Hemi Heads For Omc's

[modifiedoutboard]

HEMI HEADS FOR OMC LOOPERS !
MAJOR IMPROVEMENT IN ACCELERATION!

[David_L6]

Anthony,

Do the "hemi" chambers make any more power than the stock chambers if compression is the same?

[bh/]

Looks like a nice piece Anthony.
Are u having them poured [or ??] and did u make any for threes?
If the cc's are the same, and u did not dial in any more advance, then I do not see why changing the combustion chamber shape will significantly alter output. Do u use 'dome tops' , or are they available for the twins.
Am trying to recall where I have seen this before.;)
Regards;
bh/

[David_L6]

Brian,

Are you saying that the hemi chambers allow more advance with the same volume and that more advance will yield more power?

[bh/]

David;-we will have to wait for Anthony to come on board here,
when he recovers from partying all nite!
I know little about this , but it seems that a better combustion chamber shape would allow a bit more advance, creating more pressure earlier in the stroke, and more torque.
The go-kart/snowmobile guys run wicked advance in the mid range, and back it off at top end.
But its all a black art to me
bh/




























1 :confused: :confused: :confused: :confused: :confused: :confused:

[modifiedoutboard]

[By changing the pocket shape and the shape of the "squish band" around the pocket, the results are greater knock resistance and increased power output. With greater knock resistance at the same compression ratio, more spark advance can be used - or - you can increase the compression ratio for even more power and probably keep the spark advance the same or close to the same.]

Sam's right, we can increase compression and Squish Velocity and see a big difference in performance on the course.

Squish Velocity is a measure of the velocity of the fuel air charge as it is squished into the chamber as piston comes up. Too High Squish Velocity and detonation can occur, Too Low and performance will suffer.

Factors that affect squish velocity,
Compression ratio, Piston/head clearance, Squish Band width, rpm, exhaust port timing. All of these have to factored in to make a head that works at racing rpms