Recently I have taken the position to allow others to comment and just read, seeing how others have the answers, and my time being short due to the new job. However, this one needs a comment...
A point to remember when changing intake manifold designs is what makes what kind of power. Long skinny runners with gentle curves make great power in low to mid rpms with great throttle response, sacrificing top end power for better mid range and beginning rpm response, which is typical of a bone stock car. Larger runners with shorter lengths and straight shots to the heads make great power mid to high rpm, but suffer badly on the bottom end due to the lack of vacuum signal to the carb. Just take a look at a modern ProStock Dragster. They are also prone to having fuel vapor linger in the plenum chamber area directly below the carb, and then get swept into the next cylinder causing a lean rich condition at or near idle rpm. Sharp corners, drastic changes in port sizes from a large plenum, big carbs and large plenums, all hurt performance of the chosen parts, and tend to favor just one rpm band neglecting the others to produce a narrow range of operation. How many of us are actually going to see the rpms that the changes are for: most of us Corvair and VW alike stay in the low to midrange rpms all the time, even on takeoff (3000-3500 rpm vs. redlines of 5500 to 6000 rpm). The carb is spaced up from the turn into the head because if the turn is too sharp, then the air out runs the gas causing it to puddle in the plenum area and then get sucked into the next cylinder, rich lean surge is the result. Also oversized carbs tend to make the engine SLOW down at wide open throttle instead of speed up due to the carbs ability to give more air than the engine can actually use. Consult the Auto Mathbook available at any auto parts store or Barnes & Noble, and you can calculate the CFM requirements of your engine yourself and see what I mean about carb selection. Be careful when you begin modifying things that 100s of hours on the dyno with way more experienced technicians who were being paid to spend 8 hours a day to work out the bugs on the engine, and its successive different versions. I don't know any of us that have that much free time to experiment, and frankly I want to fly. Colin Rainey KSFB Sanford, FL.
