413 dual quad CFM question...

[62maxx]

Greetings,

I'm researching the thought of freshening up a 1963 Chrysler 413 with a mild cam (474/280 Hyd Flat Tappet 234/234 Duration) with stock pistons and the ONLY low rise dual quad intake to fit under the hood is a Edelbrock CH-28 Intake 5440 which recommends a set of Edelbrock 1405 carbs. They are rated @ 600cfm each.

Is this TOO MUCH CFM for this engine and should I find a set of 500 CFM carbs?

 

[DanielSlocum]

I think you want 500s. Edelbrock sells them set up to be used in a pair. I think they are 2 different part numbers because only 1 has a choke. Maybe check Summit Racing.

 

[496 polara]

I think 500's would be more responsive on the street. Now if you had ported heads,compression,gears,and a stall I would say 600's for "hot" street.

Edit; I never knew the 500's were that bad. 600's for the win.

 

[gtxrt]

no way on the 500 cfms if your using the ch-28 intake.

 

[33 IMP]

What kind of throttle linkage are you planning? Running on one carb primary, progressive second primary, and vacuum controlled secondaries, I'd run the 600s.

 

[lewtot184]

I use edelbrock 600's on my 440 with a ch28 and I can assure you they are none too big. They are the same size as street hemi. They have small primaries and are velocity controlled. Forget the cfm hype. 500cfm edelbrocks are garbage.

 

[rumblefish360]

A body member 318willrun uses twin 600 AFB’s on a 318 very well.

 

[62maxx]

What kind of throttle linkage are you planning? Running on one carb primary, progressive second primary, and vacuum controlled secondaries, I'd run the 600s.

I don't know as of yet. THAT is a very good question.

 

[62maxx]

I use edelbrock 600's on my 440 with a ch28 and I can assure you they are none too big. They are the same size as street hemi. They have small primaries and are velocity controlled. Forget the cfm hype. 500cfm edelbrocks are garbage.

View attachment 1764629

Thanks! For some reason , I cannot fathom a big block not getting flooded on a total of 1,200 CFM. But, it is what it is.

 

[33 IMP]

The vacuum operated secondaries won't open if the engine airflow doesn't demand them
If you were gonna run two 600 holley double pumpers.....? A different answer.



You do know it will probably run better with a performer rpm and a 750 vacuum carb, right? (and probably considerably cheaper.)

I ran two 750 competition AFB"s on mine..... but it was on a crossram maxwedge head roller cam motor. An 850 double pumper on a tarantula was just as fast, and easier to tune.

 

[rumblefish360]

Thanks! For some reason , I cannot fathom a big block not getting flooded on a total of 1,200 CFM. But, it is what it is.

It’s because you think the carbs will discourage a crazy amount of fuel but this is not how carbs work. They work on the draw of air rushing past the choke, boosters and on down which picks up the fuel to mix.

This is where “Jetting” the carb comes into play for any carb. If the jet is way too big, even on a 2bbl., you wash the cylinders down with fuel. The reverse is true with to small of a jet n any carb not delivering enough fuel causing havoc.

The engine will draw in what ever amount of air that is needed at what ever rpm it is turning at and as long as the fuel is metered to be enough, not to much, not to little, the engine will be fine.

The real question here is drivability with larger carbs.
Also, part throttle and wide open throttle.
If the carbs are tooooo large, then jetting can be a nightmare and a good smooth running engine without issues is the concern.

There is a lot to unpack behind this. But! A stock 413 can handle twin 600’s. While a smaller set will have improved throttle response, drivability & probably mileage if you can keep the foot out of it. This is why Edelbrock recommends twin 500’s calibrated for this.

I don’t think it’s a bad way to go BUT IF you need to save a few bucks and/or have twin 600’s on hand, use the 600’s.

 

[33 IMP]

It’s because you think the carbs will discourage a crazy amount of fuel but this is not how carbs work. They work on the draw of air rushing past the choke, boosters and on down which picks up the fuel to mix.

This is where “Jetting” the carb comes into play for any carb. If the jet is way too big, even on a 2bbl., you wash the cylinders down with fuel. The reverse is true with to small of a jet n any carb not delivering enough fuel causing havoc.

The engine will draw in what ever amount of air that is needed at what ever rpm it is turning at and as long as the fuel is metered to be enough, not to much, not to little, the engine will be fine.

The real question here is drivability with larger carbs.
Also, part throttle and wide open throttle.
If the carbs are tooooo large, then jetting can be a nightmare and a good smooth running engine without issues is the concern.

