Second cat enough to prevent creep?

[MSMS3]

Coyfish, it does not matter who did the tune. It's what the tune is doing. If the tune is letting you reach 20-21 psi or higher and holding at that level on a K04 turbo with the stock DP and cats in place, then it's the tune, period. If so, that is a dangerous tune.

If you have the stock DP on with its own primary cat and have the secondary cat in place you should not be able to flow enough to max out the wastegate. Nor would you max out and induce creep with a simple test pipe in place. Rather, the ECU tuning is telling the turbo to permit boost levels above stock. Boosting at sustained levels above 18 psi at 5,500 rpm, or above 15-16 psi at 6,000 rpm will kill the turbo or worse, IMHO. And boost levels that high at that rpm on a K04 do not produce more power, just more damaging heat.

Please consider turning the boost down a couple psi in your AP mapping if you want to save the engine. When the center shaft of that little turbo (center shaft is only 5mm in diameter) gets heated to above 1500 degrees, which is likely to happen at your boost level at high rpm, the inconel hardening give out. The shaft then softens. When it softens it sags. When it sags, it produces metal to metal contact, including bearing failure. Some of that contact could also be the vanes on the "cold" compressor side hitting the surrounding housing. If that happens, you don't just lose the turbo. Pieces of those vanes break off, get sucked through the IC, the intake manifold and go into the engine through the intake valves. Result: zoom, zoom, boom.

I'm not saying that will happen. I am saying it can happen and I've seen this on other platforms when the shaft softens or the bearings fail, even on more hardy Garrett turbos pushed too hard for too long. Just a thought.

 

[Darth Vader]

The fact the KO4 turbo's CS is 5 mm isn't really an issue different than any other small turbo, in my view. The Garrett T3 necks down to ~5 mm as well. The Garrett has its bearings further apart but, the shaft is also longer as well. The advantage the T3 has is is a bit physically bigger than the K04, meaning the housing can absorb more heat, taking it away from the vulnerable small shaft.

In my view, the T3 isn't really significantly stronger or more durable than the K04, if you push it the same way, it's just easier and cheaper to repair. The T4 family and up is a different kettle of fish.

Forced to use a T3, I'd take a .45/.60 Garrett T3 for a torque monster, or a .63/.60 for more high end, if I were to tack one on this engine.

 

[MSMS3]

Agree. I grenaded a T3 on a turbo 9000 Saab by pushing it too hard.

I was running a Saab approved Bosch "offroad racing only" ECU upgrade called "Red Box" which pushed boost up to a then high 16 psi on a 2.0L 16 valve engine. The remapped ECU raised boost but still had the safety feature in place to pull boost back down to about 12-13 at high rpm and load, as on our engines. But I was younger, thought I knew everything, was over-confident and bypassed that safety by running a Holman MBC set to hold at 16-17, with bigger downpipe and catless exhaust and aftermarket CBE. The car could hit 150 mph on the Interstate which was a pretty long legged car for 1988-89, but had horrible torque steer from the increased power.

The turbo just could not take sustained 16-17 psi at 6,000 rpm. I pushed it into ineffeciency with hard driving, overheated the mother and paid the price. The intake valves did suck in grenaded compressor vane pieces at what must have been extremely high velocity.

We were able to salvage the block (with some ugly dings in the top of the pistons but no cylinder wall damage or other internal damage below the piston tops). We had to do some work on the cylinder head and obviously had to replace the turbo. The engine was stout and well engineered, but not invincible. I avoided a true zoom, zoom, boom only by pure luck.

I then put on a custom reworked T3 with clipped vanes with lightened and rebalanced rotating mass. But I removed the MBC and went back to the "off road" ECU that could dial the boost back under extreme load. I ended up putting almost 200,000 miles on the car set up that way.

Little turbos are great for responsiveness and torque on the low and mid range rpm bands. They can make good power if you are careful. I was not. You can easily push them too far. Lesson learned for me -- I think. I hope!

I see the K04 as being at least as vunerable, if not more so.

 

[Darth Vader]

Good times...the last factory turbo car I had was an '86 XR4Ti...I did my damndest to kill that 2.3 with 17+ pounds of boost and no fuel control. It made alot more power at first but gradually, over a few years, it just got louder and louder. When I took it apart it was definitely showing signs of being pretty hot inside. But, back then, you could get a near new engine from the wrecker for under 400 bucks so, who cared? I just bought another, slapped that one in and backed off the tune a touch.

Life's so much better now than those crude days, when we were wowee at 200 horses (lol2)

 

[MSMS3]

Darth, I think we jacked the thread taking our trips down memory lane.

Sorry, all.

But hopefully, the point was made that this little K04 is great for our application, so long as we know, like so many other situations in life, "you gotta know your limitations." 20-21 psi sustained boost on the K04 is going to kill the turbo and maybe the motor. Period.

 

[Darth Vader]

Har, true, old farts on the porch...(gah)

 

[Wurf]

Anyone tried porting the internal wastegate? This has worked for me to eliminate boost creep on several other cars. You basically just open up the wastegate hole in the turbine housing so that hole is bigger, but not so big that the flap door can't cover it (with some overlap). Sometimes there's also some improvement to be made by removing material from the wall in the turbine housing that the WG gasses hit after they pass through the WG hole, and smoothing the transition area where the WG gasses separate from the turbine gasses in the turbine inlet area.

Of course, this does require turbo removal and porting tools.... but it's a better solution than restricting the exhaust and losing power.

This was my thought exactly but it's a lot more work than installing a high flow cat midpipe obviously and the car would likely be torn apart for several days.