Windage Work

[haasad]

Getting sorted for my 2.7 hot rod rebuild. I've got 7R cases with oil squirters etc and want to reduce the windage numbers. I've seen lots of cases with the webs boattailed etc but was looking for a spec' or dimensions to work to ?

Also has 101 projects got all the details for the oil pump by pass mod ?

AND

Shuffle pinning tips?

three in one, a bonus!!!

keep the faith

andy

[304065]

Search here, conventional wisdom is do not cut a magnesium case, they need all the strength they can get. 10hp reported by the factory on 911R aluminum case and by Kremer bros, but remember, if their main webs cracked they just got another case off the shelf, and anyway, the factory used to sell the engines after the race.

[Steve@Rennsport]

Wise man, that Cramer guy,........

Seriously though, thats sterling advice from Dr. Cramer about the wisdom of removing any metal from a magnesium engine case, especially if longevity is a criteria.

Shuffle-Pinning OTH, is an excellent idea and strongly recommended as well as the oil bypass mod and using a larger oil pump.

Love your car!!!!!!!!!!!!!

[chris_seven]

I have always worried about shuffle pinning and what to do about line boring the case after the dowels have been fitted.

I have never been convinced that the two halves of the case will be in line without this process being carried out and I guess suitable bearings are difficult to find.

There must be something obvious that I am missing.

[rvanderpyl]

1. Drill for Dowel Pins
2. Surface Case
3. Rebore to std

Seems that would solve any issue with the case being distorted by the drilling for the dowels?

[chris_seven]

I wasn'rt concerned about distortion due to drilling more about the alignment of the two halves.

I do agree that this method would solve the alignment issue but would make the engine a little more narrow.

I assume that this won't cause problems with chain length and tension?

[Walt Fricke]

A clever machinist came up with a different way of achieving what dowel pinning does. Basically he bored the holes where the case through bolts pass from one web to the other to hold thin hollow bushings. Sort of like what the factory did for where the #1 case bolts mate. He bored the holes for these bushings with the case halves clamped together, so that he got a perfect register. The trick was how he was able to do this.

He was of the opinion that the standard method of drilling one set of holes, placing transfer punches into these, and then putting on the other case half to poke holes to indicate where to start drilling for the corresponding hole for the pin, was imprecise. By drilling for both sides in one pass he avoided any chance of mis-registering.

He's not in the business any more, but this sure made sense to me, and I wish I could find someone who would do it to another case of mine.

On the other hand, I had another case (also sand cast) shuffle pinned in the usual way, and that seemed to work - case went together as easily as usual, and came apart without the need for too much prodding. Certainly did not need line boring.

But things may be otherwise with mag cases.

Walt Fricke

[kenikh]

RSR cases used shuffle bolts, similr to what Fritz mentioned: The case through bolt holes are reamed to a near interference fit on the through bolts (which are slotted to allow oil passage). Makes for a very rigid structure. Too bad no one makes them anymore.

[Walt Fricke]

Kenik

Were these the titanium through bolts that were narrowed elsewhere to save even more weight?

Walt Fricke

[haasad]

Steve, thanks for the comment on my car. You guys are the first to see any piccies since I always strugle to upload images to my favourite uk Porsche site.

So wisdom recieved is zero or very mild windage work. Shuffle pin using original case bolt holes as a register ( liked that idea going to have a look at a millilling set up tommorrow) Bigger oil pump ( already got)

So what about the oil pump by pass mod' does Waynes Book 101 projects detail it?

keep the faith

andy

[andyjboy]

I don't think it's mentioned in 101 Projects but the oil bypass modification is discussed in "How to build & modify Porsche 911 Engines".

Also if you do a search on Pelican you'll find all the necessary information.

[304065]

Andy (the Dorset one),

The oil bypass mod is a must-do for high performance engines.

A 911 oil pump is a geared positive displacement type which means that it produces the same flow no matter what. The oil pressure presses against a piston with a calibrated spring behind it, and when the pressure reaches a preset level it overcomes the spring and moves the piston, which uncovers a relief port which vents oil back to the engine sump. If the pressure falls the piston covers the port back up, allowing pressure to build.

In the original 901 engine this excess pressure was vented into the crankcase. As a result, the engine ran with a fair amount of oil in the bottom of the case with the resultant windage and aeration of the oil. So in 1976 the factory changed the design and vented the excess pressure into the INLET for the pressure side of the pump. This reduced the oil level in the case, which allowed Porsche to make the pressure side of the pump larger.

All detailed here: Oil bypass modification

[eapcpa]

Walt,

I had the alignment sleeves at the through bolt holes put in my case by Mike Bruns @ JB racing. Seems to me it is a better solution than dowl pins because it preserves more of the metal at the web and provides a seal between the case halves. You can contact him on his website jbracing.com. He is on this board as well so I am surprised he did not jump in this one.

[afterburn 549]

20 20 hind sight...I re did mine b4 for all this saga on weak case webb's...I boat tailed all the Webb's and eyebrowed the spigot bores. If I remember correctly- cut a hole in one side where the was not one (on one side of the webb) .....did all the up dates . Beat the crap out of it every since . Runs GREAT ! left the low comp pistons in knowing Or dreaming some day of adding some mild boost .
150 hp to the ground with stock cis @ 5400rpm

[haasad]

Thanks for all the help I now have the right way forward.

andy