squish/piston wash

[texasvector]

Does squish have any effect on piston wash? ?

Meaning. .. if squish band is outta wack will it effect piston wash results while tuning?

My squish is on the high side. .. Does this effect how the piston top looks?

Don't know. . Still/always leaRning. . Thought I'd ask

[baja200merk]

Yea when its too tight it will transfer the piston part number to the head :eek:

When its hitting the head over 8k it will polish all the carbon off the piston in the squish band and blow head gaskets every weekend... Ask me how I know :p :leaving:

[texasvector]

Lmao!! That's what I was trying to avoid when I had the squish"loosened" on these heads

[dwilfong]

There is a formula for calculating maximum squash velocity.
The proper squash velocity helps mix the fuel in the chamber and decrees the chance of detonation.
http://www.torqsoft.net/squish-velocity.html
Lots of good info here and on the reeds also.
http://www.macdizzy.com/2stroke.htm
Lots of good info here also.

[Mr. Demeanor]

My squish was set up loose and my wash has never looked right although the motor runs well. I always wondered if there was more to be had with a more standard squish because I really need more low end power than anything else. I just installed a set of heads with a more standard squish which is 1 degree toward spark plug and will let you know how it goes. My piston tops have always looked dirty.

[wanagofass]

Yea when its too tight it will transfer the piston part number to the head :eek:

When its hitting the head over 8k it will polish all the carbon off the piston in the squish band and blow head gaskets every weekend... Ask me how I know :p :leaving:

I've seen that show!

[RichS]

Yea when its too tight it will transfer the piston part number to the head :eek:

When its hitting the head over 8k it will polish all the carbon off the piston in the squish band and blow head gaskets every weekend... Ask me how I know :p :leaving:

You're lucky it didn't break a spark plug and eat the cylinder:eek:

[texasvector]

My squish was set up loose and my wash has never looked right although the motor runs well. I always wondered if there was more to be had with a more standard squish because I really need more low end power than anything else. I just installed a set of heads with a more standard squish which is 1 degree toward spark plug and will let you know how it goes. My piston tops have always looked dirty.

This is what I feel. ... plugs look good. .. tops still funky. .wet... but funky

Keep me posted!

[baja200merk]

You're lucky it didn't break a spark plug and eat the cylinder:eek:

With .220 hacked off the top of the stock DI/FICHT 3.3 piston it cannot reach the plug unless something very bad happens. It ended up around .042 squeeze. But Monty was correct, short rod and 8k will bust the skirts off or in our case collapse them enough to allow them to rock at TDC and smack the head and blow head gasket. Luckily we tore it down before any of the skirts came off and hurt the motor BUT it did crack 4 out of 6 like the pic below. We are getting long rod pistons so we do not have to worry about this anymore. This motor was chucked together and didnt cost anything but some gaskets and seals so we tried a few things and it kept taking it but im not really sure why. I'd rather be lucky then good I guess :D

Oh and Big thanks to Monty Racing for the donated piston rings :cheers: They were put on a turn whatever it will turn and repeat every weekend for 9 months, very strict break-in procedure :eek:

http://i408.photobucket.com/albums/pp163/hondacr8288/D5A85CB9-19B9-43E0-845F-58BB07EF245D_zpscyvan1ug.jpg (http://s408.photobucket.com/user/hondacr8288/media/D5A85CB9-19B9-43E0-845F-58BB07EF245D_zpscyvan1ug.jpg.html)

Other side

http://i408.photobucket.com/albums/pp163/hondacr8288/0579A893-A874-4B59-9812-7D15ECB47980_zpsrjknjyla.jpg (http://s408.photobucket.com/user/hondacr8288/media/0579A893-A874-4B59-9812-7D15ECB47980_zpsrjknjyla.jpg.html)

[RichS]

Mine cracked the ceramic around the electrode by the piston just touching the head at 10600... The ceramic stayed on the electrode and dropped down and killed the fire in that cylinder. I heard it 5 cylinder and idled back to the trailer. Pulled the plugs and saw what happened. Went home and pulled the head and saw that it touched. Put the head on the mill and fixed it and thanked my luck:)

[rude tim]

Squish band size, angle, radius and clearance all make a difference. As far as clearance goes 2 strokes will continue to make more power until the piston touches the head. My 3 liter Erude spun 8800 rpm with .038 squish clearance and never touched. My 4.4 liter V8 Erude has .044 clearance with no problems. I use fuse wire (soft led wire) full circle in the bore, torque the head and turn over by hand remove the head and mic the wire.

