QUOTE(davep @ May 28 2006, 05:20 AM)
What are you trying to accomplish? So far this does not make sense to me.
On any engine your crankcase will build pressure due to blowby. The crankcase breather is supposed to deal with this problem, but on stock cars they're rarely up to the task in extended high performance situtations, thus, the large breather box that JPB mentioned. However, some people prefer to run the crankcase under vacuum, the most notably being dragbike teams who are pushing over 350 RWHP out of 1500 CCs. Now, you would think that any advantage gained by the piston being assisted downward by a vacuum would be nulified by the piston pulling against a vacuum on the way back up. This would be correct if you're thinking in terms of a one cylinder engine, but that's not the case. As one piston goes down, another will be concurently going back up, balancing the volume, and thus, air pressure in the case. With that being said, the theory that those drag bike teams opperate under is that by running the entire crankcase under vacuum, the pistons will have less air molecules to push against, freeing up horsepower to turn the wheels, instead of to turning the engine. I hope I explained that right.
So, some people run a belt driven pump where their breather would normally be. Others hook a breather into their headers, so that the exhaust velocity creates a vacuum without draining engine power with a belt drive. This works but is difficult to do right without interfering with the proper exhaust flow, and ussually doesn't create as great of a vacuum as a pump. Still others run an electric pump, which is what I want to do. This doesn't pull from the engine, and also is easy to install because it can be put anywhere with no need for a drive from an external power source. Some people use smog pumps off of GM cars, but they don't produce much vacuum. My question was if anyone knew who makes an electric pump that can handle this job. It's an open question since it doesn't have to be MADE for a crankcase pump, it just has to work. Open to suggestions.
Mark D.
PS Another thing you do have to worry about is the vacuum dropping your oil pressure. It is a ligitimate problem, but it's aleviated with a larger oil pump