Is a 750 carb too big for a 327? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Spassmacher · 03-08-2012, 07:07 PM

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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ProStreet68SB · 03-08-2012, 07:07 PM

YES YES YES! It's way to big!

kriswvu1202 · 03-08-2012, 07:18 PM

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

ProStreet68SB · 03-08-2012, 08:15 PM

Quote:

Originally Posted by kriswvu1202

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.

SeventyOne · 03-09-2012, 02:08 PM

Quote:

Originally Posted by kriswvu1202

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.

GASoline71 · 03-09-2012, 05:42 AM

Find a Holley 1850 (600cfm).

You'll be very happy...

Gary

prostreetC-10 · 03-09-2012, 10:59 AM

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!

OC 72 · 03-09-2012, 11:52 AM

Absolutley! I had a 750 on my 327 hot rod...had it jetted down..still too much. Ran a 600cfm and worked perfect!

j1970GMC · 03-09-2012, 12:20 PM

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.

jhngardner367 · 03-09-2012, 03:04 PM

Where does the 3456 # come from?

SeventyOne · 03-09-2012, 03:18 PM

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?

SeventyOne · 03-09-2012, 03:44 PM

Good read on the explanation of the equation:

http://www.dragzine.com/tech-stories...e-combination/

wakeup · 03-10-2012, 07:56 AM

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!

03-08-2012, 07:07 PM	#1
Spassmacher Registered User Join Date: May 2011 Location: Portland, Oregon Posts: 26	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? Posted via Mobile Device

03-08-2012, 07:07 PM	#2
ProStreet68SB The Engine Whisperer Join Date: Sep 2006 Location: Ohio Posts: 770	Re: Is a 750 carb too big for a 327? YES YES YES! It's way to big!

03-08-2012, 07:18 PM	#3
kriswvu1202 Registered User Join Date: Sep 2011 Location: Morgantown, WV Posts: 111	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 __________________ "And when you discover what you will be in your life, set out to do it as if God Almighty called you at this particular moment in history to do it. Don't just set out to do a good job. Set out to do such a good job that the living, the dead or the unborn couldn't do it any better." -MLK

03-09-2012, 10:59 AM	#7
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	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! __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

03-09-2012, 11:52 AM	#8
OC 72 Registered User Join Date: Dec 2011 Location: CA Posts: 361	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!

03-09-2012, 12:20 PM	#9
j1970GMC Registered User Join Date: Aug 2010 Location: Northern CA Posts: 185	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.

03-09-2012, 03:04 PM	#10
jhngardner367 Registered User Join Date: Feb 2012 Location: Austin, Arkansas Posts: 248	Re: Is a 750 carb too big for a 327? Where does the 3456 # come from? __________________ Always expect the unexpected,....but don't expect the unexpected to be the unexpected you expect ! I'm busier than a one-legged cat,in a sandbox! Veteran..and proud ! I can't fix what ain't broke....you want I should break it?

03-09-2012, 03:18 PM	#11
SeventyOne Registered User Join Date: Mar 2007 Location: Oakland, Ca Posts: 1,382	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?

03-09-2012, 03:44 PM	#12
SeventyOne Registered User Join Date: Mar 2007 Location: Oakland, Ca Posts: 1,382	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/

03-10-2012, 07:56 AM	#13
wakeup Registered User Join Date: Mar 2012 Location: Havelock, NC Posts: 10	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! __________________ -1984 K10 Custom Deluxe 383, Turbo 400, NP208, 44/12 Bolt. 6/3 lift, 36 TSL's, In need of some TLC -1990 R20 Suburban 6.2, Turbo 400, Whatever came under the rear end. Totally stock, no rust, not pretty -2008 TrailBlazer SS, Stock since new, 3SS, All black, if you want it, let me know!

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