Hey guys I was looking for a carb for the 330hp 350 crate engine from summit I was planning on buying, the internet won't let me access summit right now so I can't get a link or the part #, but I'll do that later. Anyways I was looking into getting a demon carb off their speed demon line. I was thinking the 650 cfm carb is prolly best for the engine. But my problem was picking between the 650 cfm ones offered. I've never had a carb and was wondering what the difference between having a vaccuum secondary and a mechnical secondary? Also, I was wondering if you guys agreed with a 650 fm carb?

 

A 650CFM is a good ideal carb for a 350ci motor especially in a street trim. If it were above 400HP I might recommend a larger one. The secondarys on these are opened two different ways. Firs is a mechanical. It uses a linkage (rod) to actuate the secondatry butterflies open at a certain throttle point. Some do not likeit because of the abrupt opening it provides. However in a drag racing application this is usually the preferred linkage. Like the accelerator pump operation of the primaries, it uses the same lever, cam and spring stup and can be adjusted. The profile of the cam (ramp) will both regulate the rate of the accelerator pump shot and the duration. Opening rate of the butterflies is maintained the same in relation to the primaries and isnt adjustable (kinda). A vaccum secondary uses a vaccum diapram that smoothly opens the secondaries at the rate of the drop in vaccum as opening occurs, It is adjustable with different tension springs. It is a more street-friendly setup due to smoothness and economy. However a light spring cam be used to give a fast opening rate. I am using a BG Demon 750CFM w/Mech. secondaries but I only drive it occasionally and am over 400HP. From a economy standpoint its a poor setup. From a full-throttle top-end standpoint its great. The BG Demons are very nice and well built. They also have an idle ease base-plate which is another fine-tuning tool to get a nice clean idle without opening the butterflies on a big cam car.

 

We offer a 650 Speed Demon for the 330 HP crate engines in either mechanical or vacuum secondary. Mechanical Secondary P/N 1282010C330, Vacuum Secondary 1282010VE330. A mechanical secondary carburetor is recommended on vehicles with a manual transmission, or a 2800 + RPM stall speed. If you’re using an automatic transmission with less than a 2800-RPM stall speed a vacuum secondary carburetor is recommended. The vacuum secondary butterflies open based upon engine RPM and load, so they will be smoother with an automatic and tighter converter. The mechanical gives more precise throttle control, which is needed with the manual transmission, and or the looser converter. Either carburetor will come with a tuning manual, and setup DVD.