how to adapt the 800 AVS2 to the 57 and later nailheads (square bore)
Updated: Oct 14, 2021
How to: adapt an 800 avs2 to the 57 and later nailheads. An 800 cfm carb is close to 50hp gain on the 364/401/425, compared to a 600cfm, without doing anything else to the engine. Its the cheapest thing you can do to your engine for more power. This swap requires either beveling the edge of the intake ports for throttle plate clearance, or do what I did here and remove the webbing completely between primary and secondaries. That can be done easily in your garage if you have a compressor, a sawzall and a rotterie file on a die grinder. Takes a good hour of labor. Doing it on a mill is an even better option. Do not remove the vertical divider! Turning the intake into an open plentum will drastically hurt low end power and raise the power band to rpms that your engine not only doesnt breathe well at, but never sees. Even doing the mod as pictured will slightly hurt low end power in favor of HP as it increases plentum volume and removes a harsh 90 degree turn at the expense of slightly weakening the pulse. After that, use a 7/16 course tap and thread the heat risor cross over passages for set screws to keep heat away from the carb base. Ideally you want to block all heat at the intake gasket as well, and keep exhaust out of the intake all together. This eliminates heat soak and vapor lock issues accociated with the low boiling point of today's fuels, and easily gives you another 10-15hp. Fuel will still vaporize as it should, as intake will still get 140 degrees from heat transfer from the cylinder head. Once carb is installed, double check for throttle plate clearance. Pictured are both kick down adaptor kits we sell. The 57 to 63 dynaflow kit comes with a slider and hardware, otherwise you will just drive around with the VP/kickdown on and not get full throttle. The 400/300 trans kickdown micro switch is sleak and mounts behind carb. Top two terminals get used. One gets ign on power. Other end goes to terminal on trans. We sell adaptors to run stock afb pattern air cleaners on the edelbrock, but theres hood clearance issues on mid 60s cars. on later factory carbs which have the pipe plug T in back of baseplate for PCV, and booster, just recycle that onto the new carb. i never run the pcv valve off the front 3/8 nipple, although you can. i remove the nipple completely and tap in a 3/8 plug with a punch and hammer. hook your vacuum advance up to the ported (pass side) nipple on carb base. all nailheads came from the factory with ported vacuum to vacuum advance. (this can be confusing because edelbrock instruction manual states full vacuum is for non smogged vehicles.) you can run full vacuum with an adjustable vacuum advance, but why bother. otherwise, full vacuum will more than likely cause missing. missing that you may not physically be able to note, without a gas analyzer. as for the stock jetting, DO NOT lean down the jetting without a gas analyzer! you can ruin an engine in a weekend. lean mixture causes extremely hot combustion chamber temps. you can warp valves and burn a hole in a piston using our HP intake gaskets already leans down the mixture a little. pair that with lower elevation environments, and its already on the lean end of the "safe" AFR spectrum. if anything, they should be fattened up in that scenario.