Case windage mods...
 

I came by the pic below of a windage mod on the end cylinders by adding holes. Had not seen this one before. Anyone heard / seen of issues doing this mod?

http://forums.pelicanparts.com/uploa...1695921941.jpg

Looks like a hack job to me, check out the size of the piston squirter holes?? Maybe I’m wrong ask henry.

What's on the other side of the hole, the flywheel? Or at the other end, the chain box? Unusual places to drill holes.

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I would think any of the windage loss modifications that were done back in the day are now moot with running a GT3 oil pump and a check valve and/or vacuum regulator on the vent line.

Evan - you bring up a good point that I was going to ask about. Prior version of my race motor had and open case vent line. Which is better, check valve or vacuum regulator?

A vacuum regulator seems safer. GT3 run the RMS installed backwards, not sure what seals in an Aircooled motor would get unhappy first if you started pulling significant vacuum.

Yes, seen it on a 964 RSR case.

Useful? Who knows, I would bet no.

Would think the holes could create greater turbulence, and going both ways. On the subject of the GT3 pump, I have installed one on a 3.6 track motor. Pistons and heads are still on the bench. Can you explain the vacuum regulator and the special flywheel seal and its orientation and exactly how the pump performs. It is configured to help vent the case and has a second oil pickup to help under braking. At least that is what I think I know. I assume the special flywheel seal is required due to the additional crankcase venting that is going on. As I recall the seal is mui expensive, but then what isn't on these projects. Bob

Would tend to make sense if you're pulling a vacuum to install RMS backwards... If you're pulling vacuum and it's installed in normal orientation it would seem like it could "suck air" into case, and if installed backwards in vacuum it would tend to seal better.

Figured I'd check to see if 997 Cup RMS is same as standard RMS. It was not, however, when I googled the part number to find price, I found this article. btw, 999.113.426,41 is the RMS in my 993 PET.

http://forums.pelicanparts.com/uploa...1696158064.jpg


Interestingly I was reading some posts and articles on this and they talked about installing seals backwards like Evan noted.

...if I wasn't in middle of rebuild I'd just go to dyno and "plug" my case vent which is open to atmosphere, record case vacuum on my AIM and see if HP changed. Anyone possibly have data on this in our motors?

That looks like #7 main bearing web. I've seen perhaps 15 964 cases crack adjacent to that main web. Later cases were reinforced to prevent these cracks. Removing material probably offers no performance enhancement and challenges structural rigidity.

case windage
 

Love the research and response on this site

Dpmulvan, could you point out the “hack job”? I’m not seeing it. The oil squirters do look way oversize. Too much oil hitting the back of the piston doesn’t do any good. As i’ve read, oil suspended in air with the mechanical parts hitting the oil reduces performance. How much, I don’t know. Nascar engine builders go to great lengths to control oil about the crankshaft. They even separate the crankcase with partitions to improve performance.