Eddy vs Holley CFM ratings?

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WSUTARD

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I was recently watching an episode of Roadkill Extra where Freiburger and Dulcich were discussing a 318 mopar. They touched on the carb and mentioned how Dulcich put a 800 Eddy on it and how normally people would think that's oversized but it works on the 318. They then said that Holley and Eddy rate their CFM differently and thus they large Eddy.

Anyone have info or thoughts on how the two compair in CFM ratings?

Just curious. No need to get into a Eddy vs Holley fight.

Fast forward to 4min mark if you want just the carb talk.
 
Things are fussy in my mind, but Holley themselves rate (or used to rate) their own two barrel carbs differently than 4bbl. This means a 500CFM Holley 2bbl is something on the order of 350 when compared to a Holley 4bbl. 3" Hg vs 1.5 as I recall

I recall something about the Carters being rated "wet" meaning flowing fuel, or a likeness of fuel. I bet if you Google/ search this you can come up with a chart somewhere on the www

The other issue is vacuum secondary type considerations.

Holley of course has either vacuum secondary or "double pumper" full mechanical

Carter/ Ed has the old AFB style with the upper weighted door, or the newer AVS with a spring loaded upper flapper. These operate similar to either Thermoquad or GM Quadrajet, are adjustable, and make the carb operate more like a Holley vacuum secondary. That alone, makes a carb much more forgiving for sizing

Bear in mind that injection has none of these problems, because the fuel system does not need a "vacuum signal" nor does it need velocity through a booster venturi to make it operate properly
 
And how many times are people told they better get a 500 cfm for their 318...... when mother mopar put 800 cfm TQ's on them. I've ran 750 Holley double pumpers on them and had them run great. I have a 670 Holley on my 318 right now and it performs awesome.
 
Holley's CFM ratings are nothing but a joke. A 670 street avenger has the same venturi and throttle bore sizes as a regular old 1850 600. I've never understood how they actually come up with their cfm ratings. Seems like nothing but marketing hype to me.
 
I think it's got to do with the stock tune of the carb. From what I heard edlebrock are more conservative so probably work well on a stockish 318. Where Holley expects a 750 to go on something racey so would be very rich on the same 318. I think thats why 750 is considered wrong carb for a lot of combos is most probably don't tune or tune wrong.

A carb is only to big if it can't be tuned for your engine. An 800 doesn't put any more fuel and air through your engine then a 500 it just be less restrictive doing so which equals hp but as you go bigger the gains get less and less.
 
I have always run the 4782 4783 mechanical 6 pack on a 340, 1350 cfm. I had them on a 4 speed cuda and 1st gear 2000 rpm floor it and no stumble just GO GO GO. When all 3 open at the same time it's almost no vacuum so you have to dump a lot of fuel to overcome the air coming in. I have also run 850 cfm holleys on a lot of small blocks, 69 Z28 302 for one.
 
brian6pac said:
I have always run the 4782 4783 mechanical 6 pack on a 340, 1350 cfm. I had them on a 4 speed cuda and 1st gear 2000 rpm floor it and no stumble just GO GO GO. When all 3 open at the same time it's almost no vacuum so you have to dump a lot of fuel to overcome the air coming in. I have also run 850 cfm holleys on a lot of small blocks, 69 Z28 302 for one.
Click to expand...

A six pack is rated like 2bbl carbs at 3" it's more like a 950 at the 4bbl rating 1.5"
 
CFM rating is not carved in stone, but that is what most people think. I can't use a carb bigger than a 750 cfm because that's what the engine calculator says, that is just bullsh@@.
This might explain it better.
Carburetor Air Flow Ratings
 
318willrun said:
And how many times are people told they better get a 500 cfm for their 318...... when mother mopar put 800 cfm TQ's on them. I've ran 750 Holley double pumpers on them and had them run great. I have a 670 Holley on my 318 right now and it performs awesome.
Click to expand...

