Hey all,
I recently went on a trip with the evo. It is about a 2000ft elevation change and I was wondering if that could cause the dv to start fluttering. Before I left it was the most sensitive dv I've ever seen. Even at negative boost(-10 vs-20 at idle) while cruising it would open and still not flutter. Now, it flutters up to 7psi. The dv is only 2 weeks old. Also, I've been getting a lot of part throttle "over boost" compression surge. It'll boost up to 17lbs quarter throttle at 3000rpms in third or higher. I am running an AEM truboost with the spring pressure set at 8.5 psi and have adjusted up to 11 and down to 7 with no changes. Any help would be appreciated.

 

Valves don't flutter; it's compressor surge regardless of if you're boasting 1 psi or 100psi. If you're surging then the valve spring tension is set too high.

 

It is definitely DV flutter. Ill check into it. Just wondering; Why would the elevation change cause the DV to act different? The car didn't have on throttle compression surge or DV flutter before i left?

 

That's what I wanna know.

 

something tells me its not because of elevation. theres either something else factoring in, or it was doing it already, you just didnt notice it? if you have the 'yellow' spring, try taking all the preload out. worst case scenario, you get to play DV shuffle and go through each possible setup to see what works and gives you no flutter

 

If you remove the valve and plug the holes it would make the same sound. The sound is caused by the valve not opening soon enough at whatever power level, making air back up on the compressor and slow its rotation.

 

I understand what compression surge is. I just don't understand why it didn't do it before and now it is. Also, the valve for sure didn't flutter before I left. I had just taken a friend for a ride to show him how sensitive it was because he was looking at getting the same DV. I also blew the dipstick out yesterday here due to too much crank case pressure! Time for a catch can I suppose.

 

Not to sound rude, but I don't think you're following me..

1. The VALVE didn't flutter before, or now. VALVES don't flutter.. i wish people would get off that idea.

2. What happened is the atmospheric pressure change caused your valve to be too tight, which causes surge. The valve tension was set up for a different altitude. It's the same concept as if you set the valve up to hold 30 lbs of boost, then only decided to run 10 lbs.. it's too tight, and will cause surge on the low side of the power band.

 

But could 2000 ft change it that much? Also, it was only 2 weeks old, could it finally just be "breaking in"(for lack of a better term)? I will loosen the spring pressure tomorrow and see if that corrects that issue.

And as for the compression surge, I'm pretty sure it is something to do with the AEM solenoid. I ran it at wastegate pressure and it didn't part throttle surge. As soon as i turned it back up over 16lbs it would surge. Any ideas on that?

 

wow 2000 ft?

 

2000 ft is a huge elevation change...

 

Yup, 2000 ft. And all from one side of Nebraska to the other. 1090ft -3891ft, so really more like 3000ft.