Help me adjust/improve my squish

[Usmoneylover]

Rad valve, trx5 pipe, k&n filter, 38mm pwk,  93 no ethanol fuel

The bike runs OK but considering the large squish I think it can be improved....I want to continue running 93oct fuel.
I ride mostly woods, but I can deal with the low end the bike has now,  though an increase wouldn't be a bad thing.  How should I adjust my  squish?
Lower the cylinder with a different spacer/gaskets or lower the cool head/dome by going with a thinner head gasket.
Is it safe to use 2 outside pieces of a stock 3pc gasket?  Going that route my squish would be approx. .050~

Side note:  I understand I will hve to do a uccr to be sure about fuel  ratings, but the bike runs and I don't want to tear into it without  having the stuff on hand to put it back together.

Thanks in advance!

Known:

89 crank/rod with spacer plate 2 base gaskets
86 jug unmolested
86 piston (67mm)
3 piece head gasket
Pro design cool head
squish: .090-.092~

Unknown:

Cool head dome size(it was purchased as a pump gas dome so assuming 21-22cc's)

[udontknowme]

i wish i knew more about heads to offer you some help. doesnt seem to be much good info out there atleast not that i could ever find. back in the day i think it was gordon jennings said a band width of 50% area is a good place to be and that seems to hold true today.  ive never been a fan of lowering the cylinder. mostly because most stock cylinders from all manufacturers have pretty low timings as it is

you can buy blank coolhead domes for pretty cheap and have them machined any way you want. that may be your best option. of course you need to find someone like jerry or arlen that know how to cut it correctly. a regular old machinist wont have a clue

[Bowtie316]

Since you have two base gaskets, you can probably get by with just the two outer parts of the head gasket. That should bring the squish in quite a bit while still keeping the UCCR low enough to run 93.  Only way to know is to try it.

[Usmoneylover]

Here's an update...Took the head off and confirmed the coolhead dome has  a 22 stamped on the side of it.  I snapped a couple of photos of my  head and also piston crown, any comments about the build up/crust on  both?  

So if my math is correct, my original squish was .090 (measured with a  piece of solder) using the 3 piece head gasket.  If I separate the  gasket and use the 2 outsides I lose .040 from my squish, leaving me  with a .050 squish...Am I safe to run no ethanol 93oct with my 22cc  dome?

Thanks for the help!

[Bowtie316]

I would think it would be alright, but the only way to know for sure is to put it together that way and check the UCCR.  If it comes out under 13, I think it will be okay.

[Usmoneylover]

Thanks for the replies...I've been working on calculating my UCCR  without using liquid in a sealed head...my biggest obstacle and reasons  for doing it this way is I have no dial to measure exact TDC and also  the engine is in the frame and getting it level (I tried this AM) is a  big headache

The measurement that I don't have and that I  REALLY NEED is the piston crown displacement volume on a 67mm Wiseco pro  lite piston.  Can anyone please help?

[Bowtie316]

I can't help with the head displacement, but I can say that I have done it with the motor in the bike is not that hard. just have to set the front tires up on some blocks or a cooler or something. Doesn't have to be perfectly level just level enough that all of the air will escape out of the spark plug hole when filling.  

As for top dead center, all you need is a straight edge to lay across the top of the cylinder when the head is off. Roll the piston up until it stops, make a mark on the flywheel, roll it the other way until it stops, make another mark, verify these two marks are equidistant from the TDC mark on the flywheel. If it is, use that, if not, make a new mark.

[Usmoneylover]

Well by my calculations with the 2 .010 gaskets torqued down to spec my head holds about 19cc's through the plug hole at TDC...14.3:1
This is with a 22cc dome in my cool head. Checked my squish again and it was .054~

Seems hard to believe that I have a 22cc pro design pump gas dome with .054 squish and I require about 100 octane fuel.

Is it even possible to have an optimal squish clearance (.040~) and run 93 octane fuel?

[Bowtie316]

Is it even possible to have an optimal squish clearance (.040~) and run 93 octane fuel?

It is possible if you have someone cut you a new dome, getting squish where it needs to be then opening up the big hole.

[Jerry Hall]

Rad valve, trx5 pipe, k&n filter, 38mm pwk,  93 no ethanol fuel

The bike runs OK but considering the large squish I think it can be improved....I want to continue running 93oct fuel.
I ride mostly woods, but I can deal with the low end the bike has now,  though an increase wouldn't be a bad thing.  How should I adjust my  squish?
Lower the cylinder with a different spacer/gaskets or lower the cool head/dome by going with a thinner head gasket.
Is it safe to use 2 outside pieces of a stock 3pc gasket?  Going that route my squish would be approx. .050~

Side note:  I understand I will hve to do a uccr to be sure about fuel  ratings, but the bike runs and I don't want to tear into it without  having the stuff on hand to put it back together.

Thanks in advance!

Known:

89 crank/rod with spacer plate 2 base gaskets
86 jug unmolested
86 piston (67mm)
3 piece head gasket
Pro design cool head
squish: .090-.092~

Unknown:

Cool head dome size(it was purchased as a pump gas dome so assuming 21-22cc's)

Be careful trying to determine what octane fuel your engine needs based solely on the cranking compression or compression ratio.  The fuel your engine needs depends more upon how well your engine's pipe and ports are working together as well as the head geometry.  How well all of the different areas of engine design are working together affects the purity and the amount of charge trapped inside the cylinder after exhaust port closing.

The efficiency of a two stroke's engine design is somewhat comparable to the effects that installing a supercharger or turbo may have on a four stroke engine.  A four stroke engine may run detonation free on 87 pump gas.  Install a turbo on the same stock engine and the octane requirements increase as the manifold pressure is raised, even though the geometric compression ratio has not changed.

[Usmoneylover]

Be careful trying to determine what octane fuel your engine needs based solely on the cranking compression or compression ratio.  The fuel your engine needs depends more upon how well your engine's pipe and ports are working together as well as the head geometry.  How well all of the different areas of engine design are working together affects the purity and the amount of charge trapped inside the cylinder after exhaust port closing.

The efficiency of a two stroke's engine design is somewhat comparable to the effects that installing a supercharger or turbo may have on a four stroke engine.  A four stroke engine may run detonation free on 87 pump gas.  Install a turbo on the same stock engine and the octane requirements increase as the manifold pressure is raised, even though the geometric compression ratio has not changed.

Having read my entire situation, what is your take on it?  Also, what's your opinion on the buildup on the piston top and also the inside the dome?

Considering stock porting and the desire to run pump gas(as well as my other measurements), am I wasting my time trying to improve upon what I have by having a new dome made?
My current dome's squish width is 10mm, I'm assuming that is standard on 22cc cool head domes, but from what I've read seems a bit narrow for my preferred application.

Thanks!