Fire Crater or Step Head pistons---what's the difference?

zooeyhall · Nov 20, 2010

I'm going to be overhauling my M gas tractor. Can anyone tell me the difference between the "Fire Crater" piston/sleeve sets, and the "Step Head" ones? The "Fire Crater" pistons seem to have two "bumps" on the top, while the step head have just a single "step". Is there any real difference as far as power and compression?

Want to thank everyone on this discussion group who have given me so much helpful advice in the past. It is appreciated?

Anonymous-0 · Nov 20, 2010

I just put some stepped head pistons in a H they are pretty much the same thing so I was told on here a couple months ago.

Janicholson · Nov 21, 2010

From the physics point of view the cleanest internal shape of a combustion chamber (at low speeds like these engines operate) will provide the least surface to volume. (a sphere is the least)
This limits the cold metal from contact with combustible fuel. Cold (comparatively) metal quenches flame travel and costs efficiency. I would go with the single raised dome as it has the least surface area. This assumes they both have the same volume above the block (compression increase) Modern regular gasoline is able to handle 7.5:1 ratios in slow engines (and much more in high reving engines) Jim

Anonymous-0 · Nov 22, 2010

Fire Crater was last effort by IH to upgrade older models such as H,Super H, M, Super M to last 350/450, it was a pkg of 4 Sleeves & Pistons with appropriate parts for distributor & carburetor, the shop at IH dealer where I worked installed these all winter, customers wanted the most power available, as these tractors aged & were mostly secondary they put flat tops in for std altitude, stepped top was probably higher altitude.

Fire Crater or Step Head pistons---what's the difference?

zooeyhall

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Anonymous-0

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Janicholson

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Anonymous-0

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