Jump to content
SAU Community

Air Flow Meter / BOV Help!

Guest Danny32

By Guest Danny32,
in Engines & Forced Induction

 Share

Recommended Posts

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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Erelyes
      Ceramic turbine damage to engine - what did yours do?

      By Erelyes · Posted

      Ha, well, it's been.... a bit of a journey. Things have taken much longer than I'd hoped. I'll probably put up a thread at some stage. Hopefully soon. The car's not done any kms since my update in June though, put it that way.
    • Dose Pipe Sutututu
      M35 Aftermarket Fuel Pump

      By Dose Pipe Sutututu · Posted

      Here's the chart for fuel pressure vs. current draw, assuming your base fuel pressure is 3 bar and you run like 0.5bar boost on WOT, you should only momentarily hit 9amps here and there. (Ignore my prev post, I cannot read a chart these days it seems)
    • GTSBoy
      RB25 Drama's

      By GTSBoy · Posted

      Those comp test results are not hideous. Whether they are accurate or not (ie, when that comp tester says 140 psi, is the real pressure120, 140 or 160?) is unknown to us. The state of the battery used to crank it over is unknown, etc etc. Many people around here would say that the absolute values and the spread are perfectly fine to just add boost and keep going. I personally would be happier with a narrower spread than that, but even the diff between 125 and 145 is not terrible. That one cylinder at 125 though, has probably copped some damage relative to the others. You should inspect the valves seeing as you've got it open. Do you know how to measure installed ring gaps? That, and an inspection of the rings themselves, is how you will determine whether they need to be replaced. If you're not good to do these things, take the block and the pistons and rings to a shop that is, and ask them for the go/no-go on them. Do the bores need a hone at all? If so, you might well be justified in getting some different pistons in order to get away from the ring supply problem. Whether you're happy to spend a lot more money right now, on more gear, rather than less money, but an amount that looks stupid given that you will only get a handful of rings in exchange for that money, is for you to decide.
    • iain_ST44GA
      M35 Aftermarket Fuel Pump

      By iain_ST44GA · Posted

      also possibly backed up to my filler and shat down it! 🤣
    • Julsmadrid
      RB25 Drama's

      By Julsmadrid · Posted

      Ok so i would love some advice here please, i purchased an R33 a few months back and its had a few mods done to the engine, its an RB25det running a Master ECU, 1200cc injectors, bigger turbo, oil cooler, oil filter relocation kit, Spool H-beam rods, acl/ross pistons. When i removed the motor from the vehicle (as its getting a respray) i thought i would compression test it and these are the following results. Cylinder 1-145psi, Cylinder 2-143psi, Cylinder 3-125psi, Cylinder 4-145psi, Cylinder 5-140psi, Cylinder 6-135psi this test was done with the motor on the ground and powering up the starter motor. I dropped the sump and found broken oil squirters on cylinder 3,5 and 6. I was told my rings are probably worn so i stripped the motor completely to get a new set of rings for it. The trouble is no one has these rings anywhere and they have to be custom made by Ross over in the states and will cost about $600+$200 delivery. My question is how can i tell if my rings are at fault and if they are still ok and is this price ok for a set of rings?
×
×
  • Create New...