Carb size for 390??
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Postmaster
Joined: Oct 2005
Posts: 3,083
Likes: 4
From: Victoria , BC
Carb size for 390??
I see alot of guys run a 600 carb for a 390 , I got rid of my 600 in order to replace it with a 650 Edelbrock. So my question is what is the best size carb for these motors? I'm looking for bottom end torque for 44" tires I'm running..
My build:
edelbrock performer intake
rebuilt stock heads
30 over forged pistons
headers
343941 crane cam,matching springs
msd ignition box/crane cam electronic ignition,msd 8.5 wires
oil mods,melling high volume pump,new hex shaft
9:5 compression
My build:
edelbrock performer intake
rebuilt stock heads
30 over forged pistons
headers
343941 crane cam,matching springs
msd ignition box/crane cam electronic ignition,msd 8.5 wires
oil mods,melling high volume pump,new hex shaft
9:5 compression
Posting Guru
Joined: Jul 2003
Posts: 1,287
Likes: 3
I see alot of guys run a 600 carb for a 390 , I got rid of my 600 in order to replace it with a 650 Edelbrock. So my question is what is the best size carb for these motors? I'm looking for bottom end torque for 44" tires I'm running..
My build:
edelbrock performer intake
rebuilt stock heads
30 over forged pistons
headers
343941 crane cam,matching springs
msd ignition box/crane cam electronic ignition,msd 8.5 wires
oil mods,melling high volume pump,new hex shaft
9:5 compression
My build:
edelbrock performer intake
rebuilt stock heads
30 over forged pistons
headers
343941 crane cam,matching springs
msd ignition box/crane cam electronic ignition,msd 8.5 wires
oil mods,melling high volume pump,new hex shaft
9:5 compression
Posting Guru
Joined: Jul 2003
Posts: 1,287
Likes: 3
If your vehicle is a race car, turn high rpm, has good heads, headers, low gears, etc. etc. then a 750 cfm carb might be just what you want. I use a 850 cfm Holley carb on my Falcon, but I took it up to 7000 rpm when I raced it years ago. Years ago I had a 600cfm holley on my street 1966 Fairlane that had a 427 engine in it. Throttle response was very quick. It is a normal practice to have to large a carburetor on engines.
If your vehicle is a stock daily driver, seeing lower rpms, then the 600 is more than enough.
If your vehicle is a stock daily driver, seeing lower rpms, then the 600 is more than enough.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
We have a perception in this country that bigger is always better. Doesn't matter if the tail pipe is very sooty and reeks of unburnt gas that was dumped out on the road because the engine couldn't handle it.
FEs can run quite well with smaller than 600 cfm carbs too.
John
FEs can run quite well with smaller than 600 cfm carbs too.
John
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Look here for carb info. These guys know what they are talking about.
Holley Performance Products Frequently Asked Questions
Remember they are talking cars with this recommendation. Trucks, unless built to race never need a double pumper.
Holley Performance Products Frequently Asked Questions
Remember they are talking cars with this recommendation. Trucks, unless built to race never need a double pumper.
Post Fiend
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From: Big Sky Country
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Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Unless you are running your motor to 6500 rpm regularly you don't need a 750 CFM. 6000 rpm only requires a 700 CFM and a more reasonable 5500 rpm only needs 625 CFM carb. 5000 rpm needs 565 CFM in a carb. You need to be realistic when choosing a carb. Even though a vacuum secondary carb is forgiving in that it will open the secondaries only as far as then engine requires and limits the carbs CFM that way. Unless you do a dyno run and actually see the secondaries open all the way, chances are with a 750 on a stock to mild 390 you are over carburated. For normal driving and the part time racer, not a race only machine, you are better off slightly under carbed than over carbed. Better bottom end and throttle response and fuel economy.
Senior User
Joined: Feb 2008
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The old TQ's used on Mopars were 800 and 850 CFM. The trick was that the primaries were small and the secondaries were huge. The air door is what modulated the secondaries; they had to be set up properly and not fudged with. I have one in my '69 Valiant that has a moderately built 340 (the 800 CFM version; 850 was for BB & RBs') and it can pull very good mileage if you can stay out of it. I always have one guy dial in my carbs and never have been disappointed- Roger goes as far as to use a tailpipe sniffer to help calibrate each one. Yup, he'll be doing my 410 when it drops between the frame rails,too
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