surging under partial and WOT?

[funGT]

Howdy,

Just wondering if you guys can help educate me a bit before I get my car re-tuned mid next week. Your insights would be greatly appreciated re what I have been told is a compressor surge problem that is 'normal' ...

Just to put in context, I had vf34 twin scroll conversion on my 04 auto a few weeks ago- did all the recommended mods to run it on E85-202awkw. Was tuned with a TMIC but I have since put a FMIC on after much fiddling, hence the re-tune next week.

Essentially, I have been told I am getting compressor surge from the tuner that did the conversion- I get it under partial (light or moderate) and WOT what seems like almost all the time. I am pretty sure it has been getting progressively worse over the past 2 weeks since picking up the car. Occassionally, there is only the intake noise and in this dynamic it launches really hard and smooth (puts a smile on the face ). However, when there is the concurrent chh-chh-chh-chh sound in addition to the intake whoosh, it doesn't pull very hard and is annoying me as it is most of the time. In this mode it only feels like it is running at about 50% capacity compared to when it does not make this sound.

It is my understanding from what the tuner said that if the turbo makes boost around approx 3300 and the throttle is only partially open then pressure builds in the intake, hence the surging. However, when it doesn't do this, particularly under moderate or WOT, it is completely different. It is the inconsistency that is also doing my head in.

I have tried to research and watch youtube vids of cars with compressor surge and the vids I have seen seem more severe or sudden drop in power and none of them sound the same, whereas with mine, it sounds like a steam train chh-chh-chh sound (sorry about the corny attempts to explain sound!) and seems to rev slower and not pull anywhere near as hard from initial depress of throttle onwards, which is when the chh-chh-chh sound occurs (ie almost immediately after the throttle is depressed).

I am hoping some of the above may be a tuning issue in relation to the change in IC system (? I don't know) but it was doing the same thing before I took the aftermarket TMIC off (but to less of a degree, which is when I got the above explanation from the tuner- he said it was normal and that it can only be heard now because of the CAI). The partial throttle explanation for the surge makes some sense to me but I would have thought that it wouldn't do it under moderate or WOT or at least not the majority of the time? I also don't understand why sometimes it doesn't surge at all and pulls hard?

When I spoke with the tuner about it I initially thought it was the BOV as it sounds very similar to the purge when coming off throttle but he said it is definately not the BOV.

Any info or guidance would be great as to what is going on. It would be nice to have some knowledge about what is going on when before I speak with the tuner next week.

Cheers

[dr20t]

Double post

[dr20t]

What size rear housing are you using? if its still the stock twin scroll vf38/td04hla one, it may be pushing the surge line of the compressor wheel downward by choking the larger vf34 compressor wheel under moderate airflow.

If you have upgraded the rear housing to a ihi vf p20 twin scroll, then it may be tune related as I can't see the larger housing on the vf34 choking it up, especially in twin scroll.

Without starting a tuner war, could be one of the following if its not the smaller housing choking the turbo:

1. Incorrect turbo dynamics inducing compressor surge or wastegate oscillation
2. Wastegate duty cycle not tuned properly, causing boost spike / dip and thus the "surge" feeling you're getting.
3. Sticky wastegate solenoid / boost controller

Also, which boost controller are you using?

Mick

[funGT]

Hi Mick,
thanks for that info, much appreciated. Please note I don't want to start a tuner war etc either, just seeking some informed guidance so that i don't get taken for a fool... it isn't satisfactory how it is currently running.

I am not sure what size the rear housing is- I wasn't sharp enough to ask about this at the time- I assumed that it would be done well as they said they do it all the time. I am not sure how to go about measuring this?

Sorry, I have some questions Mick re your comments, hope it is ok?

1. Diagnostically, is it possible for the rear housing (assuming orig vf38 used) to still perform well even if it is too small? As noted, sometimes it does pull hard/smooth but rarely.

1.1. Is it a relatively easy job for the housing to be machined or changed to the ihi vf p20 you mentioned?

2. Interesting re wastegate cycle, a god question to ask.

3. Interesting.

I am not running any form of boost controller in the car per se (sorry, I meant in the 'cabin', no aftermarket boost controller is installed to my knowledge and there was no mention of it on the lengthy invoice either!. Cheers)- I assume whatever has been done has used whatever was there already/tuning?

Cheers Mick, thanks for your time.

[dr20t]

Hi Mick,
thanks for that info, much appreciated. Please note I don't want to start a tuner war etc either, just seeking some informed guidance so that i don't get taken for a fool... it isn't satisfactory how it is currently running.

