North American Turbocoupe Organization



SOLVED - External wastegate lagging
DR1Pilot Offline
Member
#1
Hello all,
I am having a perplexing issue with the Gnari external wastegate with a factory T3 from a Merkur. The wastegate is simply a standard dual port 38mm mounted to an E6 style log header. The issue I am having is that when I go WOT and boost builds, pressure reaches up to 5psi over what the wastegate is supposed to limit boost to before falling back to where the wastegate is supposed to limit boost to. This would not be a huge issue except that this would allow pressure to exceed the limits of my fuel system if I were to turn the boost up to 18psi (after settling from the overshoot) where I would like it.

The possible reasons for this that I could think of were:
1. Too long of a vacuum line to the wastegate so the signal was lagging greatly.
2. Too small of a wastegate?
3. The signal line is bulging under pressure (high temp line made for coolant not air.
4. A leak in the wastegate signal.

I tried shortening the signal line as much as I could and saw no difference. I pressurized the lines and found no leaks. The only way I could get results was to use the signal line only and not the top port signal which is used to set the pressure limit using a boost controller. This limits pressure to spring pressure though.

Any ideas? I was thinking about getting a really light wastegate spring to see if that would help.
Project 88 T-Bird 74k original miles
and a Loud Moped
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John B Offline
Member
#2
DR1Pilot Wrote:Hello all,
I am having a perplexing issue with the Gnari external wastegate with a factory T3 from a Merkur. The wastegate is simply a standard dual port 38mm mounted to an E6 style log header. The issue I am having is that when I go WOT and boost builds, pressure reaches up to 5psi over what the wastegate is supposed to limit boost to before falling back to where the wastegate is supposed to limit boost to. This would not be a huge issue except that this would allow pressure to exceed the limits of my fuel system if I were to turn the boost up to 18psi (after settling from the overshoot) where I would like it.

The possible reasons for this that I could think of were:
1. Too long of a vacuum line to the wastegate so the signal was lagging greatly.
2. Too small of a wastegate?
3. The signal line is bulging under pressure (high temp line made for coolant not air.
4. A leak in the wastegate signal.

I tried shortening the signal line as much as I could and saw no difference. I pressurized the lines and found no leaks. The only way I could get results was to use the signal line only and not the top port signal which is used to set the pressure limit using a boost controller. This limits pressure to spring pressure though.

Any ideas? I was thinking about getting a really light wastegate spring to see if that would help.

Are you running off spring pressure on the EWG or a combination of the EWG and a boost controller (manual)? Manual boost controllers are nice because they effectively keep the EWG shut until the desired psi is hit. This helps improve spool of the turbo; however, it can cause a short boost spike until it settles down much like what you're talking about. If you aren't running a MBC, the only other thing I could think of is that your signal line to the EWG may be collapsing. Try some windshield fluid line from the auto parts store. The stuff is a little more robust than regular coolant lines. And how do you like the Gnari manifold and EWG?? I'm looking to get this setup myself
88 Turbo Coupe: Front mount intercooler, remote mount TFI, MGW short throw shifter... murdered out
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Jeff K Offline
Administrator
#3
Just wondering why you went to an external WG with a somewhat stock T3 turbo? The stock WG on the turbo should easily be able to handle your exhaust flow unless you re putting out 400+ HP which a T3 is incapable of anyway.
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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DR1Pilot Offline
Member
#4
I had to clock the turbo and the internal wastegate arm was binding and would not function.
Project 88 T-Bird 74k original miles
and a Loud Moped
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DR1Pilot Offline
Member
#5
John B Wrote:Are you running off spring pressure on the EWG or a combination of the EWG and a boost controller (manual)? Manual boost controllers are nice because they effectively keep the EWG shut until the desired psi is hit. This helps improve spool of the turbo; however, it can cause a short boost spike until it settles down much like what you're talking about. If you aren't running a MBC, the only other thing I could think of is that your signal line to the EWG may be collapsing. Try some windshield fluid line from the auto parts store. The stuff is a little more robust than regular coolant lines. And how do you like the Gnari manifold and EWG?? I'm looking to get this setup myself

I have actually tried running with a boost controller to the top port as you described, a boost controller to the bottom port with the top disconnected and signal to the bottom port without any boost controller. In both cases of using a boost controller the spike was present but without a boost controller it was much smaller as expected.
I think I will try some more rigid lines. The lines I am using hold up well to heat but when I tested a piece of line with a vacuum pump I could visually spot the line shrinking at 20in hg ~idle vacuum with means that in boost they are likely expanding and potentially leaking at the ends even.

I would say I like the header/WG combo but until I solve this problem I cannot say for sure. I will say fit was tricky and I had to modify the dump/burn pipe as it was conflicting with the flange on the downpipe.
Project 88 T-Bird 74k original miles
and a Loud Moped
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DR1Pilot Offline
Member
#6
SOLVED!
The problem was the stock Tee fitting on the compressor outlet has a really small inner diameter. I went out an bought a similar fitting from Lowes and that fixed the problem. There is still a little bit of a surge initially after boost ramps up but only 1-2psi
Project 88 T-Bird 74k original miles
and a Loud Moped
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Jeff K Offline
Administrator
#7
That "T" is actully a pressure divider that works in conjunction with the BCS. The T beeds off pressure thru the BCS, when activated, so less than actual boost pressure is supplied to the WGA.
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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DR1Pilot Offline
Member
#8
Jeff K Wrote:That "T" is actually a pressure divider that works in conjunction with the BCS. The T beeds off pressure thru the BCS, when activated, so less than actual boost pressure is supplied to the WGA.
I removed the BCS a while back so removing the T should not cause any problems. Unfortunately after a few days of proper function the overboost problem came back and I found that the wastegate diaphragm has a decent sized hole in it (yay!). I removed the external wastegate and hooked up the internal wastegate again. Without the T the internal wastegate actually works as prescribed but even with a bleeder valve is lazy to reach full boost so I am going to try and adjust the arm to prevent boost creep.
Project 88 T-Bird 74k original miles
and a Loud Moped
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