500 cfm too small?
Thread Starter
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Freshman User
Joined: Jan 2013
Posts: 27
Likes: 0
From: Compton,California
500 cfm too small?
Im currently running a 500 cfm edelbrock carb. But im wondering if its too small? Here are my engine specs.what do you guys recommend?
390 bored over 30
Comp cams 270 magnum cam
Msd ready to run dizzy
Hooker headers
performer intake
Slightly ported c8AE-H heads
10.4 compression
3:50 posi
stock c6 and convertor
This is my weekend only hot rod truck so fuel economy is not a concern
390 bored over 30
Comp cams 270 magnum cam
Msd ready to run dizzy
Hooker headers
performer intake
Slightly ported c8AE-H heads
10.4 compression
3:50 posi
stock c6 and convertor
This is my weekend only hot rod truck so fuel economy is not a concern
Senior User
Joined: Jun 2007
Posts: 218
Likes: 0
From: Colorado
I have a 570 on my 416 . Find a CFM formula . Unless you are running 8,000 RPM and perfect engine . You might be surprised .
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
600 cfm is more than enough for your motor, on a mildly built street 390 a 600 will have better low end response, and fuel mileage then the 750.
The trick is to tune the carb to the motor, it's not that hard to do... if you're not racing you will never use all the flow that the 750 has.
Most guys make the mistake of "over carbing", don't be that guy.
The trick is to tune the carb to the motor, it's not that hard to do... if you're not racing you will never use all the flow that the 750 has.
Most guys make the mistake of "over carbing", don't be that guy.
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Fleet Owner
Joined: Dec 2009
Posts: 20,678
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From: NorCal
Dunno yet.. 'haven't installed it yet. I'll let ya know.
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Save the old ones
Joined: Dec 2002
Posts: 666
Likes: 4
From: Boyne Mich
Yeah, find a CFM formula or calculator and you'll be surprised how little is required.
But I think 500 on a nearly 400 CID is on the small side.
I put a 625 cfm on a 351W with aluminum heads, planning 5500 rpm. So far I've only broke in the cam and haven't really driven it yet.
I had a 750 double pump, mech sec. On a Windsor, 400 and a 460. Great carb. But Very thirsty.
But I think 500 on a nearly 400 CID is on the small side.
I put a 625 cfm on a 351W with aluminum heads, planning 5500 rpm. So far I've only broke in the cam and haven't really driven it yet.
I had a 750 double pump, mech sec. On a Windsor, 400 and a 460. Great carb. But Very thirsty.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
To the OP,
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Senior User
Joined: Jul 2011
Posts: 270
Likes: 0
From: North West
To the OP,
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Cool link thanks
Thread Starter
|
Freshman User
Joined: Jan 2013
Posts: 27
Likes: 0
From: Compton,California
To the OP,
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Holley has an interactive carb sizing calculator. Follow the prompts based on your engine and it'll provide recommendations.
I went through it for your rig (with some assumptions like 5500 max RPM, about 396 cubes, and vacuum secondaries given these rigs' portly weight) and the results indicate 600 cfm would be the minimum.
Here. Give 'er a try: Holley Interactive Carburetor Selector
Junior User
Joined: Jul 2012
Posts: 96
Likes: 0
From: Monticello, Arkansas
Some formula I read about a long time ago... Not sure if it is accurate or not.
Find the displacement first.
390 bored .030 over. Stock 390 - 390 bore 4.052 in stroke 3.784 in
Bore squared - 4.082^2 = 16.663 then multiplied by the stroke - 3.784 = 63.052 then multiplied by .7854 = 49.52 times the number of cylinders (8) =
396.2 cubic inches.
Take your cubic inch and convert it into cubic feet. Divide by 1728.
396.2 / 1728 = 0.229
Then reduce that number by half because the crank turns over twice to fire all of the cylinders.
0.229/2 = 0.1146
Then multiply that by the maximum RPM you want to run.
0.1146 x 5500 = 630.52 CFM.
So you would need no less than a 630.52 CFM carb.
Hope this helps you some.
Find the displacement first.
390 bored .030 over. Stock 390 - 390 bore 4.052 in stroke 3.784 in
Bore squared - 4.082^2 = 16.663 then multiplied by the stroke - 3.784 = 63.052 then multiplied by .7854 = 49.52 times the number of cylinders (8) =
396.2 cubic inches.
Take your cubic inch and convert it into cubic feet. Divide by 1728.
396.2 / 1728 = 0.229
Then reduce that number by half because the crank turns over twice to fire all of the cylinders.
0.229/2 = 0.1146
Then multiply that by the maximum RPM you want to run.
0.1146 x 5500 = 630.52 CFM.
So you would need no less than a 630.52 CFM carb.
Hope this helps you some.