I am not sure what size the rear housing is- I wasn't sharp enough to ask about this at the time- I assumed that it would be done well as they said they do it all the time. I am not sure how to go about measuring this?

Sorry, I have some questions Mick re your comments, hope it is ok?

1. Diagnostically, is it possible for the rear housing (assuming orig vf38 used) to still perform well even if it is too small? As noted, sometimes it does pull hard/smooth but rarely.

1.1. Is it a relatively easy job for the housing to be machined or changed to the ihi vf p20 you mentioned?

2. Interesting re wastegate cycle, a god question to ask.

3. Interesting.

I am not running any form of boost controller in the car per se (sorry, I meant in the 'cabin', no aftermarket boost controller is installed to my knowledge and there was no mention of it on the lengthy invoice either!. Cheers)- I assume whatever has been done has used whatever was there already/tuning?

Cheers Mick, thanks for your time.

No dramas at all

If you cannot replicate it 100 percent of the time with the same style of driving, then it may be mechanical related. That is, if WOT from 3500rpm to redline doesn't do the same thing every single time then it may not be surge.

The stock vf38 housing may be inducing surge due to providing a restriction at higher turbine flow. The vf34 compressor / wheel flows alot more cfm than the vf38, and the twin scroll rear housing will be limiting this somewhat too. It's tiny. You can buy larger twin scroll rear housings from eBay (kinugawa they make a very good product) to suit the vf38. That is if indeed it is compressor surge.

Do us a favour and list your setup. What boost are you tuned for? If stock bov, this could also be a cause (sorry I missed this above) as the stock bov are known to leak after 17psi.

List the full setup and allow us to delve deeper

Mick

[Robbks]

Definitely sounds like a surge issue.
Swapping from the TMIC to teh FMIC would have induced it.
the TMIC is a restriction very close to the compressor outlet and as such poses more of a restriction than the larger piping and FMIC further down the intake path.

the TS rear is allowing the turbo to wind up instantly, but the engine can't consume the air being produced and as such you'll get that surge.

It may also be worth checking the wastegate is not chattering either. both noises can sound similar.
remove the boost line to the wastegate and see if the noise changes. (watch your right foot, you've disabled the boost control)

[funGT]

Hi guys,
thanks for the replies, much appreciated.

I did some brief testing this arvo before reading your last posts. I noticed it does not replicate 100% of the time. Again, occasionally pulled quite hard in 1-3 but only when not making the chuffing sound, the power delivery is not consistent. Sometimes feels little better than stock (even when chuffing sound not present) whilst at other times it feels like a beast. I went for a spirited hills drive today after fitting the teins last night and under fairly constant med-full throttle, it did not make the chuffing sound much at all but still didnt feel as awesome as it can re acceleration- not sure if this means anything diagnostically.

The mods done include:
vf34 twin scroll conversion
avo silicon intake
injectors re-cal to 800cc
bigger fuel pump (tuner said MRT unit for up to 600hp but did not specify model)
new fuel filter put in (original)
Custom dump pipe using MRT flange and high flow cat (currently melting the rubber steering boot after 30 seconds of hard acceleration- smoke coming out from bonet
TCP s/s system from cat back with quads
running E85 only (computer wouldn't load 98 fuel map- I have seen mat say not enough memory on it so I assume it is this even though tuner tried mutliple times/ways)
cx racing CAI with K&N pod down in bottom of guard-had to cut out fog lights so should get good cool airflow to it
cx racing FMIC (I sourced a tiny battery so piping now goes up inside of bumper and in through between washer bottle and oil lines and then alongside battery rather than up between radiator-engine to minimise heat transfer (orig did between radiator but even ali pipe was hot to touch here after short hard run- made no sense to me to have 1.3+m of hot pipe after the intercooler).
timing belt done (car has done 182K)
tensioner pulley replaced.
O2 sensor replaced as old one shat itself ages ago
new cam seals etc (but still leaking)
new plugs
tein street flex coilovers fitted last night- awesome. will fit active system in coming week or so to minimse wife and kids complaining about ride (in theory but I doubt it! )
all bushes redone in front and rear (whiteline and another brand j-speed? because whiteline stock shortage at the mo)
22mm whiteline rear swaybar fitted
18in STI spec B rims
dba4000 rotors fitted on front
MRT pads front and rear (the tuner has lots of MRT and I didn't mind at the time as I assumed it would be good and couldn't org parts through Garage88 in time)
master cylinder support bracket
braided lines ordered
trans serviced
power steering pump recon (it was tired and leaking)

I will try and test later tonight and maybe even record brief vid. I will also try and remove the boost line to the wastegate to see if that does anything.

