Aftermarket Carb / Intake Setup

I am thinking of putting on an after-market intake / carb. I currently have the stock intake and stock 2bbl carb. My engine has a bit more cam than the stock 304 V8, 9.0 to 1 compression, stock exhaust manifold, stock 3 speed and a free flowing exhaust.

I would like to put on an Edlebrock 2131 Intake:

"Edelbrock Performer intake manifolds are low-rise, dual-plane designs with patented runner tuning and a 180 degree firing order you won't find with the competition. This combination boosts torque over a wide rpm range, from idle to 5,500 rpm. These manifolds also deliver improved throttle response over stock intakes."

With a Holley 4bbl.

When I did the online Holley car selector it said the 390cfm 0-8007 with elec choke and vac secondaries would be good. Now, being the typical guy I always think bigger is better! I want to lean towards a 500 cfm carb.... Will the 390 cfm be good for my setup? What is the cfm on my stock Carter carb??

Oh, my Jeep is driven for fun only on the street. Thanks for the help!!!

 

I'm not a big fan of carburetors, but I would definitely go with the 470 CFM Truck Avenger (TA), rather than any 4150-style carb. You're asking for a lot of tuning, parts replacement and fiddling to make the Holley street carbs work on the trail.

http://www.holley.com/0-90470.asp

 

Thanks for the advice.... my Jeep is a "road only" Jeep so an offroad setup really is not that important.

What is the stock cfm on the Carter 2bbl??

 

Actually the TA470 IS a model 4150. The 4150 uses dual metering blocks with jets in both primary & secondary. IIRC the 8007 is a model 4160 which just has a metering plate on the rear (no changeable jets).

 

What is the stock CFM on my Carter carb? Am I being silly thinking 390 cfm is not enough?? I know 600cmf is way too much but I was thinking something in the 450 - 500cfm range would make sense... ??

 

Carter? The OEM carb on a 304 is a Motorcraft 2100.

You can only guess what the CFM rating of OEM carburetors is, unless you have a flow bench. The factory does not advertise that number like the aftermarket carb sellers do.

 

Ok, so I bought a Edelbrock 2131 intake and a Holly 0-8007 390 cfm 4 barrel.

The Holley has an electric choke. Is there a place on the fuse box that I can hook the connection up to? I need an 'ignition activated 12v source'.

 

The MC2100 1.08 version was 287cfm if this guy's info is correct:http://street2mud.com/webfiles/MC-2100 set up for a 258.pdf

 

You're going to wish you had gone with a bigger carb if you like to put your foot into it now and then.

Formula to calculate CFM requirements:

CID x RPM/3456 x VE% = CFM

Volumetric Efficiency (VE%) is the big variable here, but most stock engines will come in somewhere around 75-80%. Add headers, high-flow intake and some head work and you can get up to around 85-90% VE. High dollar race engines can range anywhere from 90-110%.

Most everything I've read on the subject recommends getting a carb with a CFM that's 130-140% of what your required CFM is to ensure you never starve the engine at high RPM's.

So plugging in our numbers and using 80% as the VE and a 5500rpm redline we get a CFM requirement of 378cfm. (VE of 100% = 483cfm) Now add in the safety factor (multiply by 1.3) and you get 491cfm. So theoretically a 500cfm carb would be ideal for a relatively stock/slightly modified 304.

Here's the other thing to consider....

Even though a 600 or 650cfm carb is more than a 304 needs, a larger carb can always be jetted down to work properly with a smaller engine. The opposite isn't true with a smaller carb as the venturi's are to small to allow adequate air intake.

The old Quadrajet carbs are a perfect example of this thinking. While only offered in 750 and 850cfm sizes, they were factory installed on everything from small 231 V6's to big-block V8's.

 

The Holley has an electric choke. Is there a place on the fuse box that I can hook the connection up to? I need an 'ignition activated 12v source'.

 

As far as the question about where to hook up the choke wire... does your '74 have a fuse box?
It should NOT if its still factory.

(Trick question)

 

Ha! Sorry for the trick question

So the best place to hook the electric choke up to would be the coil ?

 

^I agree, the draw of the electric choke could be enough to reduce power at the coil. I would run it off the 12V acc terminal at the ignition switch.

 

I agree with this 100%. Yes you can dial in a too big carb and it will run-usually richer than optimum but run-and since the vacuum response is muted, you should expect to "redial" it in every several thousand feet of elevation change. If your wheelin is elevation constrained, there may be little detrimental effect other than less than optimum mileage. On the other hand, if your wheeling spans 5000' or so, as it does in much of the west, you are going to have problems. It will be way too rich at high elevation.

Too small can certainly also be a problem and I have gotten better mileage out of several engines going from a 2bbl to 4bbl. A lot will depend on driving style: do you tend to hit high rpm's often? I don't and factoring a 30% "safety factor" is ridiculous. I think you will be very satisfied with the 390.