This is partly a repost of a thread that i put on another forum. Just want to gather as many opinions as possible and engage in a productive discussion that would help to come up with new ideas.

So, here is the story:

A little intro first:

After finding out that 3 cylinders in my CTT are heavily scored and that was causing a knocking sound that kept getting louder and during about a month time, i decided to do a rebuild of that engine.

Here in Russia a lot of Cayennes get their engines scored. Don't know, maybe it is a combination of such factors as very low temps and lower quality fuel. Lower temps (sometimes -13...-22F during coldest winter periods) seem to play the biggest role. The reasoning behind an idea that freezing temperature may cause a damage to the engine is that when the car stay outside for a long period of time (like overnight) some condensed water freezes on the cylinder walls and after a cold start scratches the walls. Those who trade used engines even have a best period of sales which is early spring. It is during this time that most owners discover problems with their cars and start looking for a used engine to put inside instead of a scored one. Anyway, those are just the theories.

So, since Cayenne is a very popular car here a lot of indy workshops have acquired some knack of rebuilding those engines. The price of a new block is too high so the guys here use an old scored block. The method of rebuilding is simple - cylinders get bored to a bigger diameter, big enough to put in cast iron bushings which play the role of the new cylinder. Those parts that got damaged aside from the cylinder block get scrutinized and are replaced if necessary.

Now, i understand that the original block is made of aluminium. But cast iron has an anti-scoring protection at least. I know people who has driven 20-30.000 miles on such engines and everything seems fine. There is also an option to find a used engine and just swap it - this would save some time but will cost the same. I think that when you rebuild it, you at least know that you won't get any more scores and the workshop gives a warranty, which doesn't come with a used engine. It may get scored as easily as the original one.

Modding Part of the post:

Now, you may be thinking - why the hell the thread is called Engine Mods? Because i think it is a good chance to introduce some while i do the rebuild. What kind of mods do you think will be worthy for one looking for some HP? I am fairly new to all that. I've done a fair bit of home work and this is what i am considering:

- Porting and Polishing. Do you guys think there is a room for some more power that could be gained with this?
- Cams replacement. Has anyone stumbled upon cams for this engine? A worthy investment for gains?
- A more radical way of getting more power is to run a twincharger. This basically means to add a supercharger that would engage right after idle and pump the air until about 2500-3000 RPM at WOT. This will eliminate any turbo lag and the car would be a beast on low RPMs as well.

Now, that would require beefing up the engine with internals that would handle higher power. Partly this is achieved by sleeving the engine. But all the main components should be replaced as well. Of course, i am gonna use some aftermarket products produced by some other firm, not original Porsche's. I did a little research and prices for Porsche's original internals are sky high. A set of rods would cost about $2000, set of pistons - $800, rings - $2700, gaskets - $600, which sums up to about $6500. These prices may differ a bit in US/EU, but this is approximately what they can be bought at here in Russia.

Can someone tell me, if $6500 would be enough to buy internals that are intended for high performance?

If some one could hook me up with dimensions for pistons, rings, bearings, rods so that i could find replacement - i would greatly appreciate that.

P.S. I already have an ECU tune (will have to be updated after mods, of course) and removed cats.

 

my thoughts;
there is always power to be gained from porting/polishing if done properly. I have not seen the ports on the 955/7 motor so i cant comment on potential gain levels. As far as engine internals, unless a rod was damaged, there are people on this forum making over 700hp and internals are not an issue. Aftermarket pistons are all you need (i doubt bearings are available outside of porsche) to put your sleeved block back together with.

 

Stormy,

First, thanks for responding. I hope the rods are still in a good shape.

As for the pistons - i have an affordable offer of forged ones. But those are produced here in Russia and i doubt their reliability. Although some people give good reviews for those. Another advantage of those pistons is an ability to use rings which can be bought at a very lower price, but still produced by reputable companies. Changing the pistons geometry of the original piston is also possible, i know, but what i am not sure about is how it affects its reliability. Oh, and they are of the same weight as originals.

Maybe some one can suggest some replacement pistons for that car? All i know is that the bore size is 96mm.

 

happy to help, and i have built many engines myself.

if you question the pistons in Russia, buy them in the U.S. Custom pistons here will run around $700-800usd + shipping. I would buy the rings here as well... JE, SRP, MAHLE and others are known for excellent quality and can build what you need to handle all the boost you want to push. I would contact one of them directly with your needs and let them assist you the rest of the way.

 

Yeah, that is probably what i am going to do.

I am also considering stroking the engine just a tad, but i need to find the specs of all the parts first to do the calculations.

Will keep this thread updated.

 

I can tell you that the pistons are different on between bank one and bank two.
We saw a lot of cylinder scoring issues in Alaska also (on naturally aspirated 955 V8s), I think partly because of the cold. We also only had a maximum of 90 octane fuel available.

 

Yeah, saw the difference between pistons yesterday while i was looking at parts catalogue.

Fuel quality is awful here. They do sell it as 95-98 octane, but the quality is highly questionable.

When i have my engine rebuilt, i will install a heater like Webasto so that the engine is never started at very low temps.

According to what people around say and notice, 955's in general and especially those equipped with NA engines get scorings somewhat more often than 957s or Turbos. But still. The percentage of those that are subject for engine replacement at about 70.000-100.000 miles is enormous.

 

i would contribute scoring more to driving hard when cold versus the cold itself. Pushing a motor at those temps causes the piston to expand at a faster rate than the cylinder. Take it easy till its warm and problem is unlikely to occur imo. a block heater will definitely negate much of that though.
i don't know what the compression height is on the piston and i doubt you will find aftermarket cranks for stroking. That leaves offset grinding the crank and new rods to go along with it. that will be a very expensive path with this motor i think....

 

A faster expanding cylinder makes sense, given its lower weight, volume and proximity to the source of the heat. Usually, i never start driving until the RPM slow down at idle. But there times that you are in a rush and really have to push a little.

Block heaters are expensive, though and are pain to install in Cayennes, from what i hear. I did a research during this winter. Comes the next cold season, i will get prepared way before.

Probably, yeah. Looking at the prices of the original parts from Porsche, rods are the most expensive. A set of rods is about 2000-2100 for this engine in Russia. What are the usual prices for custom made rods?

 

i haven't priced custom rods as all of my stroked motors have used off the shelf parts, i would guess somewhere between $900-$1100 though