Forged or Cast pistons ?
Discussion
neiljohnson said:
Silly arguments aside I'm finding this an interesting read
Out of interest its been suggested to me that ceramic coating Pistons can be used too good affect, does anyone have any experience of this?
I've avoided it thus far as having seen ceramic coating start to flake off an exhaust manifold after a while I wouldn't want that to happen to my Pistons!!!
As you have correctly identified, the issue with any kind of piston coating is that it can "fall off"!Out of interest its been suggested to me that ceramic coating Pistons can be used too good affect, does anyone have any experience of this?
I've avoided it thus far as having seen ceramic coating start to flake off an exhaust manifold after a while I wouldn't want that to happen to my Pistons!!!
A lot of people fail to understand the thermal loading on pistons. What REALLY matters is the bit of the compression and power stroke between about 45deg BTDC and 45deg ATDC. IN this zone the flame temperatures are up at several thousand DegC because the volume (and hence pressure) of the combustion chamber is so small. With a realistic bulk piston temp of say 400DegC max, that means you can have a difference in temp of easily 1500degC between the combustion gas and the crown of the piston. Add that the fact that combustion chamber is enormously turbulent at this point, and the heat transfer to the piston during this time is critical. As such, reducing the piston thermal impedance, even by a small factor can make a very big difference to its local and bulk temperature. In a real engine, the layer of carbon deposits on the crown actually can make a difference as it has a poor thermal transfer co-efficient (unfortunately it's also black, which means it absorbs more radiated energy from the burning charge!).
A ceramic crown coating aims to interject a high thermal impedance between the piston and the combustion chamber. In fact, often the piston design and clearance will need to be modified due to a the lower thermal expansion of the crown when coated!. The problem comes of course if that coating falls off. Now your piston will expand more, possibly detonate, or touch the bore, leading to pre-ignition and death of that piston soon afterwards.
IME, unless you have a specific issue with piston temps (ie cracking / failing piston due to thermal loading) stay well away from internal ceramic coating, unless you really are trying to find every last 0.1bhp and have a suitable dev budget and enough spare engines to be able to properly develop that coating.......
I have complete confidence in thermal barriers applied by the piston manufacturers as they'll already have done research before putting their 'name' behind the product. I wouldn't go the diy route.
As an aside, moons ago I came across the Keroniting process where the thermal barrier was inbedded into the crown by a blasting process. The russians used to do this to their jet turbine engines. Has anybody ever come across this treatment and tried it? Maybe this is what the piston manufacturers are actually offerring?
As an aside, moons ago I came across the Keroniting process where the thermal barrier was inbedded into the crown by a blasting process. The russians used to do this to their jet turbine engines. Has anybody ever come across this treatment and tried it? Maybe this is what the piston manufacturers are actually offerring?
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