what would you do?
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Senior User
Joined: Oct 2006
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From: las vegas
what would you do?
Hey folks, I have a 72 f100 that the PO placed a 351w in. I am going to keep it cuz it works. Just looking for a lil fun hop up. Would you guys look at pulling the stock 2 brl carb and intake. Replace with a 4 brl set up. Or, just replace the stock 2 brl autolite with a 2brl 500 cfm Holley (or other brand). Do you guys think there is a big difference between the two setups. Looking foward to the opinions to follow.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
IMO.. changing the carb and/or intake won't make any real difference unless the motor is allowed to flow more air and take advantage of the "better" induction. If this is an all stock 351 start with a cam, there's loads of power just dying to get out.
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Senior User
Joined: Oct 2006
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From: las vegas
Are they hard to install? Do I need to pull the engine?
Lead Driver
Joined: Aug 2003
Posts: 6,305
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From: Boulder Creek, Ca
Drove 65 F100 w/ 302ci for some 30 yrs. and found it had all the pick up and pep ever needed. Had engine rebuild few years back and decided to swap to a 4bbl carb and had cam installed. Now wish I kept the 2bbl., feel the pick up and performance is lacking, and rarely, if ever, does it get into the secondaries. Not an authority, perhaps not the best axle ratio, and tranny, only aware with the same combination with the 2bbl had better performance. IMHO, the 2bbl for a small block V8 installed in a truck is an ideal combination. As noted, a novice but found the Holley a good carb and relatively easy to rebuild.
Hotshot
Joined: Mar 2007
Posts: 10,101
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From: Pa
I would rebuild the stock carb or put on an aftermarket carb. Get the choke, fast idle, mixture and etc dialed in and run it. I'm getting ready to rebuild the 2100 on my 74' 302. I would like to do a small 4bbl, new intake manifold, cam, lifters and etc but can't see spending the money on a 35YO motor w/80k miles on it that isn't my daily driver. Make shure the motor is running up to its potential and have fun.
Elder User
Joined: Jan 2009
Posts: 774
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From: East Tennessee
Never thought much about a 4 bbl being bad for a truck, but makes sense, because you'd have to give it enough throttle to open the secondaries all the time. Would just depend on the style of the carburetor.
And since you didn't say anything about tearing into the engine, look at some headers and duals.
I'm curious to see what the best carb would be for this truck. What's the weight on those trucks?
And since you didn't say anything about tearing into the engine, look at some headers and duals.
I'm curious to see what the best carb would be for this truck. What's the weight on those trucks?
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Senior User
Joined: Oct 2006
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From: las vegas
I guess it is all a matter of trial and error. But it seems that cheapest and easiest is to use the aftermarket holley 2 brl. Do you guys think 500 cfm is too much?
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Lead Driver
Joined: Aug 2003
Posts: 6,305
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From: Boulder Creek, Ca
If you feel comfortable with rebuilding the Autolite at cost of around $45, not familiar with the carb so not whether the Carb is worth the money and time. Not an authority, 350 CFM would probably be pushing the margin, 500 CFM might be a bit much but as 'freakshow' mentioned if tuned and adjusted well may be ok. Not familiar with the Holley remanufactured carbs, see they can run anywhere from $175 to $500. Posting link to article in 'Classic Truck Magazine' not sure if info will be of much help. Also, seem to recall, Holley's website use to have a CFM calibrater to determine the correct carb. Imagine the carb supplier decide on may be able to advise.
Choosing The Right Carburetor - Tech Articles - Classic Trucks Magazine
Choosing The Right Carburetor - Tech Articles - Classic Trucks Magazine
Hotshot
Joined: Mar 2007
Posts: 10,101
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From: Pa
A set of long tube headers and a good exhaust will help quite a bit. I put headers and dual exhaust on my 302 and it helped in the power dept. Just make shure you size everything right. For a 2bbl 351 I would get headers with fairly small 1.5"-1.625" primaries with a 2.5" collector. Exhaustwise 2" or 2 1/4" duals out the back.
Elder User
Joined: May 2008
Posts: 508
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From: Wasilla, AK
Did a quick calculation using your specs of: 351 ci engine running stock cam at a max of 5500 rpm. The max flow is around 448 cfm. I would agree with the other folks in saying, with a good set of headers and exhaust and replacing the carb with a 500 cfm Holley (I don't feel it is too big) you will see a marked improvement in performance while maintaining a resonable mpg. You might even improve the gas mileage? I didn't see if you are running and AT or a standard transmission, but if your running an AT make sure your new carb has the Ford Transmission Kickdown Lever on it! Get the engine breathing then, if you're not already running one, put a good electronic distributer/ignition in it or at least convert the old point style dizzy over to electronic (Pertronics type). These are fairly cheap bolt-ons for the power gains.
Tim
Tim