How does a supercharger work? Just installed AWE boost gauge...

[S4DIT]

First of all, thanks to everyone for all you have posted on this forum. I have learned a lot from all of you.

I installed the AWE boost gauge last night - it was quite the project, but I did it (pretty proud of myself). After installing it I noticed that there is a "vacuum" rather than boost when the engine is idling, or any time I'm not giving it a lot of gas.

I wish I knew more about how superchargers work - why is there a vacuum when there is no throttle or part throttle? Also, the most boost that the gauge measured on my way to work this morning was about 8 psi. I read that our superchargers are supposed to give 11.6 psi. It's pretty cold here in MN - about 15 degrees this morning - could that be why? Or, maybe the boost hose I ran from the supercharger is pinched somewhere?

Thanks in advance for your expertise!

Jeff

[bigblue]

The engine is in vacuum during idle unless gas is applied to create boost. You get boost when you accelerate and the belt on the supercharger turns the pulley which turns the shafts inside the supercharger which then pulls more air into the engine... For ed induction man. There are lots of things that need vacuum to worm properly on cars. Such as the brake booster, some climate control systems, etc. I'm not sure about the max being 8 psi... But keep in mind with a super charger it draws it's power off your engine as it's belt driven...

[t0mt0m]

read
http://en.wikipedia.org/wiki/Supercharger

[NWS4Guy]

To add to what blue said:

The SC also has a bypass valve the ECU controls, and it chooses when to allow the boost to enter the engine or when to hold it back and just lets the SC recycle the same boosted air. The max you will EVER see stock is about 11.6psi, that is under optimal conditions, if the ECU doesn't see that more boost is required it partially opens the bypass to bleed off some of the boost, controlling how much enters the engine (since the boost is going to grow the faster the engine spins, as the pulley that spins the SC for boost is directly tied to the engine and it's speed).

The APR tune makes the ECU keep this valve closed, always putting as much air as possible into the engine, so you will see more boost after about 5K RPM's - that is the point the stock ECU starts opening it and bleeding off boost 100% of the time, any other time it opens the valve is going to depend on conditions. APR also tweaks the fuel maps and ratios as well as timing in order to make the most of this newly achieved boost that makes it to the engine, hence their super gains up top in the RPM range.

Here's some more reading for you, though that post is old and some of the theories and thoughts have been either proven wrong, or added to in order to correct assumptions, but it's still a good read and valid.

http://www.audizine.com/forum/showth...charger-(Eaton)

[wwhan]

At idle the trhottle plate is basically closed, except for the idle bypass. With a tiny amount of air supplied there is a vacuum. Opening the throttle allows air in, the vacuum reduces and if under load and enough throttle, one gets boost.

Put your hand over a vacuum cleaner intake. Which has more vacuum, hand fully covering the intake or hand barely covering the intake.

Keep in mind maximum vacuum = maximum gas mileage, pumping very little air mass and very little amount of fuel.

Minimum vacuum or even worse boost = minimum gas mileage, pumping lots of air mass and gas.

[AAAA]

At idle the trhottle plate is basically closed, except for the idle bypass. With a tiny amount of air supplied there is a vacuum. Opening the throttle allows air in, the vacuum reduces and if under load and enough throttle, one gets boost.

Put your hand over a vacuum cleaner intake. Which has more vacuum, hand fully covering the intake or hand barely covering the intake.

Keep in mind maximum vacuum = maximum gas mileage, pumping very little air mass and very little amount of fuel.

Minimum vacuum or even worse boost = minimum gas mileage, pumping lots of air mass and gas.

the "tiny amount of air" going through the partially open throttle plate does not create the vacuum. vacuum is on every engine whether n/a or forced induction, the difference being a forced induction motor goes from vacuum to air being forced into the motor via either a turbo or supercharger when under load. But the vacuum in either case comes from cylinder pressure, when the pistons move up and down and the air/fuel is combusting it creates a vacuum and sucks air into the motor. This is how air is drawn into any motor through the intake system (the flow of air doesn't just force its way into the intake due to high speeds). If you've ever had a motor out and you hand crank it you can hear (or even feel if you have the head(s) off) the suction as your hand cranking it.

[madmadS4]

http://www.s4-mtm.com/images/925803_3.0V6TFSIengine.pdf

Search for the word "vacuum". Our engine features a vacuum system with mechanical vacuum pump.

[wwhan]

AAAA,

The engine pumps air from the intake to the exhaust. When one closes the inlet (throttle valve), one gets a vacuum. This is true for all engines (NA & FI)

But as far as boost is concerned, the engine needs to have a load to get into boost.

[AAAA]

AAAA,

The engine pumps air from the intake to the exhaust. When one closes the inlet (throttle valve), one gets a vacuum. This is true for all engines (NA & FI)

But as far as boost is concerned, the engine needs to have a load to get into boost.

that's exactly what i said. except vacuum doesn't all the way disappear when the throttle plate is opened, it depends on the angle. obviously as more load is given the vacuum becomes less and diminishes when the boost takes over. i explained it in the most elementary way in my previous post so the op would get it.

And i thing the mechanical vacuum pump is more for helping to run the accessories since vacuum is not as easily achieved with the s/c unit.

[S4DIT]

Thanks for all the explanation guys, I appreciate it. I just hammered it down during lunch and my boost gauge never registered more than 8-9 PSI. Weird. Any ideas as to why I can't hit 11 PSI?

[Ray Khan]

Does it hold that 8-9 psi to redline or does it drop off after 5000 RPM?

[S4DIT]

I believe it held it to redline. Why do you ask?

[drvolkl]

Thanks for all the explanation guys, I appreciate it. I just hammered it down during lunch and my boost gauge never registered more than 8-9 PSI. Weird. Any ideas as to why I can't hit 11 PSI?

Mine goes to 11.xx when under full throttle... almost 12. Maybe you have something backwards? It also usually reads around 0-5 under normal acceleration... and down around -20 when I'm idling or coasting. (Of course I don't pay as much attention to it since I've had it for months, so I'd have to really look at it again to get firmer readings for you)

[S4DIT]

drvolkl,
When you routed the boost line through the ECU box, did you just feed the line straight down into the passenger compartment? That's what I did - I'm thinking when I slid the ECU back in, it is pinching the boost line.

[drvolkl]

drvolkl,
When you routed the boost line through the ECU box, did you just feed the line straight down into the passenger compartment? That's what I did - I'm thinking when I slid the ECU back in, it is pinching the boost line.

I didn't install this mod, I had a shop do it... sorry bro, I usually do my own work but was lazy on this one (plus afraid of busting the vent).

[rktskicar]

If you have a VAG (VCDS), you can monitor your boost with block 436 (Absolute Manifold Pressure) to check your AWE gauge reading.

Bruce