There are many questions to ask yourself before you decide to purchase a carburetor.
First, what size carb should you have as opposed to what you think you want? Engine size is only really part of the equation. Things such as cam timing, cylinder head design, exhaust system efficiency ect. Are all major factors.
The Best way we have found to match sizing is to take cubic inches and base them off the rpm range of the engine. A good stout street strip engine with good flowing heads will have aprox an 85% volumetric efficiency, so as a guide line you can figure in a base cfm requirement by using this formula.
CID X max RPM / 3456
example: 355 x 6500 = 2,307,500 / 3456 = 667.6 cfm
Now this is assuming 100% VE ,so now take that 667.6 and multiply by .85 and arive at a cfm requirement of 567.5. Add 8 % for volume of fuel displacement and you get the 612.9 required cfm. Now you say, boy that is small and I would say you are right, because now you have to factor in some effects of atmosphere and the dynamics of a running engine. Things such as signal strength, booster buffeting, air flow turbulance ect, ect.. which could add as much as 10% requirement, bringing cfm requirement to 674cfm.
Now add in factors of vehicle weight, transmission, cam overlap, rear gearing.......cylinder head design, header design and exhaust system and the whole requirement senario changes quickly.
Now we have an idea as to what size we may need, now we have to decide on what style we should have. In the case of Holley's and like designs, you have the choice of Mechanical secondaries (double pumpers) and vacuum secondaries. If your car has stock type highway gears, stock torque converter and wieghs 3700-4000 lbs, a double pumper is just not the choice for this application. Everyone wants to be able to say " yep! I got a double pumper on Thar" but when you mash the throttle in afformentioned car it will fall flat on it's face.
Ask a reputable carb shop as to what would give the best performance for the vehicle you have, not the one you want it to be. This way you will have the best performance overall.
Now, as far as a double pumper goes, it is in My opinion that a choke has absolutely no place on a double pumper. Why? Because if your car requires a choke, this means it is most likely a mild daily driver/commuter and would perform much better with a vacuum secondary carb. This is why Holley came up with the HP line. If you are building an engine for max performance, why would you want an obstructing choke hindering it's potential?
Powder coating...
Powder coating has many benefits more than just pretty colors. Powder coat adds an insulating barrier between the cab and engine heat. Eliminates corrosion, deters carbon buildup and ensures you won't be polishing that "bright zinc" carb every couple weeks.
Some bad mouth powder coating calling it "low buck" this just shows how ignorant they are.
Setting up to powder coat is not a cheap proposition and is fast becoming the idustry standard in high tech finishes. Tough as nails, chemical resistant and environmentally friendly process.
Powder coat is applied by electrically charging the powder as it is applied to the grounded item being coated. Then cured in ovens at high temperatures to actually melt the powder over the work piece. This produces some of the finest finishes you will find for just about any object that can withstand the cure temperatures.
Ok, so Where should I get a carburetor? Good question!
You could buy a used carb and try your hand at the rebuild yourself, which is totally acceptable if your handy with some tools and a general knowledge of how they work. But (this is a big if) what has been done to that used carb? has anyone went nuts with a drill? a grinder? why is the person selling the carb? This leaves a good chance that you could drop 100-150 dollars on a useless piece of garbage and now your back where you started and out the money you just spent. You could buy a new one, but that's more money than you may want to spend, only to get a carb designed to run acceptable on most engines.
Carb specialty shops will give you the best bang for the buck hands down. and can save you money by opting for a remanufactured and custom modified carb that will more closely match your needs. There are a few shops on ebay and on the web that are excelent (not excluding us). Do your reserch and ask questions. If you see shops listing hundreds of carbs at once this is a good indication that there wasn't much time spent on getting them right. If you see them painted with a spray can, that is also a good indication they won't work right. If you see unrealistic promises or claims, than chances are they aren't what they are claiming. The best carb shops to use are the ones that are authorized distributors of Holley and or AED performance.
These shops will have special tools to do certain jobs correctly (such as install boosters, which if not done the correct way can and will fall out. This is bad! very bad!) And use only the best products available. This way the money you spend will be spent wisely and you get a far superior product.
Hopefully this brief summary has helped you with making a educated choice.
If you have questions, I am always willing to give free tech advice to anyone, no matter If you are a customer of mine or anyone else.
Thank you for taking the time to read this . Hope it has been of some help.
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