Off Boost Compressor Surge

[Stoffa]

A few specs before I start, forged engine, MSE modified VF turbo with 18G compressor wheel. FMIC, Link G4 running 3 stage closed loop boost control, GFB dual port BOV.

Im getting alot of off boost surge with my car, its been doing it when the engine is loaded up driving up a hill with about 3/4 throttle and when the engine catches up to the point im accelerating too it flutters and when it does it the engine gets a bit of a shudder.

I can easily stop it shuddering by backing off enough to open the BOV or give it some more gas but since ive been driving round all these nice curvy hilly roads in otago it been getting to me.

I did have my BOV plumbed back and it was alot worse when it vented backinto the intake, so now its venting to atmosphere 100% and I've wound the spring pressure right out which helped minimise it.

Im guessing its bad cos my intercooler pipework is an off the shelf FMIC kit and REALLY long, and when the engine doesn't need the extra air the stuff between the compressor and throttle body has nowhere to go as theres not enough vacuum to open the BOV, so it just gets forced back to the compressor again causing it?

Im not worried about it damaging the turbo as its not doing it on boost but really annoying when you've got the sounds cranked up and cant really hear when it starts it do it. So not that smooth for driving.

Does it sound like I know what Im talking about or is it something else causing it?

and if I my theory is correct, will going back to a top mount solve all my problems?

[Guest]

I think I get this in my car. Only off boost and low rpm though just as you come off go pedal. Similar set up. Ohhhh and i have flipped/twisted so slightly shorter piping. Difference is I like the sound hoping its not bad for it though. Guessing mine is surge not fluttering bov.

[Stoffa]

yeah mines definatly not the BOV, yours sounds the same as whats happening with me, im told its not bad, I like the sound too but not when it makes the engine shudder a little.

[Guest]

Dont think mine quite has parkinsons.

My racepro bov is about half the surface area of the gfb I pulled off and i adjusted it till it fluttered. Cant remember if the gfb one did but didnt run it on fmic anyway only the current one.

[boon]

I get something very similar with my setup (which is somewhat similar to yours, mildly tweaked VF34 + Link G4) although I'm top-mounted too. Mine doesn't really shudder though.

I dunno what to do about it really. I suspect tweaking the boost/wastegate map would help but I think that would sacrifice the super quick and solid spool we get with the G4 boost control...

[funkytown]

 boon said:

I get something very similar with my setup (which is somewhat similar to yours, mildly tweaked VF34 + Link G4) although I'm top-mounted too. Mine doesn't really shudder though.

I dunno what to do about it really. I suspect tweaking the boost/wastegate map would help but I think that would sacrifice the super quick and solid spool we get with the G4 boost control...

i dont have technical answer to help solve it for you but.. some example

Steve Murch vf23 on TMIC, venting bov - same as what you describe.

same as above with long route FMIC - same as above

Garrett with venting bov and flipped manifold - same as above

garrett with shortest under lights piping - same as above

Garrett x3076 with piping as above but with anti surge housing - HEAPS better.

I think its about the tune you get put on and how its mapped. The reason i think this is because when we all go to have our cars tuned, on part throttle or the turn of the boost curve to bring it on, they are all tuned for max power (with in reason) therefore tuned to bring on turbos as quickly as possible which combined with a MAP based tune confuses the tune badly on part throttle. The cars basically i believe they are not tuned for those conditions specifically.

If you went back to MAF based, and didnt aim to bring a turbo on so quickly through the low range it should smooth the transition state out when on partial throttle.

FWIW i found no difference at all between IWG or EWG set up.

[Guest]

Might be worth noting Im running the ecu for td04 and top mount now fmic and vf23 etc.

[Stoffa]

 boon said:

I get something very similar with my setup (which is somewhat similar to yours, mildly tweaked VF34 + Link G4) although I'm top-mounted too. Mine doesn't really shudder though.

I dunno what to do about it really. I suspect tweaking the boost/wastegate map would help but I think that would sacrifice the super quick and solid spool we get with the G4 boost control...

+1 on the boost control, awesome control

Have you ever logged your intake temps? What intercooler do you have? How much power does yours make?

Im sitting around the 240kw mark at the moment so Im guessing a TMIC wont harm things too much power wise but I like the idea of going back to a factory airbox. If it stops the shudder then I'm all for it.

I love the torque my car makes as it is so not too keep on restricting the boost levels down low as I get 400+NM at 4300rpm

[Stoffa]

 funkytown said:

Steve Murch vf23 on TMIC, venting bov - same as what you describe.

same as above with long route FMIC - same as above

Garrett with venting bov and flipped manifold - same as above

garrett with shortest under lights piping - same as above

Garrett x3076 with piping as above but with anti surge housing - HEAPS better.

maybe a top mount, send the turbo back to steve for a 4 inch inlet antisurge front cover and twist it muahaha.

I could put the P25 housing on at the same time......wait...note to self....stop modifying it and just drive it!!

[Swindog]

I had similar issues with my MSE turbo as well. Finally went for a Tial 50mm bov and a 7psi spring. Didnt totally solve the issue but reduced it quite abit.

