Photo of CRACKED CYLINDER due to OVER BOOST, Our Worst Nightmare

NY930 · 05:10 PM

Photo of CRACKED CYLINDER due to OVER BOOST.
Our Worst Nightmare.
If you don't watch your boost gauge, you will never know if you develope intermitant boost creep. A Tell Tale Boost Gauge will record your highest boost since you can't be watching it all the time.

equality72521 · 08-14-2011, 05:03 PM

Trying hard to sell that boost gauge huh?

Benny771 · Benny771's Garage

lol

NY930 · 08-14-2011, 05:31 PM

Hi Guys,
I wasn't laughing when I had to find a single 3.5L Mahle Cylinder.
Thank God for Pete at Andial.

Miguel Antonett · 08-14-2011, 05:57 PM

How do you know it was due to overboost - boost creep, you call?

Aussie Thunder · Aussie Thunder's Garage

I have to say that I'm worried about this - I have an 89 930 that I've just had serviced by a Porsche Specialist in Brissy - these guys really know there stuff and have 20+ years building race cars etc - they sent off my WUR, injectors & Fuel distributor for a refresh after my car was not coming onto boost smoothly.. Since it's been refreshed Wayne Park (Race Car driver & mechanic) has the car sorted and running so well that it's now scary fast. His words were it's the fastest 930 he's ever seen or driven and estimated HP at about 500 .. I've had the car since October and the Previous owner knew nothing much about it, he bought it 'cause it looks pretty . The car has a 1.5 Bar spring in and breaks traction easily in 1st 2nd and 3rd in a straight line .. I'm running 98 octane with an additional Octane booster to give it the fuel it needs - Wayne advised me that the car has had a lot of $$$ spent on it to get it to where it is now so spending more $$ to make it slower didn't really make sense.. Give it the fuel it needs and you'll be fine .. But I still have concerns about over boost .. But the car does run VERY well now that it's been tuned properly .. Don't want any blown motors ..

NY930 · 07:19 PM

I thought there were built in fail safes to prevent this, but I was wrong. If your wastegate lines fail or your wastegate diaphragm deteriorates or the diaphragm becomes slightly pinched during installation while blindly compressing the spring, you can overboost.
We are in more danger then we realize if we can't relieve that excess pressure.
When the rings break and the cylinder cracks and the pistons are not fried, then it was overboost and not detonation due to a lean fuel condition.
I had Raceware head studs so they didn't fail so
'Pop Goes the Weasel' and the cylinder cracked.

iamchappy · iamchappy's Garage

How high did it have to go to deliver the damage.

slow&rusty · 08-14-2011, 07:52 PM

How did you realize or what symptoms did you experience to lead into tearing into the engine?

NY930 · 08-14-2011, 07:57 PM

Well that's the problem.
Our factory boost gauges only show .8 & 1.0 Bar Boost. I thought that maybe the previous owner had installed a 1.0 Bar Spring.
So there's the problem. The stock boost gauge does not indicate a overboost situation over 1 Bar of overboost.

NY930 · 08-14-2011, 08:02 PM

Hi Slow & Rusty,
You sound like you have an old 356. That's how my 356 was. Very slow and very, very rusty.
To answer your question above, under wide open throttle during full boost, I heard a POP and then an audible exhaust leak before the exhaust port.
What a bummer.

redturbo911 · 08-14-2011, 08:25 PM

Sorry to hear that.

spence88mph · 08-14-2011, 11:27 PM

Quote:

Originally Posted by equality72521

Trying hard to sell that boost gauge huh?

LOL

So it will let you know how much boost it took to crack a jug, awesome.

