What is "Underdamped"

[gsxtacy]

I heard that Boost Spikes are because the turbo system is underdamped, and Boost Creep is from being Overdamped.

Does this mean Under Restricted and Over restricted?

How is Under Damped fixed?

Someone shed some light on this?

GSXTACY

 

[gsxtacy]

I bet it has to do with the length of the MBC hoses huh?

I am listening.

GSXTACY

 

[Defiant]

It means you're trying to hit it before she's really ready.

No, wait... I think that's something else.

Overdamped would be a too-restricted, or too-long vacuum route, and underdamped you could fix with an orifice- like the one you yanked out of the BCS, or a bit smaller.

 

[gsxtacy]

so a restriction orfice in which hose on the BC?

It makes sense.

GSXTACY

 

[igs]

. Your turbo isn't a wave. Well, technically everything is a wave. Doh!

 

[crankbender]

Originally posted by igs
. Your turbo isn't a wave. Well, technically everything is a wave. Doh!

no no no no everything is a string...go string theory!!!

The terms underdampped and overdampped are taken from dynamic systems controls. An underdampped system simply states that the system has to get wayyyy outta wack. To fix this problem you increase the correction coefficient (open the waste gate acutator more with less pressure change). An overdampped system contains too much correction. This is when you tend to open a little more than you want and you close it quickly. This is not the case with boost creap as you are really just overcomming the physical limitations of the system.

Think of the system as 2 curves that intersect at a point. As you move up one curve you force the other to move in reaction. If the second moves too slowly you get way above the intersection point before the second curve can come up and slow the first one down.

In a nut shell

Boost spike. The time it takes the wastegate to open to where it needs to be to allow the waste exhaust to escape is too long. This could be from a slow waste gate (high viscus frictional forces like your shocks they don't move fast).

Boost creap: you are simply flowing more air than the system can let out with the current settings. The only way to fix this is to have the waste gate flow more air (bigger or more open if it is sticking).

 

[dsm1kenobe]

Ah yes, control systems. This was my favorite coursework back in the day.

In Leyman's terms...

overdamped = term to describe an unresponsive sytem= stiff shock absorber (slow compression and rebound)

underdamped = too responsive of a system= blown shock absorber (too bouncy)

In terms of boost response, overdamped means that boost is slow and reaches boost setpoint at a late RPM. Underdamped boost response is very fast, and overshoots the boost setpoint. Ideally you want the boost to reach setpoint as fast as possible and NOT overshoot setpoint - characteristics of both an underdamped and overdamped system. The only way to do this is to get an EBC.

 

[crankbender]

I phookin hate control systems....unfotunately in R&D I have to deal with it all.....

 

[gsxtacy]

I didn't count how many people responded but I gathered what was said.

It all sounds like good info.

I just wanna know how to get it fixed, so I am not spiking to 20+ anymore.

So I need a restriction orfice put in which hose on my MBC?

the compressor housing hose.......or the wastegate hose????

Thanks

GSXTACY

 

[Enigma_Man]

I believe the term is
"terminally dampened" when something is "perfectly" dampened, as in it does exactly what it is supposed to.

Anybody ever seen the "oh sh!t" handles on the ceilings of a "new Jetta"? Those are awesome.

-Jesse

 

[pneumo]

One fix for a boost spike is to first find the bleeder hole in the line that runs from the MBC to the wastegate, and make that hole smaller. If the hole is made too small the boost will fall off as rpm goes up.

Also, it will help response if you make all the hoses for the MBC shorter.