Silvia Club of NSW

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PostPosted: Mon Aug 21, 2006 9:54 pm 
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T51 Hybrid
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Yeah I'm pretty stumped and dissapointed at the same time. Guess everyones out of ideas as I am. Perhaps maybe different camshafts might fix the issue, or a laggier turbo! As I understand, surge only happens when you have an overly large compressor which spools early (ie mismatch turbos) which in this case certainly isnt the case.

And as for the intake pipe shuddering, its the reversion 'waves' that seem to make it shake realtively violently. The motor doesn't move though. Might see if I can get a video to show you guys what I mean.


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PostPosted: Tue Aug 22, 2006 10:10 am 
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Busky2k wrote:
Yeah I'm pretty stumped and dissapointed at the same time. Guess everyones out of ideas as I am. Perhaps maybe different camshafts might fix the issue, or a laggier turbo! As I understand, surge only happens when you have an overly large compressor which spools early (ie mismatch turbos) which in this case certainly isnt the case.

And as for the intake pipe shuddering, its the reversion 'waves' that seem to make it shake realtively violently. The motor doesn't move though. Might see if I can get a video to show you guys what I mean.


I was just thinking that maybe putting in a 256 exhaust cam might fix the problem. I would try putting the exhaust cam back to zero degree first to see if that makes a difference, if it does I would then advance the cam by 2 degrees to see if it further improves it. If it does I would pull out the 264 and put the 256 in at zero degrees.

Think I might dissagree with myself... (there's a quote just waiting to happen) Advancing the cam will open the exhaust valve earlier allowing greater air flow earlier, but it wont effect total air volume so it may have no effect whatsoever. I would still put it back to zero all the same to see if it has an effect.

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PostPosted: Tue Aug 22, 2006 4:05 pm 
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Quad T66
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i dont think you need to change anything, i think theres something wrong with the current setup or something isnt setup properly.

try slowing spool up on the boost controller and increase wastegate creep, so you get less airflow around that rpm region. see if that makes a difference.

other then that when you reach a stage of being stumped, i suggest you try taking things out of the equation through the process of elimination and hopefully that will isolate the issue.


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PostPosted: Tue Aug 22, 2006 4:15 pm 
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Quad T88
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i think moko try to say to turn down the gain on the boost controller if it is electronic one you have

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PostPosted: Wed Aug 23, 2006 12:43 am 
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Yeah I could try messing with the cams. Might get round to doing it next time I can be bothered removing the cam cover. Just hate fiddling around with it! Also I might disable the NVCS and see if it still surges.

And yeah the most obvious solution is to turn down the boost in the early midrange, but it kind of defeats the purpose of having a responsive turbo isn't it? If the engine can't proprely 'swallow' 1.2bar ~3500rpm then I might as well just go bigger?

I have an AVCR which runs 60% duty at 3000rpm. Will drop it by 10% and see how we go.


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PostPosted: Wed Aug 23, 2006 9:47 am 
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Started thinking about it last night... I think changing the cam to a smaller one is a bit drastic at this stage, there is probably a lot of little things you could tweak before buying new parts.

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PostPosted: Wed Aug 23, 2006 12:31 pm 
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Quad T66
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Busky2k wrote:
And yeah the most obvious solution is to turn down the boost in the early midrange, but it kind of defeats the purpose of having a responsive turbo isn't it? If the engine can't proprely 'swallow' 1.2bar ~3500rpm then I might as well just go bigger?


thats just the thing though, SR's *can* swallow that much air at those rpm's, my SR did.

and your setup isnt exactly a one off custom, your turbo is quite popular and theres alot of other turbos that are around the same size that dont have the same problem, like mine !

its not a permanent solution, just something to test, you may even find that it still surges with you turn it down.


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PostPosted: Tue Aug 29, 2006 12:25 pm 
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I'd like to be able to help more Busky but thought the little info I have might go into the food for thought of the thread.

I had a t518z on a sr20. For a little while after installing some new stuff I ran it without the wastegate actuator hose plugged in. This meant that the wastegate never opened (unlimited boost).

I didn't punt it over 1bar (tuned to 1.2bar) on the way to buy extra hose but the response was amazing, not linear how I imagine a bmw m3 to be, but not AT ALL surgey.

