Best pistons for my build?

79 Fox

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May 21, 2019
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Engine is currently being re-machined. Bored .030 over. Need new pistons. Engine has GT40P heads B303 cam, 1.72 rockers, performer intake. Does anyone have experience with good pistons for this build? We’d prefer press fit wrist pins.
 
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HotFox

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Really was impressed with the quality of the SRP pistons for my 331. It has been 10 years now so not sure if they are still a good quality but I am still running them.
 

CarMichael Angelo

clearly, I’ve got something going on in that hole
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Sigh.......somebody please make a piston stickie...

There are three Pistons that you can choose from when considering a rebuild. Each one has its own sets of pro's and cons. I have went over this numerous times before, and I'm hoping that this time somebody will Copy and paste the content into a YTD area for future reference.

Starting at the bottom, the closest thing you'll get to factory, is a hypereutectic replacement piston. A "cast" piston. The factory used this piston for durability reasons...the alloy grows very little with heat, so the engine could be machined to provide tighter skirt clearances on the piston. Tighter clearances netted a quieter running engine, and less wear as a byproduct. The down side to this piston is its inability to handle the excessive heat and compressive loads that come when the engine is modified. The alloy in a hypereutectic is very brittle. When subjected to extreme cylinder pressures, high heat, or detonation, the piston shatters. When it fails, A shattered piston usually causes collateral engine damage that almost certainly dooms the whole engine to failure.

KB hypereutectic upgrade. A "cast" piston as well. This piston is marketed as an upgrade over the stock piston. It claims to offer enhanced heat resistance, and increased resistance to failure from high compressive loads due to a higher silicone content added to the aluminum alloy. It's still a hypereutectic piston. It shares all of the benefits of the above piston, with increased durability as a perk.
It will not tolerate incorrect ring end gap however.
The biggest complaint from people using this piston is ring land failure due to ring end butting. They simply didn't add enough ring end gap to allow for the increased heat the ring sees when exposed to a power adder. The ring expands, the ends butt, and the top ring land gets cut off the piston as a result. A catch 22 here is that if you follow the recommended ring end gap charts for your intended power goals, the ring end gap is so huge, oil control becomes an issue.

4032 forged Pistons. A very popular upgrade. Very tolerant of abuse, and shares the best of both worlds between true forged durability, while allowing tighter bore clearances to minimize wear, and excessive piston noise. Will not shatter like a hyper piston will up to a point, but is heavier than a true forged piston as a con. Cheaper to produce than a true forged piston, and as a result, cheaper to buy. Not capable of withstanding extreme cylinder pressures past a certain power level. Great street/drag perf piston.

2618 forged piston. True forged piston. Alloy is the go to for all big power builds. Alloy is softer than any other piston, and tolerates extreme heat. piston will fail via melting as opposed to breaking. A melted piston will allow cylinder pressure to escape through the hole,....creating a dead cylinder..much preferred to a blown up engine. More expensive to produce.
Lousy street piston due to the noise level they generate due to the need for excessive skirt clearance,..as the alloy grows significantly when engine heat rises. Much more forgiving when things go wrong with fuel/spark/tune...most expensive piston on the market.
 

RangerJoe

I leave the horn on while driving
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Mike does a great job at explaining the alloys, but there are some other distinctions as to the construction of the piston themselves. I am in no way greatly experienced in this category but have been reading up on as much I can lately.

Pistons can be the same alloy but one be much stronger than the other. Skirt designs and thickness above the ring lands are two things that come to mind. Also, most pistons come with wrist pins so some degree of thought needs to go into what type of wrist pin you need. For most enthusiasts builds a basic off the shelf piston of your alloy choosing will work, but if you are making big power adder numbers, you need to look at the entire construction of the piston.

Joe
 
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