I'm putting a pretty agressive cam in my 3.1
and am worried about the lowered vacuum. Right
now I'm thinking of getting a adjustable MAP
sensor, which isnt actually an adjustable MAP
sensor, just a thing you put in-line with the
MAP sensor to adjust the output. Anyways,
looking for a better answer? maybe somewhere
in the Detroit area that can custom burn a chip?

Yeah, that cam is really going to mess with the computer if it's as radical as you're suggesting. The ideal situation would be to reprogram the PROM chip to handle the change in manifold vacuum, and install a vacuum reserve tank for the brakes. If the manifold vacuum gets too low, the brake booster won't work properly.

[This message has been edited by Blacktree (edited 07-25-2002).]

quote Originally posted by Pyrthian: I'm putting a pretty agressive cam in my 3.1 and am worried about the lowered vacuum. <snip> Anyways, looking for a better answer? maybe somewhere in the Detroit area that can custom burn a chip?

The problem with rumpty-rump cams isn't that the manifold vacuum is lower, it's that it fluctuates wildly at idle and the MAP sensor can't keep up. It smooths out as the RPMS go up so this problem goes away off idle. What some folks have done is to put a capacitor on the MAP to smooth out the readings. I don't know values so you might have to play with that yourself to find the optimum value.

The trick thing to do would be to build a little circut that switched the cap out of the circuit above a certain TPS reading or rpm.

You won't have a problem with brake booster vacuum. The brake booster has it's own reservoir. Everytime you lift throttle you'll have plenty of vacuum to charge up the brake booster.

------------------
Doug Chase
Duvall, WA
'88 Fiero Formula 5-spd (autocrosser)
'88 Fiero GT 5-spd (daily driver)
'85 Fiero GT 4-spd (rally car)

well, I guess I will wait and see how rough
the idle is before looking for solutuiions
It might not be as bad as I first thjought

quote Originally posted by Doug Chase: The problem with rumpty-rump cams isn't that the manifold vacuum is lower, it's that it fluctuates wildly at idle and the MAP sensor can't keep up. It smooths out as the RPMS go up so this problem goes away off idle. What some folks have done is to put a capacitor on the MAP to smooth out the readings. I don't know values so you might have to play with that yourself to find the optimum value. The trick thing to do would be to build a little circut that switched the cap out of the circuit above a certain TPS reading or rpm. You won't have a problem with brake booster vacuum. The brake booster has it's own reservoir. Everytime you lift throttle you'll have plenty of vacuum to charge up the brake booster.