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Discussion Starter #1
Weapon: '92 1.8 GSR

This must be one of the odder modifications one would think of.. I've been looking into finding a way of switching off the turbo system on occasion, and also on whether it is safe to do so in the first place!
You must be asking yourself why I want to do such a thing. The answer is simple; fuel consumption. My friends and I like touring the countryside and that was the reason for upgraded from a Daihatsu charade 1.0 (what a refreshing change!!!). My friends' cars are nothing special - everyday Peugeot 405s, Nissan Primeras etc and I can run rings around them with the lancer. The problem is that they can happily cruise all day at 140150 kph (85-90mph) without incurring the wrath of a turbocharged fuel consumption.
In the articles that I have come across on how turbochargers work, there is no mention of how the intakeexhaust airflow is managed in order to keep the turbo out of the picture when it is off-boost, and how the turbo is brought into boost. Please help me with advice on whether this project is feasible, and if it may have any averse effects on the engine or turbo.

Cheers!
 
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Discussion Starter #2
An electronic boost controller (such as this APEX'i) will allow you to do this, you can switch it between 2 settings, say 0.5 bar (or less if you like) for 'normal' running and 1 bar for maximum attack.

Cost: ~£400|PLS|fitting

A manual bleed valve setup can achieve roughly the same result for a lot less money but requires careful setting up.
 
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Discussion Starter #3
Thanks Chunky! Is this theory correct: To keep the turbo out of the exhaust path at low rpms, the wastegate is kept fully open. At a certain engine rpm some sort of vacuum mechanism is used to close the wastegate and direct the flow though the turbo which then does its business. As gasflow increases, the wastegate opens just enough to keep the turbo running at WOT (I dont know WOT that stands for but has something to do with 'optimum operating speed').
So I'd have to find a way of keeping the wastegate permanently open, which sounds like what the electronic boost controller could be set to achieve.

I got this excerpt from Autospeed.com:
and amp;gt; Factory ECU Boost
and amp;gt; Pretty well all factory boost control systems use the same approach. The wastegate (the valve that controls how much and amp;gt; exhaust gas bypasses the turbine) is operated by a rod. The other end of the rod is connected to a diaphragm that is and amp;gt; deflected by boost pressure acting on it. If more boost pressure gets to the diaphragm, the rod moves further and so and amp;gt; more exhaust gas is bypassed around the turbo. This limits boost.How far the rod moves depends on how much boost
and amp;gt; pressure is allowed to push against the diaphragm, and also how strong the internal spring pressure is that's
and amp;gt; pushing back against the other side. But really all you need to know is this: the lower the boost pressure acting on and amp;gt; the diaphragm, the higher the turbo boost on the engine.
and amp;gt; Turbo cars with electronic factory boost control use a 3-port solenoid valve which is pulsed by the ECU. This allows and amp;gt; air to be bled out of the wastegate control line, decreasing the amount of boost seen by the diaphragm. If the ECU
and amp;gt; wants to increase boost, it pulses the valve so that it's open longer than it is shut, giving a great bleed. If the and amp;gt; ECU wants to lower boost, it lets less airflow through the bleed valve.

So, it would look like I have two options:
- Build a mechanism that would do the opposite of a bleed valve: instead of allowing pressure to bleed away, the mechanism would add onto the pressure in the wastegate control, tricking it into opening the wastgate earlier than it normally would.

- Find a physical way of preventing the wastegate from closing by putting a stop mechanism on the rod leading to the controller

Does this make sense or am I in dreamland?
Cheers
 
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Discussion Starter #4
I think that base boost on the Evolution line is approximately ten psi. You need this much boost present for the waste gate to open. Less pressure will not be able to overcome the spring in the waste gate actuator. An interrupt switch that prevents the bleed solenoid from receiving power will force max boost back to this level.

I understand the desire to control the generation of boost as a means of affecting fuel economy. These cars can really drink gas. However, please realize that the fueling is determined primarily by airflow into the engine. You control airflow with your right foot!

Stick a brick under the gas pedal to help you resist the temptation.
 
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Discussion Starter #5
The brick idea would definitely work, but I need to have my cake and eat it. For day-to-day driving the turbo is a joyful tool to have at call. Problem comes when travelling 300miles|PLS| with a convoy of average cars: I either have to slow everyone to a crawling 70mph when they'd rather be doing 85, or grit my teeth and step on the gas and end up paying several times over for it at the pump. I'd be a lot happier if the lancer's gearing weren't so short, or if MMC had provided that 6th gear that every GSR owner dreams of.
 
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Discussion Starter #7
Let me think. Older Toyota Truenos (?) ran superchargers which were clutch driven. These superchargers are the small rootes style, which are offered by most wreckers. I think the point of the clutch was to reduce power drain at lower revs (?). An on/off supercharger?

Whatabout an on/off turbo ? (that's what I thought this thread was about when I saw it).
 
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Discussion Starter #8
Don't even thonk about a Turbo bypass - the mind boggles at the Heath Robinson contraption you'd end up with. Porsche 959 had a good one though for big second sequential turbo. One exhaust is even supposed to remain cold if driven slowly!

Make sure your engine is well tuned - ignition timing, good synthetic oil (gearbox and diffs too), well gapped plugs, free flow air filter etc. and drive on light throttle. My Galant VR4 mpgs jumped from low to high 20's after resetting the ignition timing properly (didn't short the terminal first time - doh!) - and it was a whole load quicker too - on 600 mile motorway journey to Germany made 28mpg with a fully loaded car at 80mph average -cruising 90 to 95.
 
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Discussion Starter #9
I totally agree with Al. Just look after your engine and go easy on the throttle, and the mpg's will come.
The turbo by-pass idea is interesting but just not practical. Everything about your engine is designed to give optimum performance when running positive manifold pressure. If you were to run your engine as a standard NA unit, the fuel economy would still be poor. The problem is that all your engine hardware is designed for something else. Cams, cam timing, port design, inlet runner lengths, plenum volume, etc are all optimised for boosted manifold pressure. The biggest killer to NA effeciency is the low comp ratio, and there really isn't much that you can do about that.

Just go easy on the gas...if you can.

Cheers
Danny
 
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Discussion Starter #10
You might also want to consider getting an air-fuel ratio controller, like an APex'i S-AFC or HKS AFR (2nd gen).

You could tune the a/f mix tu rin close to stoichiometric as possible (14.7:1) during off-boost driving. You just need an o2 sensor or an a/f meter to determine if you are setting the a/f mix ratio either rich or lean.

I'm also planning this modofication myself soon as I do a lot of city driving at low-speeds, to the detriment of fuel economy.
 
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