rh_334

iTrader: (2)

Every APS TT i have been around has this problem. It seems like compressor surge, after a quick shift or any quick fluctuation of throttle the car stutters and falls on its face for several seconds, if you hesitate and shift slow it doesn't happen. During this the boost spikes slightly. AFRs dont change when this happens. After a couple seconds it smooths out and begins to pull again.
This weekend i changed to a HKS SSQV hoping the APS Dual Vent BOV was causing the problem by not being responsive enough, and this seems to alleviated the problem slightly if any. I have been told that it could be caused by the compressor housings being to small?
On the dyno you can hear the surging sound with every shift (normal shifting getting up to speed) and also you hear the same surging sounds when slowing down in gear or going up a hill at low rpm. At first i thought the sound where the BOV but it still happens with the HKS.

Anyone know what is causing this? Anyone found a way to fix the problem?

Thanks,
Rob

tig488

iTrader: (18)

was your APS BOV recirc'ing to your intake?

rh_334

iTrader: (2)

yea, now that port is capped off with the HKS

djtimodj

My APS tt does not do this at all. You get a little flutter on gear changes when only under partial throttle. This comes comes from the BOV and full blow off at full boost gear changes.

Are you sure it's surge?

rh_334

iTrader: (2)

well i thought the fluttering was the BOV until i changed to the HKS, I believe it is, it has been tuned twice and continues to do this. I also know of a couple Built Block APS cars that do the exact same thing.

It happens more with taller gears, it never happens 1st-2nd and depending on how quick i shift it may happen 2nd-3rd, but under WOT it always happens 3-4 and 4-5.

It also gets worse in colder weather.

When you rev the car, as the rpms come down you can hear a CHU CHU CHUCHUCHUCHU sound, well i thought that was the BOV but my car still does it this the HKS when it isnt opening, and it comes from the drivers and pass side

tig488

iTrader: (18)

is your BOV too tight?

weslutes

iTrader: (7)

internal wastegates?

Cass007

iTrader: (34)

I don't have this issue either. I have the turbo slightly modified and also switched to external WGs.

Yup, its just like this. I've grown to love the flutter sound.

BlinkerFluid

iTrader: (7)

I experienced this when I had the standard DBB turbos on the car. It was easy get the car to do it going uphill and varying the throttle between light load and coasting. The sound alternates side to side.

I can get the bigger extreme turbos to do it but I have to try.

Is it compressor surge? You could probably call it that. Is it the type of surge that will damage the turbos? Absolutely not. I've even experienced it in other makes of cars with smallish twin turbo setups. The HK$ twin kit on a local Supra does the same thing.

What I believe to be happening is both turbos are spinning, of course, and creating a bit of pressure. As load changes, each compressor's speed increases or decreases at a different rate. I believe the slower spinning compressor stalls and air backflows through the compressor, creating the noise.

While this side compressor stalls, it loses "traction" on the air. This reduces resistance and the wheel speeds back up, regains airflow, overshoots speed a bit because of inertia, and the opposite turbo stalls, backflows, accelerates, and continues the cycle. In this case I believe it's caused by
low compressor speeds, low airflow, and low exhaust energy.

Damaging stall has a distinct sound, a pop or the sound of a cat sneezing is what I have heard in the past. Damaging stall occurs at full throttle during spoolup or full boost. It also can happen if the throttle closes abruptly while in boost and the blow off valve malfunctions. Either way, you'll know something is wrong. You will also see manifold pressure fluctuations along with the boost gauge jumping all over the place.

A very very light blow off valve spring may fix it. Every time I've heard of this the owner just dealt with it.

rh_334

iTrader: (2)

thats exactly it, and i never hear anything that sounds like the damaging surge @ WOT but im not sure i could if it was happening, what else would be causing it to fall on its face and gets increasingly worse in cooler temps? the tune has been completely changed 3 times and it still does it, unless i hesitate for a second before grabbing a gear. And when this happens the boost gauge does jump but its quick small spikes, probably nothing more than ~1psi overboost.

thanks for all the help

oh and War Eagle!

BlinkerFluid

iTrader: (7)

Ha! No worries.

Where in 'Bama are you?

rh_334

iTrader: (2)

i Goto Auburn, your car is still on the main page of Bamagz
You know Elove right?

tig488

iTrader: (18)

im a member there but when they changed it a few years ago, i never went back. i know most of those guys.

BlinkerFluid

iTrader: (7)

It is?

I do, though it's been a while. I'm back home in PA now.

Off to check this out.

*edit* It sure is, along with my buddy Joe's car (the closest, black with FMIC). I had no idea, good catch!

rh_334

iTrader: (2)

i was'nt around back then but i asked Eric about your car when he first put that pic up. You should post in there sometime, its a pretty good group.

djamps

iTrader: (1)

The issue in your case sounds more tune related than anything else. Where is the MAF in relation to the BOV?

rh_334

iTrader: (2)

the standard APS Location

mx594

iTrader: (4)

My HKS kit does the alternating chug chug sound under light decel. I never understood exactly why but I figured it had something to do with the HKS anti-surge compressor inlet fittings. Either way it only happens under light decel so I know it's not damaging anything. And it's definitely not the BOV.

djamps

iTrader: (1)

Without some very fine tuning (and preferably MAP based tuning) you're going to have some instability when coming out of boost with the MAF so close to the BOV. The turbulence around the BOV is causing erroneous MAF reading. But the fact you mention it's worse in colder weather means some of that instability is definitely in your tune.

rh_334

iTrader: (2)

at first i thought the same thing, but it acted exactly the same on the Unichip (MAP based)

i know the Unichip is pretty much a base map but it wouldnt be affected by turbulence at the MAF