I dont short shift at all. But, in the turns i select a gear that puts me down in the rpm to be able to accelerate best out[of it. Often, you cant use max HP around the turn anyway, so it works to your advantage to not be way up in the rpm around a sweeper for example. we are still talking 4-5,000rpm though.

Im curious to see what is wrong with Brian's engine. I watched his video. doesnt seem like he is doing anything unusual. I still bet he had some damage when he got the car. oil analysis is so good for this kind of proof.

Actually, I just did the 3rd oil change after the last 3 race weekends. Im very scared to pull the cap off the old filter to see what is inside. If there are any problems, you would think that with 6 race weekends, the engine would have signs of problems if something was not going well.

mk

QUOTE=RKD in OKC;6464450]I can understand keeping the rpms down. I've found my autocross laps are faster if I short shift and keep the revs down below 5500. Maybe that's just the x-pipe talkin.[/QUOTE]

 

Do you think there is some causation here, 944-2 oil relief valve increasing the risk of 2/6 rod bearing failure? Or are you saying that this mod alone doesn't completely prevent the problem?

 

The person that I first heard mention restricting the oil to the head in a 928, probably around ten years or so ago now, did so because he was claiming it was to prevent the 2/6 rod bearing failures. The thinking was that there was too much oil being pumped up into the heads, it didn't drain back to the sump from there fast enough, and that resulted in air getting into the pickup and killing the 2/6 bearings. The theory that he presented was that restricting the oil to the heads would keep more oil in the sump. Louie's video showed that there was not an excessive amount of oil pooling in the heads, and that the theory was wrong.

Cylinders 2/6 have been observed to be the most detonation prone on a number of different S4 and later cars. Earlier cars don't have the ability to montor detonation on a cylinder by cylinder basis while running, so I can't give any personal first hand information on those. The same goes for whether or not the #2 cylinder of the 944/951 is more detonation prone than any of the other cylinders in those engines or not. Back when I did some asking around about the issue a few years ago, I was told that the problem rarely if ever occurred in the 968. Porsche did make some changes with the 968, including in the oil pan sump.

Detonation may very well be a contributing factor, but it's not the only factor. If it was, street only driven cars would be experiencing the failures at a high rate as well as the track driven cars, and that's not the case. There has been some data collected that shows a problem with oil pressure dropping when cars have been driven hard on the track, particularly in left turns. I think that there are several issues that help contribute to the failures, but in my opinion, by far the two biggest ones are probably the oil pump pickup becoming uncovered and allowing air into the system, and possibly the oil becoming aerated due to it not staying in the sump area and being beaten around by the rotating assembly.

 

It doesn't prevent it. In my opinion, and based on Louie's video, the oil relief valve is a solution to a problem that doesn't exist, and it's definitely not the solution to the 2/6 rod bearing issues. It won't hurt to put one in, but I'm thinking it won't really help either.

 

I think on a high lift cam, extra oil up in the heads on the bearings and lifter is a GOOD thing. More movement on the springs creates more heat, which would be removed from the area by the oil.

 

Anyone knife-edge the 928 crank while they are Chevy drilling it?

 

The more time you spend at high rpm, the more likely having too much oil in the head is going to be an issue - ie: circle track

I fully agree that the pickup is sucking air though and looking inside a stock oil pan I'm quite surprised that nobody seems to be doing much about them - there is a LOT of room for improvement.

As always, one thing isn't ever the cure, problems always seem to be a bunch of little things stacking up which is why you need to take a system approach to improving things.

I would think for a track car you really need the following:

1) External oil cooler.
2) Modified sump baffles with trap doors.
3) Windage tray.
4) Drill and prep crank.

Optionally (I would add this stuff to my own car)

1) Increased pan capacity.
2) Accusump (I consider this an insurance policy rather than a solution to anything).
3) Restriction of oiling to head.
4) Check and deburr oil return passages.

None of thatstuff is going to make your car faster, but it sure will make it more reliable..........

None of it will cure detonation either, and if your bearings are hammered, they will still fail eventually, I think in a lot of cases the hammered bearings are just the ones that fail first when the pickup sucks air (since they're already damaged).

 

Increasing the pan capacity I do not feel is either a good idea, or very feasible.

The only way to go with the pan is forward more. or possibly a tiny bit wider.
This is going to have the opposite effect of what you want to have as what you want is a deeper sump, which really isnt possible for these engines.

 

Sideways is the better way to stretch your pan - I haven't looked at one on a car personally, so don't know how much room there is to work with. If you make it deeper, it tends to be the lowest point under the front of your car which can be quite undesireable......

Oh, and re-reading your post - you can't just make it wider and have it work without installing proper baffles around the pickup, otherwise you'll end up in real trouble.........

 

what is the best lube to use when replacing rod bearings?

 

I like redline assembly lube.

 

Thanks Mark
Pulled my pan today crank looks perfect. #6 bearing has a little wear but not serious not worn to the copper or brass or whatever is under the aluminium coating. I am going to re bearing and should be good to go.

 

that is GREAT TO HEAR Sean,

 

That is good news. How old were the bearings?

mk

 

I'll post pictures of all the bearings when I get them all out. I just pulled 2 & 6 so far 2 looks good but 6 shows some wear. I will be installing a complete new set of rod bearings today .Any one have any advise?