vacuum secondaries carburetor vs. mechanical secondaries carburetor

vacuum secondaries carburetor vs. mechanical secondaries carburetor explain the difference and why do 700R's need a vacuum secondaries. Or so I was Told. I was told I need to use a vacuum carb when installing a 700 in my 51 or change the valve body to make a manual shift?? I do not get that. Sorry if this sounds dumb, have never done a trans swap.

 

lots of variables...but the basic issue is that at low rpm, wide open throttle on a mechanical secondary carb will have the air flowing too slowly thru the carb to draw fuel thru the jets. You'll get a "lean bog", the engine will cough and stumble when you floor it. So you want to make sure the secondaries are not open until you need them.

With the trans set up properly so it downshifts right away when you punch the throttle, you can get away with a mechanical secondary carb with a 700R4 trans. Might help if the car has steeper rearend gears, a good sized engine, and the torque converter and rearend gearing matches the cam, and the carb is the right size for the engine setup.

btw, Edelbrock/Carter AFB type carbs have an air valve in the secondary side, so they act like vacuum secondary carbs.

 

Thank you much any one else.