I have a set of pistons from a 1988 305 that I would like to put into a 1985 lg4. Will these be compatible? Thanks.

 

as long as they're both 305's i don't think you'll have a problem. you can have your parts store check part numbers to make sure.

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ICON Motorsports
1st & 3rd

 

ede
I had checked with a parts dealer and that's the confusing part. The ring grooves,valve reliefs, and dished top are all the same. Yet they are listed as replacement for 1987-92 305.

 

87 is when gm went to the roller cams and one piece main seals, but i don't see where that would matter with the pistons.

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ICON Motorsports
1st & 3rd

 

Apart from ede's post above, make sure they are the same bore size (ie: 3.736", +.020", +.030" etc ...).

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB
Chevy Info --> MadMike's

 

The rear main changed in 86, a technicality, but anyway...

Parts books are far from 'THE' source on what is interchangeable. You say the dish is the same, so I am assuming it had the cc listed or something like that. The compression height could be slightly different, but thats not going to create a problem on an LG4 unless it has some sort of radical cam that the valve clearance should be checked on anyway. My guess is its either a minor change that doesnt matter, or they are actually the same and the parts book lists 2 different numbers for the same part... wouldnt be the first time.

 

Note that if they are dished, they are LG4 pistons. If they are flat-top with four reliefs, they are either L69 high-output pistons, or TPI 305 pistons, both of which were 9.5:1 compression engines. These cast pistons, when coupled with a 58cc chamber on the head, and a .015" steel head gasket, made 9.5:1 compression. Hence, their higher output potential.

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Daniel Burk
http://www.isthq.com/~dan/fcar.html
'84 Trans Am WS6/L69
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