There is a lot to unpack behind this. But! A stock 413 can handle twin 600’s. While a smaller set will have improved throttle response, drivability & probably mileage if you can keep the foot out of it. This is why Edelbrock recommends twin 500’s calibrated for this.

I don’t think it’s a bad way to go BUT IF you need to save a few bucks and/or have twin 600’s on hand, use the 600’s.

Op says edelbrock recommends 600s.

 

[rumblefish360]

Op says edelbrock recommends 600s.

Thanks, I’m just thinking/remembering the Edelbrock catalog recommendations of twin 500’s.

He was wondering twin 600’s are to much and I don’t think so despite what I remember as twin 500’s advertised.

I said earlier to go with the twin 600’s.
I noted that 318willrun used twin 600’s on his 318.

 

[gtxrt]

Thanks! For some reason , I cannot fathom a big block not getting flooded on a total of 1,200 CFM. But, it is what it is.

the plenum is a lot bigger on 2x4 intake so more volume of air

 

[PROSTOCKTOM]

Thanks! For some reason , I cannot fathom a big block not getting flooded on a total of 1,200 CFM. But, it is what it is.

Just because you put 1200 cfm worth of rated flow on an engine that doesn't mean the engine will use that much.

How much of the cfm rating an engine uses is the sum of a lot of variables. A given engine might only use 800 worth of what's available.

Vacuum and airspeed play a big part of the equation.

For what it's worth I have 800 cfm AVS carbs on my CH-28 and I am not over carbureted.

Tom

 

[rumblefish360]

Just because you put 1200 cfm worth of rated flow on an engine that doesn't mean the engine will use that much.

How much of the cfm rating an engine uses is the sum of a lot of variables. A given engine might only use 800 worth of what's available.

Vacuum and airspeed play a big part of the equation.

For what it's worth I have 800 cfm AVS carbs on my CH-28 and I am not over carbureted.

Tom

I’m sure you know the below but the reply is for the board mostly. New guys and the less experienced that fully do not understand maybe enlighten after reading, or more confused.
But it is how it is.

That’s the funny thing about engines. An engine may consume, let’s just say 600 cfm. People think it should get a 600 cfm carb and they are good. But yet the engine will perform better in all areas with a 650, then better with a 750. Where it stops is a dyno test away and very variable at this point of the non descript engine.

It’s all about how well and easy the engine is breathing.
To large of a carb can have fuel metering problems at low and sometimes mid engine speeds.
To small of a carb limits higher engine power. Also as well, fuel delivery can be an issue as well.

It’s all about balance of the whole system and how it works.

 

[lewtot184]

If your looking for performance it's not about some rated "cfm" it's about venturi area; that factor that the common culture chooses to ignore. It's about filling the cylinders quickly and efficiently and cfm ratings by themselves can't do that. People also tend to leave out intake manifold efficency. It's more than just carb cfm.

Maybe the most important aspect is what are you going to do with the car? Just cruising around? Street and strip? Strip only?

 

[AR67GTX]

A lot of larger 60s engines ran 2 - 600 cfm carbs - 409, 427 ford, 428 PI Ford, 413/426 max wedges, Street Hemi, 421 Super Duty Pontiacs. The one thing that distinguished most of them was the ability to make power up to 5,500-6,000 rpm. Even the 302 Z28 optional cross Ram used 600 Holleys I think and could use them because of near 7,000 rpm red line. If your engine is going to top out at 5,000 or so, 500 carbs might make sense but I don’t know about their quality.

 

[gtxrt]

If your engine is going to top out at 5,000 or so, 500 carbs might make sense but I don’t know about their quality.

if you change your top out at 3,500 rpm or so then the 500 carbs would be alright. anything over 3,500 rpm you start losing power.

 

[lewtot184]

The problem with 500 edelbrocks is that crummy primary booster. When Carter did the 500 thing they did it right. They kept the 1 3/16" primary venturi and 1 7/16" throttle bore but down sized the secondary to 1 5/16" venturi and 1 9/16" throttle bore. What did edelbrock do? Those cheap ***'s just made a restrictive primary booster for their 600 carb. That's 2 parts vs 6-7 parts to do it right. The 600 has the same size primary as a 318 2bbl carb. What part of that is too big and needs down sized? Edelbrock may have been the worst thing to happen to a perfectly good design. Quit buying carbs buy a cfm rating!