I don't know a lot about the vacuum in the manifold, and would like to know more. Any info is greatly appreciated. I have an S-AFC II and would like to know how to use it to reduce vacuum. Please help!

Quote:

Originally posted by bzoss
I don't know a lot about the vacuum in the manifold, and would like to know more. Any info is greatly appreciated. I have an S-AFC II and would like to know how to use it to reduce vacuum. Please help!

Uhh.. vacuum is a good thing. You WANT vacuum in the intake manifold..

Quote:

Originally posted by DarkOne
Uhh.. vacuum is a good thing. You WANT vacuum in the intake manifold..

I would no nothing of this, what is vacuum? Some one explain vacuum to my cams, please.



15.9 @ 86.7mph
http://exileracing.com

Mods List:
http://highlander.dsmpower.com/sig.htm

The S-AFc & S-AFC2 don't change engine vacuum, they modify the MAP signal that the ECU sees. The MAP sensor reads the intake manifold pressure (vacuum). In efect the ECU sees a different condition than really exists, and because the ECU is programmed for economy and safety not performance, and S-AFC can adjust for more power and various engine conditions not in pramaeters for the ECU.



15.9 @ 86.7mph
http://exileracing.com

Mods List:
http://highlander.dsmpower.com/sig.htm

So if vacuum is good in the intake manifold, why does boosting help so much. In essence we are getting negative boost with vacuum. To me it seems like the less vacuum the better.
I could and probably am wrong, just using simple logic however.
Please tell me more.

your help is appreciated!

you are correct in a way.. vacuum is the opposite of boost.
YOu want the pressure in the intake manifold to always be lower than the pressure outside(you want vaccum in the manifold) thus when you press the accelerator the throttle plate opens and the difference in pressure between the inside of the intake manifold and the outside cause air to be "sucked" into the engine. This is how an engine "breathes" so as to say.. the more air you can get to be "sucked" into an engine the better. so vaccum is good. without it you would not have the difference in pressure and air would not be "sucked" into the engine.

Boost on the other hand is known as forced induction, because air is Forced into the engine, providing it with more air/oxygen thus increasing combustion. (this provided you are also suppliying the correct ammount of fuel to burn this extra air)

Hope that helps a little bit.

Thanks a lot guys, very helpful, and that all makes perfect sence.

2gnt is the most helpful DSM site out there by far, keep up the good work guys!

You're asking the wrong questions and expecting an answer that makes sense. In a NA car, vacuum is all the keeps it running. Vacuum is created by the enginme trying to draw in more air that can get through the throttle plate. Even in a boosted car you have vacuum- in any low load, cruise, or idle situation, there is no boost. In a NA car, if you do things to reduce intake manifold vacuum at idle or cruise, you car is just going to run like ass. The SAFC does nothign to "reduce vacuum" to make your car run better - it just makes the ECU think it is getting more or less air depending on how it is set, to trick the ecu into providing more or less fuel. That is all. Reduced vacuum is a side efect of some performance parts (cams, especially) but it is not the reason they make power.

you use the vacuum reading to diagnose engine problems also. like if the vacuum shakes a lot at idle you have bad valve or seals. stuff like that. Its a vacuum gauge is pretty handy to have.

in the chiltons book theres a guide that tells you what the vacuum reading means and stuff pretty handy.

vacuum runs certain component in your car also, like the brake booster, egr, bov (if you got one), fuel pressure regulator.