[dwilfong]

You can stick the wire in the plug hole and check it also. that way you don't have to remove the head. That is how I set the compression distance and check for the head being square on the Duetz 912 eng when I rebuilt them.
How close have you all seen with a 2.5 merk and not see carbon transfer?

[texasvector]

after decking the block in my rebuild my squish measured .020" with thick gaskets......i punched the heads out for a quick fix now squish is at .055" ish......
havent been able to get a uniform carbon transfer yet while tuning with the acu.

[baja200merk]

Squish band size, angle, radius and clearance all make a difference. As far as clearance goes 2 strokes will continue to make more power until the piston touches the head. My 3 liter Erude spun 8800 rpm with .038 squish clearance and never touched. My 4.4 liter V8 Erude has .044 clearance with no problems. I use fuse wire (soft led wire) full circle in the bore, torque the head and turn over by hand remove the head and mic the wire.

.040 was fine until the skirts collapsed making it loose. Squish still checked out the same.

[rude tim]

Baja200
A short rod OMC is a different animal because the piston is taller from the wrist pin to the top of the piston which allows the piston to rock harder along with the rod angle due to the short rod. Again as far as power goes the tighter the squish the more power a 2 stroke will make.

[baja200merk]

Yes sir I completely agree. This motor was ported and assembled with the intention of never turning it over 7k, with a 1.62 sporty bolted to the bottom which would make short rod survive just fine. Well we let it turn up and the inevitable happened.

We have a fresh 225 in its place as of today and GOD IT IS GUTLESS..... The stock carb jets are 14 sizes smaller in the stock motor but beef still managed to run it out of gas today :rolleyes:

[Mr. Demeanor]

So the only way to reduce squish and keep the same compression would be to CC, deck the head, and then mill the pocket to get the CC back correct?
I just cut 50 thou off a stock set of heads and the squish is .07 now. I have domed pistons with about a 7 degree angle on the squish band to match the piston dome Compression will be about 145 but that squish still seems large by comparison to what you guys are doing.
Would there be worthwhile performance increase reducing the squish band clearance but keeping the compression at 145psi ?

[baja200merk]

A stock 99 225hp measured 55-60 last time I did a quick check. We cut the pistons flat so had no dome to worry about cutting back into the heads. It is a mutt though, The heads are from an 87 225 bolted to a 07 e-tec block with carb'ed 99 front half, 97ish intake, 87 225 carbs, 89 Yamaha ignition and the list goes on....

[Chaz]

So the only way to reduce squish and keep the same compression would be to CC, deck the head, and then mill the pocket to get the CC back correct?

It's not the only way , but it is the most popular . No matter how you get there , you still need the chamber to hold the same volume.


I just cut 50 thou off a stock set of heads and the squish is .07 now. I have domed pistons with about a 7 degree angle on the squish band to match the piston dome Compression will be about 145 but that squish still seems large by comparison to what you guys are doing.

I shoot for .038 - .040 around the outer edge with a ten degree cutter .


Would there be worthwhile performance increase reducing the squish band clearance but keeping the compression at 145psi ?

Any time you can convert more of the charge within the cyl , power will go up. I dont think cast pistons are a big fan of the added crown heat that comes along with it . And if you don't get off the throttle during those wake jumping times when the prop is out of the water , you stand a good chance of "printing" the head .. other than that ... yes it's worth a couple of ponies .. ;)

[dwilfong]

what is the thinnest gasket worth a dam not cheep junk for a 2.5 Merk?

[Tom Foley]

what is the thinnest gasket worth a dam not cheep junk for a 2.5 Merk?

That would be MERC , spelling counts here !!!:cheers:

[Chaz]

That would be MERC , spelling counts here !!!:cheers:

As long as fong can "spull" God Father ... :thumbsup:

I could do an ol lead~sled Merc ... 600 inch SVO ProCharger deal .. ;)

http://cdn.rodauthority.com/wp-content/blogs.dir/34/files/2011/04/130.jpg

[dwilfong]

WOW I have not bin called Fong since high school.
Well what is the thinest Merk gasket now that we got the spelling Bee over with.
I'm a Pontiac man my self.:thumbsup:

[Mr. Demeanor]

Im pretty close to seeing if it makes a difference on my motor. What Monty told me was that less squish with the same compression is safer in terms of detonation. Ive leaned on thisthings pretty hard though and willing to try a more aggressive squish with same 145psi and see what happens.

[texasvector]

What Monty told me was that less squish with the same compression is safer in terms of detonation..

This is what I wanted to know/hear.

My compression is on the high side for pump gas safe.....maybe the looser squish will be safer.

