Turbo Flutter

[bruce]

The *wheels* in the turbo have inertia.
As you start to build, or just build a min amount of boost, the turbo starts to spool up, ie speeds up to some incredible RPM. While at full song it might be ~80,000 RPM, even at low engine speeds, it can be say 20,000 or so. What happens is the engine is able to decellerate faster then the turbo, so there is still some pressure in the intake tract, and it's try to find it's way past the still partically spooled turbo. Do to the length of the intake tract, this column of air looking to exscape just winds up bouncing from between the Throttle plate to compressor wheel, and generates the *flutter*.

Does it hurt anything?, IMO, no more so then just any throttle lift. Some combinations will be worse then others, but *does it hurt anything*, can be taken to an incredibly small tolerance. In the grand scheme of things, I'm not going to worry about it too much. That being said, a poorly tuned set-up might take it to a level that it *could* be a problem. The oem setup uses a deccleration enleanment, and Deccleration fuel cut-off, that both help to min it.
Another part of the what the problem is, that the plenum has some *wet* fuel sitting around, so when you first lift, the engine goes rich, and that fuel is wanting to *afterburn*, and spool the turbo, when it *should* be slowing down.

 

[mybuick]

what is happening is the turbo is spinning backwards, which is not a good thing. i have a 2001 subaru wrx bov on it and trying to find a way to get rid of the exhaust puck and just use the bov i have. would i be able to weld the puck hole shut but i see that i will over boost all the time. what can i do to the puck hole...

 

[Blazer406]

what is happening is the turbo is spinning backwards, which is not a good thing........

I disagree. The wheel is spinning (in some cases) upwards of 100,000 RPM... sometimes higher..... there is no way the wheel comes to a complete stop and spins backwards......

Somebody else may chime in that knows more than me..... but I seriously doubt that she spins backwards....

 

[Mad_Trbo]

for mounting instructions you can simply mount the blow off valve on your up pipe. This will eliminate any flutter and chance of damaging thrust bearings when partially closing or slamming shut the throttle plate.

 

[PHANTASM]

for mounting instructions you can simply mount the blow off valve on your up pipe. This will eliminate any flutter and chance of damaging thrust bearings when partially closing or slamming shut the throttle plate.

DO I RE-ROUTE ONE END OF THE BLOW OFF VALVE FROM THE UP PIPE TO BEFORE THE MASS AIR METER ON THE INTAKE PIPE? OR VENT IT TO ATMOSPHERE?

THANKS

 

[VadersV6]

Impellar is spinning backward? If that wheel were to stop from 100,000 plus rpm in a second, the whole thing would shatter after the shaft twisted up.
The TB closes and the huge pressure surge slams the turbine assembly into the limit of its thrust clearance. Not good for anything. I want to put together a bypass setup like I made for my old car, but Ive heard that people have run into driveability issues with them for some reason on these cars. I think its probably ECM related. You need a bypass before and after the IC to properly vacuate the 2 different pressures on both sides to work right. Otherwise it doesnt bleed off both sides of the IC simultaneously. (causes bucking) A higher flowing IC wouldnt be much of an issue, although mine only had a 1psi drop and going to a dual setup fixed everything. I had it set up with a single, and I had alot of part throttle bucking until I went to a dual setup and hosed the vacuum port side of the valves separately, and put a flow control on the vacuum line going to the fp sensor to reduce the pressure spiking that the FP sensor was seeing. (this is a late model car setup) The vacuum lines going to the bypasses were having some impact on the rest of the system for some reason. Dont know why but it worked. The bypass system is good because it routes the pressure back into the intake tube after the MAF, so that you're constantly circulating metered air. When you have a blowoff valve, you're blowing off air that has already been metered by the MAF, and has been accounted for in the fuel tables. So you end up with a huge rich spike every time you let off. Some people say they didnt have that problem, but it doesnt make sense that they wouldnt.