bov fitted need some advice.

[TimE-J]

doesnt sound as bad in the video but driving using half throttle and releasing then it is bad, standard bosch unit is back on now anyway.

[prj]

Grats, you just reduced your 0-60 and 1/4 mile time and got rid of the annoying noise.

[GazzaG60]

dont look too small to me. in fact its basically the same as my gfb unit thats happily support ing 1.9 bar from my larger turbo.

you just pumped back in that hot air.

[prj]

you just pumped back in that hot air.

Which will go through the intercooler again, keep the turbo spinning and prevent the engine from flooding itself.
Plus, the air is not even that hot, when the bypass is open, the turbo will basically spin against a very low Pr, so working with maximum efficiency.

Spin it any way you like.
The only way to make a BOV work on a MAF based car is fitting it before the MAF. But for that the MAF has to be on the pressure side.

All this for an annoying "whoosh" sound?

[Rusty]

Expanding gas cools it too

[GazzaG60]

well each to their own on this i suppose.

i know when i was motronic with bov and boost controller it was far faster than a stock car so it cant be that bad.

depends what you call annoying really. personally i think the diverter chirp is woeful. suits a vxr just fine.

i dont run a maf either as thats another big issue on the power trail.

[prj]

well each to their own on this i suppose.

i know when i was motronic with bov and boost controller it was far faster than a stock car so it cant be that bad.

And without BOV it would be even faster.
I have tested this back-to-back on the same car. Logged AFR.
I am not talking out of my ***.

[Dan]

People seem to argue back and forth all day about recirculating vs. atmospheric. Funny thing is any performance difference, in all honesty, probably wasn't worth the time spent arguing.

Personally I've never been too much of a fan of the "whoosh" noise, but if that floats your boat, then fair enough, each to his own.

The important thing is that a sufficient amount of air is getting vented somewhere.

In theory, as I understand it:
If the pressure in the intake, where the diverter air was being vented, was higher than atmospheric (eg. excess of air - air forced in by a massive scoop?) or the availiable space was insufficient for the vented air, this might inhibit the flow rate slightly compared to atmosphere.

Conversely, with lower pressure (lack of air) in the intake (insufficient air - poor intake ventilation?), recirculating could increase the pressure (since air is being added) here, aiding air flow.

But even if my theory here is right, these are edge cases (latter seems the more probable in a normal car though, which would favour a DV).

There's one thing for sure and that's as prj says: in a Bosch/MAF set up, it's going to be a PITA to switch to a BOV - at least if you want your MAF reading to be worth anything. Thus, I don't really see any reason to put a BOV on an S2 - unless, as mentioned, the sound really is to your taste.

Just my 2c.

edit:

I have tested this back-to-back on the same car. Logged AFR.

Actually, since you've posted this (since I started writing) and you seem to know more than I - any insight into the physics of why?

[S2central.net]

well each to their own on this i suppose.

i know when i was motronic with bov and boost controller it was far faster than a stock car so it cant be that bad.

I suspect a well programmed boost controller was the fundamental reason for that - versus stock software as its very conservative.

The thing that kinks me up is that some people fit the BOV with dumping noise to an S2 as they think it will sound more like the UrStig driving an S1 on full beans. The irony is that if you want something like that sound - just disable the factory recirc valve and you get the famous 'chikoh-cheekoh-chew' sound of compressor stall. If anyone has a better way of writing that noise down, be my guest !

Agreed with above that this subject of noises comes down to personal taste - live and let live and all that !

[GazzaG60]

dont get me wrong im not sayings its better by massive margins what im saying is it works better than a stock unit.

my choice for motronic would be a split gfb unit with some atmosphere and some feedback. the advantage being that excessive air can go to atmoshpere.

prj dont take it as i think you are wrong as i know you are not. afs are affected. i dont feel its as bad as on newer cars though as our motronic isn't that clever. whether the car is faster is another story. we are talking about a very brief condition state.

[prj]

dont get me wrong im not sayings its better by massive margins what im saying is it works better than a stock unit.

But that's it. It's not better on motronic.
We are talking in the context of this thread about a car which has motronic.

my choice for motronic would be a split gfb unit with some atmosphere and some feedback. the advantage being that excessive air can go to atmoshpere.

