350z twin turbo - Dump vs flutter/chatter noise

[EzeePzee]

Hi All,

 

I’ve noticed recently that the noises from my APS Twin turbo 350z seem a bit inconsistent, and wondering if anyone can advise. 

 

I get the “flutter” noise more than I’d expect tbh, and I understand that this could be an indication of turbo cavitation and lead to premature wear. 

 

Ive also noticed a lag in power delivery when doing 60-70mph in 5th or 6th gear on the motorway. Power delivery in lower gears is amazing though, so no issues there. At 60-70mph revs are between 2.5-3k I think, so maybe I just need to drop it a cog or two?

 

Car produced reasonable figures when with Abbey Motorsport when on the dyno back in April (385bhp)  and hardly done many miles since then. However weather is very hot of late so that may have some impact..

 

Should I be concerned? Should I try adjusting the APS dual-vent dump valve, or am I worrying about nothing? 

 

Cheers!

[skate2create]

I used to have a similar issue on the BOV on my Fiat coupe. It was the spring inside, slightly too stiff. Switched to a softer spring and that seemed to help with stopping the fluttering occurring at low boost.

 

Worth a go, as it's probably not too expensive to try and see

Edited July 26, 2018 by skate2create

[EzeePzee]

Thanks dude. Don’t have replacement springs in mine but it is adjustable so may mark where it’s set at and give it a tweak. 

[Daisyduke]

Haha. Flutter noise always caused big arguments over sxoc about turbo wear. 

 

Consensus was though, that it wouldn't reduce the turbo life by a very large percent and would normally not need replacement before the cars rotted. Lol.

If you want more dump valve actuation reduce the spring pressure. If you want more flutter increase it.

 

What rpm do you normally see full boost at? At 70 you may be at a point that you have very little boost and low throttle position. 

[Stevie-Boy]

It's a wonderful noise.

 

I had this on my Subaru and had the same result as the poster earlier, softer spring in the valve and it changed it totally.

[EzeePzee]

So I’ve adjusted it about 1-1.5 turns of the adjustment, hasn’t made a massive difference.

Car idles ok. When I rev the engine in neutral, at top rpms it still does the flutter, which suggests to me it still needs to be adjusted softer. Is that right? 

What I don’t understand is why I need to adjust this all of a sudden.. nothing has really changed on the engine...?

[Daisyduke]

Static revs aren't the same as revs on load. It doesn't build boost as easy with no load so you probably didn't get to relief pressure of the valve. Did you tighten or loosen the valve. 

 

What boost do you normally see and has it changed recently?

[EzeePzee]

I have loosened the adjustment so far, to lower the pre load and make the valve easier to open. 

The boost level on the car peaks at 0.8 bar (11.5psi) as is recommended by APS (turbo kit) and mapped by Abbey. It has peaked slightly higher in this hot weather but otherwise been pretty constant. 

The compressor stall noise may not be anything “major” to worry about if I take the world of google to be gospel, but if it is at all possible to reduce its occurrence then I’d be happier.

I spoke to Jez @ Horsham today whilst getting my slave cylinder replaced, and I may give Abbey a call to see what they think too - given that they mapped and know the car they may be able to advise further. 

I may also get a second pair of eyes involved so I can reset the valve to weakest setting and see what difference it makes.