Highest mileage motor? or Why do they always blow up?

[kenikh]

Given how often these cars blow up (wattup 16volt), what is the real mileage expectancy of a stock-ish 930 with CIS??? These seem to blow up with alarming frequency. I'm ignoring EFI, which can benefit from wideband O2 fuel trim, knock control, etc. which I believe are critical to longevity on these cars.

Seems to me the mode of failure (outside over boosting) tends to be poor fueling on one cylinder, which causes lean condition meltdown.

So:
Highest mileage CIS motor?
Am I off base in my suppositions?

[jwasbury]

I think Miguel's Chocolate Rocket 1978 has never been opened up. IIRC its got 100k or more on the odometer. Maybe he will chime in. Seems to be the exception rather than the rule. I've read somewhere around here that the life expectancy of valve guides on the 930 is 40k miles. Lots of variables but boost makes horsepower, horsepower makes heat and heat kills.

Other things can easily go wrong besides fueling...how about distributor boost retard failure? That will give you melty pistons and busted rings too.

I'd submit that the heightened risk that the engine needs big $ attention is what has kept the price of the 930 relatively low all these years.

In my opinion this forum is overdue for another rebuild thread.

16volt is far from blowing up IMHO. His car probably still runs great. I drove mine to North Carolina, did a track day, and drove it back with 40% leakdown on a cylinder. Ignorance is bliss...if you're not ready to dive in, best not do a leakdown test

[Ronnie's.930]

^^^

Not to mention broken Dilivar head studs (hardy har har, for Kenik - he who is tempting fate in a BIG way)!

[Norm K]

Fairly certain mine had never been opened before I rebuilt it at about 106.5K miles. The thing was actually running pretty well despite three broken oil rings and four broken compression rings.

[kenikh]

Originally Posted by Ronnie's.930

^^^

Not to mention broken Dilivar head studs (hardy har har, for Kenik - he who is tempting fate in a BIG way)!

Ye blaspheme the proclamations of Saint TurboKraft with your heretical jabbering, good sir.

[kenikh]

Originally Posted by jwasbury

16volt is far from blowing up IMHO. His car probably still runs great. I drove mine to North Carolina, did a track day, and drove it back with 40% leakdown on a cylinder. Ignorance is bliss...if you're not ready to dive in, best not do a leakdown test

He wishes - it runs like crap. It surges, bucks and farts, while blowing smoke.

[pkabush]

I have right around 80k on mine. As far as I can tell it's never been opened up.
It seems very healthy. Leakdown test showed 2-3% across all cylinders.
I don't recall the compression #s but they ere close on all six.
No broken studs.

[PrimeMvr]

Originally Posted by jwasbury

Other things can easily go wrong besides fueling...how about distributor boost retard failure? That will give you melty pistons and busted rings too.

This is one to keep an eye on. My dizzy pot rotted and froze, causing two sets of shattered rings and a scarred cylinder. Fortunately I caught it before more damage. I was seeing way to much oil blowby so I opened it up.

[Ronnie's.930]

Originally Posted by kenikh

It surges, bucks and farts, while blowing . . .

I didn't realize this thread was about Paul!?!?!?

[boosted79]

Just took delivery yesterday of a 1988 slant conversion with 102K miles. leak down on all is between 15-25%. Still runs strong though but I knew what I was getting into. Steel fenders, possibly factory?, 944 headlight mechanism, 3pc Speedline style Porsche wheels, very nice car. This will be the hot rod, 3.4 EFI is the plan. For the slant experts, could you buy steel slant fenders directly from Porsche?

[krasuskyp]

Originally Posted by pkabush

No broken studs.

that only means that Ronknees hasn't had his way with ^him^ yet

[ficke]

Originally Posted by kenikh

Given how often these cars blow up (wattup 16volt), what is the real mileage expectancy of a stock-ish 930 with CIS??? These seem to blow up with alarming frequency. I'm ignoring EFI, which can benefit from wideband O2 fuel trim, knock control, etc. which I believe are critical to longevity on these cars.

Seems to me the mode of failure (outside over boosting) tends to be poor fueling on one cylinder, which causes lean condition meltdown.

So:
Highest mileage CIS motor?
Am I off base in my suppositions?

I have often wondered about this also.
930's are a much higher stressed engine than the 3.0/3.2 or rather the 3.0/3.2 is one of the most over built engines made. So really not fair to compare between the two.
The CIS fuel system in a 930 was a real stop gap, temporary thing without real plans for production ( 8 cylinder fuel head modified for 6). So it is no surprise there were issues.
As for the cooling on the 930 it was no better than a 30/3.2 and the 930 turbo makes way more heat.
So Porsche was rather conservative with the street 930 engine parameters, and that is also a reason it 'responds so well' to tuning. And people tune and remove that safety margin.
Depending a lot on how a 930 is driving, turbo cool down after hard run, how much time at full boost, proper warm up, etc. and the all important frequent oil changes. I think it is possible to have 100,000 trouble free miles. But when I was a mechanic and these cars were new I saw failure rates that varied wildly.
I have 80,000 miles on my twin plug, 3.4L with a variable boost control/ dial of death knob.
A lot of failure is from a loose nut behind the steering wheel.

