North American Turbocoupe Organization



Boost a little unstable under full throttle?
turbokev Offline
Senior Member
#1
I've installed the Gillis valve and have it set for just under 15psi. If I ease into the throttle on the highway it will develop full boost and hold rock solid just under the 15 line. If I nail it off the line it develops full boost quickly but it pulses between 13 and 15 and you can feel the slight power difference. Still goes like heck and pulls hard with no pinging or other issues, but the gauge wavers back and forth between 13 and 15 at about a rate of twice a second.

Ideas?

(yes all intercooler hoses and vacuum hoses are tight as is the locking nut on the Gillis valve)
Kev Schofield
1989 Corvette
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85, 2x86, 87 & 88
(former TC's)
----------------
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natmac3 Offline
Administrator
#2
My old stock TC did the same thing without any boostvalves, and I believe it's a function of the bcs, opening and closing rapidly to control the pressure. I cannot explain why it differs with the gears.
1987tc
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Jeff K Offline
Administrator
#3
Where do you have your boost source for the Gillis hooked up?

Be sure the lines from the boost pressure source to the valve, and valve to the waste gate activator are as short as possible and not restrictedin any way.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 00 Windstar (wifes vehicle)
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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turbokev Offline
Senior Member
#4
I followed the directions exactly and didn't even use all of the hose that came with the kit. The longer hose runs over to the vacuum "T" next to the master cylinder and the wastegate hose is less than 12 inches long. I mounted the Gillis valve right next to the factory BCS.

Side note: If I don't use full throttle and just get into the boost with 1/2 - 3/4 throttle..no issues. It gets boost quickly and pulls right up to 14-15 psi and holds firm without waver.. it's apparently ONLY under full throttle that this is happening.

Maybe I should re-check the timing.. I use either Mobil 93 octane or Sunoco 94 all the time..never any less octane...and I've never heard any pinging from the motor..
Kev Schofield
1989 Corvette
----------------

85, 2x86, 87 & 88
(former TC's)
----------------
Reply

Jeff K Offline
Administrator
#5
OK, sounds like your Gillis is hooked up just fine.

Does it feel like an ignition miss at all? Do you have your knock sensor connected? if it is, could it be sensing detonation and pulling timing?

------------------
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 00 Windstar (wifes vehicle)
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
Reply

turbokev Offline
Senior Member
#6
Knock sensor is hooked up.. Doesn't feel like a ignition miss at all. The boost just fluxuates up and down by 1.5 - 2 psi at a rate of twice a second under full throttle.

I just did plugs, wires, cap, rotor, K&N and exhaust (cat back). Car is running awesome other than this full throttle thing... and again, if I use 3/4 pedal..full boost, rock solid, no fluxuations.

I'm going to borrow a timing light this weekend and doublecheck the base timing. I don't hear any pinging under full throttle..maybe the KS is picking up something else under WOT conditions..
Kev Schofield
1989 Corvette
----------------

85, 2x86, 87 & 88
(former TC's)
----------------
Reply





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