Gillis verses BCS Bypassed Unregulated

I just do not understand. I have read many, many posts on the subject, but I do not understand.

Other than the ability to set a specific boost level maximum, does the Gillis valve setup offer any advantage over simply bypassing the BCS and controlling the boost with the accelerator and monitoring via boost gauge????????

Thanks

What? Why would you even consider using the throttle to be an alternative to any sort of boost controller? The ability to go full throttle is a good thing...

"Bypassing" the BCS would just result in the wastegate opening at whatever pressure the actuator is set to. Eliminating the reference line entirely, as you seem to be hinting at, would allow "unregulated" (by external means, at least) boost.

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Estoril blue 1987 TC 5spd, 146k miles, a237, Bailey BOV, spec stg3 clutch, spearco FMIC, t3/t4 50 trim / stage III .63, 3" exhaust, eec-tuner, lm1 wb, 55pph injectors
Best 1/4 mile: 12.89 @ 106mph on 25psi, 1.78 60'

[This message has been edited by SteveX82 (edited 12-13-2004).]

1.If you are using the throttle to limit boost (air flow) then you are limiting air flow and fuel that make HP.

If you bypass the stock BSC and have no boost control, how long do you think you can effectively control boost with the throttle before you forget to lift in the heat of battle.

Scene !: Gee thats a realyy hot running 4 banger, too bad it didn't make it allthe way down the track before that HG let go.

Scene 2: You had me coming out of the hole, what happened? "I had to lift to control boost"

See - I told you I did not understand!

Ok - according to Pete, I want a Gillis valve to control and set the max boost so that I am free to floor the accelerator as needed without worry about too much boost. I think I can relate to that.

However, the statement by Steve:

"Bypassing" the BCS would just result in the wastegate opening at whatever pressure the actuator is set to. Eliminating the reference line entirely, as you seem to be hinting at, would allow "unregulated" (by external means, at least) boost.

I could use a tad more understanding. I thought that bypassing the BCS was the SAME as unregulated boost - but Steve's statement seems in imply otherwise.

Could someone expound just a wee bit more on Steve's statement.

Thanks - I think I am close to understanding.

What the stock bCS does is to bleed some of the boost signal away from the waste gate actuatorso that the turbo can build more boost than the stock waste gate actuator is set for.

The stock WGA is set to start opening the WG when boost reaches about 9.5, so that it can limit total boost to about that figure. The stock BCS, under control of the EEC, bleeds some of that boost signal away from the WG (sends the bleed off to the compressor inlet.) How much boost is allowed to build depends on different factores but the result is the WGA is tricked into staying shut until boost reaches a higher level

Check out this article in the FAQs
http://www.turbotbird.com/FAQpage/FAQpag...ls%20Works


[This message has been edited by Pete D (edited 12-13-2004).]

Thanks for sticking with me Pete.

I had read that FAQ previously, but it was "Greek" when I read it. Makes more sense now.

Is the following anywhere close:

1) BCS bleeds boost to limit boost to 10psi more or less at low rpm, but ceases to bleed at high rpm so boost can exceed 10psi

2) Gillis valve limits boost to set max value and above that point release boost to WGA to open WG to maintain boost at max setting

3) Unregulated boost has WGA disconnected or bypassed entirely and thus boost produced by turbo is boost seen by engine - no WG operation.

If the above is anywhere close, I will buy a Gillis valve.

Thanks again!

1) BCS bleeds boost to limit boost to 10psi more or less at low rpm, but ceases to bleed at high rpm so boost can exceed 10psi

Not quite. The BCS bleeds boost away from the WGA so the boost will build higher than 9.5psi. When the BCS does not bleed boost then all the boost signal will go to the WGA which will open the WG at around 9.5 psi.

How high boost is allowed to build is dependent on what year and what model (TC, SVO, Merkur) The early TC were limited to about 9.5-10 period. The 87, early 88 could get 15 psi in 1st and 2nd but only about 10 in the top three gears. The later build 88s could get 15 in all 5 gears but in the upper gears, 15 psi didn't come in until after 4K rpms. I don't know the exact specifics for the Merkurs and SVO but I think some of them got to 14 psi. The gillis gets you around all these limitations. It allows you to set any boost level within it's range - 9.5 to around 22-23 on the stock spring, inside the valve. And it will give it too you as soon as the turbo is capable of producing it, around 3200-3400 rpm on a bone stock 87-88. You don't have to wait until above 4K rpms.

2) Gillis valve limits boost to set max value and above that point release boost to WGA to open WG to maintain boost at max setting.

You got it.

3) Unregulated boost has WGA disconnected or bypassed entirely and thus boost produced by turbo is boost seen by engine - no WG operation

Close, The engine sees all boost the turbo makes as long as there are no boost leaks between the compressor outlet and the throttle body. What the WGA and WG do is allow exhaust gases to bypass (not pass over and spin) the turbine wheel, therefore limiting the amount of boost the turbo can make. If the WGA and the WG are disabled, then all exhaust gases drive the turbine wheel and the turbo will produce relatively unlimited boost. The engine spins faster, pumps more air (exhaust). More exhaust drives the turbine faster, builds more boost, the engine pumps more exhuast, makes more boost etc.

It's scary, but it is making sense.

Thanks much Pete!!!

And, I'll try Santa for a Gillis valve.

You defenitly want a Gillis vlave [Image: smile.gif]

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Grey 88 5 Spd. 16" Cobra wheels, G3 130 AMP ALT. New Hella Fog lights, Gillis valve @ 15 PSI,6"Front mount K&N, PST front end kit, Performance Plus brakes

Actually you can get a bit more boost out of the 87-88TCs if you remove the BCS and just connect the hoses together that went into it (or replace them by one).
You can get about 17# boost that way. That way you take the ECU control out completely. Granted it doesn't have the part-throttle response given by the Gillis and it holding the WGA open until a certain point, but when you put your foot down...you get max boost, regardless of gear.
I ran one of the 87-88 TC "T"'s on my T-3 in the XR-7 for a while...17-18# boost..no spikes. Right now on the IHI in the Ranger I have a "T" from one of the SVOs..it gets about 15# boost.

It's free and easy......


I have controllers on the Tbird and the XR4.


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83 TC Clone, 87 Ranger 2.3T, 84 XR7, 80 XR7, 86 XR4 AND 88 Scorpio
NATO Member