess i'd like to make it a little more street friendly.Any reason that i should'nt do this besides the cool factor?

 

[Satellite65]

I'm not so sure that switching to a single quad is going to improve your mileage by very much.

The engine needs a certain amount of fuel to run properly (not rich/not lean) and doesn't really care whether it gets that fuel from 1, 2, 6 or 8 carburetors. The demand is (should) be split between the carbs.

Of course, a single quad is going to be much easier to tune than any multiple carb setup and for that reason you may get better economy. The single may be slightly more efficient as well. You didn't say what size carbs you're running on the dual setup. They may be a bit too large.

Unless there's something wrong with your existing carbs that would be corrected by switching to a single quad, You probably won't see much of a gain.

I'm more inclined to believe that your .590" lift cam and the gears/converter that go along with it are the more likely culprits.

 

[696pack]

I'm not so sure that switching to a single quad is going to improve your mileage by very much.

The engine needs a certain amount of fuel to run properly (not rich/not lean) and doesn't really care whether it gets that fuel from 1, 2, 6 or 8 carburetors. The demand is (should) be split between the carbs.

Of course, a single quad is going to be much easier to tune than any multiple carb setup and for that reason you may get better economy. The single may be slightly more efficient as well. You didn't say what size carbs you're running on the dual setup. They may be a bit too large.

Unless there's something wrong with your existing carbs that would be corrected by switching to a single quad, You probably won't see much of a gain.

I'm more inclined to believe that your .590" lift cam and the gears/converter that go along with it are the more likely culprits.

Not necessarily. If the dual quads are set up progressively the first carb coming in is really the only one you do much tuning on as the second one is only used when you are in it all the way. So, once you figure out what jetting you need (depending on your intake) it is done. With the duels the carbs are smaller than one single and will be more economical than one large single when you are loafing around. Depending on your cam the duels will usually have better street manners as well.

There are many things to consider regarding what carb you need and can put up with.

The dual quads and six packs were set up from the factory as progressive linkage for economy and street manners. The only reason you would want to change to mechanical (all carbs comming in at the same time) is if you are running a HUGH cam that can take all of the gas at one time.

 

[Satellite65]

Not necessarily. If the dual quads are set up progressively the first carb coming in is really the only one you do much tuning on as the second one is only used when you are in it all the way. So, once you figure out what jetting you need (depending on your intake) it is done. With the duels the carbs are smaller than one single and will be more economical than one large single when you are loafing around. Depending on your cam the duels will usually have better street manners as well.

There are many things to consider regarding what carb you need and can put up with.

The dual quads and six packs were set up from the factory as progressive linkage for economy and street manners. The only reason you would want to change to mechanical (all carbs comming in at the same time) is if you are running a HUGH cam that can take all of the gas at one time.

Dual quads are not usually progressive. The secondaries on each individual carb are, but the linkage between the carbs are 1:1. The primaries on both carbs feed the engine at all times and the idle circuits on both carbs are active. Chrysler factory Six-Pack setups were vacuum secondary. GM Tri-Power (my friends 66 GTO comes to mind) were progressive linkage.

I still say that a single quad is much easier to deal with than any multi-carb setup but if his car is running well now, there's not much to be gained - he obviously went through the motions of getting it all dialed in already. If everything is correct now, any improvements in fuel economy will be small.

 

[rumblefish360]

I'm about to do this on a small block (360) and I'll be running 2 X 600 Edelbrock AFB's. (While I'd prefur a pair of 500 AVS carbs...well, the wallet aint so fat these days)
The linkage can be set up ethier way on this. I'm shotting for the progresive way. The engine is stout for a street ride, but we'll stop there. I'll take a bit of single carb primary for tooling around town.

 

[Meep-Meep]

Dual quads are not usually progressive. The secondaries on each individual carb are, but the linkage between the carbs are 1:1. The primaries on both carbs feed the engine at all times and the idle circuits on both carbs are active. Chrysler factory Six-Pack setups were vacuum secondary. GM Tri-Power (my friends 66 GTO comes to mind) were progressive linkage.

I still say that a single quad is much easier to deal with than any multi-carb setup but if his car is running well now, there's not much to be gained - he obviously went through the motions of getting it all dialed in already. If everything is correct now, any improvements in fuel economy will be small.

Seems to me all the factory installed dual quad setups (I.E. 426 HEMI) are progressive, unless you are talking about a Max Wedge or something built for racing. Ford 406 Tri Power, early Vettes, Buicks, 409 Chevys and the aforementioned Pontiac setup are all progressive from the factory. It's also my experience that multi carb setups on a plenum type manifold are not too hard to deal with and much less temperamental than an IR setup. I think the trick to running dual carbs on a mild street engine is to use a divided plenum dual plane intake and don't use huge carbs.

I'll agree that the .590" cam and loose converter has a lot to do with the poor mileage and my recommendation would be to swap the .590" for a HEMI grind or similar because 10:1 compression ain't cutting it for that monster cam. Matching the cam and compression ratio will be the single biggest improvement you can make to the engine. THEN start fiddling with the carbs.

 

[Cranky]

I'm kinda curious to how much cylinder pressure it has.....and I find that once ya learn how to tune a dual setup, it's not really any harder. Takes a bit more time is all....

 

[Satellite65]

Seems to me all the factory installed dual quad setups (I.E. 426 HEMI) are progressive, unless you are talking about a Max Wedge or something built for racing. Ford 406 Tri Power, early Vettes, Buicks, 409 Chevys and the aforementioned Pontiac setup are all progressive from the factory. It's also my experience that multi carb setups on a plenum type manifold are not too hard to deal with and much less temperamental than an IR setup. I think the trick to running dual carbs on a mild street engine is to use a divided plenum dual plane intake and don't use huge carbs.

I'll agree that the .590" cam and loose converter has a lot to do with the poor mileage and my recommendation would be to swap the .590" for a HEMI grind or similar because 10:1 compression ain't cutting it for that monster cam. Matching the cam and compression ratio will be the single biggest improvement you can make to the engine. THEN start fiddling with the carbs.

I always thought that dual quad linkages were 1:1 with the secondaries being progressive to the primaries, at least that's the way my friends Chevy 409 was. It had two AFB's. I never had the distinct honor of wrenching on a Hemi so I can't say how they operate. As far as I know, all GM Tri-Power setups are fully mechanical with the outboard carbs being progressive.

I would think that a dual quad setup running on the front carbs primaries (light throttle cruise) would exhibit severe fuel distribution problems, but maybe I'm wrong.

Multi carb setups are not extremely difficult to deal with but certainly moreso than a single. You have to figure more of everything, gaskets, jets, floats, needles and seats, metering rods, power valves, whatever and oh yes, time.

Although I may seem down on multi carb systems my original response was not aimed at making him ditch it for a single quad. He said his car can idle all day without loading up. With a cam that big, in order to do that it's obviously tuned quite well and I don't think there's a whole lot to be gained.

I'd stick with it for now and look elsewhere for fuel economy improvements. Besides, Dual quads just look so cool.

 

[696pack]

Many people changed their factory progressive linkage to mechanical earlier on thinking it was going to make a big difference, it didn't unless they had changed the cam to handle it. Any factory dual quads i ever owned were progressive and i started with owning them in the late 50's.