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Really want a Turbo S but scared about the 4.5L block reliability?


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Hi there.

Coming from a few years of happy modified RS6 ownership and XJR ownership before that, I have a good idea of running costs on big forced induction V8 lumps. I have been doing my research on the Cayenne Turbo/Turbo S and test drove a turbo recently to make sure that it was the right car for my other half. She loved it and really wants one but the more I read about engine knocking the more I want to steer clear!

I had three Imprezas before I got in to high end machinery so I know engine knock only too well.

On other forums I read people saying that due to different bore liner coatings between the S and the turbo/turbo S, the forced induction blocks were tougher and didn't suffer from knock? This forum, which seems to know what it is talking about, contradicts everything else I have read. Been there, done that with the Nikasil lottery on the XJR.

I am in the UK, will be buying a Turbo/S with under 85k miles on it if at all possible, will be running it on 99 Octane fuel (Shell V-Power/Tesco 99) and will be looking to remap it as soon as possible along with swapping out the exhaust system for a full Milltek one.

As an example of the sort of car I am after, I was considering this example and had talked to the owner - http://www.pistonheads.com/classifieds/used-cars/porsche/cayenne/500-bhp-porsche-cayenne-turbo-v8-4-5l------------------2005/1967747

He explained to me that it had burnt out a valve after "not running right" one day. He then linked me to pictures of the head work carried out, including shots of the burnt (exhaust?) valve - http://www.pistonheads.com/classifieds/used-cars/porsche/cayenne/500-bhp-porsche-cayenne-turbo-v8-4-5l------------------2005/1967747

He only had the valves that appeared to be worn, replaced. This seems like cost cutting to me that makes no sense while the tops were off? Should I be right to want to steer clear of this one? I did ask for before/after compression test results of each cylinder but he doesn't know if this was carried out or not. I do personally think that it is overpriced.

If any of you wonderful chaps could give me your input on whether I am right to be steering clear of a Cayenne Turbo/S or if it really is a much rarer case for the blocks to fail I would really appreciate it. Last year I made a "chemo brain" purchase of another Impreza and I lost 11k in 6 months getting that right! With that and the 7k slushbox fund for when the RS6 ZF slushbox finally fails, I have to try to be a little sensible!

Thanks,

Nick :).

Edited by Mr Footlong
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To start off with there are far more posts asking the question that you are asking that there are unique posts documenting the problem.

There is no cylinder lining in the Porsche M48 engines which cover all Cayenne and Panamera V8s, they are manufactured entirely from a hypereutectic aluminium alloy called Alusil where the silica crystals are exposed to form the bore wear surface. There are documented instances of bore scoring in these engines which are more prevalent in very cold climates; my Indy (probably the biggest independent Porsche specialist in the ME region) has not seen this problem in any of the V8s over here. Where it occurs it is limited mainly to Normally Aspirated engines with Forced Induction engines being relatively trouble free more than likely due the oil spray piston cooling which on the 4.5L turbo engines; all 4.8L engines have this feature. There is no definitive answer as to why this problem occurs but indicators point to poor lubrication at start up caused possibly by very cold oil or low oil levels. Over here the vast majority of available 4.5L Cayennes have +200,000km on them.

It may be prudent to run a bore scope but I certainly would have no issues buying a V8 Cayenne; I'm now on my 3rd.

I would be more concerned about buying a car with an engine with a burnt valve where the owner had only taken care of the immediate problem.

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Thanks for your reply, any others also gratefully received. I was also concerned about what caused the burnt valve in the first place and what had been changed in order to sort it but he didn't seem to know why.

I wonder why other forums seem convinced that the Turbo/S blocks have a different cylinder coating to the standard S lump? If they are the same lump then why would there seem to be a consensus on those forums that the problem is only seen on what I would expect to be the less strained engine?

I am in no rush so I think I will scratch that one as I would have to go up to the other end of the country, put a deposit on it subject to it passing a bore scope and compression test on all eight cylinders, then go all the way back up there again.

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Thanks again for the reply. So, just to confirm, it is your belief that the 955 TURBO blocks all come with piston oil squirters as standard? I saw this comment among your posts on Rennlist "The 957s and I believe the 958s all of the V8s have oil spray piston cooling".

Still struggling to understand then why the NA blocks seem to fail far more if that are made from the same material. I see that the compression is higher on the NA and that the Turbo lumps use forged pistons but other than that.....

Thanks again, this is putting my mind at ease a little and that is great as the other half was contemplating me getting another RS6 just for her and having to of those would be boring ;)

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IIRC, on Rennlist there is a thread in which Jake Raby says that he thinks the problem is that the NA V8s have cast pistons that expand at a different rate from a very cold condition relative to the bore material. According to him, the turbos have forged pistons that do not have this problem.

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You guys are great thanks. I have had a good trawl through Rennlist and read the 8 pages of that thread. My concerns have been settled pretty well. I still like the look of that Tubby on Pistonheads, just a shame that I don't think I could trust it based on the valve failure/work.

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There are a lot of Cayenne's out there. Many with over 200K or even 300K miles on them. Yes, it seems that the scored Block issue is only the 'S' versions. The Turbos do have different pistons and the Piston squirters that spray up from the bottom so they do get oil on the Block. One problem may also be that Porsche had a 20K oil change interval, kind of ridiculous. Most do much less, 8K with a top quality Synthetic for me. Porsche has shortened the interval on the later Cayenne's but maybe they didn't shorten the interval on the earlier ones as that may have made them liable for a bad first decision?

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