Gtr Compressor Surge, (shuffling Noise)

[mark morris]

Hi every one,

I have a 33 gtr with the usual mods for about 300-350 rwkw.

* n1s

* z32s

* pond cams, gears

* pfc

* larger intake piping with twin pods

* full exhaust

* injectors (700cc), pump, rail, reg, etc.

"keep in mind I done all of this in one go from an stock engine"

My issue is a surge noise coming, (shuffling from pod top pod) from air filters).

Now when I made the new intake piping, I did not put the link tube in between the two turbos, didn't think it was necessary but boy was I wrong! the thing wouldn't even idle, let a lone drive properly. any way I made a piece to link the two, behind the afms obviously. and the surging was removed and the car became drivable, did tune got over 300kw, driving quite well, other than that shuffle between the turbos (compressor surge at cruise). just wanting to try and get rid of it apparently a lot of gtrs have this problem when the things are opened up i.e., 80mm afms etc.

Now I have heard a few things such as the original bovs actually recirculate slightly when a after market vent to atmosphere would normally be closed , if this is the case, I guess it would help as what I think is happening is the air is being forced against the closed, or almost closed throttle body at idle or cruise, and backing up through one turbo and then the other, so if the air at this point was vented to the intake side of the turbo instead of backing up to the outlet side I guess it would work. but then if the original bovs do recirculate all the time then how would it make boost?? I ask this as the car has those poxy supper sequential hks bovs on it, (not my doing they were on the car when I bought it.)

Also I have heard that linking the two signal wires from the afms to the ecm so they read the same voltage also can have some effect, this sounds a little dodgy but have hear that they do that when running two afms on a large single set up.

I do think it may be something to do with the afms double reading air as I know it was when I had no link pipe in the intake as you could see the afm voltages on the pfc. but now they are pretty close to the same.

any feed back, opinions, experiences etc. on this would be appreciated as it pissing me off, especially at idle.

Regards, Mark.

[R31Nismoid]

Put the stock BOV's back on.

Problem solved. Very common, easily fixed

[Amaru]

Get the problem tuned out... I run Z32's, HKS 2530's with Blitz blow off valves (non recirculating) and only occasionally have a problem loading it up in 5th gear going up a hill.

It was bad, but the tuner somehow managed to get rid of most of it (I know this is also true for people who have had the same problems and had it tuned at other tuners).

[mark morris]

Ok,

so do the stock BOV's recirculated all the time? just want to make sure this is going to solve my problem, as I dont have any stock BOV's. they gone when i bought the car, and will have to buy some to test it out.

Also has any one heard of a GTR shuffleing during idle? thought base timing may have been out, but it is correct.

Thanks for replys.

[R31Nismoid]

Lots of GTR's do it. Seen it all the time with cars who've changed BOV. Change it back, solved.

They only only recirc @ idle as far as i know.

[mark morris]

Ok, its just it wasnt doing it at all when the engine was stock, ecm, injectors, ams turbos, etc....

just will have to get stock bov's and give it a go.

thanks again.

[Beer Baron]

i don't think it's the bovs. I mean it wasn't doing it before when you had the bovs but with stock AFMs etc. I would say it's due to the change in intake piping, and afms, turbos etc.

[JimX]

I was typing up a thread asking about this because I didn't know what to search for and even didn't know how to describe it properly, but suddenly decided to stab at searching for "+vent* +noise +air +boost" and turned this up. So thank you Mark Morris for making this thread and using the right words

This seems like the same problem I have. Going back to stock bovs would be nice, but is there a cheaper (free) way to do it? I'll do that if I have to, but it means having to spend money and look for a pair to buy and probably re-manufacture some of the plumbing (I seem to have HKS intake plumbing). Are there any lines that can be linked to help? eg vacuum lines, AFM wiring, exhaust/intake? etc.

I also have the high idle problem which I have gathered from searching is due to a vacuum leak, but I can't find it even after spraying half a can of Start Ya Bastard around the place.

