Re[2]: Mac-01 vs. Mac-02

["Mike Hopton" <mike@genesis-microchip.on.ca>]

     Scott,
     I realize a 272, 276, etc. are not turbo cams, I don't think I said 
     they were? They do however help North American ur-qs rev more quickly 
     past 4,500, a big problem in my opinion. I'm sure you can remember 
     RDH's posts on the problems he had when he installed a 272 and the way 
     he fixed it? 
     
     Correct me if I'm wrong (need I ask), but while adjusting the CO 
     mixture can be used to supply more fuel at idle, it will also  
     supply a non-ideal mixture throughout the rev range?
     
     I don't agree that the MAC02 is a lost cause, all the functions except 
     knock control are available (within the constraints of CIS) and this 
     can be addressed by advancing the ignition timing in the EPROM and 
     using an additional knock sensor circuit to dial back the timing to 
     avoid detonation. 
     
     I'll repeat this, I'm not "knocking" Paul's mod, it's a very cost 
     effective way of improving performance. Personally though  I don't 
     like the resistive divider approach because all it does is change the 
     output signal from the pressure transducer. Now the ECU sees less 
     pressure at the inlet manifold, the timing is advanced because the 
     timing versus RPM look up tables are a function of boost and now the 
     ECU thinks the engine inlet manifold pressure is less than it actually 
     is and so you run more ignition advance because your operating on a 
     lower boost RPM versus ignition advance curve, it works, but it is 
     crude. The relationship between timing and RPM as a function of boost 
     is complex and in my opinion not well controlled by only changing the 
     slope of the output voltage from the pressure transducer. (Although I 
     know you need to either change the pressure transducer or modify it's 
     output in some way to go any where beyond 16psi boost).
     
     Once I've BTDT I'll be sure to post. I really wish I had more time to 
     spend working on the car... oh well, in the mean time I'll keep trying 
     to learn and offer advice when someone makes a blanket statement that 
     I don't agree with, of course YMMV. 
     
     Regards, Mike
     
     p.s. My 2 cents, only worth about 1.4 cents US.