OK, but a TQ has that adjustable flapper, and "just sayin" you might have found that even though it seemed great with a 750, it might have run better with a 700 or even 650.

Isn't a 670 a vacuum secondary? They are much more forgiving than a DP
 
The story I heard was that the Holley's were rated for "wet" flow, meaning, fuel air mixture. Carters, and then Edelbrocks, are rated for "dry" flow, meaning, just air. Which means that the wet flow cfm rating is lower than the advertised cfm for the carter/eddy carbs. So an equivalent carter/eddy would have a higher advertised cfm rating than a Holley would to have the same wet flow.

Somewhere I had this all looked up and sorted out, there's a conversion factor you can use to estimate the wet flow cfm so you can better compare carburetors. If I remember right wet flow is between 8 to 16% less than dry flow depending on conditions. Problem is just like any flow bench the cfm also depends on what the vacuum number is on the bench for the test, and different manufacturers have been known to use different vacuum settings. I think that was the deal with the 2 barrel carbs too, they were wet flow rates but at a different vacuum than the 4 barrels so the numbers weren't straight across comparable.
 
67Dart273 said:
OK, but a TQ has that adjustable flapper, and "just sayin" you might have found that even though it seemed great with a 750, it might have run better with a 700 or even 650.

Isn't a 670 a vacuum secondary? They are much more forgiving than a DP
Click to expand...
yes, 670 is VS. Yes, the TQ has the adjustable back flap. Last, they may have ran "as well" with a smaller carb, I doubt better.
Carbs don't "push" air and gas into engines. The engine "pulls" what it needs.
 
It's weird there's still all this confusion when it comes carbs. People have prove time and time again what works.
Street and street/strip Small blocks
Basically go with
350 hp or less 650
350-550 hp 750
550 hp plus 850 plus
Race probably add 100 cfm to each
And in general 750 can be made to work on most street and street/strip engines.
 
Well said 273.

I seen a video of a Holley tech set flow testing a carb. There all wernflow tested I beileve. I don't know about the Carters.

Now 318 willeun made a mention of "Better put a 500 on that 318."
That would depend on the engines useage and power output.

A TQ carb is a super flexable carb due to the spring loaded secondary side. Once it opens without an issue, your done. IF it opens fully, then the engine needs (or can use) it.

I wouldn't want to use a Holley 800 inplace of a TQ on a small engine of questionable power rating.
 
The only thing the air valve does on the secondary's is act like a acceleration pump. As long as it is closed it sucks fuel. Then when the air speed gets high enough it opens and it leans out. It also lifts the metering rods to keep it rich enough to make power.
 
273 said:
It's weird there's still all this confusion when it comes carbs. People have prove time and time again what works.
Street and street/strip Small blocks
Basically go with
350 hp or less 650
350-550 hp 750
550 hp plus 850 plus
Race probably add 100 cfm to each
And in general 750 can be made to work on most street and street/strip engines.
Click to expand...


So what you are saying is the bigger the carb the more HP it will make?
 
To a degree, I'd say yes.
Also at the same time, 273's list makes good sense but is not mandatory ether.
 
brian6pac said:
So what you are saying is the bigger the carb the more HP it will make?
Click to expand...

Not really, the carb rating is arbitrary it's based on at what vacuum level your reading it at.

Think of it more likes headers we know 1 5/8 goes on a mild engine 1 3/4 on a healthy one 1 7/8 on a healthy stroker etc...
All will move the same amount of air but smaller you go the more restrictive they become robbing hp. But as you go bigger there's a point where the gains get smaller and smaller and may rob low end efficiency.

Same with carbs going too small just throws away hp. Like say a 390 4bbl might kill 50 hp over a 750 but a 750 might only lose 1 hp over 1050 on a certain engine.

