I get the impression that many, if not most engines are running less efficiently than they could be.
Yes, and not necessarily due to tuning or ____!
Phil, quick and short story... but not necessarily pertaining to Chrysler engines.
Previous to the early 70s, GM's SBC used a piston profile that offered a quench..... even back to the first GM 265 cu in V-8.
These little engines actually produced decent power.
Then in the early 70's, our government demanded stronger emmision control measures.
So GM (in the Chevrolet scene) came up with the full dished piston as to reduce emmissions that were being demanded of the car makers.
This idea worked OK to lower the emmissions for cars and trucks.
Since the gasoline Marine Engine is basically a modified auto engine, GM just continued with this piston, and the marinizers fell for it. :rolleyes:
The Marine Engineers now needed to figure out how to avoid detonation issues.
The fix: hold back ignition advance.
This actually helped GM in that it reduced the load on the engine, giving it a slightly longer life in the Marine environment.
But at the same time, it prevented this engine from developing it's potential.
Here's what this piston looks like.
(I put the red cross-out line through it a few years ago!
)
The above GM full dished piston has a very small quench band around the perimeter only, and cannot create a true quench effect.
The correct piston should "mirror" the cylinder head's full quench surface, similar to this piston profile below.
This is such an easy and relatively inexpensive piston profile to obtain, it amazes me that people can't see the advantages and use it.
Good quench = less detonation potential.
Good quench = a point or two increase in the Static C/R.
Good quench = proven better fuel economy.
I've built quite a few SBCs over the years, and have never used the GM style pistons.
You can bet that the Chrysler Wedge Head boys understand this.
End of story!
.