IPSC

Can someone (who has actually taken a head off) and not just a repeater of internet lore show an example of this happening from running rich? I mean how much fuel is really injected into the cumbustion chamber? How rich do you have to run for this to happen?

When my head gasket on my 89 was replaced for me (I was in Iraq at the time) the shop shot some picture of my cylinder walls and they looked perfect and I am running way rich at the moment and I have no idea how long the PO had this set up causing this condition.

So is this a real concern or rennlist lore?

IPSC

mark944turbo

Rennlist lore if you ask me. Nobody has a real answer for the cylinder wall scoring, just opinions.

To be safe, listen to all opinions by not overheating, not detonating, and not running rich, just like you would hope to do in any engine.

You could buy a boreoscope for like 100 bucks (I think) and look at your cylinder walls without taking the head off if it bothers you.

RKD in OKC

I had a 2001 BoxsterS that the dealer inadvertently installed the wrong MAF causing it to run rich most of the time. While I don't know if there was a problem with the cylinder walls, the engine ended up spinning a rod bearing about 5000 miles after the MAF install. It also ate 2 mufflers and a catalyic converter from the backfiring on deceleration. Took the dealer and Porsche techs over a year to figure out they had put the wrong MAF on the car. It was kind of frustrating for me because EVERY TIME I took the car in, I told them that this problem started when they replaced the MAF!

When they replaced the engine (under warranty thank goodness) it basically replaced everything EXCEPT the MAF. And they still didn't suspect the MAF sensor when the problem persisted after the engine replacement!!! Arrgh.

I had such great luck with my Boxster S ! Even with the wrong MAF and running rich, I was the fastest Porsche on street tires at our local autocrosses.

badass951

Well I know from my own experience that even dipping as low as 10 to 1 air-to-fuel ratio will not ruin your cylinder walls. Anything below this I am not sure and would not want to attempt.

cpt_koolbeenz

True fuel wash is like a dry startup... No oil whatsoever on the walls or rings. Of course that is not good.

But it takes a lot of fuel to do this. I could be wrong, but I have not really heard of fuel wash on fuel injected engines, (except on Rennlist). I usually hear of fuel wash on carbureted engines, because you can flood them easily.

I have also seldom heard of fuel wash happening to a running engine, (only cranking). If you are pouring that much fuel into your engine to get fuel wash, your car will not run very well at all... You would notice it. Liquids are not very compressible - you would most likely run into symptoms of the car beginning to hydrolock.

Also, if the engine is running at operating temp, the fuel will want to vaporize. Thus, rising the amount of fuel required to fuel wash. Your injectors don't just dump the fuel in, they atomize the fuel.

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Now, on another note, running rich causes carbon deposit buildup. When the carbon pieces come loose and get trapped between the piston and walls, then you WILL get scoring!

There are also different signatures of scoring. One deep line on the wall of a cylinder would be most likely caused by debris, while minute scoring and wear all around the cylinder would be caused from improper oiling (or old age) - whatever the cause.

As is, I also would not go below 10:1. There really is no need... (If you think you need to, you may want H2O/Alcohol injection!)

Sorry I cannot prove this with pics, but maybe some of that makes sense...

aeronautica86

I found this rather interesting, and made an observation in my mind:

Obviously this isn't a scientific analysis, so I could be totally off here, but most of us know that APE chips run incredibly rich in through much of the RPM band. APE has also been around for a very long time and its seems that many many 951s run or have run APE (or clone) chips at some point in the past. Also, it seems to me that in almost every thread with pics of 951s with the heads off, there seems to be some mild and sometimes not so mild scoring. Could there be a correlation here? The former popularity of APE chips leading to the scoring of cylinder walls in so many 951s due to carbon deposits left by running everyday in an overly rich condition...

Again, I could be missing something here, and if not, a more objective study would be needed

Imo000

The wash down will only happen if the cylinder is without a spark for an extended period of time. Even if the mixture is rich it will mostly burn during combusting so wash down is not really possible, but if the injector is continuously firing and there is no spark, the walls will be washed down.

mark944turbo

I dont think it is autothority's problem, I have taken apart plenty of engines that were never chipped and had bad scoring, including na engines. The one common characteristic that I have seen in the badly scored engines is overheating, or recent reciets for things like radiators, showing that the car was running hot.

Ski

I think it's more "old wives tale" than fact. I mean damn, if you're running in the 10s or below, you should look like a greyhound bus going down the road.

Fuel wash, washing the small amount of oil maybe, with bad rings...so many variables that have no way to be confirmed. But when you blow a headgasket, the small "junk" that's free'd up causes most of the scoring, and I would include carbon deposits off the valves too, which is set free by the steam cleaning that takes place.

ehall

off topic but related,
What is the safest way to clean carbon deposits without breaking potentially harmful deposits loose? I've seen seafoam users, what else?

cpt_koolbeenz

Pull the head...
You can try SeaFoam... It does something. But what how much is debatable!

Really, don't bother with it... You can't do anything about it. Your engine is a big kid, it can handle itself.

Ski

didn't Porsche used to recommend Chevron Techron?

SeaFoam was originally intended for marine engines, which on average, operate in a much cooler temp range with the regards to the main engine block temp. My 350 in my MasterCraft runs around 130°.