[Tippy]

I've never heard a lot of these cars blowing up? They're probably the most robust engine for boost next to a Supra I can think of?

[krasuskyp]

^Audi I5t^

I've seen mention of acouplefew 180k-240k original lower bottom ends here over the years - an inspiration to us all

[kenikh]

I'm sensing the theme: Maintenance is everything, as the modes of failure for these cars are numerous, coupled with minimal margin for error before failure.

[ObrHaus]

I have mine opened up right now, 130 000 KM's on the motor, reason was just to upgrade to ARP bolts and studs as running hotter cams, twin plug heads, bigger turbo and EFI. Prior to this my only issue was fueling from the CIS itself ( too rich on boost low rpm, too lean on boost high rpm), leakdown was good, no busted rings, no signs of detonation, no broken head studs. I was very surprised as this car has been running .9 bar with a Kokeln turbo, big IC, headers and zork on 91 octane (all that is available). Something that I think has saved mine is the fact that I put an AFR gauge in and it has tipped me off about fuel problems more than once, essential upgrade IMO.

[Tippy]

I've been on this board quite awhile, and the failures have been minimal. Of the ones I remember were mostly operator error; ie., too much boost, too much timing, starving for fuel, etc. Never remember anyone having a freak failure.

Knock on wood.

Look up any V8 from back in the day that made over, say 400hp, and you'd see a plethora of failures that can be attributed to cheap components not designed for bigger power over stock.

[ficke]

Originally Posted by kenikh

I'm sensing the theme: Maintenance is everything, as the modes of failure for these cars are numerous, coupled with minimal margin for error before failure.

I think you summed it up well.
Very few thing are free in this world, Hp. is one of those thing that comes at a cost.
With turbocharging you are essentially doubling the displacement with every atmosphere boosted. High heat is generated quickly in small areas, cooling is critical as is fuel and spark management under these boost conditions.
930's were cutting edge, first generation street cars running turbocharging.

Coupled with the fact that gas is a poor fuel for turbo charging especially compared to Diesel. Diesels are compressing just air not an air/fuel mixture like a gas engine.

So not having detonation and an ability to remove heat is tough with the rather primitive fuel/ignition system and air cooling of our gas fueled 930's.
The temptation to gain seemingly free HP. from our engines with out doing some of the necessary cooling mods our fuel management mods.
Makes 930's a real ??? especially when buying cars modified by who? with what background? and even not modified, how was it driven or maintained? Did the previous owner of that stock 20,000 mile 930 drive on the freeway, then pull over and shut their engine off so they could pee right away? Did they do this regularly?
Turbochargers do not really wear out if maintained and driving properly.
Lower ends are not an issue with 930's, it is almost always damaged P/C,s and then head/valves. Most of this damage was caused by the boosted fuel/air mixture, ignition, etc and not the way the long block was assembled or parts used.

Bolt on engine parts seem innocent and non-invasive and done thoughtfully can be a lot of fun. But... Hp. comes at a cost

[timc]

135K(ish) Engine never been apart. Oil (Amsoil) every 5K, no smoke and no leaks. 90% highway miles. Only failures that I can remember is the CD about 5 years ago, and the Alt right after I bought it in 06, other than that just normal maint and upgrades.

IMHO, All depends on how they are driven and serviced. I bought the car with 35K on it, and since I've owned it, its' never been used for short trips or city driving, and not on track, yet. Mostly highway miles and long trips. Amazing highway car, so comfortable to drive long distances (over 1000 mile trips) Prob one of the most reliable cars I've ever owned.

A good friend of mine had 180K on his bottom end when he finally pulled it apart, and no wear.

Amazing engines if you take care, no stop and go city traffic, no short drives where the engine does not get the chance to get up to normal temp and remain for a while to get rid of the cond, and of course you keep them in the 180-210 range.

tim

[Ronnie's.930]

Originally Posted by timc

Amazing engines if you take care, no stop and go city traffic, no short drives where the engine does not get the chance to get up to normal temp and remain for a while to get rid of the cond, and of course you keep them in the 180-210 range.

tim

No offence Tim, but with such specific operational conditions, one would conclude that these engines are remarkably one dimensional, delicate and finicky.

By the way, I couldn't agree with you more that these cars are fantastic highway cruisers - amazing how they chew up the miles, at high speed, and with remarkable ease and comfort.