[paulr33]

the custom intake piping is causing the chuffing.

take them off and see how it idles and drives just with open airflow meters. of course dont leave it like that, but try it. i replicated this problem when doing some mock up cold air intake pipes with some PVC pipes. chuffing on the compressor side caused the AFM to be unhappy and bouncy bouncy idle

[JimX]

the custom intake piping is causing the chuffing.

take them off and see how it idles and drives just with open airflow meters. of course dont leave it like that, but try it. i replicated this problem when doing some mock up cold air intake pipes with some PVC pipes. chuffing on the compressor side caused the AFM to be unhappy and bouncy bouncy idle

Oh, ah, by intake piping I mean everything behind the airflow meters up to the plenum (intercooler piping). Which would surely affect how it breathes somehow, otherwise the previous owner wouldn't have done it. In front of the AFM's it just has 2 HKS pods, which I would like to replace with non-oiled filters (apexi are my favourite) and some sort of cold air box. Do you think it's just the pods that are doing it? I would have thought that the pods would just make the chuffing more audible. The idle is also fairly nice and smooth, just uniformly too high all the time. It doesn't even get the stalling problem that my GTS had (but that could be because it's idling too high to stall).

[paulr33]

hi colin

im not sure which problem you are taling about but the original posted said he made up some customer cold air intake piping to the pods. this would likely be the cause.

[mark morris]

Hi All,

I havent been on this site for a while, but just got an email as I was still subscribed to this thread.

I still have this problem I have not had another tune yet but I will shortly as I just fitted a larger front mount ect. so I will let you know how it goes. its of the road right now as I have some panel work getting done so this is all probably still a month or so away.

As for the custom intake I made;

All I made is a replacement ally pipe from the AFM to the rear turbo, wich now tees off into the same pipe on the fromt turbo, the rest of the intake consists of a HKS intercooler and hard piping kit and 80mm apexi super suction kit, where the pods just bolt straight onto the AFM's

I have heard of this problem when people have moved the pods and AFM's closer to the turbos, they say that the AFM's should be as far away as possible so most of the back surges dont make it to the AFM's and get read twice as intake air. though my AFM's are in the same spot as when it was stock, which is about as far away as you can go anyway, with out making some very large modifications.

Stock blow off's are now not an option for me as I have no room for the recirculation pipe be hind my new larger intercooler.

none of these are really questions nor answers to any of your questions. just letting you guys know what I have done so far.

"Jim x" I would definitly try to sort out that vacume leak first before getting to worried about the shuffeling, as it maybe contributing. I am guessing you have already tried to set the idle AAC valve ect.... is it pulling a decent amount of vacume during idle on you boost guage?? make sure the vacume sides of your brake booster and clutch vacume assist are not leakig internally by just disconecting them and pluging the holes in the intake. vacume leaks can be sneaky little barstards! good luck!

Regards, Mark.

[JimX]

Hey Mark, thanks for replying and indeed coming back to the forum, it's a great place!

I'm not too sure it has a vacuum leak now, because even though the factory boost gauge is disconnected and the aftermarket one is not set up properly (long story, basically neither reads the correct bosot) the boost controller seems to read a constant reliable -0.5 bar of boost at idle, which is what my last car did with exact same model boost controller (Greddy Profec) and idle is otherwise smooth and not fluctuating.

I haven't cleaned or adjusted the AAC valve yet but from other people's posts I'm not holding much hope for that to fix it. Although for a small minority of people it did work so I will get to it tomorrow.

I will also try disconnecting the brake and clutch boosters, thanks for the tip!

[The Alchemist]

well you gave a perfect description of good ol compressor surge. Unfortunately its a product of the turboes you are using and the engine they are bolted to rather than the intake piping leading to and from them or anything else for that matter.

I had surge on the standard turboes on my GTR but only light and only in 5th gear on light throttle.

