High Compression Pistons

[dlaing]

Thanks!

I'd probably skip the compression ratio measurement, because whatever 0.040" squish leaves me with is what I would have to tune to.

Milling down the barrels is probably more than I would care to do...but then again if it turns out the squish is far too much, it may be worth it.

I was kind of hoping thinner gaskets might just give it that little extra more better.

[luhbo]

Interesting! Thank you for the pictures.

 

Do you have any numbers about the weight of these beauties?

What is the recommended play between piston and bore in comparison to the OEM part?

Do they come complete with the bolt?

The bolt will probably fit 1/1 into the upper end of the rod, won't it?

 

Thanks for any answers

 

Hubert

[dlaing]

Interesting! Thank you for the pictures.

 

Do you have any numbers about the weight of these beauties?

What is the recommended play between piston and bore in comparison to the OEM part?

Do they come complete with the bolt?

The bolt will probably fit 1/1 into the upper end of the rod, won't it?

 

Thanks for any answers

 

Hubert

The FBF comes as a complete kit with rings and pin (I think you meant pin, not bolt).

Not sure about the Mike Rich option, which seems to be the most appealing to me, for the reasons that Pierre mentioned.

I have no idea about the other questions.

 

 

 

In short, I'm blushingly pleased to report that according to the experts I'm blessed with perfect squish.

 

Too much information

PS you missed another great meeting at the Lookout! <_>

[luhbo]

Thanks Dave. I meant pin, of course.

 

The Mike Rich version I do like better than the FBFs, but all the pictures are taken from a different angle, so it's hard to tell.

 

And you know, I like the Guzzis most!

 

The cut dome of the MRs surely is a good idea, but I don't think that the so greatly enlarged squish area is an idea as good as the one before. Assumed that I interpret the picture right.

 

I'm not sure about it, but I expect that this causes a very sharp pin in a thought compression over stroke curve. The ignition happens before TDC, then this CR peak is added (when the squish area closes) and immediately after that the CR again shows a significant drop when the squish area opens again.

 

BTW, the actual BMW R1200S 4-V engine has a CR of 12.5! Without any piston dome. 122 HP straight out of the factory.

 

Hubert

[pete roper]

BTW, the actual BMW R1200S 4-V engine has a CR of 12.5! Without any piston dome. 122 HP straight out of the factory.

 

Hubert

 

Yes, but that is one of the advantages of a *modern* cylinder head design with a very narrow included angle on the valves. Both the Guzzi and the BMW have the disadvantage of not being able to have straight ports with a direct tract to the valve head/s but having a narrow included angle does mean that you can make the combustion chamber very compact AND have large valve area, the only serious problem is likely to be dumping of waste heat due to insufficient matterial around the seats. The Guzzi, which still uses the old two valve hemi design is much more limited and therefore will always be defficient in power compared to a *modern* 4 valver of reasonable design.

 

Incidentally while I'm sure Mike knows far more about combustion cahmber design than I do I think that the squish band on his slug looks too small for my liking. In many ways it resembles a 'Big Valve' piston which are a truly horrid thing, although his are forged and no doubt a zillion times lighter than the horid cast Guzzi big-valve pistons.

 

Pete

[al_roethlisberger]

No news to anyone who's been hanging out in v11LM for any length of time, I'm a big fan of Mr. Roper's generous contributions & have yet to find anything I disagree with in any substantive degree in anything he's said. To lend further support to his point:

 

I got a nice email over on Wildguzzi a while back from someone who'd been inspired to look up Sir Harry Ricardo after I mentioned him; I decided maybe I should read his book myself, having only had read reference to it over the years. Great stuff, so good I'm thinking of shelling out the $80+ to get a copy of my own, since the Ricardo Institute has seen fit to finally reprint it for the first time in 20+ years, & who knows how long that will continue? (FWIW, 1st editions sell for over $600 & that's not even a signed copy!)

 

That led to a whole lot of further reading, with which I'm even now engaged; oddly enough, all of it seems to agree with what Sir Harry wrote 80-odd years ago: you want more power, you can squish it harder, spin it faster, or build it bigger, but they all have their tradeoffs. In the end, it comes down to basics, and one of those is that the smaller the combustion chamber, the more resistant to detonation, so the higher the compression can be. A hemi-head, "spectacle" combustion chamber like Guzzis w/ hi-comp pistons possess have a broader combustion chamber than the bore! [Due to "folding"] This is why Guzzi had to go to a twin-spark layout on the Breva & onward models. The alternative would have been to go to a bathtub chamber like H-Ds use (quite effectively!), but I guess Guzzi/Aprilia/Piaggio decided that it would be easier/cheaper to go the former route than to have to change their castings & machining programs to redesign the combustion chamber & pistons. Too bad, as the dual-plugging just keeps them even with smog cert. requirements, w/o necessarily bringing the higher combustion efficiency that a better chamber would. [Or were you thinking Harleys going from the

 

I hope that anyone with a Guzzi who wants to run the hi-compression pistons has a dependable source of hi-octane gasoline around, & I'm not talking about the p!ss that's sold as "premium" here in L.A.-la land! Either that, or carry around a can of Avgas 100LL (& ditch the stock silencers w/ cat converters, if your model is recent enough to have them; no sense ruining them by running leaded gas!)

