Carb Tech

[SNL62]

Not much experience w/the "detuned" '73 351C 2BBL. Not really wanting to "rip it up" for a complete remod/rebuild. Was wondering though, any idea on performance difference between say, a 500CFM 2BBL Holley on the stock manifold and a 600CFM on a Edelbrock Performer?

Just looking for some more initial "punch". Has a 2.75 rear so, I'm not talking about serious launch, just a bit more.

 

[72fastback]

if you want more punch I suggest the air gap from Edelbrock .I just had my engine rebuilt {it does have a big cam in there} And when I ran it with the stock intake and a quick fuel 750 cfm I made 389 hp {not enough hahaha}so I got an air gap now I'm at 435.mind you this is a 4bbl engine with closed chamber heads.just a carb change will not give you much difference.but adding an intake will give you a good amount of extra power.With a set of aluminum heads and a cam change then there is no limit.my engine guy told me that with a set of heads I would be pushing over 525 hp.unless you have a funtional ram air that you absolutely want to keep I would get the air gap over the performer.And it fits under the hood no problem.

 

[Mister 4x4]

Yeah - a carb alone won't get you much more than a little 'seat of pants dyno' feeling... and that's mostly because you have a freshly rebuilt carb on there. Getting all of the tunable components running right will make the car feel a little more powerful as well... but only because everything's just running as well as it can with what you have.

Adding a 4BBL carb and intake will offer more power, but only to the point of what the valve train and cam can stuff into the cylinders. You'll need to go with a more performance-minded cam to really get more power. More lift and duration will have those valves open more and longer to stuff more fuel/air in, and suck exhaust out to really make use of the combustion.

Don't forget to go with a better distributor & coil and hotter plugs to help burn the extra gas you're stuffing in there as well.

A good friend told me once, "Speed costs money. How fast you can go depends on how much is in your bank account."

 

[flashback]

I'd have to agree with the previous posts...a RPM type intake coupled with about a 750 QuickFuel carb and a set of FireCore50 wires would be a good start. A cam and ignition system upgrade along with a set of gears would be the next logical step.

Let me know if we can help ya out with some parts.

Gene

 

[cobra3073]

Well Steve, the answer to your question is "it all depends" because there are other things to be considered. The other posters provide some good suggestions relative to building up performance but I will try to respond to what I believe is your "key" question as to which carburetor to go to - - 2V versus 4V for performance improvement.

Generally speaking, going to a 4V carburetor should give you better gas mileage (if you keep your foot out of the other 2V), better acceleration and a higher top end. Unfortunately, it is not as simple as that because other things come into play with one of the main ones being the RPM to which you are operating.

Attached is a link to a February 2009 issue of "Rod and Custom" magazine article on the subject which may help you in making a decision. Please pay particular attention to the paragraphs "Choosing a Carburetor" and "How to Calculate CFM" as that hopefully will help you in your decision.

http://www.rodandcustommagazine.com/techarticles/135_0402_four_barrel_carburetors_howto/index.html

Hope this helps.

BT

 

[SNL62]

Well Steve, the answer to your question is "it all depends" because there are other things to be considered. The other posters provide some good suggestions relative to building up performance but I will try to respond to what I believe is your "key" question as to which carburetor to go to - - 2V versus 4V for performance improvement.

Generally speaking, going to a 4V carburetor should give you better gas mileage (if you keep your foot out of the other 2V), better acceleration and a higher top end. Unfortunately, it is not as simple as that because other things come into play with one of the main ones being the RPM to which you are operating.

Attached is a link to a February 2009 issue of "Rod and Custom" magazine article on the subject which may help you in making a decision. Please pay particular attention to the paragraphs "Choosing a Carburetor" and "How to Calculate CFM" as that hopefully will help you in your decision.

http://www.rodandcustommagazine.com/techarticles/135_0402_four_barrel_carburetors_howto/index.html

Hope this helps.

