300/4.9L carburetion options for future project?

[85lebaront2]

So from what I am gathering, the Clifford dual intake is sold with a pair of Weber 38’s. It is rated at 390 cfm with 2.5 inches of depression, which calculates to 302 cfm at 1.5 inches. They are a progressive 2 barrel. I don’t know what the cfm of just the primaries would be, but there are some specifications here:

http://www.lcengineering.com/LCTechPages/pdf/38DGAS.pdf

They may be progressive, but the external gear system would concern me getting crud in the teeth and sticking. The Pinto and Vega ones use a link to open the secondary throttle shaft. The Chrysler ones use a vacuum diaphragm to open the secondary. These can be synchronized with a small vacuum hose linking the vacuum diaphragm housings (like Ford did on the 427 setups).

[Ray Cecil]

They may be progressive, but the external gear system would concern me getting crud in the teeth and sticking. The Pinto and Vega ones use a link to open the secondary throttle shaft. The Chrysler ones use a vacuum diaphragm to open the secondary. These can be synchronized with a small vacuum hose linking the vacuum diaphragm housings (like Ford did on the 427 setups).

Going to follow this thread. Ive had the idea of doing a 300 3 Pack. 3 singles. Each feeding 2 cylinders. But I am unsure about velocity, and sizing. If I ever find two more stock 300 intakes, maybe Gary or Dave or anyone else with more carb knowledge could recommend the proper carb.

 

[Gary Lewis]

Going to follow this thread. Ive had the idea of doing a 300 3 Pack. 3 singles. Each feeding 2 cylinders. But I am unsure about velocity, and sizing. If I ever find two more stock 300 intakes, maybe Gary or Dave or anyone else with more carb knowledge could recommend the proper carb.

The "proper carb" for a 3-carb setup is very similar to those for a 2-carb setup, only maybe smaller if that is possible.

Carb sizing can be summarized by two limiting factors: the carb must be small enough that at off-idle conditions the throttle response is still good. Too big of a carb will cause a bog or a soft feeling just off idle. But, too small of a carb will limit performance at high RPM.

That would seem to be a hard problem to solve, but fortunately we have progressive carbs, meaning ones that run on a smaller primary and then open up the secondaries when needed. Some Webers are that way. The Holley/Weber that Bill mentioned is. And most 4bbl carbs are, although it is very unlikely that you can find a small enough 4bbl to work properly with a 100 cubic inch engine, which is what you'll have with 3 carbs on a 300.

And, speaking of that, if you cut up three manifolds as I think you are suggesting, you will have three separate engines connected by a crankshaft. And that's a slightly different problem to solve than the Clifford manifold that serves all six cylinders from two carbs. In the two cylinder case the carb will see only those two cylinders and the pulses will be strong and widely spaced. But with the Clifford manifold there will always be six pulses to the carbs, although each carb will see three moderate pulses and three weaker pulses.

The issue is the start/stop that strong pulses try to invoke. Fuel has a significant mass to it when compared to air, and because of that it is harder to tune a carb that sees really strong pulses than it is a more even set of pulses.

[Ray Cecil]

The "proper carb" for a 3-carb setup is very similar to those for a 2-carb setup, only maybe smaller if that is possible.

Carb sizing can be summarized by two limiting factors: the carb must be small enough that at off-idle conditions the throttle response is still good. Too big of a carb will cause a bog or a soft feeling just off idle. But, too small of a carb will limit performance at high RPM.

That would seem to be a hard problem to solve, but fortunately we have progressive carbs, meaning ones that run on a smaller primary and then open up the secondaries when needed. Some Webers are that way. The Holley/Weber that Bill mentioned is. And most 4bbl carbs are, although it is very unlikely that you can find a small enough 4bbl to work properly with a 100 cubic inch engine, which is what you'll have with 3 carbs on a 300.

And, speaking of that, if you cut up three manifolds as I think you are suggesting, you will have three separate engines connected by a crankshaft. And that's a slightly different problem to solve than the Clifford manifold that serves all six cylinders from two carbs. In the two cylinder case the carb will see only those two cylinders and the pulses will be strong and widely spaced. But with the Clifford manifold there will always be six pulses to the carbs, although each carb will see three moderate pulses and three weaker pulses.

The issue is the start/stop that strong pulses try to invoke. Fuel has a significant mass to it when compared to air, and because of that it is harder to tune a carb that sees really strong pulses than it is a more even set of pulses.

Gary, the plan was to use three center sections, and tie them together with steel pipe so that it is one manifold.

So, are the dual webers that clifford uses progressive?

Maybe I cant find the right carb for a 300 3 pack. But Id like to keep trying before just throwing clifford money.

[Gary Lewis]

Gary, the plan was to use three center sections, and tie them together with steel pipe so that it is one manifold.

