75 v 82 cams

[canuckxxxx]

Just doing some figuring: 1100 (1085cc) has 271cc per hole and 9.2:1 compression. So combustion chamber volume must be 33.1cc. If I put that same 33.1cc onto a 1200 (1182cc) cylinder with 295.5 cc then I should get a compression ratio of 9.9:1. So that would give a performance boost too. :laptop: :read:

 

[ekvh]

33.1 is what I got on them when I cc'd them, but the 1200 has a different piston top, much less dome. The 1200 on mine came up out of the block 0.040"' the 1000/1100 have more of a hemi shaped piston and are recessed a bit in the block. I thought it would bump compression quite a bit, but I now don't think it did much. I don't have sophisticated enough tools to check and compare. Others who probably have pretty good techniques and tools felt the compression was about stock. I shaved 0.025" off the head, which some thought was too much, but it cranks over fine. If I burn 87, I don't hear pinging, but my hearing is poor.

 

[canuckxxxx]

Yeah you're right Eric. If both engines had the same piston dome then maybe but not if they are different. oh2:

 

[joedrum]

if anything and its hard to tell .. it seems my 1200 mod motor turns over easy ...and i agree with eric no big change here if anything its the other way seems to turn over easier ....it should also be said cam makes big difference in compression along with ports size and valve size witch all theses things are different on stock specs that are in the book ....i think higher compression to a point is a performance boost ..pass that its a drag and causes drag in the system an hard to turn ...once you get to where compression is good and no problem firing charge ...next best thing over higher compression is flow ..it trumps compression big time as power getter in my opinion .....

one thing for brian ...if you get a 1200 to work with ... there a huge power boost to be had ... its not mythical blab ...there are examples right here on this forum ...ive about quit giving opinions of mine ...as it seems the internet is female and suffers from pms 24-7

 

[Ansimp]

Here is an interesting article that explains the advantage of cam duration to performance, it also explains that this will reduce the static compression figures.
https://www.badasscars.com/index.cfm/pag ... /prd68.htm

 

[joedrum]

yep that was nicely said article....

 

[ekvh]

Moving the cam timing around can bump the compression and move the power band down. On my hybrid with 1000 early cams, I moved it back 3 degrees or so. It bumped my compression readings 10-15 psi. By closing the intake valve earlier it allows a little longer duration on the compression stroke. It probably causes a little more reversion on the beginning of the overlap, but on mine it seems to have effectively moved the power down a few hundred rpm.