 

I would dearly love to experiment with redesigned heads, try going to a 3-valve head, maybe a 2v wedge head, at the very least building up some of the combustion chamber to provide more squish band & taking some of the crown off the piston. Ah, rampant empiricism! What fun!..

 

You can also go to a dual-plug head conversion, which Mike Rich also does a great job at, as well as TLM.

 

Now that there are more choices out there for programming the ECU, and even TLM offers a reflashed unit with a different ignition curve just for dual-plugging, one can in theory take advantage of dual-plugging in a V11 engine and ECU.

 

I still have detonation issues though when it is really hot and under hard throttle. Maybe it can be further tuned out, but I just frankly haven't tried as it is pretty mild, and they all seem to do it

 

Al

[dlaing]

 

I still have detonation issues though when it is really hot and under hard throttle. Maybe it can be further tuned out, but I just frankly haven't tried as it is pretty mild, and they all seem to do it

 

Al

My endlessly procrastinated goal is to better tune the temperature and altitude trims in the ECU.

First, so I have a clue...I have to install the WBO2 logger that I have owned for about 8 months.

Then it is just a matter of trial and error.

I'll be able to log throttle position, RPM, and engine temperature.

I'll try to post whether of not it can make a difference.

Generally the map gets leaner the hotter the engine and air get.

I think that after a certain temperature it would be good to enrichen...sort of a built in thermostat.

With regards to the altitude compensation, the compensation is conservative, because they don't want it to get too lean if the sensor fails. But I almost never ride over 7000 feet, so the compensation is OK for my general use, but it might be nice to get a little more punch out of the engine while up on Mount Palomar and Mount Laguna...I think high altitudes could really benefit from the high compression pistons and optimized squish.

[Pierre]

The cut dome of the MRs surely is a good idea, but I don't think that the so greatly enlarged squish area is an idea as good as the one before. Assumed that I interpret the picture right.

Hubert

 

Incidentally while I'm sure Mike knows far more about combustion cahmber design than I do I think that the squish band on his slug looks too small for my liking. In many ways it resembles a 'Big Valve' piston which are a truly horrid thing, ... .

Pete

 

OK guys - which is it?

Too much or too little squish?

More is better?

More is worse?

 

[luhbo]

OK guys - which is it?

Too much or too little squish?

More is better?

More is worse?

 

As I said, these pictures may lie, but to me it seems as if the idea of MR was to follow the head contour as close as possible, so giving him the chance to reach a high CR and a well cut down dome. That's nothing more but a greatly increased squish area.

 

What is better or worse? What we call squish area is in fact just a result of the attempt to rise the CR. It somehow blows the gas away from the cylinder walls, but without any resulting swirl to fasten the burning front, without any target as for instance the spark plug could be one.

 

Consider also that, as Pete already has said, the direction of inlet and outlet ducts are everything else but optimal and then you will hopefully not expect too much of all this squish fiddling.

 

That's why I mentioned the 4V BMW. It's just the different system that makes the advantage possible. And even they have recognised that 122 HP is already right on the edge, just because they suffer the same restrictions as Guzzi when it comes to optimising the porting directions.

It looks identical to the Guzzi 4V engines. Two high camshafts, chain driven here. Could it be that Guzzi had this solution first?

 

A serious dealer/mechanic should tell his customers that of all this very expensive stuff and time max. 30% will be effective, compared to every 08/15 4V-Jap bike, the rest is just for the good feeling to have well supported him and to have well expensive parts built in.

 

And what about the difference between static/theoretical and dynamic/effective CR? Did anyone mention it already? What if someone says that such an expensive high CR piston reduces the effective CR by reducing the delivered amount of fresh gas under certain conditions?

 

Hubert

[luhbo]

A picture of the above mentioned engine:

 

 

Also the sump shows some interesting details.

 

Don't get me wrong: that's the brand I'd buy only in fourth or fifth place. Not that it was of nonsufficient quality, it's just a bit to chilling.

 

Hubert

[Skeeve]

...

Generally the map gets leaner the hotter the engine and air get.

I think that after a certain temperature it would be good to enrichen...sort of a built in thermostat.

 

Absolutely! Leaning the intake as stated is due to the lower density of hot air making for less fuel needed for available oxygen, but at a certain point, the "flash cooling" of the intake air by evaporation of the fuel charge leads to greater charge density, & hence either a surplus of oxygen (& propensity to ping) under hot conditions or greater power (if the additinal fuel needed is available.)

