2.5L Mercury Heads

[Reel Life]

Is there any difference in the combustion chamber size in 18488 C2,C3,C4 &C5 factory heads? What is the typical combustion chambersize of the stock heads and how small can you go and still run pump gas. Thanks for the info.

[Jay Smith]

Yes there are differences in combustion chamber bowl depths and widths. I have great luck with 34 CC's using a 1 MM head gasket using pump gas premium..With either head as long as the CC's are reduced to only 34 CC's you will be fine on pump gas..

Jay

[Reel Life]

Thanks Jay. Do the differences in combustion chamber shape result in different volumes or are they all pretty much the same and what is the "stock" head CCs? Thanks again
Mark

[Jay Smith]

Mark,
The wider the combustion chamber bowl width across the diameter the more volume CC it will yield in stock trim. Most of the wider bowls end up being 41 CC's and the MORE material you would need to remove ( mill ) to end up with a 34 CC head. Hope I have answered your question if not call me 1 281 576 5088 cst...

PS: Stock heads come in many CC's from 41, 38,37, 26, 21 according to the vintage, motor they were from and application...

Jay

[Reel Life]

You answers were spot on. The reason I asked was I always match the casting numbers in addition to the part number on the heads when rebuilding an engine to ensure consistant compression across both banks of cylinders. I've recently seen several rebuilds where this was not done. I was wondering if I was over reacting or doing the right thing.

[speedinstream]

Not to hijack but how many cc's are 18488 c2 heads uncut?

[Jay Smith]

My guess is 41CC's on the wide combustion chamber. Most 2.5 200 carbed motors are the wide width bowl.....But I would have to CC em to be sure. You never know when they have been already whittled on.....

Good luck,
Jay