Carb size for stock 350? - Team Camaro Tech
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post #1 of 52 (permalink) Old Apr 5th, 15, 11:24 AM Thread Starter
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Carb size for stock 350?

Is has a correct Quadrajet on it now but I may be changing it to something newer. I was told it needs to be rebuilt and Id rather store it at the estimate I got. I was thinking of the Demon 650 elec choke and vac secondaries. What is the general rule on cfm size? I tried the cfm calculator but I don't have the data for the fields.
Cam is summit .465 intake .442 exhaust and I think 9.0-9.5 Pistons. Heads are 041 cast. Is 650 sufficient?

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.
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post #2 of 52 (permalink) Old Apr 5th, 15, 01:47 PM
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Re: Carb size for stock 350?

a 650 VS would be fine for a 350....but just a warning, Demon Carbs are wet flow rated Vs. Holleys dry flow rating
A Demon Tech once told me a 750 Mighty Demon (DP carb, which I run) would flow 900+ cfm on Holleys flow bench.

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post #3 of 52 (permalink) Old Apr 5th, 15, 02:09 PM
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Re: Carb size for stock 350?

A normal Q-jet is rated at 750 CFM.

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post #4 of 52 (permalink) Old Apr 5th, 15, 03:00 PM
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Re: Carb size for stock 350?

I have had several different Holley's on my 383ci SBC and for best overall drivability and ease of tuning I highly recommend a Holley 0-80783c 650CFM 4bbl. It comes with an electric choke, and is a vacuum secondary carb. I got one factory refurbished for under $300. Brand new they go for just over $400.

I got better performance from an HP series 750 4 corner idle but it was not easy to tune and gas mileage was not the best.

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post #5 of 52 (permalink) Old Apr 5th, 15, 04:02 PM Thread Starter
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Re: Carb size for stock 350?

1282010VE speed demon 650 elec choke vac second caught my eye. I will look into the Holley too. So if qjet is 750 then they should be pretty close I assume if Demons are more cfm than advertised?
I'm buying an intake with the carb. Would the Edelbrock rpm air gap work well with these carbs and my application?

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.
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post #6 of 52 (permalink) Old Apr 5th, 15, 04:39 PM
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Re: Carb size for stock 350?

I replaced a Holley 650 Double Pumper on my 350 with a Quickfuel 600 CFM with elec choke:


$320 from Summit and it is nearly bolt on and go. Very little adjustment needed and the 350 likes it.

Phil


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post #7 of 52 (permalink) Old Apr 5th, 15, 05:24 PM Thread Starter
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Re: Carb size for stock 350?

I see Road Demon 625 is about $175 less than speed demon 650. Would the road demon 625 be sufficient with a little room to spare? I need to read up on quick fuel too.

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.
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post #8 of 52 (permalink) Old Apr 5th, 15, 05:36 PM
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Smile Re: Carb size for stock 350?

Quote:
Originally Posted by TClovis View Post
1282010VE speed demon 650 elec choke vac second caught my eye. I will look into the Holley too. So if qjet is 750 then they should be pretty close I assume if Demons are more cfm than advertised?
NO ! The Quadrajet is a spread bore carburetor with small primaries and large secondaries.
A square bore carburetor like a Holley or a Demon have the same size primary's and secondaries.

A 750 cfm (square bore) is on the large side for a 350. Not if you use a quadrajet ! The small primaries give you the best response on the street and superior gas mileage !

The quadrajet (IMHO) is your best choice for engines of 350 cubic inches or less !

69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1
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post #9 of 52 (permalink) Old Apr 5th, 15, 05:41 PM
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Smile Re: Carb size for stock 350?




69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1
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post #10 of 52 (permalink) Old Apr 5th, 15, 06:21 PM Thread Starter
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Re: Carb size for stock 350?

Makes sense. However, I'm not looking at a 750 cfm unless the speed demon 650 is equivalent to a qjet 750? Are these equivalent? My car sputters when reved up and car keeps dying when I put in reverse unless it warms up a long time. I ran all new gas and it's still doing it. Timing made needs readjusting too.

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.
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post #11 of 52 (permalink) Old Apr 5th, 15, 08:55 PM
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Re: Carb size for stock 350?

If you need to adjust the timing etc then maybe it is not the carb? How much are they asking to rebuild?
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post #12 of 52 (permalink) Old Apr 5th, 15, 08:59 PM
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Smile Re: Carb size for stock 350?

The quadrajets primaries are even smaller than those of a 600 cfm carburetor. That is why it runs better on the street than any 650 ever will ! 90% of the time you only use the primaries ! When you go to full throttle your secondaries kick in and you can have up to 750 cfm. If your car was a drag only car, I would say go with a 750 Holley !

Save your money and rebuild that Quadrajet !

69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1
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post #13 of 52 (permalink) Old Apr 5th, 15, 09:17 PM Thread Starter
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Re: Carb size for stock 350?

Quote:
Originally Posted by bigblockragtop View Post
If you need to adjust the timing etc then maybe it is not the carb? How much are they asking to rebuild?
About $350-$375 to rebuild. It's not original to the car but correct model. For $450 the Road demon 625 can be had.

I mentioned timing earlier because of a little run on at shut off. However it was unknown if the old gas was a cause of this or timing. I think I ran out the old gas so tomorrow ill run it and see what happens.

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.

Last edited by TClovis; Apr 5th, 15 at 09:32 PM.
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post #14 of 52 (permalink) Old Apr 5th, 15, 09:29 PM
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Re: Carb size for stock 350?

Quote:
Originally Posted by TJS69 View Post
The quadrajets primaries are even smaller than those of a 600 cfm carburetor. That is why it runs better on the street than any 650 ever will ! 90% of the time you only use the primaries ! When you go to full throttle your secondaries kick in and you can have up to 750 cfm. If your car was a drag only car, I would say go with a 750 Holley !

Save your money and rebuild that Quadrajet !
Best advice you'll ever get regarding a carb for what you're doing.
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post #15 of 52 (permalink) Old Apr 5th, 15, 09:35 PM Thread Starter
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Re: Carb size for stock 350?

Yeah sounds that way. I hope timing and fresh gas fix my current issues then I don't have to rebuild it anyway.

1969 Camaro SS350, original motor/12 bolt/interior and build sheet in Fathom Green.
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