My 34 seems to surge when coming on boost, but only when i plant my foot to floor in a 4th or 5th gear. 1st, 2nd, 3rd doesn't really do it.

Even when it does, doesn't seem to make any noticeable difference to performance, just an interesting noise. Has been doing it since it went on and was tuned by sean. Hasn't seemed to impact the turbo either - has been on for 20km or so.

__________________
[SIGPIC][/SIGPIC]
Should have bought an STI

That's exactly what I want to do (1.5-1.6 at redline)..... I think I need a load mappable EBC to limit the boost around 3-3500 to around 1.25 bar (to prevent the comp surge I have in that rpm region) then have it ramp up to 1.6 from 3800 rpm and above...OR a P20 to delay the onset of boost a little (induce a little lag).

Otherwise I need to find another way to slow the boost ramp up under 3800 to 1.25 bar & have it hold 1.6 from 3800 rpm & up.

The EVC 4 can't do it as it only has one target boost setting, same with the PFC's on board boost control, 1 target boost & solenoid duty gain only.

Any ideas?

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

My surge is moderately severe (it will 'burp' back through the turbo unless I lift off), remember that I have cams & a little more engine capacity which provide more exhaust flow/gas pressure than a stock motor. This spools the turbo hard & I need to find a way to induce some lag down low (that's why I want a P20 housing).

The VF29 didn't surge as bad but it still did a little. The VF34 compressor is more efficient & slightly larger than the 29's & hence I smack the 34 compressor's surge line at low rpm coming on boost (turbo pumping more Air than the engine can consume - stalling the compressor).

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

I thought your bigger cams would have accomodated for this, in addition to ported heads etc.

__________________
[SIGPIC][/SIGPIC]
Should have bought an STI

1. I don't have ported heads but I do have a little more than 2l in capacity.

2. Cams create more gas flow & lower pumping losses (through longer valve open duration & higher lift)

3. The small a/r of the P18 exhaust housing is designed for stock gas flow.

Compressor surge explanation (ignoring wastegate function):

Imagine the way our turbocharger's compressor is driven, right back to basics: The turbine wheel is spun by exhaust gas, utilizing also the energy stored in the exhaust gas as latent heat.

This force on the turbine shaft generates torque at the compressor end as they are physically connected. Remember that part as its the key element, Torque

Now lets imagine our turbocharger compressing air, forcing it into the engine, the engine is utilising it.. what happens then? Ok, The engine expells it, and our turbine housing pressure goes up accordingly, the torque applied at the turbine wheel increases, increasing the spin speed and compressor efficiency at the other end. Great chain of events!

End Result? boost is climbing smoothly & nicely.

Now imagine this scenario:

The turbo begins to spin, as above, but the compressor wheel is generating more air than the engine can consume at a given RPM and the torque required to spin that huge compressor is not being met?
Remember that unless the air is processed by the engine, and expelled as hot, rapidly moving air into the turbine housing, our turbine shaft torque will not increase to spin the compressor faster, and it may well diminish.. our compressor is slowing, braked massively by the compressed air its trying to overcome and increase the pressure of.....

Result? Compressor starts to slow a little.. (beginning of a compressor stall)

So now what?
The engine is still rotating and consuming air, but the turbo has stopped producing an excess, so our engine has now had chance to consume what excess was available and the inlet pressure is now diminishing, the turbine torque is now increasing again...

VERY IMPORTANT: Remember also that at same time, compressor resistance to spin has also dropped due to housing no longer being as pressurized and as a result, the torque required to spin it has dropped massively..

Boom.. Suddenly the Turbine (exhaust wheel) torque massively exceeds the compressors resistance and the turbo spins to speed in an instant!!
Sounds great, rapid boost climb!! The compressor's accelerating at over 2G

BUT:
We just hit the same problem again, our huge compressor has made so much boost (& flow), so fast, and is trying so hard to push the massive volume of air, that our engine cant use it.... so we start to slow again........

So the turbo's shaft speed goes: Fast, slow, fast, slow (at high frequency) or in other words: The turbo is Surging.

As you can imagine, it continues this cycle until it hits the revs your engine consumes all the air.. then your boost is stable & safe again!

Severe Surge will snap the compressor blades off the compressor wheel with catastrophic consequences!

Not to mention the leaning effect the air reversion has with MAF based systems.

Sorry for the long Blurb ha ha!

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

I believe an Eboost might do what you need it to.

Problem is most ebc's go for either a target pressure, while some go for a target pressure per gear.

You need one that can change the target based on rpm.

__________________
I am only an asshole on the internet :)

[SIGPIC][/SIGPIC]

That's my conclusion too TJ......Or just go straight to a TD05-18 with the 8cm2 hot side & let a little lag avoid the issue all together!

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

As long as you dont downsize to a VF29 I am cool with that

__________________
I am only an asshole on the internet :)

[SIGPIC][/SIGPIC]

ha ha! when did you want it?

__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

I get paid Wednesday

__________________
I am only an asshole on the internet :)

[SIGPIC][/SIGPIC]