BT

Thanks BT,

I'd seen the article before and that's how I came up w/the 600...(351x6000). Just wondering if anyone had particular experience with the simple "either or". But you DID answer, MY question. I certainly can appreciate what the motor/tranny/gear swap outs are TOTALLY capable of, but I'm not wanting to go down that road.

Thanks again.

Steve

 

[vertstang73]

Why dont you correct the cam timing? The 73 351C 2V had the cam timing retarded from the factory. Change the time to straight up and that should be a good first step without changing anything.

 

[SNL62]

Why dont you correct the cam timing? The 73 351C 2V had the cam timing retarded from the factory. Change the time to straight up and that should be a good first step without changing anything.

Cool...good idea! Thanks!

 

[cobra3073]

I "hear you" Steve, as it relates to not wanting to go down that road. Based on your cited experience, You know how this "disease" can escalate as we start changing things - - almost EVERYTHING is interrelated.

The stock 351 2V for the 1973 Mustang has a published BHP output of around 164 @ 4000 RPM with maximum torque being 276 @ 2000 RPM. My 1973 Mach I's original 351 CJ cam was "all in" at 5400 RPM with 266 HP and a corresponding 301 @ 3600 RPM on torque.

Considering your apparent stock 2V cam timing and performance, I would suggest any modified carburetor needs be readjusted from the 6000 RPM you cranked into the formula to something significantly lower for the "best" performance. Again, it would depend on where you want the primary focus to be in your application.

Just a thought!

BT

 

[SNL62]

I "hear you" Steve, as it relates to not wanting to go down that road. Based on your cited experience, You know how this "disease" can escalate as we start changing things - - almost EVERYTHING is interrelated.

The stock 351 2V for the 1973 Mustang has a published BHP output of around 164 @ 4000 RPM with maximum torque being 276 @ 2000 RPM. My 1973 Mach I's original 351 CJ cam was "all in" at 5400 RPM with 266 HP and a corresponding 301 @ 3600 RPM on torque.

Considering your apparent stock 2V cam timing and performance, I would suggest any modified carburetor needs be readjusted from the 6000 RPM you cranked into the formula to something significantly lower for the "best" performance. Again, it would depend on where you want the primary focus to be in your application.

Just a thought!

BT

Good Points...Thanks for the follow up...You guys have given me some good starting points...once I get back from Afghanistan...

Thanks!

Steve

 

[flashback]

Not a big believer in that formula....as a 950 sits atop the Windsor we're running and it's been about 4 tenths better than the 850 was that alot of people said was too big for our combo.

Now, street only use may be a little different but still think that something in the 750 range (especially with a manifold upgrade) would be about ideal for a 351C setup. We ran the 850 on my buddy's 63 Fairlane w/351C in it and it was fantastic...4 speed car & singleplane intake though.

Gene

 

[cobra3073]

Lots of difference in "fuel requirements" for a "race" build (that might be operating well in excess of 100% efficiency) versus a stock 2V build.

Again, food for thought.

BT

 

[flashback]

Obviously a diff in application...which I addressed...again, the ole Fairlane is a street only application even with the single-plane intake and it absolutely loved the 850 on it. He was having some problems with one heck of a bog when he'd go to take of at the change of the signal with his carb (it was either a 600 or 650....this was 20+ years ago) so we put the 850 on her just to see what it'd do and went out cruising that night....dang near had to fight to get the carb back the next day!

For comparison....my friend and his father ran a Holley 600 and an Edlebrock on his street rod and the Edlebrock was better around town and the Holley was better at the track....not a 'racecar' by any stretch...a mild 302 w/highway gears that runs 16's but we wanted to see the diff at the track as we knew the driveablilty and mileage was better with the Edlebrock on the street.

A 600 will work but if you're gonna play with it a bit I'd go bigger...I think that formula works ok for Chevy's but since the Ford's have always made more power they like more cfm per cubic inch.

G.