JamesS

Andy,

Did you confirm coil packs by replacing / testing?

Was the effect similar to boost-cut?

Cheers!

dowser

Re. induction kits and surge; I thought that surge was caused by the turbo running out air. But if it's more likely to do it with a freeflowing intake, then it cannot be related to this. You can assume there is more of a vacuum between stock airbox and turbo than on a cone filtered car, so is it correct to say then that surge is caused by an inability to collect the air and force it through the compressor (as the blades are accelerating so quickly) - the vaccum in the inlet pipe would then help this, no?

Or am I wrong....again

Richard

EMS

Lot´s of people assume a big induction kit will increase flow because of the decreased resistance. But I could imagine that at low revs where the flow is quite low, the standard setup has advantages because of the higher air speed. Or perhaps there is some sort of "tuned length" which will help flow at certain (low) RPM.

Mark.

Andy.F

James - On the car I referred to, I was only able to increase boost from 1 bar to 1.2 bar by decreasing the plug gap. It was not a full 100% cut but probably 2 or 3 cylinders cutting. I guess that would be dependant on how many packs were breaking down.
If you can run higher boost at say 4500 rpm then it is not coil packs.

Mark/Richard - As surge is primarily an air speed issue, it could be as you say Mark, that the higher velocity on the small bore inlet pipe actually assists with air flow through the compressor at low outputs. Unfortunately the small bore induction starts to limit output at higher flow rates by causing a pressure reduction at the compressor inducer.
This is how a ported shroud works, at low flows it has a high recirculation/bypass which maintains high intake velocity.
I think the AVCS on the Sti7 may also have positive VE effects at the spool up stage which helps to allow more boost.

Andy

nom

Surely it's the same as with any restricted system - the thinner (more restrictive) pipe will speed up flow, but the total gas flow rate will be lower?
In the case of compressor surge, the problem I'd have thought could come from either end - either not enough air being available on the 'in' side (restrictive inlet), or nowhere for it to go on the 'out' (restrictive engine & all that stuff ). Which in this case leads me to believe that the problem is with the engine not being able to shift air out fast enough. Or it's shifting air our very nicely, thankyou, in fact nicely enough to mean that the maximum flow rate of air is reached (before surge sets in) at a lowish boost. Tricky to check as I know of no easy method of measuring flow rate through the inlet manifold

But, of course as Richard says -

Or am I wrong... again

EMS

No big concerns at that side, as the car produced normal (nice) power figures at higher revs. The car behaved absolutely "normal" except for the fact it didn´t like boost at lower revs.

Mark.

Jake

Sorry for the stupid question but what exactly is compressor surge and what are the symptoms???

nom

Erm, without getting too technical , sort of the compressor trying to hoosh more air through the system than it is able to.
A particular compressor will flow a certain amount of air at a certain PR (so boost level), given the chance. If it can't because of a restriction (either not enough air available on the 'in' side, or there's a blockage - that's the engine - on the other), it 'surges'. Reducing the boost reduces the flow rate and removes the surge. Making the engine 'process' air faster at the same boost/rpm will also reduce surge (as would putting a bigger engine in ). And if the inlet side is the problem (trying to suck air through an ants' nest has been known, IIRC ), then opening that up can sort it.
Which is where the problem lies, as there's no obvious restriction anywhere, and the 16G should work very nicely with the engine/exhaust set up in question...

If you apply that to the graph up there ^^^, taking a 'flat' PR of 1.3 bar (2.3 PR) you'll go past the surge line (left-hand-side) at I think ~220cfm? I couldn't be bothered to do the maths so I'm not going to work any more out, actually
I've never really looked at a compressor map for the 16G - I can see why they put it on the original cars at around 1 bar!

After all my drivel, Andy will presumably be able to give a technicaly excellent description, which will doubtless mean bugger all to most of us

andycasey

Hi i havent long had a TD05/hybrid on my 2.0l my00 wrx AUS delivered, the turbo has got a TC06 comp cover (not TD06) with a garrett V1 Dash 24 Wheel and a standard Subaru TD05 rear housing with a Garrett P Trim wheel A/R 0.63,or in other words i think they re T3/4 wheels, the problem i have with it is it has bad surge when im in 4th or 5th gear cruising then i floor the pedal,the boost pressure gets to around 10psi i can start to feel it pulsing then it goes "whoosh" "whoosh" "whoosh" violently then looses boost pressure, But if i use 3/4 throttle it's fine or i drop back to 3rd and floor it no problems.Now my tuner said i should bin the thing because of the surging and he cant tune it out, so i have decided im going to get the turbo rebuilt and have a 20G Comp cover & wheel put on and leave the rear alone if the turbo rebuiler thinks thats viable but just reading through hundreds of posts through here it seems large high flow intakes are the problem with 20g's am i right??? i have not long put on a high flow AVO silicon pipe and APS cold air intake would this cause issues like i explained above? Also theres something about how the boost is brought on can someone explain this to prevent surge?? I just dont want to have another turbo do exactly what my previous one did..

Cheers Andy

David MY99

I've had serious boostcreep issue's on a deadboltspeed td05/06-20G. Had the turbo ported and no creep at all, still suffer with some surge between 4000 and 4700 rpm.

I'm running GT spec headers, ported heads,Apexi AVC-R (1.5bar till 7500rpm) Blitz airfilter and a 70mm intake hose.
I'm curious whether i have to reduce the intakehose to a 50mm or make it more free flowing to solve the surge?

I do have an appointment with EMS/Mark for next week to check my mapping, but want to solve the problem first. There was no difference with different AFR so i think it's not the mapping. The car give's descent power and runs from 100km till 200km in just 9.0 seconds (anyone who quote an powerfigure for such times bij any chance?)

Aztec Performance Ltd

iTrader: (234)

on a stock internals??

Bob

Andy.F

The 20G does not respond well to an oversize intake hose, it is possible to make circa 400bhp from the standard intake pipe, or fit your 70mm pipe with a short 50mm section prior to the turbo to increase the intake velocity.

Andy

David MY99

BOB'5
i'm running wiseco forged piston's, STI rods, crank and bearings and some other stuff but on a regular open deck ej20T. 1.5 bar is the max for the shortblock by the way, if you raise the boost more you'll blow out the headgasket (been there done that ) But then again this was with an VF34

Andy,

I tried it and that did not help, actualy it sucked the restrictor hose into the turbo shortly after
I'm now gonna try a heavier wastegate actuator and see if this reduce the surge.
If not i'm gonna put back an original intake and pray that it will solve my surge problem and won't cost me spoolup or power