The MGA With An Attitude
PISTONS, High Compression for the Twin Cam - TC-310

At 09:44 PM 11/18/04 -0500, Jonathan Stein from mgatwincam group wrote:
"Quite a few of us have had highish compression pistons made up by Arias to a design conceived by Ralph Steinberg at Cloverleaf Auto near Philadelphia."

At 01:20 PM 11/19/04 +0000, Don Haynam wrote:
"I too have the Arias pistons and I believe the design is such that the pistons are all made to the original 9.9/1 and they then machine off the top to whatever ratio is requested. I ordered mine at 8.3/1 not knowing that you could get higher. When they arrived they were 9.9/1. I called Arias and they gave me the dims. to remove material to make them 9.3/1, which I did."

On 8/3/2010, Mick Anderson wrote:
I have attached a couple of drawings for interest. [see links below]
I have arranged the drawing of a Twin Cam 9.9 CR standard bore piston.
I am rebuilding a Twin Cam engine at the moment. If I cannot get a set of originals I will get a set made up by Arias.
I would specify the BMC design from the top of the cylinder bore to the top of the crown and Arias design for the lower section.
The diameters would of course be increased as required for oversize bores.
This should give a much lighter forged piston.
There are very slight differences from the measurements in the Technical Data Book, but I think that measuring a production original is a better idea as BMC were messing about with diameters, particularly ovality, and the latest details may not have been recorded in the book.

MGA-P-01 - MGA Twin Cam 9.9 CR Piston Drawing (401-KB pdf)
MGA-P-02 - MGA Twin Cam 9.9 CR Piston Skirt (121-KB pdf)

More piston notes on the following pages.

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