Head shaving and/or piston porting

[zombie]

You have to figure in ring sealing, and bore wear for compression. 135 sounds about right to me.

Use this Calc, and fudge the dome numbers until you get the right CC's. When your cc's are right your Ratio will be right.

Then once you have your total cc's use this site, https://www.cbperformance.com/v/enginecalc.html to figure the displacement. Those numbers will allow you to subtract, and find your combined combustion chamber cc's at TDC.

Then with the head off you can measure the Combustion chamber volume w/ water (you tube for the process).
The difference in those numbers is the Piston dome area in cc's.

Sounds like a bunch of work but it's not. It's all easy breasy stuff.

Post it up. I'd like to see.

[TheAmishSasquatch]

I'll try to bang this out tonight if possible. I have a concern over the numbers though. My cyl head (though square and seals) does not have even depth in the dech height. I measure from the edge (where deck meets CC) just as you would for squish but the numbers varry. The lowest point is in the low .8's with 90% of the rest in the .9mm range. Is this pretty common to be off a little, and how badly will it affect my calculations?

[TheAmishSasquatch]

What is the bore and stroke of a stock AC super 9?  I measured 4.9 ml/cc in the combustion chamber with tbe plug installed.

[zombie]

All mass produced, cast aluminium, machined parts are "off" somewhere.

For your squish, you have to set it using the lowest point so it will throw the effect off some but nothing that you would ever see on a dyno.
It's getting more theoretical than real.

[TheAmishSasquatch]

Great to know.  I was worried there would be an unbslanced burn from either a mistake I made during milling or that the head was warpped or something.  Today I might remove the poston an weigh it against a Koso replacment I have. Maybe polish it as well.  Going to check the service manual for bore and stroke specs and post up compression figures. Thanks Zombie

[TheAmishSasquatch]

So I sanded a little more off the cyl head and have a more accurate CC volume of 4mL.  With a bore of 34mm and 41.41.4mm stroke and deck height of .91mm gives me a compression ratio of 8.8
I will probably chamfer the cylinder skirts and possibly piston skirts today. Ive also read that a slight grinding of around 1-2mm off of the edge of the piston crown side which passes the exhaust port (usually has a cast arrow) will slightly open the timing of the exhaust pulse without changing tbe stock port timing, and allows for higher rpm.

[zombie]

I call that Kerfing the piston. If you take the exact center, and taper a "pie wedge" to the port(s) it does change the timing, allows in more fuel sooner, and more exhaust out sooner.

Problem is unless your pipe is matched it will lower your red line rpms, and give no advantage in torque or hp. This is usually done in high compression engines to eliminate ping.

A better option would be to continue shaving the head, and raise the jug. You will get higher compression (more torque), and lessor timings that will allow for regular pump gas to run without pinging.

What pipe do you have?

[TheAmishSasquatch]

I currently have a tecnigas RS? RSII ?. Im concerned its too late on the cylinder skirt. I wanted to simply grind off some casting marks and not change the profile, but it seems just that was enough to throw things off. I also ported the stock intake manifold from a 14mm opening on the carb side to 20mm and opened the exhaust port on the cyl (just the part that attaches to the muffler, and the muffler opening itself) needless to say, everything is outta whack. It only runs for 2 seconds and dies.  I think I f***ed up   Might just have to get the Malossi setup while they last

[0BARK4322]

I currently have a tecnigas RS? RSII ?. Im concerned its too late on the cylinder skirt. I wanted to simply grind off some casting marks and not change the profile, but it seems just that was enough to throw things off. I also ported the stock intake manifold from a 14mm opening on the carb side to 20mm and opened the exhaust port on the cyl (just the part that attaches to the muffler, and the muffler opening itself) needless to say, everything is outta whack. It only runs for 2 seconds and dies.  I think I f***ed up   Might just have to get the Malossi setup while they last

Too much grinding and porting

[TheAmishSasquatch]

Too much grinding and porting

My thoughts exactly. The skirt I literally just cleaned up and smoothed but I have a feeling that I inadvertantly changed the profile. The exhaust port is another concern. Even though I didnt grind into the port map area, I think I did too much. Im more concerned about my pipe then the jug to be honest. I did use a stepped bit an routed out some material at the inlet. I dont figure tbat has much effect though.

[zombie]

You didn't read the book did you...

That sucks but it is a learning experience. I have a shed full of wacked up parts that oddly all seem to work in combinations that I did not intend. Like a Malossi that's running a piston meant for a 12k rpm yamaha 80 but it runs better on an 8k rpm Technigas pipe.

Porting is an exact science. No mysteries... one mm in the wrong direction...

[TheAmishSasquatch]

How the crap do I post resize pics to post em here? I found a couple 70 & 75cc kits Im interested in as I obviously missed the Malossi stuff posted in the other thread.  Im unable to post links or do any real picture editing because I dont have a computer.  The kits are not S9 specific but fit AF18, ZX50 and Dio. I seem to recall that the cylinders fit but other non cylinder/head related parts wont work. Is this correct or am I misinformed?

[zombie]

Honestly I don't know if the parts swap. I really don't think they do.

I THINK it is the like, and the people 2t's that share the same engine/parts.

Posting from a phone? I can't help w/ that either. I don't own one. Sorry sir!

[TheAmishSasquatch]

Yeah using phone and tablet. Mostly tablet. I would really like to get the Malossi kit, but cant justify $200+  currently. If I were able to find the kit tbat was on sale I would have bought it as Malossi seems that its a dirrect swap and I need not worry about gasket spacing for tuning port maps and such. Ill just have to keep looking. Until then Im hoofing it

[TheAmishSasquatch]

Just ordered a Malossi 70cc kit. I really wanted an Airsal kit but too much $$ considering the kits I seen require you have to buy the head seperatly. I really liked the all aluminum construction. Great for even thermal expansion and cooling properties, not to mention weight savings.. (Especially nice for a squatch like me)   Oh and my PHBG arrived yesterday