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Old 03-08-2012, 07:07 PM   #1
Spassmacher
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Is a 750 carb too big for a 327?

There's a good price on Edelbrock 1407 Performer series 750 cfm carb right now, but I was wondering if it's too big for my 327. I went the Vortec route w/ appropriate Edelbrock intake. I don't have the specs on my engine on me, but it's built up pretty well. I hear different things about whether 750 is too big for a 327, but i think I'm up over 400hp (if only barely) with my setup. What has been your guys' experience with this?
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Old 03-08-2012, 07:07 PM   #2
ProStreet68SB
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Re: Is a 750 carb too big for a 327?

YES YES YES! It's way to big!
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Old 03-08-2012, 07:18 PM   #3
kriswvu1202
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Re: Is a 750 carb too big for a 327?

The way to accurately size a carburetor for an aplication is to take the cubic inches divided by 2 multiplied by the maximum RPM over 1,728. (327/2 x 6,500/1,728) = 615.017. The biggest carb your engine will need is a 650 cfm, and unless you plan on running wide open, high rpm all the time, a 600 cfm will be plenty. Plus, with a smaller carb, the throttle response is much better. The P.O. of my truck put a 750 cfm Edelbrock on the original 307. It ran fine, but was an absolute dog when you put your foot in it. Just bogged and accelerated lazily. I switched to a 600 cfm Holley and the difference was like night and day. Much crisper and when you stomp it, it goes right now...That said, I have a nice 750 cfm Edelbrock performer I'll sell you cheap. HAHA
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Old 03-08-2012, 08:15 PM   #4
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Re: Is a 750 carb too big for a 327?

Quote:
Originally Posted by kriswvu1202 View Post
The way to accurately size a carburetor for an aplication is to take the cubic inches divided by 2 multiplied by the maximum RPM over 1,728. (327/2 x 6,500/1,728) = 615.017. The biggest carb your engine will need is a 650 cfm, and unless you plan on running wide open, high rpm all the time, a 600 cfm will be plenty. Plus, with a smaller carb, the throttle response is much better. The P.O. of my truck put a 750 cfm Edelbrock on the original 307. It ran fine, but was an absolute dog when you put your foot in it. Just bogged and accelerated lazily. I switched to a 600 cfm Holley and the difference was like night and day. Much crisper and when you stomp it, it goes right now...That said, I have a nice 750 cfm Edelbrock performer I'll sell you cheap. HAHA
That is all very true. Also remember that equation is designed for motors that are 100% volumetric efficient. Most street motors are lucky to be around the 80% range.
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Old 03-09-2012, 05:42 AM   #5
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Re: Is a 750 carb too big for a 327?

Find a Holley 1850 (600cfm).

You'll be very happy...

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Old 03-09-2012, 10:59 AM   #6
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Re: Is a 750 carb too big for a 327?

Agree with the above. Just remember the cfm calculator is just to get you into the ball park. There are a lot of variables in correctly picking the right carb though. 400hp is a lot of HP out of a 327. The Corvette 375hp 327 L84 was a nasty motor. You would have to have some pretty serious compontent to be in that range with a compression that is almost not streetable. How do you arrive at the 400 HP? Cool thing about a well built 327 is you can pull those rpms to the moon!
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Old 03-09-2012, 11:52 AM   #7
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Re: Is a 750 carb too big for a 327?

Absolutley! I had a 750 on my 327 hot rod...had it jetted down..still too much. Ran a 600cfm and worked perfect!
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Old 03-09-2012, 12:20 PM   #8
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Re: Is a 750 carb too big for a 327?

I think a 750 is too big. I have a David Vizard book that talks about a 750 on a small block, but it's really complicated, and he's building efficient, powerful engines. I didn't go that route because I'm not David Vizard.

I had an 750 Edelbrock 1411 on my 350. Ran like a pig but with a lean feeling spot when the secondaries opened. Jetted it with a calibration kit and no better. Talked to Edelbrock and they said that if I could make it work then I should call them to let them know how I did it (they were NOT rude, in fact they had excellent customer service). I switched to a Holley 670 Street Avenger I bought from a friend (which I think is actually more like a 600, per my conversation with the Holley tech) and it runs great.

I have an Edelbrock 1406 (600cfm) on my 327 and it runs great and still seems a little rich to me, although I have not tried to jet it yet so I could be wrong.
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Old 03-09-2012, 02:08 PM   #9
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Re: Is a 750 carb too big for a 327?

Quote:
Originally Posted by kriswvu1202 View Post
The way to accurately size a carburetor for an aplication is to take the cubic inches divided by 2 multiplied by the maximum RPM over 1,728. (327/2 x 6,500/1,728) = 615.017.
Your equation is technically right, but you're doing way too much math.

327 x 6500 / 3456 = 615.017

CID x Max RPM / 3456 = CFM

No need for that extra division by 2.
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Old 03-09-2012, 03:04 PM   #10
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Re: Is a 750 carb too big for a 327?

Where does the 3456 # come from?
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Old 03-09-2012, 03:18 PM   #11
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Re: Is a 750 carb too big for a 327?

Well like I just simplified the equation posted above, I am sure the 3456 is some formulation of air volumetrics, x Pi x the moons gravitational pull, etc, simplified down to a simple number...being 3456.

I have also seen the equation with an additional step...multiplying by a coefficient of efficiency. Most carbs/setups being only 85% efficient so you would then multiply the 615.xx cfm by .85 to give you a closer number.

Racing setups or blown applications might raise the coefficient to 1.1. 615.xx cfm x 1.1.

But it won't REALLY matter. just leave that step out and you're in the ballpark. It's not like someone actually makes a carb that fits your equation number EXACTLY...I mean can you go out and buy a 522.xx cfm or 676.xx carb?
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Old 03-09-2012, 03:44 PM   #12
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Re: Is a 750 carb too big for a 327?

Good read on the explanation of the equation:

http://www.dragzine.com/tech-stories...e-combination/
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Old 03-10-2012, 07:56 AM   #13
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Re: Is a 750 carb too big for a 327?

I agree with most of the others above, it's probably more than that engine needs.

I've got a Edelbrock 1406 (600cfm) on my 383 and it turns 6000 rpm and feels strong!
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