Blow Off Valve & Exhaust

[Stoffa]

And. the backfiring comes from letting metered air out of the system. monentarily running rich untill the bov is closed again

[vorigan]

 WRXONP said:

Haha I love threads than pan out like this !!! People bagging out a legend such as Steve haha great

So a quick summary - a quite valve ( even if venting ) that's stopping surge is working very well ??? And is basically restricting the outlet what's making it louder ?? Correct me if I'm wrong but I use to have a greddy rs on my old rb30 and the thing was quiet venting but had no surge

Pretty much bang on the money the trick is elevate enough air to prevent surge but not too much to induce lag, b/v despite what the people selling them say don't have hp ratings the engine their deem for will make power whether the valve is there or not, the cfm ratings is most important most need to dissipate 100-150 cfm to be effective and that's the issue no aftermarket valve comes with a cfm rating based on inch/water.

This may sound a tad primitive but you can blow though a straw making a sound is easy now try using a 4" pipe,im sure everyone gets the idea, years ago on Andrew hawkwoods evo i was doing my bit for we fitted 3 stock b/v with fliters and dam it would good

[vorigan]

Borg Warner copied mitsi with the built in recirc valve it ws first used on the volvos using the 13t TD04 its down side is the scroll limits how big you can go

[Nick_96_RSB]

 Stoffa said:

And. the backfiring comes from letting metered air out of the system. monentarily running rich untill the bov is closed again

is this also true with 50/50 recirc? or is this thread more or less pointed at full atmo venting valves? im using a GFB hybrid 50/50 and have seen no issues from using it, idle is fine ( is above 1k when really cold & around about a steady 500rpm when idle at lights etc), no backfiring etc and everything else under the hood is stock standard, or are these issues that develop?

I'm not here to stir the pot, just trying to better understand

[vorigan]

your not stirring and fair question cause its 50/50 its not as evident with an external vent the main thing is no surge

[Nick_96_RSB]

yeah no surge etc, so shouldn't cause me any real headaches?

[ben-jamminn]

I have my GFB 50/50 too and I often wonder how effective it is, because wouldn't the air take the path of least resistance, ie straight out the trumpet, not back to the intake?

[BINKZ]

 ben-jamminn said:

I have my GFB 50/50 too and I often wonder how effective it is, because wouldn't the air take the path of least resistance, ie straight out the trumpet, not back to the intake?

yeah id be interested to know this as i was going to get a 50/50 GFB valve....

[vorigan]

 ben-jamminn said:

I have my GFB 50/50 too and I often wonder how effective it is, because wouldn't the air take the path of least resistance, ie straight out the trumpet, not back to the intake?

as has been stated as long as it works and no surge its working and yes itll take the least resistance path but on the recirc side its been drawn in by the comp wheel that would be the easiest path.

[WRXONP]

So is letting too much out bad ? This is very interesting thread I must say - I never got back firing on my v3 Sti with ssqv but I get heaps of back firing using ssqv on my sr20det - not on full boost tho

[Stoffa]

on those gfb 50/50 valves dont forget the outlet thats recirculated opens first as its set lower on the valve, also your intake work as a venturi so it actually sucks the air from the BOV hose.

I've got one as well, I run it recirculated on the street with the second hole bunged up, and put the other trumpet in for thrashing/track

[vorigan]

Releasing too much doesnt hurt a thing but it does induce lag as does not releasing enough, nissans are well known for backfiring and killing turbos in the process.

When you run to atmosphere using a afm as stoffa pointed out the afm sees that as air being used by the engine when it isnt and dropping 100 plus cfm is a large amount of air when you consider your garage compressor is only 15 cfm.

When this happens the ecu thinks your running part throttle and drops fuel then when opening the throttle again theres more fuel than air and bang,very mild anti lag without the performance gains.

When inducing surge air is stopped due to closed throttle and has no where to go and tries to make its way back out the turbo intake but the exhaust is still being driving thus the returning air tries to spin the comp wheel backwards creating that lovely churpping sound, this can do thing like spin compressor nuts off,bend comp wheel blades or brake them off and brake shafts in half,kills thrust bearings.

Induced surge puts over 100lbs of load on a thrust bearing or just bash it with a hammer same results are produced.

[WRXONP]

How does the back firing kill the turbo ??? You explained how surging harms it - what does the back firing do to it ? Is also running no fuel cut on de cell bad for the turbo ? How it just pops and bangs on decel

[vorigan]

 WRXONP said:

How does the back firing kill the turbo ??? You ex

on nissan GTR's and GTST the turbine is ceramic and they dont handle the shock loaded and the wheel comes off also the GTR is well known for the broken bits to make their way back into the exhaust port, im sure you know the end result $$$$$$$$$$$$$$$

[WRXONP]

what about garrett t28 off a gtir? isnt that a inconel wheel? or steel?

sorry for adding to the off topic ness - just getting some knowledge off the master himself haha

is the backfire the fuel igniting on the exhaust manifold? does it speed up the exhaust wheel ?

[vorigan]

t28 were never ceramic and inconel based so if you've got one your fine....but the thrust bearing is another issue

the backfire is a high frequency explosion not controlled like launch control or anti lag so it does damage