No...

prj dont take it as i think you are wrong as i know you are not. afs are affected. i dont feel its as bad as on newer cars though as our motronic isn't that clever. whether the car is faster is another story. we are talking about a very brief condition state.

It's not about clever. A system which measures mass-airflow can NOT work properly with a BOV if the BOV is after the MAF. And even then it will have some issues.
It's not a problem with motronic.
It's the same with any car that uses a MAF to measure airflow.
STI? yep.
Evo? yep.
Your engine might not stall due to it, but when you get back on the power, you will have a LOT more fuel in there than needed this results in loss of power on gearchange and it directly affects the cars performance. Take your standalone and map it to run at 9-10 AFR. See how well it accelerates then.

Actually, since you've posted this (since I started writing) and you seem to know more than I - any insight into the physics of why?

This is actually pretty simple.
A maf based system injects fuel based on the amount of air that goes through the MAF at any given time.
This amount of air shows exactly how much air is going into the engine.
If you take some of that "counted" air and dump it into the atmosphere on the pressure side, then there is a rush of new air suddenly entering the MAF. The ECU reads the MAF and the MAF shows a much higher amount of air, than the engine is really taking in. This results in a momentary rich condition.

When you change gear, you already get some bogging down, because you go off power and in that EXACT moment when you get back on the power the bov causes the engine to run super rich and bog down even more.
It's really noticeable and AFR graphs prove it as well, when you test back-to-back.

Simply put - if you are running a speed-density system, the BOV will have no effect on the AFR. If you are running a mass-airflow system which has it's MAF anywhere other than in the intake manifold (as some modern cars have) you will have a rich condition on gear change. Some cars will even stall on gearchange when coming off high boost and venting to atmosphere.

[Dan]

Cool, that's as I thought - thanks for confirming.

So with a speed/density system, or MAF in the intake manifold, it really makes sod all difference?

[prj]

Yeah, I don't think it will make any noticeable difference.

[quattro]

I have run a open bov since I had the car and I love it, apart from the axhaust its the only non standard thing thats noticable to joe bloggs, it really is a personal thing.

As for running a bov on a maf car I personally think its perfectly fine to do so, some tuners may say not but in my eyes there are so many other variables from fuel, electronics, boost leaks, driver error, temperature, worn/old parts etc....... so on maf cars I think an open style bov causing loss of power is the least of your worries and its mostly theoretical buII s.h.i.t from over use of reading the internet.

Do you really think that 100% of all the air dumped by the standard dumpvalve is ingested by the turbo???? I think definetly not, there would be so much air dumped in to the intake so quickly that its inevitable for some of the air to get forced outwards towards the air filter......

Im sure that some one will come back with some 'evidence' that im incorrect, so ill save you the bother...... most of us drive and modify our cas because we like them, they give us pleasure and make us happy, (pshhhhhh included) if i was over worried about being 0.01 second faster to 60 today than i was last time I'd probably work in F1.

Rant over!

[Acidburn]

I have run a open bov since I had the car and I love it, apart from the axhaust its the only non standard thing thats noticable to joe bloggs, it really is a personal thing.

As for running a bov on a maf car I personally think its perfectly fine to do so, some tuners may say not but in my eyes there are so many other variables from fuel, electronics, boost leaks, driver error, temperature, worn/old parts etc....... so on maf cars I think an open style bov causing loss of power is the least of your worries and its mostly theoretical buII s.h.i.t from over use of reading the internet.

Do you really think that 100% of all the air dumped by the standard dumpvalve is ingested by the turbo???? I think definetly not, there would be so much air dumped in to the intake so quickly that its inevitable for some of the air to get forced outwards towards the air filter......

Im sure that some one will come back with some 'evidence' that im incorrect, so ill save you the bother...... most of us drive and modify our cas because we like them, they give us pleasure and make us happy, (pshhhhhh included) if i was over worried about being 0.01 second faster to 60 today than i was last time I'd probably work in F1.

Rant over!

I agree

good comment, each to there own as thats what makes the world interesting.

@ timE-j - the dumpvalve jamo has is the same as this one

http://www.youtube.com/watch?v=7YbnloVUEE8

I had one on my car for a year, sounded good, went well enough and never had any issue's with it.