SCHNELE · SCHNELE's Garage

Quote:

Originally Posted by Aussie Thunder

I have to say that I'm worried about this - I have an 89 930 that I've just had serviced by a Porsche Specialist in Brissy - these guys really know there stuff and have 20+ years building race cars etc - they sent off my WUR, injectors & Fuel distributor for a refresh after my car was not coming onto boost smoothly.. Since it's been refreshed Wayne Park (Race Car driver & mechanic) has the car sorted and running so well that it's now scary fast. His words were it's the fastest 930 he's ever seen or driven and estimated HP at about 500 .. I've had the car since October and the Previous owner knew nothing much about it, he bought it 'cause it looks pretty . The car has a 1.5 Bar spring in and breaks traction easily in 1st 2nd and 3rd in a straight line .. I'm running 98 octane with an additional Octane booster to give it the fuel it needs - Wayne advised me that the car has had a lot of $$$ spent on it to get it to where it is now so spending more $$ to make it slower didn't really make sense.. Give it the fuel it needs and you'll be fine .. But I still have concerns about over boost .. But the car does run VERY well now that it's been tuned properly .. Don't want any blown motors ..

935 ran 1.5 bar and 930s with very well dialed in EFI and big time mods may run boost approaching those levels but it is unheard of in the CIS world.

911TT33 · 08-15-2011, 01:56 AM

Quote:

Originally Posted by Aussie Thunder

I have to say that I'm worried about this - I have an 89 930 that I've just had serviced by a Porsche Specialist in Brissy - these guys really know there stuff and have 20+ years building race cars etc - they sent off my WUR, injectors & Fuel distributor for a refresh after my car was not coming onto boost smoothly.. Since it's been refreshed Wayne Park (Race Car driver & mechanic) has the car sorted and running so well that it's now scary fast. His words were it's the fastest 930 he's ever seen or driven and estimated HP at about 500 .. I've had the car since October and the Previous owner knew nothing much about it, he bought it 'cause it looks pretty . The car has a 1.5 Bar spring in and breaks traction easily in 1st 2nd and 3rd in a straight line .. I'm running 98 octane with an additional Octane booster to give it the fuel it needs - Wayne advised me that the car has had a lot of $$$ spent on it to get it to where it is now so spending more $$ to make it slower didn't really make sense.. Give it the fuel it needs and you'll be fine .. But I still have concerns about over boost .. But the car does run VERY well now that it's been tuned properly .. Don't want any blown motors ..

How can you be running 1.5 bar of boost on crappy 98RON fuel in a CIS 930?

That's the equivalent of 93 MON in the USA.

What kind of intercooler are you using?

I'd turn that boost down before you blow that motor. All it takes is a few seconds under load and BANG!!! 1.1 - 1.2 bar is probably safest for a well sorted car on our pump fuel.

Aussie Thunder · Aussie Thunder's Garage

It's running motronic, the motor is a 965 - not sure what difference this makes .. Is CIS and Motronic different ??? I'm new to these cars ..

slow&rusty · 08-15-2011, 04:26 AM

Quote:

Originally Posted by NY930

Hi Slow & Rusty,
You sound like you have an old 356. That's how my 356 was. Very slow and very, very rusty.
To answer your question above, under wide open throttle during full boost, I heard a POP and then an audible exhaust leak before the exhaust port.
What a bummer.

Actually Slow&Rusty originated from my Datsun days! Thanks for the reply and sorry to hear about the tragedy..cringing

Yasin

JBL930 · 08-15-2011, 04:47 AM

Quote:

Originally Posted by Aussie Thunder

It's running motronic, the motor is a 965 - not sure what difference this makes .. Is CIS and Motronic different ??? I'm new to these cars ..

Is it a stock 964 turbo? If so it will be CIS (K-Jetronic). Do you have a picture of the engine, we'll be able to tell you straight away what you have.

spence88mph · 08-15-2011, 05:12 AM

I've seen it in another thread, it's K-Jet, if it's making 500hp and holding together at 1.5bar, it's a very special car

krasuskyp · 08-15-2011, 05:16 AM

NY930... what about your overboost switch cutting the pumps @ 1.2bar? Both the WG and that have to have failed to overboost for any amount of time beyond a very brief (and very violent) second.

Er, why you selling the gauge - seems you're touting how much it's needed to prevent blowups? Just querious...