77MM Pistons?

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77MM Pistons?

Postby Veefan » January 25th, 2011, 2:16 pm

I'm selling some spare parts on e-bay, one item I have listed is a set of 77mm .020 over pistons.

Providing all the below rules are met, shouldn't they be legal?

The GCR says

"The engine shall be a standard VW power plant, as normally fitted
to VW sedans as defined herein. Any engine part(s), listed by the
manufacturer (VW) as a current, superseding, replacement part for
the standard VW 1200 series, Type 1, U.S. model sedan and interchangeable
with the original part(s), may be used."

4. Pistons and wrist pins minimum combined weight without clips
or piston rings = 330.0 grams

a. Maximum bore: 3.040 inches
b. Stroke: 2.520 inches +/ 0.005 inch.
c. Minimum capacity of combustion chamber in head: 43.0cc
(Polishing and/or tooling is prohibited.)
d. Minimum depth, top of cylinder barrel to top of piston:
0.039 inch


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270696652986
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Re: 77MM Pistons?

Postby FV80 » January 25th, 2011, 2:32 pm

John,
No - they are not legal. VW has never defined the 0.020 over pistons as "replacement parts". I sent you an email a few minutes ago. VW HAS, however, just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). The pistons do not define "the bore" - the cylinders do that.

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Re: 77MM Pistons?

Postby SR Racing » January 25th, 2011, 7:14 pm

FV80 wrote:vw just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). Steve, FV80


And a good idea if you need another 14 lbs of ballast. :lol: We have built some of the hyper Bug engines with them, but they are pretty heavy for FV.
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Re: 77MM Pistons?

Postby tiagosantos » January 26th, 2011, 1:32 am

Are they cheap though? I could use the ballast! :D
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Re: 77MM Pistons?

Postby SR Racing » January 26th, 2011, 6:29 pm

About $100 more than a stock case. You can probably find 15lbs of ballast cheaper than that. :)
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Re: 77MM Pistons?

Postby tiagosantos » January 26th, 2011, 6:33 pm

Gee.. For that much money, I can probably EAT 15lbs of ballast! :D
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Re: 77MM Pistons?

Postby hardingfv32-1 » January 26th, 2011, 7:42 pm

Is this new case extra strong, a rhino case?

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Re: 77MM Pistons?

Postby brian » January 27th, 2011, 3:12 pm

I know there are some heavy duty after market aluminum cases but aren't the new cases simply made of different material?
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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Re: 77MM Pistons?

Postby hardingfv32-1 » January 27th, 2011, 5:02 pm

So the 15 lb. might come from the loss of magnesium?

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Re: 77MM Pistons?

Postby DanRemmers » January 28th, 2011, 1:34 pm

The density of magnesium is about 1.74, and aluminum is about 2.8. So if the magnesium case saves 15 lbs, then it weighs about 25 lbs and the aluminum case weighs about 40 lbs.
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Re: 77MM Pistons?

Postby hardingfv32-1 » January 28th, 2011, 4:41 pm

I did not appreciate that the case was pure magnesium.

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Re: 77MM Pistons?

Postby brian » January 28th, 2011, 4:52 pm

They weren't. The cases were a blend of materials. AS41 casted on the cases described the mix of materials. Cant remember the exact combination but the AS41 included zinc.
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Re: 77MM Pistons?

Postby smsazzy » January 28th, 2011, 6:11 pm

AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM
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Re: 77MM Pistons?

Postby FV80 » January 28th, 2011, 7:38 pm

smsazzy wrote:AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM

Hmmmm... 94% Mag - I think we can call that pretty much a Magnesium case :-).

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Re: 77MM Pistons?

Postby SR Racing » January 29th, 2011, 12:34 am

The aftermarket AL cases also have larger webbing etc. They are quite a bit beefier.
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