Measuring squish through the spark plug hole

[Pierre]

Spotted this article then remembered this thread. All you ever wanted to know about squish ... and then some. Focuses on Harleys but should translate nicely to the equally ancient Guzzi. Actually that's not fair, Harley has made some interesting advancements in their head design (bathtub - angled squish etc.). Nice read I think

 

Lots of additional hot rod ideas in other sections of the article.

http://tinyurl.com/j8tad.

[Guest ratchethack]

Great stuff, Pierre. Many thanks for this invaluable link!!

 

Unless I can find solder with a diameter considerably greater than .130" , I reckon my next step will be to do a full heads-off analysis of the entire squish perimeter using modeling clay (plasticene).

 

BTW - if you'll be at EMFW II http://socal-guzzi.com/PHPBB/viewtopic.php?t=26 I'll look for you there!

[dlaing]

Spotted this article then remembered this thread. All you ever wanted to know about squish ... and then some. Focuses on Harleys but should translate nicely to the equally ancient Guzzi. Actually that's not fair, Harley has made some interesting advancements in their head design (bathtub - angled squish etc.). Nice read I think

 

Lots of additional hot rod ideas in other sections of the article.

http://tinyurl.com/j8tad.

"Put simply, a squish band is the area or areas where the piston comes in close proximity to the chamber as it passes through top dead center (TDC). Fuel trapped in this space gets squeezed out at high velocity and generates turbulence in the chamber. Turbulence in the chamber promotes better atomization and less separation of the fuel and air, encouraging it to burn."

While I kind of buy the squish it till it turbulates as the piston reaches TDC theory, I was thinking a more important reason for it helping combustion is when it leaves TDC, the tighter the squish, the greater vaccum is left behind, suckin' the flame front to where it is needed.

I ain't know engineer, but that is my patented and copylefted idea, and I am stickin' to it.

But I do like the idea they mentioned of having the squish angle towards the spark plug. :

[Skeeve]

30 % of the diameter would be a ring of 13,8 mm around the bore. This is hardly possible with the Guzzi engine.

 

'Nix: Mr. Wilson misquoted; the statistic isn't 30% of the bore diameter, it's area that's the critical measure. Ergo, a slight band way out there at the periphery has an area all out of proportion to it's width, due to the transcendental f/x of the magic number pi...

 

2-smokes can run squish bands up to 50% of the area or even more, but that's due to their primary compression generally being rather low. [Not going into the shamanistic rituals associated therewith; 2-smokes aren't even engines so much as they are pipe organs! ]

 

The other thing to remember is that on a 2v engine like the Guzzi, it's better to put all the squish in at the sides, aka, run a bathtub chamber like the Evo & later H-Ds are using; that way, you've got the use of the full width of the bore for valve area, w/ adequate squish & turbulence. Why do you think I've been going on about that in all the tech threads here on V11LM for the past couple years or so?

 

Anyway, back to the bickering...

[motoguzznix]

Almost good;

 

'Nix: Mr. Wilson misquoted; the statistic isn't 30% of the bore diameter, it's area that's the critical measure. Ergo, a slight band way out there at the periphery has an area all out of proportion to it's width, due to the transcendental f/x of the magic number pi...

 

So, with a chamber diameter of 81 mm and a bore of 92 mm we get 22,4 % squish area....

[mike wilson]

'Nix: Mr. Wilson misquoted; the statistic isn't 30% of the bore diameter, it's area that's the critical measure. Ergo, a slight band way out there at the periphery has an area all out of proportion to it's width, due to the transcendental f/x of the magic number pi...

 

2-smokes can run squish bands up to 50% of the area or even more, but that's due to their primary compression generally being rather low. [Not going into the shamanistic rituals associated therewith; 2-smokes aren't even engines so much as they are pipe organs! ]

 

The other thing to remember is that on a 2v engine like the Guzzi, it's better to put all the squish in at the sides, aka, run a bathtub chamber like the Evo & later H-Ds are using; that way, you've got the use of the full width of the bore for valve area, w/ adequate squish & turbulence. Why do you think I've been going on about that in all the tech threads here on V11LM for the past couple years or so?

 

Anyway, back to the bickering...

 

_Mr_ Wilson?????

 

I can't find anything about area of squish bands. Got a reference?

 

I would say that two strokes can run bigger squish areas due to the superior design of their cylinder heads, which offsets some of their disadvantages. Primary compression not being one of them. Unless you have a super/turbocharger, a fourstroke has much less impetus for the mixture to be propelled into the combustion space than a two stroke. If you argued that the tortuous path the mixture has to follow through the ports is a hinderance, I might agree.

 

I do agree that four strokes are not able to employ the elegant simplicity of a two stroke squish band but need to make allowances for all the paraphernalia that has to be included up there. It's just another step in their unnecessary complexity. 8-)

[Skeeve]

_Mr_ Wilson?????

 

Well, excuuuuuuse Meeee! [/steve Martin]

 

If I knew ya better, I'd have just sed "Mike," but that warn't the way I was raised. While I did not concur with your post, I felt you were due some minimum of respect (in my reply) for daring to make it in a civil, non-sarcastic manner. Sue me.

 

I can't find anything about area of squish bands. Got a reference?

 

The High-Speed Internal-Combustion Engine

by Sir Harry Ricardo

 

Motorcycle Tuning Two-Stroke

Motorcycle Tuning Four-Stroke both by John Robinson

 

Sorry, no page numbers, but I just recently read these books & others [this past summer] when on a binge of reading/research so I could better defend myself/follow along the various threads here on V11LM & elsewhere...

 

I would say that two strokes can run bigger squish areas due to the superior design of their cylinder heads, which offsets some of their disadvantages. Primary compression not being one of them. Unless you have a super/turbocharger, a fourstroke has much less impetus for the mixture to be propelled into the combustion space than a two stroke. If you argued that the tortuous path the mixture has to follow through the ports is a hinderance, I might agree.

 

I do agree that four strokes are not able to employ the elegant simplicity of a two stroke squish band but need to make allowances for all the paraphernalia that has to be included up there. It's just another step in their unnecessary complexity. 8-)

 

Well, say it however you like, the fact that 2-smokes can have/do have/need to have bigger squish bands than strokers doesn't change the fact that the basis for the computation thereof is based on area not radius or diameter of the bore... The key thing being that even a paltry 10% of the bore area being a properly executed squish band can make a monumental difference in overall performance wrt to things like resistance to ping/detonation, etc. (iirc! )

 

I cannot recommend Sir Harry's book enough; I'd have it on my personal bookshelf today were it not for the fact that the 35quid plus shipping to USA is going to translate to close to $80, money which quite frankly I don't have at the moment, with a live-in gf who's been functionally unemployed for the past 1.5 years. Talk about your financial drains! I'm hoping that if I'm very, very good, that the Hogfather will leave a copy for me come next Hogswatchnight...

 

Ride on!