

| Subject: | Re: Boston Bob Engine - Follow Up |
| From: | Frank Grunthaner |
| Date: | Sun, 12 Aug 2001 00:59:06 EDT |
In a message dated 8/11/01 9:27:35 PM, ingalls_mark@HOTMAIL.COM writes: << Yes, it seems strange. When I first got my van,I checked my general auto repair books and they all mention 16 to 18" at idle. I figured maybe my low vacuum was because of the 1.9 liter's retarded timing. But for the past year I have been monitoring posts that mention vacuum and 10 to 12" seems to be the norm for the 1.9 or 2.1 wasserboxer. >> Must say that two thoughts come to mind: 1. Heavy overlap on the cam. This will give a lousy flow at idle with plenty of residual exhaust to foul the burning of the fresh charge. High overlap cams need resonant exhaust flow to place a low pressure node in the combustion chamber, thereby enhancing filling and developing more power. Probably begins to be effective around 3K rpm, maybe more like 4K. Also a function of valve lift. This negative effect can be minimized by playing around with ignition timing, but its only a Band-Aid. These comments are in agreement with an earlier post. 2. The POS engine has very high frictional losses (endemic with boxer configurations) and can barely turn over. Low vacuum says that a high load is drawing down engine rpm at a given air/fuel ratio. (This sometimes indicates a high slipper load (referring to the bottom of the piston as the slipper) because of too tight a tolerance at the base of the cylinder bore, or too large of a piston) Taper is the usual cause I believe. 2a. All waterboxers leak (vacuum too that is). BTW, Classic fuel-economy-in-the-toilet-with-cruise-control relates to porous vacuum diaphragms at the actuator or control valve. This leak is often continual, but not so bad that the cruise control doesn't work. The leak translates in the end to poorer air/fuel ratios, and poorer precision of control. Both effects knock the hell out of fuel economy. Comments relevant only to vacuum operated cruise controls operating off manifold vacuum. I use an electrically (stepping motor) articulated cruise control. Still sounds wrong to me! Frank Grunthaner
Have something to add on this topic today? Revive this thread in the forum »