[dwilfong]

I have found on the two stroke eng I have had the most experience with the closer the squash the less detonation with the CR being the same.
Have also found that a flat squash compared to a squash band with a 3 deg angle to the piston top also helps stop detonation.
I have found you can raise the CR with theses to things combined.
You don't have to run as lean to get good throttle response with a good squash design.
You lean on the eng because you cant burn the fuel. If you can burn the fuel on hand you do not have to run as lean.
You have to account for the chamber burning more fuel if you make the changes. so if you do not richen it up it will detonate and you will think you have gone the wrong direction.
You are stuck with a fuel map on a ECU eng so you need to be able to make changes to the fuel delivery to see what is what.
The combustion chamber design also changes how the fuel burns.

The flat top flat sided chambers have yielded the best results on the eng I have played with.
The percentage of squash area to boar also play a part in the equation.

[Mr. Demeanor]

Im intersted to see if my loose squish was why I have had to run such enormous jets. I am way bigger than what anyone of the Yamaha gurus and even Gordon would have guessed. If it goes super fat first time out I will know.

[texasvector]

Keep us posted

[Mr. Demeanor]

Results are in and the change is pretty dramatic.
These are pistons #2/4 before. #2 is on the right for some reason it turned the pic:
305565

Cleaned up:
305566

I didnt pull the head but used my borescope to take a pic. You can see there is a lot more wash and its more even.

305567 305568

[Mr. Demeanor]

Same area before/after. Same jetting.
Red circle:

305569 305570

Blue circle:
305579 305580

[Mr. Demeanor]

Played with the scope some more and wanted to try a video.

This is #4 before and after:

305581

Video of #4 now:


https://www.youtube.com/watch?v=xyHETID_p_s&list=UU7qzWnmd21EcgsWq92tjjKA

[dwilfong]

How close was the squash?

[texasvector]

see if i follow.........same compression...tighter squish...same jetting = more wash (richer)

[Mr. Demeanor]

see if i follow.........same compression...tighter squish...same jetting = more wash (richer)


Thats what I am seeing. Now I dont know if its actually richer or just showing me a more accurate piston wash which is what I think is happening.
I dont see how a loose squish could effect air/fuel but I can see how it would effect how the wash looks.

[200valeroyt]

Maybe just not enough time to soot back up as before? I believe you said you cleaned piston tops prior to new heads? If so, that'd be my guess, probably end up looking the same with more running. If not, id say its rich and your leaving some power out there.

[texasvector]

Thats what I am seeing. Now I dont know if its actually richer or just showing me a more accurate piston wash which is what I think is happening.
I dont see how a loose squish could effect air/fuel but I can see how it would effect how the wash looks.

GOTCHA

thanks for the follow up.

[Mr. Demeanor]

Maybe just not enough time to soot back up as before? I believe you said you cleaned piston tops prior to new heads? If so, that'd be my guess, probably end up looking the same with more running. If not, id say its rich and your leaving some power out there.


Piston wash stays the same over time so I dont think thats it. I agree its a little fat right now but its also 95 degrees and fall is coming.

[200valeroyt]

I thought you just cleaned pistons prior to taking it out? If so, it'll take longer than an hour or two to fully soot up. Mine does anyway.

[Mr. Demeanor]

Yes but the piston wash should stay the same. We will see.

[200valeroyt]

Ok. Mine takes several hours of riding to fully minimize the fuel wash.

[dwilfong]

How the fuel burns in the chamber will change the carbon build up on the piston.
If there is less carbon left from a more complete burn it will show less on the piston.
A pyro as you all call them will give you a better idea of how the burn has changed.
Ex gas temp is a great tuning tool. I log it on my small nitro eng with a data loger to tune it.

[Mr. Demeanor]

Ok. Mine takes several hours of riding to fully minimize the fuel wash.

About 5 hours and wash looks the same. Still think I may try and get the squish down from the current .070

[200valeroyt]

I see, at least your sure of what ya got. Probably be pretty close with the cool weather around the corner, be nice to see what she'll do!

[baja200merk]

.070 is double what beefs is. The gaffrig tach works. Yes this pic was tough to take holding my phone and driving...

http://i408.photobucket.com/albums/pp163/hondacr8288/26E550A6-D4A8-4127-8234-5679A1770C30_zps91p0z7t8.jpg (http://s408.photobucket.com/user/hondacr8288/media/26E550A6-D4A8-4127-8234-5679A1770C30_zps91p0z7t8.jpg.html)

[PanRonnie]

squishband according to 2 stroke tuner handbook