Cleaned all the pipework etc in the front mount. Maybe it just flows really well? Had a twisted setup too.

[B4 2000]

 Swindog said:

I had similar issues with my MSE turbo as well. Finally went for a Tial 50mm bov and a 7psi spring. Didnt totally solve the issue but reduced it quite abit.

Cleaned all the pipework etc in the front mount. Maybe it just flows really well? Had a twisted setup too.

same here, and thats the main reason that im getting another turbo!

Steve says it's probably a BOV issue. Few other ppl (tuners and turbo shops) reckon the turbine is too small and causing it!

[titian]

larger BOV will do this.(flutter) But you need a large one at the higher end of boost to prevent compressor stall.

Fitting two BOV will sort it out . One small with very little spring pressure,(i.e. opens at around 5'' vac) it will then open fully at the lower end when the turbo is generating boost that the driver does not require.(std one works well).The after market one set to lift at around 20" vac....For the higher release required at the upper end of boosting.

Or a BOV with two stages of lift.

[Swindog]

I had a td05/td06 25g so large wheel but yeah i shoulda just put another vf22 back on. Kinda made me dislike the car to drive.

[vorigan]

first off chris you could have rung me second too higher load and low rpm itll do it along with many other things, stock b/v are designed to deal with a certain cfm based on stock setup some get away with upgrades without an issue others dont.

i can induce surge even on a stock turbo if i try had enough but in saying that if it keeps happening well im sure you can figure the rest out

if its a mismatch of turbo it would surge on boost not part throttle or trailing throttle

[Stoffa]

I will ring you Steve, just away on holiday with a bung phone, I did wonder if a much bigger BOV might help the situation. P.s love the powerband from your turbo.

Is it possible to tune out some of the surge? or will it hurt overall torque

[pl0x]

Sounds similar to all 3 of my subaru's with links

First one twisted & modified td05 & it would surge when part throttle with enough load and you could hear EWG kind of a "flapping" open and closing noise.

My current car and my old car - both had unmodified vf22, silicone intake, zorst & fmic. They surged coming on boost in higher gears and under load with part throttle

Questioned it and got the response that the motor can't swallow/use all the boost at that RPM, high cfm low rpm, the way to control would to play with waste gate duty at those rev's (lower boost at those rev's)

I have learnt to ignore and drive around it

[Stoffa]

On that train of thought maybe my modified factory headers cant get rid of the exhaust quick enough?

[funkytown]

 Stoffa said:

On that train of thought maybe my modified factory headers cant get rid of the exhaust quick enough?

my larger diameter aftermarket headers do it as well stoffa, has an enlarged up pipe to boot.

[vorigan]

does anyone actually read what i post instead of looking for scientific answers to something thats quit simple?

thus why i have a facebook page

[Stoffa]

Steve, Im not using a stock bov its a gfb one, do you think one with a much bigger piston and soft spring would help? If so any recommendations? new bov would certianly be an easy fix

[vorigan]

all aftermarket b/v are crap ive lost count how many times ive read or had phone calls saying " i changed to a aftermarket b/v now it surges" that in itself should set alarm bells of for people but it doesn't........amazing.

if it was me i would use two stock units and plumb back which under one of the up and coming LTSA regs is no vent to atmos b/v unless it came factory setup which we all know non of them do.

ive just got one of my turbo bmw conversions going and NO GAY BLOW VALVE VENTING and you cant hear a thing and 100% no surge, in your case chris put two stock units on it no adjusting needed and no need for internet scientific solution but there is however calculations used to design a b/v which someone forgot to give to the aftermarket manufacturers on how its ment to work and what cfm is needed to be vented to control surge without emptying the system inducing lag and ive covered what that criteria is and i cant be assed doing it for millionth time.

broken turbos are great for business but that chirping sound is soooooo cool.......not

if aftermarket b/v are sooooo smart why do they cause soooooooooo many issues? Tui's billboard

[Guest]

Dont mean to sound thick but do you just need two for the flow side of things?

Ive never had a stock bov to compare too..

[vorigan]

without getting into a whole bunch of calcs then the usual crap that follows you need to dissipate enough air/cfm to prevent surge at all throttle openings thus aftermarket b/v wont do that under full throttle decel they work but part throttle their crap not sensitive enough to compensate, normal part throttle is around 0 atmos or slighty minus vac on trailing throttle the factory unit responds great using around 1-2psi spring aftermarket use such a heavy spring to keep the valve closed at idle you need to be pulling high vacuum to make it work.

translated pretty looking and sounding b/v arnt worth the 10 bucks you pay for them

[Guest]

So loosening the spring as much as possible would help with sensitivity? I always did wonder why a lot of quick tuned cars have factory bovs...

[funkytown]

interesting discussion, that 0 atmos slight boost / vac at part throttle is indeed exactly where i can induce crazy sure like conditions.

raised the question in my mind as to why factory bovs are only using such small springs compared to A/M ones. My experience with an aftermarket one trying to back the spring off nice and weak - i guess emulating factory spec they dont remain closed like they are supposed to.

my question is - is there something inherit in their designs that make them not behaving crap with low spring pressure?