Re: EGR and MAP

["Bruce Plecan" <nacelp@bright.net>]

|  I have a 1/4" OD vacuum spider of copper tubing under my modified
| Hilborn intake.  The Hilborn is an independent-runner manifold with
| eight butterflies.  The vacuum spider handles the flow through the IAC,
| provides a vacuum signal to the MAP sensor, and has a takeoff for the
| power brake booster.
|
|  I'd like to hook the EGR valve to the spider.  Is 1/4" OD tubing likely
| to flow enough for that to work?  I could add a second spider just for
| EGR, but I'm hoping to avoid that much work if I can.

OEM uses less than that, there is no real flow, just enough vol. to move
diapharm, some have a small vac leak, but not much.
  Some times thou the MAP sensor gets real fussy about sharing.  With a
fairly healthy cam, I wound up having to use a short min diam hose for
getting a good clean response from it.
  As far as power boosters go, I've also had good luck with introducing a
slight restrictor in line with it, ie 3/8" hose with a 1/4" restriction.
Seemed to help with a better idle with the brakes applied, on a TBI.

|  It strikes me there must be some code in the speed-density chips to
| balance EGR and MAP signal, since vacuum will drop when the EGR valve is
| open.

There is.  The calculation is usually vac based, ie Baro-Map as I recall.
Grumpy
|