[ds968]

Saw your post on the wines thread - definitely a motivation to get that cab. It's not just for tne enjoyment factor,, it's a therapeutic necessity at this point

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[Chris Vais]

Trevor knows the way to the winery.

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[ds968]

Planning to call the shop tomorrow to check on where things stand. In the meantime, flash had to let more worms out of the can by trying to figure out what could have been the cause of the RPM staying near the redline for about two or three seconds without it shifting, or hesitating to drop the rpm immediately as I let off the gas pedal. And of course that worries me as well . Happened only once before ( or I think it did, I was not paying too much attention to that aspect at the time, so did not give it any further thought ) So only twice in about two years, out of the countless times it's been taken to the redline ( it does that if you stomp on it while it's in D-4th at around 60 mph, because it drops all the way to 2nd gear ) but still...should that even happen at all ?! And flash even programmed it to a slightly lower redline but that's still a lot of " hanging " RPMs. Don't want to put words in Bob's mouth , but if I understood correctly he thought although bitj are very small probabilities, maybe the transmission valves were briefly stuck, or the tiptronic computer hesitated to retard the timing...so these couple of seconds at 6400 rpm might have just been the straw that broke the camel's back ? Thoughts from the collective wisdom ?

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[flash]

maybe i should have set the redline at 5k

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[unknown4u]

Funny I recognise it. Have had it once. Shifting down from 4th till 2. About the speed of 120 km/hr. In my mind when i bought the car long long time ago. I was surprised it goes down so far and hit the red line as well and in my mind it takes ages to shift up again.

Perhaps there is a bug in the software from the beginning when the car came out the factory.

Ive never bin in the same circumstances since...
Car is stock.

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[ds968]

So how much performance would I really lose if you lowered the redline to 5 k rpm ? Wow, I can't believe I am reading what I just wrote ..is that ME contemplating giving up even an iota of speed ?!! Lmao . But unlike the six speed, it's not as if I'm trying to squeeze every fraction of a second out of the tip, with the SC it's plenty fast in every situation ..

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[flash]

frankly, if we just lowered it a few hundred more rpm, you wouldn't lose much in terms of power.  i peeled off so much timing up top on your chip that it pretty much flattens out after 5k.

 

the real issue is the trans.  if it isn't going to shift, then the engine needs to be able to sustain those rpms.  the valves float on these engines at just over 6200 when they are new.  as the valve springs weaken over time, they float sooner.  that isn't really an issue on a street driven normally aspirated car.  however, on a boosted car, it opens the door for the pulse to go the wrong direction.  this can mean detonation, oil being sucked into the intake, and even backfire.

 

i think your failure was due to a number of things that all added up to a perfect storm.  dirty thin oil likely burned out when you had a high rpm float condition, which then allowed the pulses to go in the wrong direction at the wrong time, then the trans failed to shift, which then popped a ring.

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[az968]

So why would an engine that was designed to be able to run at over redline, presuming redline is set at a safe enough level below where damage would occur, and has "Rev limiting" software in the ECU to keep it from going too high, blow up when running at redline for just a few seconds? That engine didn't have all that many miles on it. I would think the problem was something else besides just hitting redline.

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[flash]

first, that engine had a LOT of miles on it.  i think it was about 130k.

 

second, it is supercharged.  that makes valve float and cam overlap a much bigger deal, when you get up into the higher rpms.

 

third, this engine is NOT designed for higher rpm running.  it's designed for big midrange.  stock redline is 6700rpm.  stock valve float is just a bit over 6200, and that is with everything new and tight.  it's much lower on an older motor.  i wouldn't be surprised if the valves were floating below 6k.  normally aspirated this isn't that big of a deal.  supercharged though you get the forced air pushing things around to places they aren't intended to go.  that's one of the reasons i recommend changing the head gasket and doing a valve job.

 

the tiptronic is designed to shift at a max of 5500.  that's exactly why i couldn't dyno the tip.  no matter what i did, it would not let me go to redline in 3rd.  one problem is the slow processor, but more than likely, the trans has old dirty fluid that has never been changed, and the valve body is weak and/or gummy.  that would delay shifting.  i had a torqueflight do that 40 years ago.  it blew and took out a motor with it.  after that, i change the fluid and filter in my automatics every 3 years or 30k miles.

 

factor in dirty and therefore thin engine oil, and you get problems.

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[wildcat]

I beg to differ, I've taken mine up to redline many many times.  It depends on how hard you're pushing it and whether you're in tip or manual.  In manual mode it'll almost always go there if you're on it. 

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[flash]

6700?

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[az968]

So Dan's car didn't have the valves and head gasket refreshed before the supercharger?  Then that makes a little more sense to me.  I hope 130k isn't really a LOT of miles on this engine, but it would certainly be on things like head gaskets and fluids if never changed.

 

When I first read the description of the situation my first thought was the trans failed and dragged the engine into the gutter with it.  I hope that wasn't the case or the bill will go higher.

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[unknown4u]

Lowering the revs from the engine will not solve the tip from downshifting. It will perhaps may things even worse. If the tip thinks it must downshift and the engine must make more than 5000 rpm... than you will have a big brake in the back... I'd hope you will not be cornering at that time... or Flash were you be able to reprogramming al the modes from the tip? Even the selflearning mode?

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[94SilverCab]

Dan prides himself on careless maintenance, and is ever surprised when things blow up...

 

JMHO,

 

Jay

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[ds968]

The head , gasket, valves , lifters ,guides, were redone before the supercharger was installed ,  flash was talking about the Transmission valves because it did not shift.  As for the head rebuild no idea how well it was done, i have no info on the capabilities and work quality shop the PO used for that job.  could have been great, could have cut corners..   

 

Careless maintenance was probably just one part of it a series of factors ( as flash put it was likely a a " perfect storm " ) that caused this, so let's not jump to conclusions, who knows what shape the piston rings, or rod bearings or whatnot might have already been in - could have been its last leg when I got the car ..        

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[flash]

130k is a lot of miles.  if you have over 100k, you'd better be thinking about rod bearings.  pete constantly found them to be shot or just about shot when he would open up a motor with that kind of mileage on it.

 

the mains, crank, and rings were generally good for much longer though.

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[az968]

Great, something to add to the preventative maintenance plan, replace the rod bearings at 100k. I've been using Mobile 1 since I got my car in hopes of avoiding that, but maybe just in case..... At 3k miles/year I've only got 5 yrs to save up the $.

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[94SilverCab]

Rod bearings at (No Later Than) 100k, no joke!!!

 

Jay

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[MCL968]

All this talk about rod bearings has me worried. Mine has 110k, and has had excellent maintenance back to when it was sold. Oil pressure is good, so it's probably not something I have to do tomorrow, but it's something I need to start thinking about.

 

Is there a thread on here about the replacement process? Any tips or warnings, and what about that oil pick-up tube? Any fixes for that?

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[vliegwielolaf1234]

I have seen 968's with over 250k , never been opend , just regular maintanance .

One of them a tiptronic as well .

My  guess on this one is , rod bearing failure because of oil starvation , wich is not common wih these cars , there are just way to many high mileage engines wich never had rod bearrings replaced , 944 or 968 wich have the same piston and bores   , just minor differences ,  there are plenty of high mileage 944 as well

 

The way the car has been used does make a difference ,track time will shorten any cars life .

 

I have rebuild plenty of these engines and replaced many rod bearings , never seen worn out bearrings on street cars  , the ones wich had problems was of oil starvation on the racetrack when cornering these where mostly 944 2.5 engines .

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