I had no cams.

So.. point is I don't think it's the turbo, and if it is it will be that particular one and not the model. I'd be looking in the engine perhaps... maybe foulled spark plugs? (ok maybe it's not the compressor surge sound but if its exhausty surge sound then maybe that's it).

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PostPosted: Wed Aug 30, 2006 2:51 pm 
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Hey guys.

Yeah it looks like I've got some experimenting to do. I only get to drive the car once a fortnight (because I have a rural job atm) so next time i get a chance I'll try muck around and see how we go. I know there is no problem when the boost is set at 1 bar. Just when it gets closer to 1.3 bar it starts going nuts. Not sure if its the turbo itself or something to do with the motor thats causing it to surge.

Btw its definitely not plugs. The power curve on the dyno is smooth despite the turbo surging.


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PostPosted: Wed Aug 30, 2006 3:49 pm 
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If it's surging when it get close to the limit, is it a boost controller issue maybe???

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PostPosted: Thu Sep 07, 2006 10:00 pm 
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is the wastegate actuator still hooked up?


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PostPosted: Wed Oct 11, 2006 2:22 am 
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Hey guys, just awakening an old thread.

Got the old girl on the dyno on a SAU dyno day. Thought it'd be a good opportunity to let you guys see first hand the comp surge. The easiest run to hear it was the last one, which begins at 3:42.


http://www.youtube.com/watch?v=x2bJpQJj0WI

You can hear the 'flutter' as the turbo spools up earlier in the rev range [3:47-3:48]. Whilst it doesn't appear to be much, it is annoying when you are sitting in gear around the 3500-4500rpm mark in the hills etc.

What do you guys think? Might just give up and accept it lol.


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PostPosted: Wed Oct 11, 2006 8:06 pm 
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hey
I had the same problem this time last year when i put a gt30/40 on my sr with a 0.82 rear housing. i got gcg turbochargers to put a surge compressor cover on it like all the hks tubos have in which they now sell the 30/40 as an option to get it. i have 256 inlet and 264 exhaust cams
what causes surge is the engines in efficient there is a restriction somewhere basically the compressor wheel is trying to push through more air than the rear wheel is pushing out you can try and tune it out eg. bigger cams,port head, bigger throttle body etc but it may just be that the front wheel is to big for the rear wheel and you can fit a surge cover or get a smaller front wheel put on the compressor side with a new front housing. i have heard of guys in the states controlling there boost through the blow off valve so therefore it gets rid of all unused air but unless its plumback its going to be a little bit of air leak noise coming out of there . i know it sounds unusual but its true.


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PostPosted: Wed Oct 11, 2006 8:19 pm 
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zap200 wrote:
hey
I had the same problem this time last year when i put a gt30/40 on my sr with a 0.82 rear housing. i got gcg turbochargers to put a surge compressor cover on it like all the hks tubos have in which they now sell the 30/40 as an option to get it. i have 256 inlet and 264 exhaust cams
what causes surge is the engines in efficient there is a restriction somewhere basically the compressor wheel is trying to push through more air than the rear wheel is pushing out you can try and tune it out eg. bigger cams,port head, bigger throttle body etc but it may just be that the front wheel is to big for the rear wheel and you can fit a surge cover or get a smaller front wheel put on the compressor side with a new front housing. i have heard of guys in the states controlling there boost through the blow off valve so therefore it gets rid of all unused air but unless its plumback its going to be a little bit of air leak noise coming out of there . i know it sounds unusual but its true.


he could also just drop the boost around the surge area, would be much simpler/cheaper then getting a new compressor cover. BUT whats interesting with this case is that people with the same setup havent had any issues, he hasnt exactly got some custom turbo its a very popular off the shelf kit suited for SR's, and ive never heard of others having the same problem.


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PostPosted: Wed Oct 11, 2006 8:30 pm 
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yeah your 100% right you could drop the boost but that wont fix anything cause then the car wont have the power he wants . i
i understand that other people have done the same thing but maybe there is something differant on the car or maybe either the compressor wheel or exhaust wheel have a differant trim to other people


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