When I upgraded to a ball bearing turbo the surge was so bad it would choo choo at idle, 50km in 3rd or 4th was a joke. Sounded like my blow off valves releasing every 2 seconds.

Part of the problem was that I had adj cam gears and tomei cams set up to decrease my standard turbos spool up time. This did the trick but when I upgraded to the ball bearing turbo setup, HKS GT-SS, the cam gear set up was no good at all. It causes the turbos to make boost while the throttle is practically closed.

This was confirmed when we measured boost/vacuum on the dyno pre and post the throttle plates. On the engine side I was just pulling vacuum but on the plenum side I had 2 to 3 psi boost !.

This causes the air to back up behind the throttle plates and bounce backwards in the reverse direction back towards the turboes > AKA Compressor surge < creating the chuff chuff sound on light thottle openings.

I set the cam gears back to zero/zero , widening the lobe centers and decreasing overlap, and the problem almost disappeared except at 100km in 5th where you can just notice it ( back to how it was with the original turboes ). Acceptable but I'm sure I could improve it some more but have not had the chance to experiment further with cam timing. As far as "tuning it out" is concerned I guess ignition timing could have a small effect and I'll try that out too next time I'm on the dyno.

Mike

[govich]

hi guys, i'm having this same problem with my GTS25t. i get a harsh 'shuffling' noise at about 1500rpm in any gear above first at any throttle opening. i'm going to try putting back the stock BOV and that'll hopefully get rid of it.

my question is, how much harm is this doing to the turbo or engine?

[GTsauRus]

Oh, ah, by intake piping I mean everything behind the airflow meters up to the plenum (intercooler piping). Which would surely affect how it breathes somehow, otherwise the previous owner wouldn't have done it. In front of the AFM's it just has 2 HKS pods, which I would like to replace with non-oiled filters (apexi are my favourite) and some sort of cold air box. Do you think it's just the pods that are doing it? I would have thought that the pods would just make the chuffing more audible. The idle is also fairly nice and smooth, just uniformly too high all the time. It doesn't even get the stalling problem that my GTS had (but that could be because it's idling too high to stall).

at closed or small throttle openings your bov opens when the pressure between the turbo compressor and throttle body is higher than the plenum pressure after the throttle body where the bov vacuum signal comes from, then at wide open throttle there is no pressure difference so the spring keeps the bov shut. The shuffle your hearing is compressor surge so it means your bov is not opening, It is possible that the vacuum leak is a hole in the bov diaphram which would also prevent it opening causing compressor surge.

My gtr stock boost didnt work because the vacuum line was not connected to a little tube at the rear of the throttle bodys just like the one at the front that goes to the fpr vacuum hose . replacing it lowered the idle 300 rpm. It is well hidden

You can get compressor surge if the spring preload of the bov is set to high

[Busky2k]

I've got the same problem on my car. From 4000-5500 rpm you hear compressor surge on full throttle, and it sounds like flutter. On the dyno you can see the pod filter/intake piping shuddering.

The car still goes smoothly though but I'm not sure why it does it. Its supposed to happen when the engine can't swallow all the air the turbo is pumping. Only thing that solves it is to turn the boost down, but thats no fun now is it?

[paulr33]

i always thought it was reverbration going past the airflow meter hotwires, which makes it cough n fart as the ecu see's all sorts of crazy airflow meter signals

[StockyMcStock]

busky it sounds like your compressor stage is attempting to work outside of its flow efficiency island, usually when pressure is high but flow isn't, like when you close the throttle and get reversion.

turning the boost down will work, as will anything that gets more power out of the engine like bigger cams, bigger exhaust side etc - this will get the flow up higher instead of lowering the pressure, which is just another way of correcting the discrepancy in the two.

it's not a very good thing though i beleive, as when you go outside the compressor's limits like that your outlet charge from the turbine is much hotter than it normally would be, if it was working within its design limits. so your inlet temps at the plenum might be getting up there, which is not so good.