wookie@alice.UUCP (07/25/84)
The camshaft you have installed has a higher "valve overlap" meaning the exhaust valve and intake valve are open at the same time for a longer duration than the stock shaft. This is what produces the poorer idle in a hotter cam. The reason for this higher duration is to allow the exhaust to flow out and the intake mixture to flow in better at higher RPM. The result is poor idle and poor vacuum at low speeds. The carb installation should not affect the vacuum and yes a larger reservoir will help some but you're probably only getting a good vacuum when going down a long hill and so won't be able to store much away the rest of the time. This is a common problem and most people just do away with the brake assist. There is no way I can have a brake assist on my Sunbeam race car! The engine rarely produces and vacuum!! Keith Bauer White Tiger Racing
wwb@ihuxn.UUCP (Walt Barnes) (07/25/84)
The key to your loss of vacuum is the overlap between exhaust valve and intake value openings. In addition to increased duration and lift, wilder cams have more overlap. Thus the incoming fuel mixture helps push all the exhaust gas out. Another advantage is the increased turbulence in the combustion chamber further aids in fuel/air mixture. Oh yes, another point, if you add the intake duration and exhaust duration you may get additional insight into why the overlap increases for wild cams. Walt Barnes ...!ihuxn!wwb