Coolguy949

iTrader: (10)

To the right of the exhaust manifold under that air scoop leading into the intake. One side of the valve goes into the turbo inlet pipe and the other end has a small radiator type hose leading from the upper intercooler pipe. It's a plastic thing with a vacuum line coming out of it.



To everyone else, I wont bother explaining how blow off valves work when venting to the atmos vs. back into the intake. I've only explained it about 20 times.

Ahh, I give up here it goes (brief version):

It's specific to mitsubishi and some other brands, not all blow off valves. The MAF knows how much air was blown off by the valve and it includes it in it's next calculation for air.

air from valve + air from air box = air engine is expecting

if you dont let it vent back in to the turbo inlet:

air from air box < air engine is expecting = air/fuel ratio will have less air than it should (running rich)

ADMstunna

yeah but does the blow off valve vent at idle? shouldnt it be completely closed? and the engine under vacuum?

seattle944t

It depends on the blow off valve. The vacuum pressure is what causes them to open. The line that goes into the top of the valve is manifold pressure. When your boosting it puts pressure on the valve, in addition to the spring pressure, to keep the valve closed. If the spring is too weak then boost will leak out, this is one reason why people upgrade the valve.
Anyways, when you come off the throttle and the throttle body closes, the intake manifold goes into a vacuum state - even thought the rest of the intake tract is pressurized. This vacuum pulls against the spring pressure in the blow off valve to open it and allow it to either vent to atmosphere or direct it back into the intake. If the sping is too weak then it will be open under idle vacuum pressure. Conversly, if the spring pressure is too high then the valve will not open when needed, and the pressure wave of the boost will bounce off the throttle body, back through the intake, and back to the compressor wheel in the opposite direction of the flow. In extreme cases that can actually damage the compressor wheel, but most often just stalls/slows the turbo compressor. This effect will also make the car buck/surge briefly when getting out of the boost.

ADMstunna

great explanation. so what seems to be the problem is with aftermarket blow off valves - a stiffer spring may lead to complete closure under idle and decent idle but atmospheric vent leads to bog in between shifts. conversely, in aftermarket blow off valves where poeple are getting funny idles, it seems to be a improper installation of the manifold pressure hose and adjustment of the spring pressure where it is venting pressure at idle as well as under boost leading to bogging in between shifts and crappy idle. right. lol.

zstryder

iTrader: (19)

So I guess the question really is...

Does there exist a venting BOV that won't be detrimental to daily driving and performance?

(assuming that we have no control over the A/F ratio)

Seems like our best bet is to just get a recirc BOV. You can always get a new intake, that would help with the "pssshhhhh" sound, I guess...

Coolguy949

iTrader: (10)

Yes, on mitsubishis, if you run the BOV dumping back into the intake then you will notice no change in driveability - none at all. I have a Greddy Type-S in my eclipse and it drives just like stock but it can hold more boost because the stock plastic valve leaks.

The key on all blow off valves is adjustment. You have to adjust it correctly, then it should run just like stock. The little screw on top of the valve adjusts how much vacuum opens the valve. If you have the screw too lose the car will idle funny simply because it takes hardly any vacuum to open the valve. WHen the valve is too tight you'll notice it too. When letting go of the gas the car will decellerate aburptly, almost like you tapped the brakes. This is because the pressure in the intercooler pipes wasnt fully relieved and the air went colliding back into the turbo impeller (bad - defeats purpose of BOV). They key is to get the right adjustment. It takes weeks to get it right. Weeks of stopping off the side of the road, opening the hood and turning the screw some more because it doesnt feel right.

As soon as I get my evo i'm sticking my greddy in there and i'll let you guys know what the ideal setting is for me. THe setting is also dependant on how much boost you are running. More boost will most likely need a tighter setting.

Hope this helps.

Rob

VOLSBimmer

Good info. Coolguy!

For those of you that are worried about losing the pshhhh sound when you don't have the BOV venting to the atmosphere, I wouldn't worry to much because I think you'll still hear the sound. My brother had a Greddy Type S on his old Stealth twin turbo and it was recirculating back into the air intake like stock, and it still had a loud sound to it, you could hear him coming from down the street!

Coolguy949

iTrader: (10)

Yes, once you get an aftermarket intake filter you will hear it loud and clear. It acts like a large speaker. You can hear the turbo whine and even the stock BOV whoosh. Aftermarket BOV is even louder. With the stock airbox you can hear the whistle, but no whoosh sound.

Ultimate Racing

iTrader: (13)

Hey guys,

We have our own HKS SSQV Blow-off Valve kit for the Evo VIII. Doesn't stall at all. Off of high rpms it generally falls to a nice idle. Every so often it will dip a bit lower...but nothing too bad. Never had it stall once.

rt turbo

iTrader: (4)

i was talking about the MAF hot wire systems that cause the stalling. its because it puts more gas in the engine compensating from air from the blow off, when there is no air because it is vented into the atmosphere, then it still puts the extra fuel in, causing it to run way rich. i thought the evo 8 had a MAF system? am i wrong? if it has a MAP then there shouldnt be AS MUCH of a problem. but it will still over compensate for the blown off extra air.

Incognito

iTrader: (8)

Hi. How are you guys getting your blow off valves on the aluminum piping? I picked up the Greddy type S BOV with the aluminum flange. I was just going to use a reducer silicone coupling to join the little pipe from the BOV flange to the little pipe that the stock BOV's radiator-hose-looking thing is clamped to. The stock pipe's outlet for the stock BOV's hose is like 1", maybe 1 1/4". The Greddy thing is like 1.5". The thing points down. I tried just mounting the whole thing on that part of the intercooler pipe, and it simply doesn't fit. The BOV is too wide. Doesn't fit in the space between the head and the side of the battery. What to do? Does somebody make a pipe with flange that puts the BOV to the side, like closer to the mass air meter, or is there some other way? I do want the Greddy BOV to vent back into the intake.

Might have to rig something up....
I wanna know what you guys are doing though.

Thanks in advance.

TaiwanEvo

iTrader: (1)

Get the 95'99 eclipse kit

Coolguy949

iTrader: (10)

Since you already bought the greddy universal BOV, all you need is this thing sold on eBay:

http://search.ebay.com/search/search...clipse+adapter

For those who havent bought their type-S yet, the greddy 95-99 eclipse kit comes with something like the link above plus a cap to allow you to blow off atmospherically (easy to rig up your own) plus the greddy type-S.

PM me if you need help.

AustinEvo8

I have the Greddy and it does drop RPMs if I go from boost to clutch in..ie:getting caught at a light.

Vents to the atmosphere and do not have any problems with full boost or gear changes.

Just don't worry about it anymore.

I do know of someone that has the BOV recirculating and there evo stalls all the time...don't know if that is the fix either.

Coolguy949

iTrader: (10)

IF it still does it when it recirculates that means the BOV isnt adjusted properly.