Is my Carb too small or too big? - Team Camaro Tech
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post #1 of 11 (permalink) Old Mar 12th, 00, 10:16 AM Thread Starter
 
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I have a 350 Chevy crate motor in my Camaro. I have a Crane Cam (282 470) with Edelbrock Performer Intake and Dynomax headers. Right now I am running a Holley 4150 650cfm double pump carb. I am not getting the power I think I should and I am getting conflicting stories from people. Some say the Holley is too small and some say I need a smaller cfm and dump the double pump. I am looking at an Edelbrock 600 cfm. Any advice? Anything would be appreciated.
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post #2 of 11 (permalink) Old Mar 12th, 00, 11:26 AM
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What is the list number on your carb. At one point it seems you are saying you have a double pumper and the next it seems like you say you need one. What gearing do you have, what is the stall of your converter, have you gone through your distributor or is it stock?

Steve R.
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post #3 of 11 (permalink) Old Mar 12th, 00, 12:06 PM Thread Starter
 
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The only number I know about the carb is it is a Holley 4150. I have put a new Accel coil and wires and had the distributor rebuilt. I put an adjustable vacuum on it also. I currently have a double pump and some people say it is too much. Do I keep it or get a smaller cfm single pump?
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post #4 of 11 (permalink) Old Mar 12th, 00, 05:21 PM
 
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How does the car run.You talk about the power?
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post #5 of 11 (permalink) Old Mar 13th, 00, 03:03 AM
 
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Under-sized, or more correctly under-jetted carbs, will usually surge at mid throttle. My personal experience is going down the road at around 40 to 45 and feeling surge.

A vacuum secondary will kick in when the motor needs the extra fuel, which might be before the mechanical linkage of a double pumper would open the secondaries. This would give you the feel of more power when you need it. You can test this by standing on the throttle with your double pumper at different times - if you get on it enough to mechanically open the secondaries (and don't have a huge bog - but that another dicussion) you should feel the power you are looking for. If this is true, the vac sec. should help allot.

good luck
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post #6 of 11 (permalink) Old Mar 13th, 00, 07:12 AM
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Your carb is the right size. 4150 is little help, all it means is the carb has a full metering body on the primaries, and a metering plate on the secondaries. Double pumpers can work OK on the street, see some of the other posts on this subject. I think some fine tuning is in order to give you the power/response you're looking for. Best bet would be a dyno tune. Expensive but worth it unless you want to play with timing, jets, and power valves.



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post #7 of 11 (permalink) Old Mar 13th, 00, 05:24 PM
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Dave
 
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4150 have primary and secondary metering block. 4160s have a secondary metering plate. I agree with above post proper tuning is probably all that is required.

[This message has been edited by snakedr (edited 03-13-2000).]
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post #8 of 11 (permalink) Old Mar 14th, 00, 01:54 AM
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i'm sure most of you already know this, but here is a formula i use to check what size carb you need.
CID x RPM x V.E./2820 = CFM
V.E. = .9
so if you have a true 350 and will take it to 6000 rpm's x .9/2820 = 670cfm's.
hope this helps,
bruce

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post #9 of 11 (permalink) Old Mar 15th, 00, 07:53 AM
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Gene
 
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I have a 350 (started out as a ZZ3 crate motor) with a COMP 274, Torker II intake, and a 650 dp. I agree with everyone else, it's in the tuning. I got 360 hp from the engine with this set-up naturally asperated and over 500hp with a supercharger.

rrent, a vacuum secondary card will almost never kick in as fast as a double pumper. I can punch the throttle at idle (900 RPMs) and open all four barrels all the way. The typical secondary spring won't begin to open the secondary throttle blade until around 1,600 RPMs. BUT, you are correct that the engine may not need all of that air and it takes major tuning to get the dp working right.

------------------
Hugger Orange & white 69 Camaro with supercharged 350, Tremec TKO, and 3.73 12-bolt
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post #10 of 11 (permalink) Old Mar 15th, 00, 09:29 AM Thread Starter
 
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Thakns everyone! I am going to take my car to a place called Chassis Dyno down the street from my house and let them do teh tuning on the carb! Thanks so much for all of the input!!!
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post #11 of 11 (permalink) Old Mar 15th, 00, 03:09 PM
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Bruce69-

My Holley manual has the formula CID*MaxRPM*VE/3456

How did you derive your formula?

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To see a picture of my car http://www.geocities.com/casanoc
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