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Air Flow Meter / BOV Help!

Guest Danny32

By Guest Danny32,
in Engines & Forced Induction

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Jay95R33 Grand Master

Jay95R33

Posted
Posted

Guys,

That pchu pchu pchu sound is not good for your turbo. It's called compressor stall.

Basically when you block off the BOV the turbo compresses the air and when you come off the throttle the pressurises it so much that it is forced to come back throught the turbo (in the wrong direction!!) and out the AFM !!

This why the car is stalling. When the air comes back out the AFM, the AFM messures the air again (the AFM does know which way the air is flowing, it just messures anything that goes through it) and then pumps more fuel in for the extra air flow. So much more fuel that the car stalls at idle.

Unblock the BOV - I know it sounds cool cause mine was blocked when I bought it, but it's not a good thing.

J

carlo Veteran

carlo

Posted
Posted

Modifications to the stock BOV is not the best way to go. If you remove the plum back it will leak boost, if you remove it then you will have al your boost going back through the turbo.

some cars come like this from factory (some supra models inclusive) so its not the worst thing, I have a aftermarket BOV which I have set to not open at low boost. (hence i get the phew phew phew noise :) but at full boost the BOV opens and does its bit.

It will slightly decrease the life of your turbo, so i recomend at full boost you have a proper BOV.

Also the stock computer will not adjust for life with out the Bov. It will run rich when your bov goes, and you will get a little bit of back fire. This is normal, and if you want it to go away change your computer.

ps.. Cant wait to get out to the track, remove my cat and see what flamage I get.. :P

DAMQIK GTS-T Community Regular

DAMQIK GTS-T

Posted
Posted

A blow off valve (plumback or atmo venting) protects the turbo from spinning backwards. imagine a turbine shaft spinning @ 80000rpm the car backfires and presto the turbo spins @ 20000 rpm or faster the other way, this can and break the turbine shaft break cermic turbine wheels and generly stuff the turbo bearings.

not a good thing also the bov takes pressure off the throttle body butterfly which can be jammed open or closed due to a backfire.

my 3 cents for what its worth.

Damqik

\\\Wiktor Enthusiast

\\\Wiktor

Posted
Posted
Originally posted by carlo

I have a aftermarket BOV which I have set to not open at low boost. (hence i get the phew phew phew noise :D but at full boost the BOV opens and does its bit.  

Also the stock computer will not adjust for life with out the Bov. It will run rich when your bov goes, and you will get a little bit of back fire. This is normal, and if you want it to go away change your computer.

why not? it's still not good for the turbine to get those extreamly fast stops and you get turbo lag that you dont need.

this is not very good eigther cus' you will fri yo' cat to h*ll and it will cus' power loss due to higer backpressure in the exhaust.

but if you remove it problem gone... :)

Wiktor

TTT Grand Master

TTT

Posted
Posted

The turbo NEVER spins backwards.

It just slows down alot more than it would if the standard bov was there..

that sound is called COMPRESSOR SURGE.. not stall.

lots of cars come without bovs.. VL turbo, cordia turbo, 180sc with a CA18DET to name a few.

I have gone through an atmo venting bov, an aftermarket plumback bov and I am now running the standard one because the car just runs better..

good enough reason for me..

whatsisname Grand Master

whatsisname

Posted
Posted

There's no reason (other than failure or for the noise factor) to replace the standard BOV.

The factory BOV only becomes a potential problem when closed throttle air flow exceeds what the factory BOV can cope with. In other words the BOV can't dump enough of the intake air on closed throttle & some of it escapes to atmosphere via the compressor. This will be obvious due to compressor surge that will occur. This situation isn't reached until ~400hp.

I started to get CS issues after my last round of modification so I switched to a GFB "Basic" BOV. It's a great value BOV as it's cheap (~$190) & is much quieter than most aftermarket BOV's. It also outflows just about every other GFB valve (noise ='s restriction ='s extra cost ;)) I don't have stalling issues as I don't have an AFM.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi whatsisname, you said.........

"There's no reason (other than failure or for the noise factor) to replace the standard BOV. "

We replaced ours with an atmosphere vented one because the standard one was recirculating the already compressed (hot) air. This was causing detonation due to the high inlet air temperature. Change of BOV helped heaps, about 7 degrees on a 28 degree day.

That's our reason.

Jay95R33 Grand Master

Jay95R33

Posted
Posted

Alot of good stuff being discussed here :uh-huh: :uh-huh:

Just on the compresor surge/stall. I'm pretty sure that compresor surge is caused by a massive miss-match of the turbo wheels, and at or very close to 0 boost the turbo will surge/jerk on and off boost (not much boost, but enough to feel). I'm sure it's due to having a large compressor wheel and a small exhaust wheel.

I think Mario had this problem at one stage, and also someone on SDU with a GTR running a large single turbo reported the problem too.

Compressor stall is when the compressed air is forced back through the turbo and slows the spinning of the wheel, and I suppose in some extreme cases my slow it right down (almost stall it).

A question - I'm new to aftermarket adjustable plumback BOV's. They must be adjustable for a reason, so what is the adjustment dependant on? Do you adjust them depending on boost levels or how much air you want them to pass???

Cheers

J

adam 32 Grand Master

adam 32

Posted
Posted

as previously mentioned a few cars were released std with no BOV and while it aint ideal, running with no BOV is not going to kill anything within a matter of days...

surging is caused by mismatching wheels, normally too small an exhaust wheel/too big a comp wheel which means compressor speed is too low

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