Colin Great explanation, darn helpful knowledge, thanks! Pat ----- Original Message ----- From: "Colin & Bev Rainey" <[email protected]> To: <[email protected]> Sent: Monday, August 15, 2005 10:08 PM Subject: KR> Intake manifold
> 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. > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to [email protected] > please see other KRnet info at http://www.krnet.org/info.html