The dyno sheet said 202awk at 17psi however the graph looks like boost is just over 20psi and tuner mentioned 'just over 20psi' when going through results, so not sure why summary prints 17psi. the sound it makes is similar to BOv sound but slightly different.

I wil have more info later tonight hopefully re different driving styles and results.

thanks again for your insights

[funGT]

Howdy,

Forgot to mention that it was fluttering when the TMIC was on, so it has not started since changing to FMIC.

I went for a test and under full fairly fast progressive throttle at night (about 16 degrees) it did not make the sound (murhpy's bloody law!) and pulled quite well compared to what it has been doing during the day-
eg: http://www.youtube.com/watch?v=cJa3i1Gd3cE

Under light slow throttle, like taking off from slowing down behind traffic, it made the noise fairly consistently from about 3800rpm. The vid doesn't capture the volume and sharpness of the fluttering (much louder playing it directly on the smartphone- but a little bit of an idea can be had. It also seemed to be less pronounced than during day time (not sure if ambient air temp has an inpact on it).

eg:
http://www.youtube.com/watch?v=-NnwW4kXGxk
http://www.youtube.com/watch?v=k55dPtgORvo

I didn't get a chance to remove the boost line to the waste gate yet to test that. was a bit concerned about potentially overboosting it.

Forgot to note the BOV is standard.

From the hardcopy of the dyno results, it looks like it is running between 20-21psi (bit higher than 17 re potential BOV leak as well?)

Hopefully the above highlights a bit better what is going on.

I look forward to the late night analysis...thanks again!

[funGT]

Howdy,

I recorded this below and sound is clearer but prob also seems more pronounced during day, Again, it is inconsistent but happens often to different degrees, the vid below is a moderate example. daytime 10am about 25 degrees.



<iframe width="420" height="315" src="//www.youtube.com/embed/Tj1sm7-DkEQ" frameborder="0" allowfullscreen></iframe>

hope this info makes my excessively descriptive explanation clearer any guidance would be greatly appreciated

[KiDo_Tuning]

Done around 10 of the VF34 TS conversions. It should have 20psi by 2800rpm and hold to 4200rpm and then 15 to 16psi at peak power so it should have a boost curve as boost tapers off up top etc

The issue could be the AVCS Solenoid filter baskets.

[bigBADbenny]

Meaning log it with a tactrix for starters

[dr20t]

That's some serious surge

[bigBADbenny]

Have you tried a pull with it locked in say 2nd gear to see where the reversion kicks in?

Whereabouts your location?

[funGT]

Howdy,

Thanks for the feedback, much appreciated.

I checked the print out and the boost description you mention Mat, and it is similar but it does not have rpm on the graph. (steep incline from 13-19psi & then drops back to 17 in first colomn, then similar incline up to about 21psi in second colomn and the progressive decline to about 16psi over remaining 5 colomns). I have been trying to find the AVCS Solenoid filter baskets in the workshop manual to inspect if possible but haven't been able to find them yet! Are they visible externally? (sorry, not a mechanic's a-hole but confident to pull anything apart and put back together, usually with a few spare bolts left over ) Are you coming to Adelaide any time soon Mat?

If the issue issn't resovled properly on Wednesday with the tuner (hope it is but it was doing this after I picked it up and upon inquiry he said it was normal-- but I am thining/hoping he must not have understood my explanation..?),then I will explore the log etc avenue, cheers.

Just went for a test while kids and wife aleep (in Adelaide ) held it in second and the surging happens from about 3700-4000rpm and then the fluttering clears but big loss in power, slower reving to redline or there abouts.

Forgot to mention fuel usage is absurd, like 1/3 of a tank in approx 70km driving through burbs & mostly light throttle as wife and kids in the car! I understand E85 is supposed to use 15-20% more fuel, but I am wondering if this excessive fuel usage is part of the problem?

Thanks again for your input guys, much appreciated.

[pranayshrestha]

...
The stock vf38 housing may be inducing surge due to providing a restriction at higher turbine flow. The vf34 compressor / wheel flows alot more cfm than the vf38, and the twin scroll rear housing will be limiting this somewhat too. It's tiny. You can buy larger twin scroll rear housings from eBay (kinugawa they make a very good product) to suit the vf38. That is if indeed it is compressor surge.

...

Sorry to go off topic. Mick, sent you a PM regarding this post.