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Hi all,
The carburetor in my '65 LTD is fairly shot. It's time for an upgrade, but I'm trying to figure out the best CFM for a balance between economy and performance. (Who isn't?)
I have a 352 with the standard 4-valve carburetor and it SEEMS as though stock was 600 CFM. My next best option ($15 more) is a 650 CFM carb. I've already decided on electric choke, but as I dig through information, I'm finding that putting in a larger CFM carb may (or may not) burn more fuel without a return in performance that's actually worth it.
Any help is appreciated, thanks!
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Welcome to the forum!!!
the basic formula for carb sizing is
CI * max RPM
3456
so lets say your engine will not see more than 5500 RPMs
352 * 5500
3456 = 560
Now there is one more factor to this puzzle and that is volumetric efficiency. In simple terms it is how well your engine breathes. as an example If a cylinder can hold 1 cubic foot of air and on a normal intake stroke you draw in 1 cubic foot of air the engine would have a volumetric efficiency of 100% IF you can draw in more than it would be a percentage above 100% less would be below. Rather than trying to figure out volumetric efficiency I just look at the performance parts on the engine. I use this formula to get a rough figure and go from there In your case (assuming your engine is stock) I would think a 600 CFM carb (same CFM Ford used) would be perfect.
As an example of volumetric efficiency playing in I have a 302 in my galaxie with high flow aluminum intake/heads, aggressive cam, and headers. The math says I need a 480 CFM carb for a max RPM of 5500 BUT I am running a 600 CFM to accommodate the added flow. It probably still a little big for my engine but my only choices were 500 and 600. if I really wanted to tune it and get it perfect I could change out the jets and needles.
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You can get restored Autolite carbs on eBay no problem. In fact you can get the exact carb your car came with. There are several on there right now for a 352.
Unless you have some off the wall use for your car, like hill climbing or vintage racing , you are money and time ahead if you go with the Ford Autolite carb.
Z
PS if you have no use for your old carb, I'll take it. Send me a PM and name your price.
Last edited by zray (June 19, 2014 11:57 pm)
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+1
The autolit 4 barrel is one of the best carbs ever made. I currently have a edelbrock on my car but have been toying with swapping it out for an autolite I have.
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Thanks so much for the info. It gave me some searchable terms which led me to figuring out that the 600 cfm is perfect for my uses. I purchased an Edelbrock carburetor and now I'm kind of stuck on trying to decide whether to rebuild my carburetor or hang on to it or sell it. They seem pretty rare, but it also appears that an Edelbrock will do the same job (but with a more reliable choke). In the words of a wise man, "From the moment you lay your hands on a vehicle, it will never be more original. You can put original parts on it, but they are stock, not original. Why waste effort trying to make something original when you can't? Don't make it original - make it better." He meant this conservatively of course, but the point remains. If the Edelbrock works as well as an Autolite, why bother going to the extra effort to return the Autolite?
Again, thank you guys so much for the help. Much appreciated.
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David@GF wrote:
"From the moment you lay your hands on a vehicle, it will never be more original. You can put original parts on it, but they are stock, not original. Why waste effort trying to make something original when you can't? Don't make it original - make it better." He meant this conservatively of course, but the point remains. If the Edelbrock works as well as an Autolite, why bother going to the extra effort to return the Autolite?
Normally I would agree with you. I am the king of modifying my classic cars. My 62 galaxie has a 302 and T5 5 speed in it, hydraulic clutch, 4 wheel disc brakes, hydroboost power brake assist and Subaru bucket seats just to name a few of the "improvements" I have made. Also I am a huge fan of edelbrock carbs. They produce grate power, they're easy to tune and once you set them up they are virtually maintenance free. I like them so well have one on both my galaxie and my Mustang. All that being said the OEM autolite carburetor is still the better carb. The 4100 series carbs are one of the best ones ever made! They perform as well as the aftermarket units AND have the benefit of grate gas milage (relatively) when not dipping into the secondaries. They are also one of the best carbs for providing the most consistent fuel air delivery through the entire RPM range. This means consistant power, better MPG, les carbon buildup and les fuel washing the oil off of the cylinder walls (in other word longer engine life) The only reason my Galaxie has an Edelbrock on it rather than the autolite 4100 I have, is I haven't had a chance to replace the vacuum diaphragm on the secondaries on the 4100 so I can swap the two carbs out.
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"........but the point remains. If the Edelbrock works as well as an Autolite, why bother going to the extra effort to return the Autolite?.....".
Your car will never run as well with the edlebrock, or a Holley for that matter, as it will with the Autolite that was designed specifically for your engine and transmission combination. You can rationialize all day long about the edlebrock having a more reliable choke (it doesn't ), or any other nonsense. But the engineers that Ford hired to spec out a carb for your engine are just a little bit smarter than you, or me, and to ignore their research is only going to hurt your cars performance. Just because you have the edlebrock in hand is hardly a compelling reason to pick it over a well restored Autolite.
Z
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