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MG TD TF 1500 - MG TD Pistons Brand

Hi, I have recently purchased a mg td Engine that was race prepared full race cam, cut block, balanced, etc., and completely ready to run. It has .100 stamped on the flat top pistons with MM1A or MMIA stamped on the inside (or underside) of the piston. I know the .100 means oversized by .100, but Any idea of the brand or type of pistons? Also any idea on compression ratio? No other identifying marks. The engine is assembled, so I used a fiber scope to view the top of the pistons. Thanks, Rick
RS Kusy

Rick, you'll need to measure the thickness of the head to determine the compression ratio. A standard, uncut, head measures 3.022 inches. There are a few areas on the head that overlap the block where you should be able to measure the thickness. If you can tell me the thickness I can probably tell you the compression ratio and displacement for .100 over flat top pistons. Bud
Bud Krueger

If the engine has been modified that much, it is quite likely that there has been head work other than skimming, plus block decking ("cut block"), etc., so you cannot tell anything without taking it apart or trying to measure actual chamber volume by filling the chambers with liquid while assembled - not easy or accurate in most cases.

FRM
FR Millmore

Bud, The head measures 2.095" Plus or minus 0.001 or 0.002". So it has been skim cut 0.025-0.030"?
Thanks, Rick
RS Kusy

Rick, I'm guessing that your 2.095" number is a typo where you meant 2.905". Your .100" overbore pistons would give your engine a swept volume of about 1348cc vs. the standard 1250cc. The combustion chamber volume of a 2.905" head is about 38cc. This results in a compression ratio of about 9.80:1. As FRM has pointed out, these figures go to pot if the block has been decked, etc.

These calculations were obtained from the use of the excellent article by Hal Kramer, "Tuning the Head of a T Type Engine" from the June 2001 TSO. Bud
Bud Krueger

Bud, I made a typo 2.905". Your interpretation of my number is correct. Thank you. Rick
RS Kusy

Engine is on eBay 140918362401. With all of that work and $$$$ I wouldn't have expected to see a banana port head on a late block. Bud
Bud Krueger

This thread was discussed between 21/02/2013 and 23/02/2013

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