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Discussion Starter #1 (Edited)
COMPRESSION RATIO for my 2012 Ninja650 race bike build?

Ok so it's seemingly impossible to simply ask racers (that I won't be competing against) for the details of how much they milled off of their heads, I can understand wanting to keep trade secrets when it comes to head porting, and prototype work, but a simple figure to mill of the head..... lol
Anyway, I'll buy some fluid measuring equipment, and calculate the last few factors required to calculate my own CR, question is.... What CR would accept E20 (98-99Ron) fuel, alternatively I can run straight 95Ron benzine, both of which are available at all Thai fuel stations. :)

As it stands, I'm thinking of calculating how much to mill off the head and aiming for 12.5:1, this should be safe (correct me if wrong), and later I could bump the CR a little higher if needed buy either milling the head further or removing the middle section of the head gasket (as you have previously mentioned on your forum).

I assume (prior to measuring) that the removal of the middle section of the head gasket would add 0.3:1 - 0.4:1.
Again, thanks for any advice and sorry if I seem to be 'prying information'


Head Porting

15491624_10154833816278156_2045885688_o.jpg

I'm thinking of removing the hump on the floor and roof of the throat up until about and inch before the divider of each intake port, effectively enlarging the rubber throttlebody mounts and entrance of the throats and tapering off and inch before the dividers.
The rest of the port job is just basic valve seat matching, removing of flashings, knife edging dividers, 80 grit finish on the intake and 400 grit on the exhaust.
A little approval or disapproval towards removing the humps in the throats (pic attached) would help me finish my porting job :)

All this work will be complemented with the Versys cam mod (which I still need to look into a little more), Polished and smoothed combustion chambers and also stock pistons, Arrow headers, Custom longer mid and tail pipe, PCV with ignition adjustment, DNA filter, Modified Airbox and around 12.5:1CR. Bottom end has been blue printed :)
 

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I can see the benefit of shaving the entry into a more cylindrical shape but I wouldn't veir too far from stock shaping unless you have some custom cam grinds, valves and try to figure out what kind of air velocity you will need to make that system work. You shouldn't just aimlessly port out a head without really understanding it first. Shape, tunnel diameter and turn radius will all play a hugh role in your engine's performance. I know you want top end, but not too much off the side walls as it kills velocity.

I really wish I had some experience with the 650 head as I wish to build my motor as well with cams, crank, high compression pistons and the works but I have not seen too many ppl posting their experiences or know-hows on this head and how to port and polish for air flow, velocity and excellent air/fuel atomization.
 

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I can see the benefit of shaving the entry into a more cylindrical shape but I wouldn't veir too far from stock shaping unless you have some custom cam grinds, valves and try to figure out what kind of air velocity you will need to make that system work. You shouldn't just aimlessly port out a head without really understanding it first. Shape, tunnel diameter and turn radius will all play a hugh role in your engine's performance. I know you want top end, but not too much off the side walls as it kills velocity.

I really wish I had some experience with the 650 head as I wish to build my motor as well with cams, crank, high compression pistons and the works but I have not seen too many ppl posting their experiences or know-hows on this head and how to port and polish for air flow, velocity and excellent air/fuel atomization.
I too am pulling the heads and hugs this winter, to build a "hopefully " full blown race bike by spring. I have zero experience with this model or even style at that! I've rode cruisers mostly, but I've build 2 stroke banshees in the past and a few sb v8's for mud trucks. I can already tell that my weak part will be fuel injection. I know **** when it comes to the subject. So any advice for tuning or gains in general? Thanks in advance for any pointers or tips. I would greatly appreciate it
 
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