john banks

http://www.i-club.com/forums/showthr...0&goto=newpost

I am trying to work this one out. He is taking his source from the blow off valve rather than the turbo nipple and says this works better. Can someone work this out? If you were hoping I would I am a bit baffled when it comes to BOVs and which tube goes where.

Gavin? CosieConvert? Anyone else that knows about oily bits?

Luke

Hi John

Where is the Blow off valve????? What are your thoughts???

Here we go again!!!

john banks

Have a look at the pictures from Vincent's posting at the end of the I-club thread.







Links from http://www.boostvalve.com/images/cars/wrx/wrx1.html

Damn - that is one clean engine bay! Should there have been a in your post Luke? "Here we go again..."

[Edited by john banks - 1/28/2002 11:17:20 PM]

mutant_matt

got me



Matt

Cosie Convert

Oily Andy to the rescue !

The advantage of taking the pressure tapping from the blow off valve is that it compensates for the pressure drop across the intercooler and pipework.
At high RPM and boost the pressure at the turbo can be a few psi higher than at the intercooler outlet, as it is the manifold pressure you are trying to control, it is more appropriate to take your 'controlling' pressure from that area.

God, you guys are on to all those little 'secrets' I had on my cossie !

One effect of taking the pressure tapping there is to hold the boost pressure better at higher RPM.
You are now controlling the manifold pressure and not the turbo discharge pressure.

CC

UkLegacyT

is that a blitz blow of valve? does a blitz blow off valve work with an airflow meter?

thanks

ian

Luke

Does a Legacy (96)have a blow off valve????? Looked but cant find anything like the photo!!!

UkLegacyT

mine is an n-reg '96. is a very late registered one. as standard, they have a blow off valve, but it recirculates. it is a black cylindrical thing, not very big, and is above the turbo on mine. it has two pipes, one to the inlet hose from the air meter to the turbo, and one from the boost pipe between the turbo and the intercooler (chargecooler). it also has a small vacuum pipe conected to the top of it coming from the inlet manifold.

hope this helps.

ian

Cosie Convert

The BOV set up changed in 96/97 early cars BOV is on the turbo discharge, later cars on the intercooler outlet. They both recirc back to the turbo suction.

A BOV will work with a MAF as long as it has a strong enough spring in it to hold it shut during Idle or cruise conditions.

cc

HarryBoy

Is this not the same as taking the feed to the Dawes directly from the spare manifold nipple on UK cars?

If so, taking a feed from the mainfold will cause excessive spiking of the boost. This point is mentioned in the in the Dawes instructions. I really can't see the idea behind this.......

Harry

EMS

If you guys want to damage your turbo´s because of passing the surge-line you should defenitely try this!!!

The BOV line is coupled to the inlet manifold AFTER the throttle. At part throttle there is very little boost pressure available in the inlet manifold and therefore the wastegate will be completely shut. This is resulting in a VERYYYYY high boost pressure at the turbo outlet, this in combination with low flow rate will kill the turbo in a very short time. (There is some reason why EVERY modern turbo engine taps the waste gate control line at the turbo outlet!)

I think some americans can better stay with their low-tech V8 engines, than playing around with a high-tech engine without any knowledge.

Mark Verhoeven.

john banks

Thanks for keeping us right Mark. After the throttle it seems a definite no-no - like taking the supply off the manifold.

It is odd that this was posted as a way of REDUCING part throttle boost - I would have thought it would worsen it in this config as it would always try to make say 16 PSI even at 1/4 throttle by spinning the turbo up as much as possible - must be horrific pressures at the turbo outlet and ridiculous heat? So why are his EGTs IMPROVED?

I am puzzled I have to say... any more info really welcome!

Thanks again.

GavinP

I guess it also goes against keeping the volume (pipework) as small or short as possible which conflicts with our findings so far....

Severe compressor surge apparently produces some "interesting" (read expensive!) noises when the pressure is forced backwards through the turbo when the throttle shuts - I'm surprised he hasn't mentioned that.....

Thanks

Gavin

Cosie Convert

Oops

I probably added to the confusion ? I meant take the tapping from the engine side of the Intercooler but before the throttle valve, this takes account of I/C pressure loss which can be as high as 1 - 2 psi.

cc

Cosie Convert

Tapping here also keeps your Dawes valve up to 100+ degrees cooler which can only be good for it !

john banks

No problems - all contributions welcome whether they are correct or not (otherwise I would be in the doghouse). This is why I asked the question rather than just tried it. We all need to weigh this and decide. Thanks to Mark for keeping us right (again!)

If we tap off after the intercooler and take account of its drop them we could also influence the shape of our boost curve for better or worse at the top end? Obviously some of us with small turbos don't want to take it any higher! But with a big turbo you might?

I suppose it depends on how airflow influences losses across the intercooler? Is it a proportional pressure loss which takes a fraction of the intercooler "IN" pressure? If so just adjusting the Dawes would do and relocation would not help. If higher flow at higher revs adds another variable then it might be worth thinking about if you have a large turbo and are dropping too much up top?

Just a few thoughts to throw in - probably wrong!

GavinP

I would think the extra volume in the pipework (and intercooler) would produce more problems than it solves ???

Spiking would increase and boost control would be more prone to the effects of heat soak...

Would be interesting to try though, eh John

Thanks

Gavin

Cosie Convert

On my Cosworth the pressure drop across the intercooler was 2 psi at 6000 rpm (23 psi turbo, 21psi at throttle valve) mounting my tapping post intercooler allowed me to run closer to the fuel cut at higher rpm. Boost spike was not a problem (1 psi)
Not sure if scoob will react in the same way but intend trying it soon !

john banks

The I-club thread completely confuses the hell out of me what they are saying - anyone get it? Are the connecting before or after the throttle?

HarryBoy

John,
the BOV it's self is upstream of the throttle but its actuation tube (if I may call it that) is after the throttle taken from the manifold. On our MY00 cars the BOV opens or dumps air back to the Turbo with any negative manifold pressure, it shuts with positive pressure. The thread on i-Club seems to indicate that they are taking the source for the Dawes from the BOV actuation tube, therefore after the throttle.

Harry

john banks

Thanks Harry it is all starting to make a little bit of sense. I never did read up on blow off valves! So it sounds like a crap way of doing it then.

Cosie Convert

I agree with Mark, if you take your tapping from after the throttle (vacuum side) you will run your turbo closer to, or possibly in, surge.
This may well result in decreased lag/ quicker spool but increase the risk to the turbo mechanically.
The pressure before the throttle could be extremely high as it would not be under 'Dawes' control until the throttle is full (or nearly full) open.
You could of course control this with a BOV !