So, are the dual webers that clifford uses progressive?

Maybe I cant find the right carb for a 300 3 pack. But Id like to keep trying before just throwing clifford money.

The Webers I see in Clifford's kit are the 38/38 DGAS, and this Redline writeup says they are synchronous, which means both throttle plates open at the same time. It would be the 32/36 DGEV carb for progressive linkage.

I don't know why Clifford is using those carbs, but they've probably done a lot of research and I haven't, so I'll bet it works.

As for yours, I think joining the sections with pipe is a good idea as it will smooth out the pulses. Sorry, I missed that.

I'm still thinking the progressive Holley/Weber 5200's have merit. Bill suggested them and the info I've found looks promising.

[85lebaront2]

The Webers I see in Clifford's kit are the 38/38 DGAS, and this Redline writeup says they are synchronous, which means both throttle plates open at the same time. It would be the 32/36 DGEV carb for progressive linkage.

I don't know why Clifford is using those carbs, but they've probably done a lot of research and I haven't, so I'll bet it works.

As for yours, I think joining the sections with pipe is a good idea as it will smooth out the pulses. Sorry, I missed that.

I'm still thinking the progressive Holley/Weber 5200's have merit. Bill suggested them and the info I've found looks promising.

Ok, further thoughts, partially for Ray Cecil. Ray, being a brand C type you are probably aware that the original potra-potty's (Corvettes) were 235 ci 6 cyl engines, called "Blue Flame" and were a slightly higher compression hotter cam version of the standard Chevrolet 235 engine. These had 3 one barrel carburetors, but due to the height of the engine and the low hoodline of the Corvette, they used a Marine carburetor, modified to a hand choke. The choice was the Carter YH, which is essentially a Carter YF on it's side.

These were probably the size of the Rochester B one barrel, just three of them. The intake did have equalizer passages between the three intake ports (235 had a design with square and rectangular exhaust ports and round intake ports, all were paired except the end exhaust ports which were single. On the Blue Flame, there were split exhaust manifolds and dual exhausts.

On a truck where there is plenty of clearance over the engine, I would expect that 3 singles could be fitted with out a problem and if three EGR spacers were used a maybe 1/2" ID balance tube between them would work unless you wanted them progressive in which case you would be better off simply adding the flanges like the performance kits for the small Ford sixes with the integral manifold used.

On the Clifford intake, two 32/36 DGEV carbs would be my choice for new, the Holley Webers from Pintos, Vegas or Mopars would be a good alternate.

[Ray Cecil]

Ok, further thoughts, partially for Ray Cecil. Ray, being a brand C type you are probably aware that the original potra-potty's (Corvettes) were 235 ci 6 cyl engines, called "Blue Flame" and were a slightly higher compression hotter cam version of the standard Chevrolet 235 engine. These had 3 one barrel carburetors, but due to the height of the engine and the low hoodline of the Corvette, they used a Marine carburetor, modified to a hand choke. The choice was the Carter YH, which is essentially a Carter YF on it's side.

These were probably the size of the Rochester B one barrel, just three of them. The intake did have equalizer passages between the three intake ports (235 had a design with square and rectangular exhaust ports and round intake ports, all were paired except the end exhaust ports which were single. On the Blue Flame, there were split exhaust manifolds and dual exhausts.

On a truck where there is plenty of clearance over the engine, I would expect that 3 singles could be fitted with out a problem and if three EGR spacers were used a maybe 1/2" ID balance tube between them would work unless you wanted them progressive in which case you would be better off simply adding the flanges like the performance kits for the small Ford sixes with the integral manifold used.

On the Clifford intake, two 32/36 DGEV carbs would be my choice for new, the Holley Webers from Pintos, Vegas or Mopars would be a good alternate.

Bill for the WIN!!

I hadnt thought about the 53 vette blue flame! Dad had a 59 vette 283.

Anyway, i like where this is going.....

[Gary Lewis]

On the Clifford intake, two 32/36 DGEV carbs would be my choice for new, the Holley Webers from Pintos, Vegas or Mopars would be a good alternate.

Yes, Bill for the win!

I like the idea of the 32/36 DGEV's, but they are pricey. So the Holley/Webers would be a good option as they should be available from a salvage. But, as Bill said previously, get several of them to have parts.

[1986F150Six]

Bill for the WIN!!

I hadnt thought about the 53 vette blue flame! Dad had a 59 vette 283.

Anyway, i like where this is going.....

The 2 X 4 Clifford intake and adapters will be at the Garagemahal Truck Show so it can be looked at, by anyone interested.

[grumpin]

The 2 X 4 Clifford intake and adapters will be at the Garagemahal Truck Show so it can be looked at, by anyone interested.

“the original potra-potty's (Corvettes)“

Wow, Bill! Never heard that term before!