Into the weeds engine design for fuel efficiency discussion.

mgoblue9798 said
Point of this thread is discussing engine building strategies for both fuel efficiency and running on cheap gas.

@mpgmike I am hoping you might be willing to share some of the latest info on the topic.

Part 1: Combustion chamber design.

Assume a couple givens:

Good quench is a given in this hypothetical, no matter the type head chamber involved.

Also the theoretical engine will be a street engine. Jack of all trades 1500 to 5000-5500 rpm. Some would consider it a truck motor based on the rpm, or daily driver, call it what you will.

1 A: Cylinder head chamber design.

What (if any) cylinder head chamber type offers the most in terms of efficient burn? All things like compression ratio and quench being equal, is there an advantage to a heart shaped closed chamber (IE magnum small block head),a bathtub closed chamber (think 60s big block 516 head), and a regular open chamber like a 906 or J head. Assume each has appropriate piston to achieve quench.

Which chamber shape could run on the lowest octane fuel all else being equal? Or asked another way, which
could run the highest compression ratio on 87 octane?

1 B: Piston top design. Is the flat top closed chamber combo the best for efficiency and low octane tolerance, or would a step head piston set up for quench in a closed chamber be? Not talking about the 80's giant pop up dome pistons here, think KB pistons with the step designed for quench.

1 C: Mods to be considered to 1A and 1B: Given is to relieve all sharp edges. What about Signh grooves? Are they beneficial for either fuel mileage or octane tolerance? How many grooves and what part of the chamber should the grooves be pointed towards?

How about dimples in head chamber or on piston top? What if any benefit would chamber relief cuts around the valves or a 15 degree top cut in valve job have in efficiency terms? Does either effect swirl in the chamber and if so in what way?

Related article: A New Diesel Piston That Increases Power And Reduces Emissions

If there is any interest in the topic, part II will be about the rotating assembly- ie bore v/s stroke, rod ratio, pistons and rings, etc.

Depends what we're talking here, actually recoup the money spent plus a sizeable savings in a reasonable time frame? I'd say that's generally a waste of time, say you spend $ 3000 a year in gas and spend $ 3000 to save 20% that would take 5 years just to recoup, and 20% over a well tuned engine would be huge gain.

Now if your talking decent mileage for a given power that's different cause hp cost dollars and doesn't over matter if it's recouped, still wouldn't go to crazy expenses to gain mpg cause over a certain point fuel mileage is hard to gain, My Avenger with all it's fuel mileage tech only gets 5 mpg better than my old 5th Ave and I did zero to get the best out of my 5th Ave.

For mileage I'd say besides a good tune and exhaust, cam cr gearing gonna be the lowest hanging fruit above that gains will tend to be small per mod and generally $$$ per mpg gain will go up. For NA power that won't overall kill mpg good heads will be best bet.