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Registered:
August 2002
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boost spiking problem
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Sun, 22 September 2002 08:44
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I have a turboxs dual stage boost controller and I have set low boost to 5psi and high boost to 9psi. The only problem is that on high boost it spikes to 9 and then drops fairly quickly to 6 higher in the rev range. Is there a factory boost control solenoid that I have to disconnect or is there something else wrong?
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Location:
Adelaide
Registered:
May 2002
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Re: boost spiking problem
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Sun, 22 September 2002 13:02
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Im no expert, but i hav done a little reasearch on boost control.
It might be the following
Where is the Boost controller taking its pressure signal from? and also where is the boost guage taking its signal from?
Eg: The Compressor outlet, Manifold etc.
Think about it like this:
The wastegate opens by pressure on the actuator diaphragm. If the actautor is connected straight from the compressor outlet then the diaphragm gets an instantaneous pressure signal and the wastegate may creep open a little letting boost come on relatively gentle.
If the signal is taken anywhere after the compressor housing then the wastegate will stay clamped shut untill the entire area between the outlet and signal origination point. This means that the turbo will build boost as fast as it can because no exhaust is being wasted off.
Now, if the boost guage is taking its pressure signal between the wastegate signal origination point and the compressor outlet the boost guage will recieve a higher signal than the actuator until the pressure is built up in the actuator line. then the wastegate opens and boost pressure drop back to where it should be.
Maybe Im well wrong, but like i said I'm no expert. Take it to your locak trusted performance workshop and see what they think it is.
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Location:
Sydney
Registered:
May 2002
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Re: boost spiking problem
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Mon, 23 September 2002 00:42
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More than likely you will find its the factory control solenoid.
Check your wastegate actuator, if it has two fittings on it, one will be from the compressor cover (positive boost) and the other a factory boost solenoid, if so then plug the line on both ends going from the actuator to the solenoid and the solenoid to the actuator.
If thats not the case, then check for a sticky wastegate actuator or a leak in the vacuum lines somewhere.
Most of the Toyota ECU's use a VSV for the ECU to control how boost comes on and exactly how much, the spring might only be tensioned for 5 or 6psi, but with standard ecu you will see more.
Michael
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Location:
Perth
Registered:
August 2002
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Re: boost spiking problem
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Mon, 23 September 2002 04:37
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No, no, no.... there are no factory solanoids in the MKIII supra with a 7mgte engine.
The problem is it's mechanical components. Check you intake system completely.
I used to own a Supa MKIII with 7MGTE engine.... 270Hp at rear wheels with standard intercooler, running 0.80Bar boost. It had a High flow turbo, and by the time, I ended at red line, boost was down to 0.70 Bar boost.
Check your intercooler, piping, and intake. Also make sure you
have the boost controller connected right as per your manual supplied. Do not take reading of Fuel Pressure line, as there is a VSV inline, and hence, will give inaccurate reading.
MIKE.
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Location:
newcastle
Registered:
June 2002
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Re: boost spiking problem
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Thu, 26 September 2002 00:54
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One of the biggest causes of boost spiking is a long section of hose used between the compressor housing and the wastegate actuator.You simply have a much bigger volume of hose to fill.
The easiest way to remove a spike is to keep your hose size the same as stock i think 1/4 inch on a 7mgte and keep the hose length short .a leaking intercooler hose will actually remove a spike because your bleeding air off .
It is however possible to have a spike due to a leak in the boost pressure line (from turbo to actuator).
Having said all that the most successful boost control system i have ever used has about a 2 second overboost(depending on load) .The overboost allows a short burst of higher boost up to around peak torque .This much better than running a fixed high boost setting .
With an 19 psi overboost,dropping back to 16 the car is actually quicker than if boost is set at 18 psi ...WHY less heat .0-100 times dropped from 5.3 to 4.8 peak power was the same with both setups
This does not prevent detonation at peak torque but does prevent high rpm detonation usually caused by heat from a turbo being boosted beyond its boost efficiency threshold .
So IF its not pinging around peak torque (i think 4500 rpm for 7mgte??)leave it it makes much better acceleration
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