The nut didn't go up, it actually went back. Both turbos get their air from the airbox right, this is piped down the back of the engine into the "Y" section you see in the above pic and then down into the two plastic pipes you see and on to the intake of each turbo. I can only assume as the turbo stalled the momentum basically caused the nut to spin off as the hot side was still spinning, as the turbo was stalled the suction of the other turbo drew the nut back around the air intake pipe, over the "Y" section and down into the other turbo. I can only assume this all happened very quickly?

Yes Toby, my luck is shocking! Like you said i guess the turbo shop should accept responsibility, but if they can show that it is down to the turbo stalling then the blame passes onto someone else right? I am curious as to what other failures can cause a turbo to stall, i know the BOV malfunctioning is one, are there any others?
You can imagine the stress involved if the cold side of the turbo is suddenly stopped when the hot side is still spinning at whatever RPM, it's a shame that there isn't some sort of pin through the nut to prevent this kind of thing happening.
Maybe i should have stock BOV's fitted? The ones that were on the car were odd, both aftermarket units but different. I thought it was prudent to fit matching ones.


ETA: The pics of the turbos are after the rebuild, you can see some red paint on the nut. If you look at the turbo you'll see that the nut could have never gone up past the impeller and into the intercooler, and even if it did it wouldn't have gone any further than the intercooler end tank, that would have been preferable to be honest but not the case.

 

I see what you're saying -- that makes more sense than my first guess.I guess it could have stalled or the nut came off and then the whole game went south.

 

I saw the paint -- I meant that the photos could have been before the rebuild -- that's why I asked if the photos were before the work. But okay, it sounds like there's no simple "oversight" of quality. Again, it's not really a forensics problem -- one turbo failed and I don't think there's merit in arguing that a BOV or any external design factor contributed to the failure. Of course it could still be a foreign object damage or overheating or oil starvation, etc. Cause and effect. It will be interesting.

 

BOV's were shot, apply vacuum with a pump and the piston doesn't move. I don't understand how these bloody things can be reliable anyway as they don't have any diaphragm in there, they just reply on an engineers fit and a bit of oil.
New turbo's on their way, hopefully should be back up and running by next week, subsequently I'm having stock BOV's fitted.

I've also ordered the RSR suspension, and i have Big Reds now, can't make my mind up about wheels, what wheels would you guys fit to a 930 so i can get these big brakes fitted, what about the Ruf CTR wheels?

 

Jonathan,
Man if it weren't for bad luck you'd have no luck at all! Sorry you had to go to LeMans in "only" a BMW ;-) Wish I could've actually seen the parts. Weren't those new BOVs you'd installed? Maybe Steven at IA could give you an explanation. You've got a great attitude about it all. I'd been yelling and throwing things by now. Good luck with her and let us know what you find. I'm sure once she's all sorted you'll have real fire breather.

 

Can you think of anything better looking on a 930?

http://www.lindseyracing.com/mm5/mer...=WHEELSLINDSEY

 

Yep, but it has nothing to do with cars.

 

I'm progressing through the thread but wanted to comment on the above.

It has been known on the 930 for people to totally remove the bypass/recirc/blow off valve with no failures. So I doubt this is the reason the nut came loose...

The reason we don't use the stock bosch valves (despite them functioning perfectly well) is a reliability issue. It has been known for the rubber diaphragm to get out of the valve and end up causing problems...

 

Are you sure they are meant to open on vacuum alone? Don't they need some boost pressure to bypass as well?

The popular brand used is Forge IIRC. There was a thread on the 964t forum discussing these valves and fine tuning them with different springs and shims. Do a search and get the brand name.

 

John I run a piston BOV, and have, under 9m's original mapping ran 1.4 bar and had no issues with the BOV and its function.

 

Jim, my brother says to me "Jon, your luck knows no beginning" which i think fits nicely too. The BOV's fitted were originally on a 993 GT2 that was being put back to stock, I had the 5 Bar regulator off it too.

What i don't understand is how these Turbosmart ones can fail, or even work in the first place for that matter as there is no diaphragm. When you put a Mityvac on the top of the BOV and pump, the piston should pull back and stay pulled back until you release the vacuum. I tested this on the two old BOV's that were fitted to the car and they worked faultlessly (one was an FVD model and the other was EVO or something), albeit they opened at different pressures which couldn't be good for balance? I also checked a stock one which again opened and held it's pressure. The Turbosmart ones have nothing more than a brass piston and a spring relying on a snug engineers fit, if there is oil on the piston you will get some movement but air passes down the side of the piston and it quickly goes back into it's closed position, it just seams like a really bad design. Maybe they were badly worn and out of spec?
It may be advisable for you chaps to check the functionality of your BOV's when you have the intercooler off, make sure they hold vacuum and that they open at the same pressure, just a thought.

Nathan, if you don't vent off the pressure after you come off boost the turbo will really bog down or at worst completely stall, I wouldn't understand anyone purposely not fitting a recirc, blow off, dump valve to keep the exhaust and intake side of the turbo spinning freely ready to build boost again.
I'm not sure if the 993 generation turbos K16 or K24 have the thread for the nut turning the normal way or left hand thread, what i am told though is that on the 996 and later turbos they have reversed it to prevent this "turbo dismantling itself" situation happening. I also believe you can have the 996 centre shafts fitted to your turbos. So if you are having your turbo rebuilt, it may be worth asking for the 996 shafts to be fitted, just a thought.

James, the two BOV's originally on the car (FVD and EVO) were both piston BOV's too, they held pressure perfectly. I haven't taken them apart to see if they are the same internally as the Turbosmart ones, they may well be, which simply says the Turbosmart ones fitted to my car were badly worn and basically knackered.



Jean, I would LOVE a pair of those Lindsey P2's, i'm concerned about the time Lindsey take to turn them around though. I've heard some horror stories about them taking nearly a year to sort out a set of wheels, not sure i can wait that long! Would those 17" wheels be big enough to fit the big reds behind? And will i be limited on tire size with 17"s and should i really be thing of 18"s
Also, where can i source disks that will fit the 930 and work with the big reds?

 

Always loved the old Ruf's on the 930's

 

DM, I really do like the Ruf wheels, I’ve heard they are mega heavy though


I managed to get rid of the over boost situation, one of the actuators wasn’t behaving quite the same as the other and it was near impossible to make it do so. I bought new actuators and actually fitted them myself, I used an old fire extinguisher as a container to hold a constant 0.5bar of air pressure, then set the actuators separately so that they would open 4mm from closed at that pressure. The nut closest to the actuator pot was 35.5mm from the end of the shaft on both units when correctly adjusted which put more preload on the actuator than I would have expected, however everything now works great.
As added safety I have run a manual boost controller in parallel with the N75 valve like in the pics below (which I have pinched from another thread) I really like the simplicity of this idea, if all else fails the MBC will open the wastegates at my preset 1.1bar. I also set the MBC using the same method as setting up the actuators. I have not yet run the car without the MBC to see what the ECU would do with boost as I only did all of this today, I tried the MBC last week and was still getting over boost which pointed me at the actuators as the cause of the over boost issue. I feel really quite pleased with myself for getting stuck in and doing a bit, especially when it worked out so well.
It wasn't exactly a "on my driveway" job, I did use the lift and tools over at Northway, the lads there let me crack on with it as they didn't have time, they'll be offering me a job next!

Here is the graph and picture