Racecar Project - Case Preparation
10-05-2005, 09:22 AM
#1
Nordschleife Master
Thread Starter
Racecar Project - Case Preparation
I received my case back from the machine shop yesterday where I had the following done:
1) Case bored out for 109mm cylinders. This is the modification Porsche does for the Bore in 102mm 3.8l cylinders found in the RSR engine. The 993RS does not require the 109mm but instead retains the stock 107mm bore size.
2) Case has the main webbing modified to promote better airflow. This modification is commonly referred to as "boattailing" You can see the difference when compared to a standard case. I also had the cylinders cut at the bottom to match the boattailing. Bruce Anderson claims a 10hp gain for this modification. I have seen evidence of case "walking" on stock 964 Cup car engines so I believe this to be a worthwhile modification for my purposes.
3) Case has been shuffle pinned. These cases tend to "walk" under hard usage which means the crankshaft is no longer held correctly, and the case wears, main bearings wear, etc. The shuffle pinning keeps the case aligned and prevents "walking"
There are a few other modifications and the case was cleaned with all of the plugs pulled, oil passages brushed out, oil squirters (2mm) were cleaned and checked. So all I'll need to do is to hot tank it once prior to final assembly.
1) Case bored out for 109mm cylinders. This is the modification Porsche does for the Bore in 102mm 3.8l cylinders found in the RSR engine. The 993RS does not require the 109mm but instead retains the stock 107mm bore size.
2) Case has the main webbing modified to promote better airflow. This modification is commonly referred to as "boattailing" You can see the difference when compared to a standard case. I also had the cylinders cut at the bottom to match the boattailing. Bruce Anderson claims a 10hp gain for this modification. I have seen evidence of case "walking" on stock 964 Cup car engines so I believe this to be a worthwhile modification for my purposes.
3) Case has been shuffle pinned. These cases tend to "walk" under hard usage which means the crankshaft is no longer held correctly, and the case wears, main bearings wear, etc. The shuffle pinning keeps the case aligned and prevents "walking"
There are a few other modifications and the case was cleaned with all of the plugs pulled, oil passages brushed out, oil squirters (2mm) were cleaned and checked. So all I'll need to do is to hot tank it once prior to final assembly.
10-05-2005, 10:10 AM
#3
Three Wheelin'
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Geoffrey,
Still dont understand the shuffle pins ! Turbos / GT3 dont need it or are you going for something very spectacular!!!!
Just for interest-no offence .
Geoff
Still dont understand the shuffle pins ! Turbos / GT3 dont need it or are you going for something very spectacular!!!!
Just for interest-no offence .
Geoff
10-05-2005, 10:51 AM
#4
Nordschleife Master
Thread Starter
Geoff,
I chose to shuffle pin this case for several reasons: When I rebuilt my 911 Turbo engine after 6 years running MoTeC at 521hp it clearly showed significant walking of the case, evidenced by the scuffing on the main webbing. Every 964 Cup car I've rebuilt has shown similar scuffing. Ollies Machine shop which has done more 911 cases than anyone has seen this issue on most 911 engine cases used in racing. This is a common modification for the early mag cases and is identified in Bruce Anderson's book on page 137 as the fix for case walking. I'm not one to argue with facts, and the facts that I've seen say the case is walking and the fix is shuffle pinning. This includes at least 1 turbo engine.
The issue with the cases is that the through bolts only hold the case halves together, they don't prevent movement side-to-side because they don't contact the case in the through bolt bores due to the oiling that is provided by these bores. There are only a few small alignment studs to keep the case together.
I have been involved in only 2 water cooled projects, one being the twin turbo GT3 Cup car engine Rick Deman designed, so I can't say for sure. However, knowing that the GT3/Turbo case is a derivitive of the 964 case, if they did not make updates, the I suspect they are prone to walking as well.
I chose to shuffle pin this case for several reasons: When I rebuilt my 911 Turbo engine after 6 years running MoTeC at 521hp it clearly showed significant walking of the case, evidenced by the scuffing on the main webbing. Every 964 Cup car I've rebuilt has shown similar scuffing. Ollies Machine shop which has done more 911 cases than anyone has seen this issue on most 911 engine cases used in racing. This is a common modification for the early mag cases and is identified in Bruce Anderson's book on page 137 as the fix for case walking. I'm not one to argue with facts, and the facts that I've seen say the case is walking and the fix is shuffle pinning. This includes at least 1 turbo engine.
The issue with the cases is that the through bolts only hold the case halves together, they don't prevent movement side-to-side because they don't contact the case in the through bolt bores due to the oiling that is provided by these bores. There are only a few small alignment studs to keep the case together.
I have been involved in only 2 water cooled projects, one being the twin turbo GT3 Cup car engine Rick Deman designed, so I can't say for sure. However, knowing that the GT3/Turbo case is a derivitive of the 964 case, if they did not make updates, the I suspect they are prone to walking as well.
10-05-2005, 02:08 PM
#5
Three Wheelin'
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Geoffrey,
OK understood. I knew that the mag cases needed this but someone ,somewhere had made the comment that for aluminum cases it was not a good idea.No idea why ! as it certainly makes sense.For info GT3/GT1 cases have 993 part numbers !Case of stick to what works !
Good luck with your new monster !
Geoff
OK understood. I knew that the mag cases needed this but someone ,somewhere had made the comment that for aluminum cases it was not a good idea.No idea why ! as it certainly makes sense.For info GT3/GT1 cases have 993 part numbers !Case of stick to what works !
Good luck with your new monster !
Geoff
