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[Dead_Reckoning]

Ok, I just read this on an S$S Web Page.

**As a general rule of thumb, for every 1 cc change in chamber volume equals a .1 increase in compression ratio.
http://www.sscycle.com/feature/featureview.php?s_id=16

Combustion chambers are available in the following volumes
89cc- Recommended for up to 117" engine displacements

So, If I am understanding this correctly, I could change out my 03 FLHRSEI2 SE103 Heads, with Big Bowl, 98cc Compression Chamber Volume to these S&S CNC 89cc Compression Chamber Voliume Bowls and increase my Compression Ratio by 0.9:1.

Comments please?

[cherryseeg2]

It depends on the shape of the chamber how much comes off each cut. For example a stock twin cam head(bath tub style chamber) will loose more CCs than the same cut on our heads(hemi chamber).  It would be much cheaper to cut your heads than to replace them to get the compression you want.

[HD Street Performance]

No dice on the formula
Bore and stroke variances blow that theory when applied to all motors
This spread sheet should help for the answer

[HILLSIDECYCLE.COM]

When surfacing cylinder heads, the rule of thumb, is measure twice, cut once, and creep up to where your want/need to be, regardless of any calculators.
Not uncommon here, to have each head in the milling fixture, 3 times.
Scott

[Dead_Reckoning]

It depends on the shape of the chamber how much comes off each cut. For example a stock twin cam head(bath tub style chamber) will loose more CCs than the same cut on our heads(hemi chamber).  It would be much cheaper to cut your heads than to replace them to get the compression you want.

Actually, I am considering changing heads, not machineing my SE103 Heads.

[HD Street Performance]

You may be making a mistake. Those 103 heads can be made to work quite well and regular short dome (6cc) pistons can help if the CR needs to be over 10.
All heads are cut here on a lathe on a custom fixture, the angled band at the edge is returned to match the bore. These heads have no squish and that is a pounding point for the nitpickers but in real world use they work just fine and when the parts are matched without too much mechanical compression built in they work well

[cherryseeg2]

You may be making a mistake. Those 103 heads can be made to work quite well and regular short dome (6cc) pistons can help if the CR needs to be over 10.
All heads are cut here on a lathe on a custom fixture, the angled band at the edge is returned to match the bore. These heads have no squish and that is a pounding point for the nitpickers but in real world use they work just fine and when the parts are matched without too much mechanical compression built in they work well

  Couldn't agree more.