You mention high boost, then later on quench pads, but high boost pistons don't really have quench pads - only a small ring around the circumference. If they do have quench pads then to arrive at a low CR the compression height is going to be large, and burn inefficeint. Really high boost stuff doesn't gain from squish effects associaed with quench, and can even lose power.

There's lots of trash out there, but there are also good ones out there and you can choose from them. High power turbocharged pistons are relatively unsophisticated slugs really. I'm not sure what make of piston you were looking at or what exactly on the ring lands was crap about them. It must have been really bad because usually, if anything, they're overbuilt - even the lower tier stuff.


If the engine is NA and a one off then yah you need a custom piston. I'm still not sure whether your engine is NA or TC though.


How aggressively you get with compression height depends on how much stroke you want to run and how desperate you are to keep a certain rod length, so reduced compression height is not a given. You never want to compromise your ring package. It is priority. You have block height, you have stroke, and you're left with piston and rod variabled. You design your piston knowing what is going to be left for rod length, so you design your piston (including ring package) accordingly. You can do things with the block and piston that allow a large degree of flexibility with rod length and related thrust loads. With modern heads (airflow) there really is no other concern.

As for how many people have run 100mm cranks to 9K or higher, I don't know. What really is the limit? Refer to earlier posts in this thread.

 

I'm saying the compression height for all the 2.3 stroker pistons I have seen...as they all want to keep the 150mm rod off of the shelf...or so it seems...

as for quench pad on a turbo car, I'm reffering to the footprint of the combustion chamber with a low quench height (yes, lowers the pad, not ideal but helps out)...as to make the burn surface only that of the flat footprinted section of the piston. Flat is relative to: valve reliefs and filleted edges for the "ring" which is now the edge of the combustion chamber.
this leaves a flat pad, as seen by the flame front, and makes for less distance for the flame front to travel (shorter distance down than front center outward of course relative to many factors) and makes for less unburnt fuel in the combustion process. Also reduces hot spots helping keep det down.

As you said lots of what I'm discussing is rather minimal in a highly turbocharged motor. But everything I have stated does aid in the engine to make more power one way or another...be it broader powerband by spooling the turbo sooner, being able to run higher boost due to higher threshold of det or by simply having a higher peak combustion pressure through a faster combustion time (based on flame travel time)...
I know it works on paper and in simulation but haven't been able to play enough in the realworld in a closed test environment to see whether or not it makes a difference.


As for 9k I know AMS has done it but I'm not sure if it was the 2.3 or the old 2.0 set up...doesn't shep spin to 10k or something like that...:starts searching for video:

be it both are race motors not meant to live a long time


for my needed custom pistons...no one makes a bore, compression height or CR for what I want/need.

 

They can keep it if they want, but the motivation there is likely to keep costs low by using stock rods, so it is not a performance focused specification - in terms of the stock rods, and its length taking priority over the proper piston and ring package.

There aren't any high power, low compression pistons that are designed to reflect the footprint of the combustion chamber... at least any good ones I've ever seen or heard about. I would like to see or read of exceptions.

I can't follow your description. When you look at say a Cosworth 4G63 piston, what do you see wrong with it?

Like I earlier mentioned, too tight of a quench distance or large a quench area on a highly turbocharged engine can hurt power because the charge is already at high pressure, high turbulence, and because quench pads actually causes a pumping loss on both the compression as well as exhaust stroke, and limit flame front access (initially) to lower cylinder periphery which raises cook off time and can present a problem.

In fact, the author of your beloved simulation program you challenged me about a long time ago, wrote about these effects in his fat book. It has also been backed up in real life by several people across different continents that compete on a national and international level with very high pressure engines.

 

hmmm...this I did not know...is the pumping loss from the lack of tumble/air-movement (pushing a brick) caused by the flat face of the quench pad? The limited flame front does make sense in a flat piston scenario as the distance to burn is further away (assuming center plug: distance = half bore) and I would imagine the complete burn time to take longer as well in such a case...not the case for what I'm talking about as the "quench pad". In my case the distance is just the distance from center to the edge of the combustion chamber and the full face can be seen by the plug at TDC. The "quench pad" is recessed to make for the correct CR and limits to a higher CR in a lot of cases.

As for forced induction motors with footprinted combustion chambers...TWE, Cobb, Ross, JE, etc...they are a few that I know off hand that do.

 

bump for a responce

 

There is no lack of air movement from pushing a brick. The loss is just from flow-inefficient geometry. There are no good nozzles that have sharp edges of flat face perpendicular to flow. There are other considerations though. As you go to slanted squish the pumping loss is reduced, but squish effects are also reduced. The tradeoff is not proportional and does not balance in all cases. Optimal balance has to be found - this is assuming there is enough space or lack of other considerations to even want to try slant squish. In most high performance 4 stroke engines there is not enough benefit to slant squish.

Yes distance, but in addition to it, the quench effect of two relatively cool surfaces very close together not encoraging consumption, but subject to high pressure from main combustion area. In other words, if air fuel in cylinder lower periphery isn't burnt early, then later on it is very volatile.

Took a look at one company's product and see what you mean. It has quench pads round the edges. I don't even know if 4G63 heads have quench pads on the sides (90 deg from thrust surfaces). At equal strength, the piston can be made a little lighter with dish instead. The tradeoff is quench. Quench priority depends on what type of engine and what kind of loads the engine is going to see. Weight is not a big deal in most any FI engine though , it helps but isn't priority.

 

ok..what I thought for the most part...