Quote:

"modern" combustion chamber "design"

hmmmm

turbos are modern. oh wait they were designed in 1905. over 100 years ago lol.

get off the modern thing and think instead.

the shape of a combustion chamber is only going to change things minutely. what really matters is flow, velocity, compression ratio, etc. quench/squish/all that crap comes into play if you are not using race gas. if it's a street engine then you are limited by fuel.

if you have lots of E85 available local to you then you can go 12.5:1 compression.

that being said, the heads with raised ports will outperform the stock sized port heads every time.

so W9's and Victors and some others with raised ports will eat up the other ones, especially at higher rpms. combustion chamber design has little to do with this. but if you are on the street you are not going to be runnin around at 7200 rpms and stuff.



You and the gentleman above you are misinformed/mistaken if you think combustion chamber shape is of little concern.

Look no further than a Gen 3 Hemi. They make big block power, get slant 6 fuel economy and the max timing advance is in the low 20's. They can do this because the combustion chamber shape gives it the ability to actually burn ALL the fuel in the chamber BEFORE it gets to BDC.

Another example would be a new LS7 GM. 11:1 CR from the showroom. You haven't been able to do that with a 915 chamber since the sixties.
Hot Rod did an article when the Vortec head first came out and on a mild 355 SBC with the usual bolt ons, a set of parts counter Vortec's were good for 70 HP with less than 30 deg timing.

And yes the new engines have all kinds of electronic management but you can pile computers up 3 deep on an RPM headed Mopar and it won't run at 11:1 on pump gas and make power without a huge cam to vent cylinder pressure out the exhaust at lower engine speed.

The difference in flame travel speed is minute maybe a millisecond +/- but in terms of efficiency it is FOREVER. To use the Gen 3 analogy, same/more power as a BB at 10-15 deg LESS timing and a lot less cubes. The less timing part is the clue as to what is happening and when it is happening.

Kevin