Reply to "Bad brakes"

When it comes to vacuum accessories and IR EFI, I recommend running an electric vacuum pump and plenum. Stock Panteras used vacuum for brake (majority of demand), ignition advance, carburetor secondaries, actuating the air cleaner door on inlet air warm up circuit, and a few other warm up and emissions gadgets.

The only thing left to talk about on an IR EFI converted engine are the vacuum assisted brakes. The brakes don’t need to be vacuum assisted. That’s just a choice. The problem with all the vacuum driven devices is they are all set up to work for a given engine combination, and changing the cam and induction systems usually means the vacuum condition is no longer sufficient nor reliably predictive of engine operating condition when it comes to driving things like ignition advance.

On subject of IR EFI, there is another recent thread (and many more) on useful sensors that discuss some of the reasons for separation of vacuum accessories and sensors and ECU control schemes. The short answer is that vacuum accessories can interfere with more important engine control and sensor schemes and vacuum is unreliable on high performance cam shafts.

http://pantera.infopop.cc/eve/...841081836#4841081836

Soooo, if you want to preserve vacuum brakes and simplify your life as far as engine tuning, a pump and plenum located as close to the brake booster/servo as possible is a good alternative. You’ll need a relay, fuse, to switched power and also to insure you have sufficient amperage available from your alternator system to run the pump.

Tony, on the matter of only using 4 of 8 cylinders for vacuum, do you find you are able to maintain uniform rich/lean conditions in all cylinders at idle? I’d be concerned about the potential for lean conditions over time. The other reason I suggest a separate vacuum pump for accessories is it takes big plumbing between the 8 cylinders to flow enough to achieve sufficient vacuum, and as mentioned, depending upon cam, sometimes never enough. At the same time it can foul up idle conditions and also if you are trying to run a MAP sensor off this vacuum circuit to do predictive enrichment routines (speed density approach), it can wreak havoc with this as well. -It can take some experimentation.

Best,
Kelly