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Old 01-19-2009, 09:00 PM
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650 cfm for a 454

OK i have a 454 BBC and i was wondering if i could use my edelbrock 650 cfm carb till i got enough money to buy a bigger one? thanks

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Old 01-19-2009, 09:14 PM
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Yes it will work. Matter fact you will like the 650 better for the street over the bigger carb. I referred 650 for more torque over the bigger carb.
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Old 01-19-2009, 09:20 PM
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ok sweet, ya its not going on anything to powerful i just added a mild cam. its going in a pick-up btw
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Old 01-19-2009, 10:06 PM
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Here's a formula for determining CFM requirements ... from Holley's website . (First in the list of FAQ's)

Quote:
QUESTION How do I tell what size carb I need?
ANSWER You take the engine cubic inch and multiply by the maximum RPM and divide by 3456. If you have an automatic transmission you will need a vacuum sec. carb, a standard transmission can use a Double Pumper carb.
So let's work that out ... (assuming a 5500 RPM redline)
(CID x MaxRPM) / 3456 = CFM
(454 x 5500) / 3456 = 722

Manipulating the formula mathematically ... we should be able to determine the max RPM (under ideal conditions) for a 650 CFM carb

MaxRPM = (CFM x 3456) / CID
MaxRPM = (650 x 3456) / 454
Max RPM = 4948

Those RATS just gotta breathe! LOL
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Old 01-19-2009, 10:19 PM
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WOW!!! that really really helps i honestly took notes on that lol. so would i have to turn the carb up high to let it breath better
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Old 01-19-2009, 10:46 PM
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Quote:
Originally Posted by redneck_9018
WOW!!! that really really helps i honestly took notes on that lol. so would i have to turn the carb up high to let it breath better
I don't know what you mean by turn the carb up high, but I think you do not understand the fundamentals of a carburetor and how flow is measured.

A four-barrel carburetor is manufactured with a certain size throttle bore, throttle plates and venturi at the factory. It is then flowed by hooking the air source to a manometer, a U-shaped tube with mercury in it. The flow through the carburetor venturi and throttle bore is measured when the air has pulled the mercury up into the manometer by 1.5 inches. The only way you can change the CFM of the carburetor after that is by physically altering the throttle bore or venturi bore so that more or less air flow through the carburetor is required to move the mercury up in the manometer tube by 1.5 inches.

If you need more or less airflow for a given application, you simply purchase a different carburetor that flows more or less than the one you are currently using.

There are people who alter carburetors for more flow, but that knowledge is way down the road for you. You just need to know that a different rated carb is what you need to do for now.

I'll give you my take on sizing a carb for a 350 Chevy. A 600 CFM will do a great job on a daily driver, providing good throttle response and reasonable mileage. It will not, however, allow max horsepower out of the motor. For that, you need to bolt on a 750. It's the same formula used for max output on any motor, cubic inches times 2.0-2.2.

Just to help confuse you a little further, cylinder head intake and exhaust runners are measured the same way, with a manometer and U-shaped tube, but instead of mercury, a column of water is used. When the air being pulled through the port pulls on the water enough to make it rise 28 inches in the manometer tube, the CFM is noted and that's the CFM rating of that particular port. Readings are normally taken with the valve off its seat by certain amounts, usually 0.100", 0.200", 0.300" 0.400", 0.500", 0.550", 0.600", 0.650" and 0.700".

Oh yeah, and another ringer. Two-barrel carburetors are measured at 3.0 inches of mercury.

Isn't learning new stuff fun??

Last edited by techinspector1; 01-19-2009 at 11:25 PM.
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Old 01-20-2009, 09:41 AM
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It's important to remember that a carburetor's cfm rating is at a particular pressure drop, and they will flow more or less air than their ratings at different pressure drops.

Probably the best way to describe it is to imagine your engine is breathing through the carburetor like you're breathing through a straw. The straw might be big enough to give you all the air you need when you're relaxed, but if you start working or exercising you have to suck harder through the straw to get the air. Just when you really need the extra air for your body to perform your work, you have to put in extra effort on top of that to suck in the extra air.

When talking about your engine, the pressure drop shows how hard your engine is working to get its air. As techinspector1 said, 2bbl carbs are rated at 3 inches of vacuum. 4 bbl carbs are rated at 1.5 inches.

There has to be some vacuum or else air won't go from outside your engine into it. If your 4bbl carb is the right size, it'll give your engine all the air it needs at a low vacuum level. If your carb is too small, it'll still give your engine all the air it needs but your engine is going to have to work harder to get it. So that 650 cfm carb can flow 722 cfm if that's what your engine needs, but it'll cost you some HP. And you won't see a vacuum reading as low as 1.5". It'll be higher. If it's 3" of vacuum, that means your engine is sucking over 900cfm through that 650cfm-rated carb (just like there are formulas to tell you how big your carb should be, there are formulas to tell you how much air a carb will flow at different pressure drops). And using up some HP that to get it.

The OEMs used both bigger & smaller carbs than the formulas would make you think they'd use. If they thought the engine was going to be raced in a class that required the stock carb, they'd put a big carb on it. Otherwise, they'd use a smaller one. Ford used a 600cfm carb on the 460. It gave really good throttle response. It just cost some HP at higher rpms.

The bottom line is the 650 will work fine. Later if you modify your 454 to improve performance, and drive your car like a performance vehicle, you'll want to move up to a bigger carb.
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Old 01-20-2009, 01:03 PM
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As the other posters mentioned, it really depends on the demands of your engine. If this is going in a truck that won't see much over 4500 RPM and will live 99% of its life between 1000 and 3000 RPM a 650 is a great choice.

I agree with techinspector about carb fundamentals. You can adjust the amount of fuel your carburetor disburses, but not (easily) the amount of air. You can bolt a carburetor which is "too small" for your motor, and still have it run rich!

K
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Old 01-20-2009, 04:22 PM
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wow ok ya i kinda had a major brain fart about the air flow. i just barely learned about them in school, and all the fun stuff that goes with them. thanks alot guys. is there any speacial things i need to know about tuning the air/fuel?

Last edited by redneck_9018; 01-20-2009 at 04:28 PM.
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Old 01-20-2009, 04:47 PM
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If you don't have the paperwork that went with the carb, I think the first thing you should do is go to the Edelbrock website & download or print off the tuning guide. You have a 650cfm carb, so that would be one of the Thunder series AVS carbs.
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Old 01-20-2009, 04:50 PM
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ok sounds good thanks alot guys
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Old 01-20-2009, 07:50 PM
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Redneck---
Just noticed you live just up the road from my mom and sister.
They're in I.F.

I grew up in Blackfoot
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Old 01-20-2009, 07:55 PM
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o ya thats sweet, i didnt think anyone would know where this small town is, ha ha
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Old 01-21-2009, 12:59 AM
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http://www.edelbrock.com/automotive_...ers_manual.pdf
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