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Location:
Sydney
Registered:
September 2004
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Removing boost Spike 3SGTE
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Fri, 26 November 2004 07:16
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Hi all,
My apologies if there is a thread already covering this, but I have searched and have found boost spike threads but none specifically relating to the 3SGTE.
I have a 2nd Gen 3sgte with a turbosmart dual stage boost controller. My questions are as follows:
1. My Boost controller is connected to the wastegate actuator hose via t-piece, now researching the topic a bit i know that its function is to bleed off pressure away from the actuator to hold it closed under higher than normal boost conditions. Boost spike is caused mainly by lengthy hoses leading to the wastegate not allowing the boost pressure to act on the actuator as promptly as required, however in my setup the length of hose remains the same length as standard, just with a t-piece installed. Now the hose leading from the t-piece to the controller is significantly wider, but as far as i understand it should not have much bearing on the problem as it is just the 'bleed' hose for excess pressure and should flow more freely than the standard actuator hose. People I have spoken to have said that the turbosmart item is prone to boost spike, im wondering how this is so. What is it about the design of this controller that causes the spike? Or is it my method of install?
2. When my car was dyno tuned the mechanic said that my boost pressure spikes to 17psi, then falls back to 12 ( I have the BC set to 14psi on the high setting, set by my boost gauge) but I have never noticed this spike on my gauge. Now, it gets fed from a port on the manifold after the throttle body, could this be the reason why it doesnt show the spike?? and what would be causing the pressure fall off if its all setup for 14??
3. If anyone has experience with this type of boost controller and can suggest an ideal method of installation please let me know. my car has a standard spec ST185 ct26.
Thanks for your time. 
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Location:
Sydney
Registered:
September 2004
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Re: Removing boost Spike 3SGTE
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Fri, 26 November 2004 07:22
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Sorry, just to add... my main concern is making sure the spike/fall off is nothing to do mechanically with the engine or the turbo...if its a matter of the method of install or just a shoddy product let me know and ill rip the bastard out in favour of a decent BC hehe 
cheers!!
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Location:
South Australia
Registered:
July 2002
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Re: Removing boost Spike 3SGTE
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Fri, 26 November 2004 15:14
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Find out where the mechanic measured the boost from?
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Location:
Melb, Victoria
Registered:
April 2004
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Re: Removing boost Spike 3SGTE
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Sat, 27 November 2004 07:48
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i'm interested to hear your results too. i'm looking to buy a dual stage mbc for my genII 3sgte.i have used a gfb bleed valve on my car and it seemed to spike a bit a night, but during the day it was quite good. 
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Location:
Sydney
Registered:
September 2004
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 02:14
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This was done on a dyno, and from what i was told most of the input was taken directly from the ECU (not sure how) if thats the case im not sure how/where they got the reading from as the factory turbo pressure sensor would be fooled by my FCD and always register only up to 8psi.
I might call the dyno place and ask a few questions. If this is a topic the people would like explored I would be willing to provide pictures of my current setup, and if achieved a means of resolution.
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Toymods Vice President
Location:
Sydney
Registered:
May 2002
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 04:54
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The spiking I'm not going to cover other than to say take a look at http://www.mr2oc.com or the alltrac forums out there.
The boost pressure being read from the computer is using the MAP sensor that the computer uses for the boost control on the 3S.
The boost falling away in the top end is a result of the restrictive design of the CT26 twin entry exhaust housing. There just isn't the capacity to flow enough air through the exhaust housing to be able to hold steady boost to red line.
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Location:
Sydney
Registered:
September 2004
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 05:27
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Thanks Joshstix for your info, have yet to join mr2oc but i think i will.
The only way I see them getting the correct signal is if they got it straight from the MAP sensor under the bonnet (before the FCD)
If I was to look for a turbocharger that could hold 18psi steady to redline on the 3SGTE what would i be looking for? Can it be determined by compressor maps, or should I look at compressor and turbine sizes, or flow capacities??
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Location:
Melb, Victoria
Registered:
April 2004
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 07:23
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hey silverghost,fuel cut is at approx 12psi, which read on the TPS is 4.4volts. if ur fcd is set to about 17psi (or about 4.39volts), then the TPS and ECU would read up to about 11.9psi max.
it would be great if u could post up pics of ur setup and stuff. i made my own FCD, from the mr2 forums.
atm i really cant decide on what sort of BC i should buy. i'm not really prepared to go electronic, due to the money factor. but i'm looking for a good performing MBC and ideas on the best setup for my car.
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Location:
Sydney
Registered:
September 2004
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 07:32
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Hi Aust162,
Unfortunately I have only just recent entered the market for a BC. Im learning as i go along, but dont have much solid atm.
The best is obviously electronic boost control, but the price is high. I think the reason why it is the best is because EBC's employ a stepper motor rather than a solenoid for venting of boost pressure which apparently makes them more stable at holding boost with less or no spike.
That is the only fact I have to share unfortunately, the rest or differing points of view on MBC's. Some people claim they dont suffer boost spike at all from their particular brand, or vice versa...but i think a contributing factor would be their particular setup and level of boost they wish to attain.
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Location:
Low Head (Tasmania)
Registered:
September 2004
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Re: Removing boost Spike 3SGTE
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Mon, 29 November 2004 09:07
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hey there, boost spikes in gt4, its pretty normal, but not that much, have you checked your vsv valve, that can play silly buggers sometimes, try cutting the line for it (line from wastegate actuator and dissapears under the cooler and around the engine, then plug anything into it, eg bolt with a hose clamp around it, both ends.
Or put it back to standard and see if you get a spike with normal boost.
sign up to www.gt4oc.net, its the best 3sgte web site around, with the smartest posters when it comes to the 3s.
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