 

With regards to the altitude compensation, the compensation is conservative, because they don't want it to get too lean if the sensor fails. But I almost never ride over 7000 feet, so the compensation is OK for my general use, but it might be nice to get a little more punch out of the engine while up on Mount Palomar and Mount Laguna...I think high altitudes could really benefit from the high compression pistons and optimized squish.

 

Well, the higher the altitude the higher the compression can be before pinging (due to decreased charge density.), so you're on the right track again there...

[Skeeve]

OK guys - which is it?

Too much or too little squish?

More is better?

More is worse?

 

 

Ceteris paribus, more squish is better (generally.) Why? At a given compression ratio, the larger the squish band, the smaller the combustion chamber. Detonation & preignition are closely related to combustion chamber size, so the smaller you can make the combustion chamber, the higher the C.R. you can sustain. (Up to a limit, which for petrol-burners is around 15:1, iirc: above this, you should just plan from the start on burning exotic fuels or diesel...)

 

 

 

 

 

 

 

 

What is better or worse? What we call squish area is in fact just a result of the attempt to rise the CR. It somehow blows the gas away from the cylinder walls, but without any resulting swirl to fasten the burning front, without any target as for instance the spark plug could be one.

...

 

And what about the difference between static/theoretical and dynamic/effective CR? Did anyone mention it already? What if someone says that such an expensive high CR piston reduces the effective CR by reducing the delivered amount of fresh gas under certain conditions?

 

Hubert

 

Hube, ol' buddy! Squish is all swirl (it's like blowing a smoke-ring; all that gas squirts in from the edges @ once & sets up a huge amount of turbulence...); no targets are necessary!

 

As for the static C.R. vs. dynamic: since nobody is talking about swapping cams, the C.R. numbers for static is a convenient point of comparison. Yes, if the cam is changed to something w/ more overlap, then the dynamic C.R. is going to be decreased, & higher C.R. pistons would be in order to just to stay even w/ the stock setup [the engine must be treated as a whole, not just individual pieces...] but since nobody has gone off on that tangent yet & I'm pretty certain we're all still talking about changing the pistons while leaving the stock cam in place, we can ignore all that & go back to our arguing...

[dlaing]

Absolutely! Leaning the intake as stated is due to the lower density of hot air making for less fuel needed for available oxygen, but at a certain point, the "flash cooling" of the intake air by evaporation of the fuel charge leads to greater charge density, & hence either a surplus of oxygen (& propensity to ping) under hot conditions or greater power (if the additinal fuel needed is available.)

Well, the higher the altitude the higher the compression can be before pinging (due to decreased charge density.), so you're on the right track again there...

That is the confirmation I need! Thanks!

[al_roethlisberger]

Ceteris paribus, more squish is better (generally.) Why? At a given compression ratio, the larger the squish band, the smaller the combustion chamber. Detonation & preignition are closely related to combustion chamber size, so the smaller you can make the combustion chamber, the higher the C.R. you can sustain. (Up to a limit, which for petrol-burners is around 15:1, iirc: above this, you should just plan from the start on burning exotic fuels or diesel...)

Hube, ol' buddy! Squish is all swirl (it's like blowing a smoke-ring; all that gas squirts in from the edges @ once & sets up a huge amount of turbulence...); no targets are necessary!

 

As for the static C.R. vs. dynamic: since nobody is talking about swapping cams, the C.R. numbers for static is a convenient point of comparison. Yes, if the cam is changed to something w/ more overlap, then the dynamic C.R. is going to be decreased, & higher C.R. pistons would be in order to just to stay even w/ the stock setup [the engine must be treated as a whole, not just individual pieces...] but since nobody has gone off on that tangent yet & I'm pretty certain we're all still talking about changing the pistons while leaving the stock cam in place, we can ignore all that & go back to our arguing...

 

 

Yeah, I put in the MR pistons and a Megacycle cam, so everything is all confused

 

As far as speculating on the MR design, as I've said before... Mike really doesn't mind talking at length about his ideas, theories, and products.... so I'd suggest giving him a call if you have any questions.

 

He's a great guy, and is happy to tell you exactly what he thinks.

 

I think he and Pete would get along great

 

Al

[antonio carroccio]

I would step by with a simple question,

Where or by who can I get those high compression pistons? Please, don't mention FBF 'cos I know it already.

 

Is there in any part of the globe, France, Germany, USA some manufactory who makes those pistons?

I would say, some member of this forum has mention it already, am I wrong?

I Need also the valve... duhhh

 

 

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I think I have got it, it's Mike Rich, isn't?

 

Well Mike Rich's price Piston + valve=482,- USD

FBF price pistons + valve= 440,-USD

 

A difference of 40,- Dollrs,

 

What should be the difference in quality?