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350HP930 350HP930 is offline
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Join Date: Jun 2003
Location: St Petersburg, FL
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Cool 930 Engine Balancing Results

For the benefit of those who are curious about how well porsche motors are balanced I have decided to share my balacing project results with you all.

Over the past few weeks I have spent many hours balancing my pistons, pins and rods in an attempt to weight match everything as well as can be done. In this case my limit was the accuracy of my scale and balancing equipment.

The good news is that the worse weight difference was only a few grams, but everything is now within 0.05 grams of where they should be. For regular jobs getting everything to within 0.3 grams is concidered good enough.

Here is how far out everything was to start with.

The rods' total weights were all within 0.5 grams of each other but their distributed weights were way off. The largest big end weight difference was about 3 grams and they all were different.

The wrist pins were within about 0.5 grams of each other so I made 3 matched sets to minimise having to remove weight from most of them.

The beauty of the flat six is that the reciprocating weights only need to be balanced between each opposed pair of cylinders.

The pistons were obviously in weight matched sets. Here are the details for those of you who are curious how close porsche decided to balance these weights.

444.2g - 443.4g
442.4g - 442.7g
441.2g - 441.6g

I took a lot of care to remove piston material from a location that would not effect the structural integrity of the piston in any way. On 930 pistons there is not a lot of excess material to choose from.

Luckly I didn't have to do anything to the crank. The crank was extremely well balanced from the factory.

To put it into perspective we usually balance a couple reciprocating assemblies a week and nearly everything we see starts out with a measurable imbalance of several inch-ounces at each end of the crank.

A balance job will usually involve in getting that down to less than 0.5 inch-ounces.

After spinning it up my 930 crank we measured less than 0.05 of imbalance at each end with no flywheel or pulley. Thats amazgingly good. Next week I will spin the assembly again with the pully and flywheel+PP attached so I can balance those items seperatly.

If I have a chance I will try to post some pics up of my recently lightened items.

Last edited by 350HP930; 01-05-2005 at 06:02 PM..
Old 01-05-2005, 06:00 PM
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