Head shaving and/or piston porting

[TheAmishSasquatch]

Has anyone here had any noticable gains by either shaving the cylinder head,  shortening the piston skirt or porting the piston itself?  I just knocked roughly .010 in or .25mm off the cylinder head. So far I cant really "feel" much of a power increase. Maybe a slight improvment in TQ but nothing to write home about. Todays test ride was under high heat and humidity and was made with a slightly out of tune carb. I seem to recall mention that the S9 head can have considerably more then .010 in removed safely. Any first hand experiance/ posted gains would be great. Thanks

[zombie]

Hey, Squatch.

You HAVE to measure the squish band when you shave the head. It's the only safe way to know the clearance.

All the head shave does anyway is raise the compression ratio. That will do two things for you. One is a alight increase in torque, and two is to move you closer to pre-detonation. You need the highest octane you can find to prevent pre- det.

I would suggest reading the Two Stroke Tuners Handbook. It's on this site.

Portint the piston only works if you know how, and where. It's better to port the cylinder for many reasons.
Shaving the skirt(s) changes the port timings, and duration's. Again you have to know what you are doing or you might end up w/ a paper weight.

Find the book, and read it. It's the best zero dollars ever spent.

[TheAmishSasquatch]

Thanks zombie. I made sure to measure the amount above the cylinder that the piston crowns at TDC as well as the depth of the edge of the head deck mounting face. From the deck to the edge of the CC it varries from 1.07mm to 1.15mm. I knocked it down by .25mm giving .82mm edge/deck height. Im not sure what the new compression ratio is currently.  Im glad you mention high octane gas. I found a place nearby that sells 100 + 110 octane racing fuel which I plan to run. I do not want to raise the compression so high that it requires 100 or more, nore do I want to move the powerband to high and have a peaky motor.

[zombie]

Is it the OEM cylinder, and head?

[TheAmishSasquatch]

Yeah, Im working with stock parts currently.

[zombie]

Look on Josh's sight, Scooter Invasion, and look for "port maps".
There are a ton of them all well defined, and you can choose anything that sounds like what you want.

As a shotgun approach on the OEM jug you can taper, and raise the intake ports by 5mm. Same for the boost port.

This will give you a higher power-band by about 1krpm, more intake charge per stroke, and about 5mph more top end.

From there you can maintain the height, and increase the width. The goal is getting more fuel in. You will need to open the pipe at some point but you can go pretty far w/ the porting before a performance pipe is a must have.

Even getting the angles cleaned up, and flowing faster is a bonus. I use one of those fluted steel cutting wheels on a dermel. It cuts better, and lasts longer than the cheap grinding wheels you get for dremels. about four of those cutting wheels will complete a through port job.

[TheAmishSasquatch]

Great info! I'll check that out. I have a pipe and PHBG 19 on the way. The bike has normal mods. Just thought it's time to mess with the engine without BBK ... yet

[zombie]

You'll get about the same results, and it costs nothing but your time.

The only things I would do to the piston is sand, and polish the crown to prevent carbon from sticking, chamfer the skirt edges at a 60* bevel to force oil between the skirt, and cylinder wall, and drill two 1/8" oil holes in the wrist pin bosses.

When you look at the piston from the bottom you drill the holes in the bosses to allow oil to get onto the wrist pin to keep it floating smoothly. Between the skirt work, and the oiler holes, you can get a free'r reving engine.

[TheAmishSasquatch]

Thanks Zombie. I created an account and did some searching on port maps and even super 9 port maps, but didnt really have anything useful jump out and bite me, and some of those threads/builds are 30pgs long! Id like to give those mods a try very much. Maybe youtube has something?? Thanks again, Im enjoying that site.

[zombie]

You can email Josh or PM him from the site. He'll give you the best maps for what you want.

His email is on his "The Scooter Garage" web site.  Tell him I said hey.

http://www.tsgtuning.com/location.html

[TheAmishSasquatch]

Thanks, I'll give him a shout. I did find some good vids on youtube. I've done similar mods in the past, I just didn't know it was called port maps. Lol.

[zombie]

Be careful of the Utube stuff. There is a LOT of misleading crap on there.
If you find something that sparks your interest, post it up here, and  I can help to determine if it is worth pursuing.

I've just ordered another one of those JiangWayne 50mm cylinders, and I'm planning on copying the Polini Corsa porting into it.

I should see the jug in a week or two so if you like I can post the Corsa numbers/map up here. It will work great w/ a 8.5-9.5k pipe in OEM porting. I opened mine to run 10.5 - 12k, and love it. It's just too much for a daily driver so I'm building another engine for daily, and keeping the race engine on the shelf.

[TheAmishSasquatch]

That would be be great Zombie! Probably alot more reliable and safer then blindly shaving 5mm out of my ports. Im glad I read this when I did. I literally have the 9 apart and the rotary rasp ready (unintentional tougne twister there).  I did knock the head down a couple thousanths more. Not sure what my squish or CR is but the piston crown potrudes 1.05mm above the jug iircc and the head deck height to CC is in the upper .80s not including a .25mm head gasket. I didnt notice any pingging on 93 octane so I guess Im okay.  Anyway thanks for offering up the corsa port maps. Keep me posted when the new kit arrives. Thanks

[zombie]

https://www.rbracing-rsr.com/compstaticcalc.html

http://www.wiseco.com/Calculators.aspx

https://www.lunatipower.com/Tech/Pistons/HelpfulCalculations.aspx

To measure the squish use a piece of solder. Insert it into the sparkplug hole all the way to the edge of the piston, against the cylinder wall.
Kick the engine thru one stroke, and measure the thickness of the solder.

You want as close to one mm as you can get. 0.5 is the smallest, and 1.5mm is the largest. It's best to adjust this number with head gaskets, and you can find all sorts of materials to make them.

These guys are the best. Go with either the softest aluminium or copper, and anneal it before installing it. Generally these will flatten out 0.0001 - 0.0002" when installed

[TheAmishSasquatch]

Just performed a compression test on the 9.  Results shown 120psi on electric start and 135 on kick-start. How do I set about calculating my compression ratio ?  Is 135 a little low for a decked head? Seems like 150 would be more of an expectation, no?