Compression Ratio and Head Porting Question - KawiForums - Kawasaki Motorcycle Forums
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post #1 of 3 (permalink) Old 12-18-2016, 11:25 AM Thread Starter
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Compression Ratio and Head Porting Question

Hi all, I hope with a little guidance I can start to make further progress with my 2012 super Twin 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(ish) (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.

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

I'm thinking of removing the hump (photo attached) on the floor and roof of the throat up until about and inch before the divider of each intake port, which will effectively enlarge the rubber throttlebody mounts and entrance of the throats, then 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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post #2 of 3 (permalink) Old 02-02-2017, 01:53 PM
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Location: North East Iowa
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If you insist on doing it all yourself here is a quick guide to determining your existing compression ratio. When you have that in hand the only number you will need to fiddle with is your deck height or as they mention in the wikihowto "piston to deck clearance" the smaller you make this clearance of course your compression ratio will go up. I helped a Drag racer for a number of years and a good source for engine building was a forum on where there was a plethora of information. Most of these guys are professional engine builders or hobbyist that will build 2 or 3 engines a year.

If you would rather just send the head and cylinder out. A good company to contact is

Good luck with your racing. The ninja 650 is very rare on the racing grid here in the United States. Everyone prefers the Suzuki SV for a lightweight class bike. I think its because there is not enough R&D done on the racing side, and the ER6 or EX650 is underpowered when it comes to the Lightweight sportbike or super stock classes. I had good luck with mine last year and the only thing done is an exhast cam swap and different valve springs.

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post #3 of 3 (permalink) Old 02-03-2017, 12:49 PM
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Location: Houston, Texas, United States.
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Not sure if this can be of any use, or if you can get one for the 650,
but the RACE KIT MANUAL for the zx6r has a lot of technical info that could possible be useful...

Man uals Ninja-650-Ser vice .pdf
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