View Full Version : a few questions

10-02-2012, 04:39 AM
90 st185
Where is the stock bypass valve located?
If its not recirculated will it make a fluttering sound when you let off boost( or should it be silent since its recirculating)
On the water coolant neck what is the wire running in the bottom left, closest to the block? (Bvsv?)

10-02-2012, 11:44 AM
The ST185 has no blow off or by pass valve stock. It's not like the MR2. For some reason Toyota decided not to put a by pass valved on the 185 but did have one on the MR2. You can add one but to recirculate it you'll have to either modify the stock intake rubbers or make an intake and add a port to recirculate. The noise you're hearing when you let off the boost (if the whole thing is stock) is the compressor surge from the pressure backing up against the turbine blades.

As for the wire, I'd have to look at mine to see which wire you're talking about.

10-03-2012, 02:05 AM
Hmm that's weird they didn't add one to the st185 when its the same motor as the Mr2

10-03-2012, 04:20 AM
That's what all of us 185 owners have always thought. Doesn't make a lot of sense. The only thing I can figure is it might have had something to do with homolagation of the car for WRC but who knows.

10-03-2012, 06:59 AM
Its because there is no reason to have one there in the first place.

Every OEM manufacturer to have ever installed a recirc valve did so to reduce engine noise... No OEM manufacturer has EVER put a vented to atmosphere BOV on a production vehicle... Period... On top of that most professional racing teams dont bother with them at all, atmo or recirc...

Contrary to popular belief, flutterdump (not compressor surge) is not harmful to your turbo... Think of how many guys have run their ct26's well over 150k without ever having to replace the turbo.. Or just about every diesel engine ever...

True on-Boost compressor surge is what damages turbos, and this only happens when the size of the turbo is mismatched with the engines VE capabilities...

In fact, running without a recirc valve will actually increase shifting performance (which is why they arent in race cars). Boost is not completely lost out the recirc valve, but instead is partially retained within the intake system, especially if you are fast at shifting.

10-03-2012, 11:29 PM
Fascinating! I didn't know any of that

10-04-2012, 09:08 PM
So basically, if you hear "surge" and blow you're turbo, it's only cause the turbo shouldn't have been on that engine anyways?

I always thought BOVs were useless, even though I have one (long story). Good to know I was right.

10-05-2012, 09:08 AM
Trust me, true compressor surge is really really nasty sounding and much much louder than the little bit of fluttering you might hear after letting off boost. True surge also only happens when you are on boost, not when you let off the throttle...

Basically this happens when your motor physically cannot flow the amount of air that your turbo is trying to force into it. On a turbo compressor map, there is this neat line called the surge line, and its basically a point at which the turbo will surge because the RPM of the turbine wheel is too fast for the pressure differential it is putting out.

Its pretty important to understand compressor maps when you are selecting an aftermarket turbo.

Usually this happens when you install too small a turbo on a vehicle with very high flowing exhausts...