Which carb should I run? - Team Camaro Tech
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post #1 of 11 (permalink) Old Aug 28th, 08, 02:01 PM Thread Starter
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Which carb should I run?

I hope some of you carburetor guys will chime in here and give me a hand.
I currently have a 408 SBC, with a TH350, and 3.73 gears. Right now I have a brand new Holley 650 DP on the motor. Should I be using a a 750 vac. secondary carburetor?

Here is my cam specs if it matters.
Adv. Duration: 290°/280°
Gross Lift: .489''/.520''
RPM Range: 2500-6200

As always Thank you for the help!!!

1969 Camaro


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post #2 of 11 (permalink) Old Aug 28th, 08, 03:36 PM
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Re: Which carb should I run?

at least a 750
650 is too small


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post #3 of 11 (permalink) Old Aug 28th, 08, 04:42 PM Thread Starter
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Re: Which carb should I run?

Dawg, why did I know someone was going to say that.

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post #4 of 11 (permalink) Old Aug 28th, 08, 10:53 PM
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Re: Which carb should I run?

I just put a 700 double pumper on my 388 and runs great. I had the same debate and went in the middle. I don't think a 750 vac secondary would run any better than the 650 double pumper.


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post #5 of 11 (permalink) Old Aug 28th, 08, 10:59 PM
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Re: Which carb should I run?

Personally I would run as big a double pumper as it will handle!
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post #6 of 11 (permalink) Old Aug 29th, 08, 07:01 AM Thread Starter
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Re: Which carb should I run?

What about using a Holley or Proform body to convert my 650 DP over to a 750 DP. I really don't want to spend another $400 - $500 on a carb right now.

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post #7 of 11 (permalink) Old Aug 29th, 08, 08:15 AM
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Re: Which carb should I run?

I have run a 650 double pumper )list 4777 I think?) on a 406, and it worked great.
Motor was set up for midrange grunt, but it ran 108 in the qtr with no traction at all.





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post #8 of 11 (permalink) Old Aug 29th, 08, 10:15 AM
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Re: Which carb should I run?

You didn't say what the intended use of your vehicle is. That really determines if a Vac secondary Carb is in order. If it is a street car it really should be using vac secondaries. You really give up a lot of driveability, gas mileage and responsiveness without vac secondaries. Plus you are not spending most of your time at WOT which is really what a double pumper is about. Also automatics tend to benefit more from vac secondaries and manuals mechanical secondaries.

Check out this tool:
http://www.holley.com/applications/C...bSelection.asp

This is even Holly's take on the matter:





It would seem this tool recommends a 750cfm carb for your application (assuming street and mildly modified).

This is also a good reference:
http://www.holley.com/data/TechServi...Carburetor.pdf

Which seems to indicate about a 700cfm carb at 100% VE but if you plug in 85%, a 600-650cfm carb would probably work. If anything I would go one size too small for a street car, give you a little better responsiveness and better gas mileage. Everyone tends to over-carb their street engines.

Ed

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post #9 of 11 (permalink) Old Aug 29th, 08, 07:41 PM Thread Starter
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Re: Which carb should I run?

Thank you guys for the info. The car is just a street car. So it looks like I need to go with vac. secondaries. Will the car still get up and go with vac. sec, or will it be a gutless pig.

I have a 750 Holley with vac. secondaries, but it has a Proform main body, and it has been converted to a metering block in the rear. Do you guys think this will be to much carb for my motor.

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post #10 of 11 (permalink) Old Aug 29th, 08, 07:50 PM
 
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Re: Which carb should I run?

a 750 is perfect for a street 406,also don't think a double pumper doesn't work for a street motor.
vacuum secondaries are for motor homes
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post #11 of 11 (permalink) Old Aug 29th, 08, 08:05 PM Thread Starter
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Re: Which carb should I run?

So a 750 DP will work okay for a street car with a auto transmission.

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