deilenberger

Carl - thanks for the info. Somewhere in the very back of my mind, I recall once hearing about a 2010 that an engine rebuilder did - I'd have to guess that was the one you did. So far - no reported 958 failures - and lots of those cars are now approaching 100k miles (as CTT is) - so I'd expect to hear if the problem still existed.

Flat6 Innovations

No, iron/ steel sleeves belong in a chevy- not a Porsche..

Here we only work with Nikisil.

tats

Petza914

That's correct. Letting the car sit there and warm up in enrichment mode just dilutes the oil with fuel and does wash the cylinder walls. Much better to get in, give it a few seconds to move the oil around and then drive off and warm it up under light throttle and load.

Same advice in the 997 forum and really for any car.

Flat6 Innovations

The whole warm- up discussion has changed as cars/ engines/ fuel and emissions have evolved. With catalytic converters and secondary air the whole idea when the engine starts is for the catalytic converters to "light off" as fast as they can to begin doing three job with emissions control. To do this additional (secondary) air is delivered into the exhaust system, and fuel enrichment that is well beyond what the engine needs to have an effective cold start is used to fuel the catalyst process. This additional fuel is "cat food" because it provides the additional fuel to mix with the secondary air to light off the catalytic converters. The bad part about this, is the excess fuel has to pass through the cylinders/ combustion chambers as unburned fuel before it makes it to the exhaust system, so It can do the job as "cat food". This is better for the environment, but horrible for the engine, as gasoline is a great solvent, and a horrible lubricant, as mentioned above.

Now, the longer an engine runs at idle, with no load, the longer it will stay cold, and the longer the ECU programming will continue delivering excess fuel to provide the "cat food" for the catalytic converters to do their job. Letting the car warm up is no longer the best regimen due to these things.

Get in, fire it up, buckle up, and drive the car very conservatively. This will still allow adequate warm up time, but the additional piston speed, and thermals will help to progress the car through the "cold start" and "just started" fuel enrichment periods. It can take an engine 20 minutes of idling to warm up to the point where it is heat soaked enough to open the thermostat fully. If the car is driven lightly, the thermostat will open 4X faster than that. Put simply, the longer the engine runs with no load, the longer excess fuel is being introduced into the cylinders, and the more oil is being washed from the cylinders.

With DFI things changed, we no longer have secondary air. The DFI injector has another cycle period that injects fuel during the exhaust stroke, with the exhaust valve open. This fuel provides the "cat food" for the catalyst process. It gets more technical than that, but I am trying to help people understand this, without using 13 letter words.

Carl Fausett

An excellent post by Flat 6 just above. He makes a solid point, good advice.

This is consistent to the other ideas we have discussed to combat upper cylinder scuffing during the cold start period, like: use of high ZDDP oils, using fuel additives that contain lubricants, and garaging or plugging in your Cayenne so the cold start period is not so severe. I like Flat 6's point too. All of these are addressing the same issue (upper cylinder scuffing), coming at it from different directions.

Petza914

Jake & Carl,

Not specifically related to scoring, but since we have both of you Porsche engine gurus involved in this Cayenne engine thread, I have another DFI motor question that you guys would definitively know the answer to and put an open forum question to bed for us.

See this graphic that was part of both the Cayenne DFI and 997 DFI Technical Model Release notes (same graphic is used in both, but captioned differently).



Also, in this video at exactly 1:36 you can see the intake stroke with the injector firing. Not sure how accurate this animation is with respect to timing and pulse angle, as it looks like the stream doesn't hit the back of the valve except for maybe a tiny bit at the end of the pulse, creating the mist in the chamber, but again, it's an animation, so who knows.


Because of the angle at which the graphic was created, it looks like the injector pulse might actually spray and wash the backside of the intake valve. If so, this might help to explain why the DFI Porsche engines don't seem to accumulate as much carbon on the backs of the intake valves as other DFI engines, do, specifically like those from BMW that actually have a specified decarbonization service interval. Since valves rotate during regular use, the spray would actually hit in in different spots over time and keep the build up from occurring on one spot. I also thought that it might help to distribute the fuel mixture within the combustion chamber more homogenously, but someone told me that DFI motors tend to be designed around a more focused fuel blast into a specific area of the chamber, so maybe that's not a potential benefit.

Anyway, for the two of you that have been inside the 997 & 957 DFI motors, does the fuel pulse hit the the backside of the intake valve at all, and if not, how does Porsche keep the carbon buildup minimized.

Thanks a lot for sharing your knowledge.

J'sWorld

Hmm. They worked pretty good for Lozano Brothers who built the winning engine @ Daytona in 2010 and they are working pretty good for me too. They make the block stronger than an alusil sleeve or removing bore material and plating will ever. Porsche, Chevy, Ford, Fiat- their all mechanical contraptions. Many don't have the experience to do steel sleeves and they can be unforgiving installed improperly. Darton MID sleeves go into plenty of BMW engines and they do pretty well too. I like Porsche obviously but that's a retarded statement, kinda like saying a Chevy rear end doesn't belong in a Porsche.

https://928motorsports.com/parts/wet_sleeves.php

Carl Fausett

We do at least 2 or 3 steel-lined 6.54L Porsche 928 engines a year. We start with a 5.0L block (100mm bore) and bore it and sleeve it with ductile iron sleeves to 4.125" bore, install custom forged pistons, then add a stroker crank to boot. Been doing this for 12 years, many customers cars and my own race car. We have gotten 900 HP on our supercharged engine for about 4 years, and recent camshaft improvements have now taken us over 1000 HP. No problems. The engines like it, and oil consumption is low.

Before you ask: we have not put steel sleeves in a Cayenne yet. We think the cylinder spacing is a little tight - I would not want to bore it out too big, but we think we could do it.

Pic below is from our 4.125" bore 1000 HP 928 engine. Steel liners are visible. The 928 block is an open deck design, which has its own issues with cylinder wandering. The Cayenne is a closed deck design, and should handle the steel liners even better.


Porsche 928 with steel cylinder liners. 928 Motorsports