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You cannot control a Tial WG with the Cycling Valve. A 0.7 bar spring is still quite a bit stronger than the stock WG!
Connected in single-port mode, with full boost pressure sent to the diaphragm, the Tial will limit boost to around ~10psi (0.7bar). The stock WG will limit boost to ~4.5psi. The computer/CV can't react quickly enough to control the Tial. Been there, done that - even experimented with Josh @ Rogue with a custom KLR. No dice without taking up a lot more development time.
Connected in single-port mode, with full boost pressure sent to the diaphragm, the Tial will limit boost to around ~10psi (0.7bar). The stock WG will limit boost to ~4.5psi.
I assume this is written correctly (?) but something about it isn't making sense to me.. either the words used or the numbers, lol. Can I get some clarification?
I'm in between buying and remodeling my first house, and looking for a second car for the winter... so money is quite limited at the moment. Any upgrades will have to be put on the backburner for a couple years. Actually, though, I do feel the stock power of the turbo S to be quite adequate so I'm in no hurry to mess with a good formula for primarily street driving duties.
Still not understanding from the explanation Omni gave how running the Tial in this manner resulted in the spectacular engine failure. If the Tial starts to open at 10psi then how could it overboost. And how is the stock WG only 4.5 psi. Ignoring the numbers for a second, the difference is 5.5.. on top of stock boost of 12 would be 17.5 psi which doesn't sound dangerous.
And why a rod, wouldn't the headgasket let loose first?
I'm obviously missing something.
Could someone please explain?
BTW - extremely common for people to install a Tial backwards. The stock wastegate opens outwards and the Tial opens inwards. Usually means that if you used the way the stock gate was oriented to install the Tail then its backwards. Bad things happen....
Still not understanding from the explanation Omni gave how running the Tial in this manner resulted in the spectacular engine failure. If the Tial starts to open at 10psi then how could it overboost. And how is the stock WG only 4.5 psi. Ignoring the numbers for a second, the difference is 5.5.. on top of stock boost of 12 would be 17.5 psi which doesn't sound dangerous.
And why a rod, wouldn't the headgasket let loose first?
I'm obviously missing something.
Could someone please explain?
Certainly part of the problem is right in the name "cycling" valve. One of the functions is to cycle during the boost building on or part throttle phase. As the valve cycles back and fourth the stock waste gate is more responsive to the inputs and bleeds off more drive pressure than the tial would. I'm not sure how the CV works at high load high throttle, if it's still cycling instead of steady state, then all bets are off. The tial doesn't "start to open" at the spring pressure, it will fully open at the stated spring pressure if the line has no interruptions; ie, boost controller, cycling valve etc.
As for the failure, it's hard to predict what will happen when you turn the boost up to infinity. certainly the headgasket would have been a friendlier outcome, but it's not completely shocking that the bottom end let go. Some of the later turbo S cars had cast rods instead of forged, so that could be part of it... or the failure could be mostly unrelated and just exaggerated by running the car harder.
really the OP says the chips are stock so it really should have hit overboost protection before too much damage was done, but again it's hard to predict exactly what would happen.
BTW - extremely common for people to install a Tial backwards. The stock wastegate opens outwards and the Tial opens inwards. Usually means that if you used the way the stock gate was oriented to install the Tail then its backwards. Bad things happen....
Still not understanding from the explanation Omni gave how running the Tial in this manner resulted in the spectacular engine failure. If the Tial starts to open at 10psi then how could it overboost. And how is the stock WG only 4.5 psi. Ignoring the numbers for a second, the difference is 5.5.. on top of stock boost of 12 would be 17.5 psi which doesn't sound dangerous.
And why a rod, wouldn't the headgasket let loose first?
I'm obviously missing something.
Could someone please explain?
I'm not suggesting that the WG install caused the motor to spit a rod through the pan. Though if the bottom end was already questionable, the extra boost and power could have put the final nail in the coffin.
I don't know that just because the difference is "5.5" on the springs that the Tial would only run 5.5psi more than a stock WG.
The WG opens when you have (a) sufficient exhaust pressure pushing against the spring AND (b) sufficient intake manifold pressure, pressurizing the rubber diaphragm inside the WG. This is why, if you merely unplug the vac line from a stock WG, you suddenly get LOTS of boost. It's both the exhaust working against the spring PLUS the manifold line pressure that open it.
If you run an uninterrupted vacuum line straight to the stock WG, then 4.5psi in the vac line + 4.5psi in the exhaust (ok likely higher in the exhaust, but using 4.5 for simplicity), both working together against the spring, opens the valve inside the WG. Likely the valve actually starts to open SOONER than 4.5, because *peak* boost is somewhere around 4.5-5psi.
If you do the same with a Tial 38, you have to get to ~10psi before the WG opens... and it's likely higher than that. I have a 38 on my car, and *peak* MINIMUM boost setting is closer to 12psi with the 0.7bar spring at redline. It likely starts to *crack* at 10, but finally opens fully (enough to maintain equilibrium) at 13.
The stock WG spring is also kinda lazy... combined with a stock sloppy CV, it works fine. Once you add in the much stiffer spring of the Tial, the CV just can't react fast enough to open the valve. My guess is he was running quite a bit more than 17psi, hooked up in the manner it was.
BTW - extremely common for people to install a Tial backwards. The stock wastegate opens outwards and the Tial opens inwards. Usually means that if you used the way the stock gate was oriented to install the Tail then its backwards. Bad things happen....
Also a very real possibility.... though even if he'd had the WG mounted correctly, it still wouldn't have run right if he tried using the CV+KLR to control boost.
I took some pics because I just wanted to dispel any suspicions that the tial was installed backwards causing the rod failure...
as you can see the dump pipe (actually just an elbow) is hooked up to the side of the wastegate (exhaust outlet) and not the bottom (inlet). I did read about a couple instances where the tial was installed backwards before I did any work so I made sure that wasnt going to be a problem for me.
Any other ideas as to what might've caused such a failure?
The reason I ran the WG with the stock CV was because I also did not think there would be so much risk since I assumed the wg would open regardless at 10 psi solely because of the spring... little did I know...
10-03-2016, 07:42 PM