The main reason you got to match carb with engine and not just go for the biggest is cause of tunablity. On a drag race only car basically you only got to worry about idle and WOT so you get away with a bigger carb. Look at the Holley sniper efi they don't sale a 550/650/750 etc.. (different restrictions) They sale one for 800 hp or less so it's good from a /6 to a bad *** 800 hp 572 inch stroker. The only reason to add restriction on your engine at this point is so all the carb fuel mixture circuits will work and only need just enough to do so or your throwing away hp.

Also look at that formula that tells how many cfm your engine needs that's pretty accurate.
But here is where it gets tricky. That has nothing to really do with what carb you need.
Let's say that formula says you need 550 cfm. Doesn't mean you grab yourself a 550 cfm carb and be done with cause basically any carb you put on that engine technically becomes a 550 cfm carb from a 390 to 1050 will all flow about 550 cfm on that engine cause what will change is the vacuum level (restrictiveness) at WOT. So you want to pick a carb the will give you the right amount of vacuum. A full race car might go under .5" a street/strip might go around 1" and if you don't care about throwing away hp for mild street 1.5" aka a 550 cfm carb will do.

Think of a carb as a necessary restriction and like all restrictions you want the least you need.
 
"engine technically becomes a 550 cfm carb"

Disagree in a big way! A particular engine will consume that much at max but it is not a carb or becomes a carb.
The carb is a carb and the engine below it is the engine, not the carb, never a carb etc....

This is so wrong.
 
rumblefish360 said:
"engine technically becomes a 550 cfm carb"

Disagree in a big way! A particular engine will consume that much at max but it is not a carb or becomes a carb.
The carb is a carb and the engine below it is the engine, not the carb, never a carb etc....

This is so wrong.
Click to expand...

What I mean by that. Is this won't be mathematical accurate just for e.g..

But say your engine is a 360 has a VE% of a 100% at all times (its a magical engine lol)
And makes peak power at 5300 rpm if you use that formula it will add all the intake strokes at 5300 rpm and give the total volume of air that engine will consume in 1 minute. CFM. Be about 550.

Now if you put a 390/550/650/750/850 carbs on that engine that vacuum will change for each one. Just a guess here but say 2"/1.5"/1.25"/1"/0.75" now if you test each one of those carbs at that vacuum level that carb would flow 550. So a 390 @2" = 550 cfm, [email protected]" = 550 cfm, [email protected]" = 550 cfm etc..
Now like I said those numbers are mathematical gibberish (didn't have time to throw everything into formulas so they would work out) but I think you can see my point. I bet if some one with a dyno test a bunch of carbs like that they prove what I'm saying.
 
I understand the above but the comment I mention above is miss leading and inaccurate.

I do get where your coming from.
 
The full quote would be
"any carb you put on that engine "would" technically becomes a 550 cfm carb"

I think i forgot the word "would" after engine.

I'm mildly dyslexic so I forget words and have bad sentence structure and spelling, take me forever plus I check it 20x and still it's f#$ked up lol
 
brian6pac said:
So what you are saying is the bigger the carb the more HP it will make?
Click to expand...

Another way to answer your question is YES to a point but it's really the opposite.

The more hp you make the larger the carb you need. Lot of people seem equate engine size with carb choice but it's really hp level.
Plus others like engine size, weight, gearing etc.. and application. But hp is the biggest factor.

Take a 300 hp engine no matter what cid flow about the same air.
Cid@rpm = cfm
225@7200 = 470
318@5100 = 470
360@4500 = 470
440@3700 = 470
So you could go 650 for each but depending on application like street or race car, weight, gearing, stall, cid, carb type etc... might step up 750 or down to 550 or somewhere in between.
 
273 said:
The more hp you make the larger the carb you need. Lot of people seem equate engine size with carb choice but it's really hp level.
Plus others like engine size, weight, gearing etc.. and application. But hp is the biggest factor.
Click to expand...
Unless you go pro charger, then you shrink the carb size as the HP goes up....
 
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