High Compression Pistons

[Baldini]

....A friend of mine decided to enlarge his LM1 engine with plaine simple 1000 SP pistons...the most pleasant Guzzi engine I've ever seen. Never pinging, as powerfull as the 3C-Laverdas and the Ducs, consuming around 5l/100km and less, and all that with standard LM3 cans. Really silk smooth....

 

I have SP1000 barrells/pistons w/ stock LM11 heads, 36mm carbs on my Tonti. It is a lovely motor to use. Loads of grunt from nothing, no detonation, & fast enough. It must be very low compression I guess but it's really sweet to ride. Even stock, the LM11 was prone to detonation unless carbs & timing were spot on. This recent hot weather was causing detonation on the Scura - first time it's been an issue. Guzzirider uses the FBF pistons - I thought he was pretty happy with them , tho course it's colder up thur....

 

Would twin plugging solve the pre-ignition issue when using high comp pistons?

 

KB

[Greg Field]

There're lotsa these high-comp pistons running out there—the ones Moto Intl. used to sell, the FBF ones, and Mike Rich ones—that are ridable on street gas. The guy who developed the Moto I version has probably 100,000 miles on his.

 

That implies that there is something wrong with this particular machine that prevents use of high-comp pistons. I'm suggesting that it's mechanical and fixable, but will require a skilled builder/machinist, not a progammer. I'd bet looking for and correcting any problems (defect with the pistons, wrong gaskets, burr in the chamber, burned or bent valves, partially clogged injector, bad crank sensor) and then setting squish will go a long way toward making it rideable. Perhaps a change in riding style (not pinning the throttle below 5,000 rpm, for example) would cure the rest? Dual plugs would almost certainly fix it.

 

Talk to Ed. He knows Guzzi engines and has the skills. Squish depends on motor configuration. I would trust whatever Ed is comfortable with.

[Pierre]

Wouldn't twin plugs sort this?

 

I don't think so - at least not alone. If I understand correctly, the advantage of twin plugged heads is that they enable a complete burn with retarded timing. Cuts flame path in half. I think it's the retarded timing that actually reduces / stops the pinging. The twin plugs just ensure a full burn with retarded timing.

 

Instead, I'd pay close attention to what Greg has pointed out. There's too many of these high comp versions running around without problems (mine is one, but I got there by decking the heads, not installing high comp pistons) for this particular tired example - that Ratchet so enjoys trotting out - to be the norm.

[guido]

Twin plugs would reduce the flame-travel above the piston. IOW start a controlled combustion from two fronts. It would thus cut the combustion time in half, other things equal, (which they never are )

But yes, it certainly would help. The pinking phenomenon starts when you have conditions (temperature, pressure) which will make the mixture explode. That is what you hear, at low speed. High speed pinging is what you don't hear. It causes rapid loading of the piston, localized heat transfer at a multiple of the normal, as it breaks down the boundary layers, and it will ruin your engine, if severe and prolonged.

Have a look at the new Breva 1100 engine. Twin plugs, and no, it has never made a wrong noise with me. My EV often does, My V11 occasionally.

[Guest ratchethack]

There's too many of these high comp versions running around without problems (mine is one, but I got there by decking the heads, not installing high comp pistons) for this particular tired example - that Ratchet so enjoys trotting out - to be the norm.

Pierre, I've never suggested this is the norm. It's been clearly presented as simply one example. My Guzzi - identical in most respects to the one in question except for stock pistons - tends to ping on high-octane pump gas, especially on hot days. I have to "ride around" it or risk holing my pistons. No, it's not running lean. From my perspective, the C/R on my Guzzi seems to already be at the limits of reliability from several perspectives, as Pete has suggested. The last thing I want to consider is anything that could: 1. make pinging worse, and 2. as Pete has pointed out many times, decrease the reliability and/or longevity of the motor. I'm in it for the long haul.

 

I have seen many many riders who do things to their bikes without regard to reliability - as if it has a life expectancy as far as tomorrow or next week - and after that, who cares? Sometimes this turns out to be the case.

 

BAA, TJM, & YMMV

[Pierre]

 

I have seen many many riders who do things to their bikes without regard to reliability - as if it has a life expectancy as far as tomorrow or next week - and after that, who cares? Sometimes this turns out to be the case.

 

BAA, TJM, & YMMV

 

There you go again. No one is talking about reducing reliability to "tomorrow."

 

In stock configuration there are examples that go 150K miles. If I were given the opportunity to choose to reduce that by 10K miles (or 20K or even 50K) in exchange for another 20 horse power I'd do it in a heart beat.

 

You keep posing extremes (straw men) and suggesting this is dispositive of something.

 

Frankly, the guy who rides a bike 100K miles is a rare bird indeed. I'm guessing that within the bell curve of "normal" lifetime mileage ownership, most of the mods discussed here would be non-issues - but I'd be guessing. Just like you. I just think my guess is a lot closer.

 

A final thought. Why buy a bike in the first place? Is it really to get a machine that runs trouble free forever? For a very few maybe. But not for the average bike owner. As for me, If my hopped up version runs trouble free for half it's projected stock trouble free life span, it'll still run trouble free for farther than I'll ever ride it.

[big J]

I dunno lads,thanks for the theoretical stuff,I know about faster burn and advancing flame fronts and all that,but I can only speak from experience.

On my old shovelhead H@rley,big bore pistons,hot cam,short stroke motor,it would pink like a bastard under load.Dual plugs,removal of potential hot spots within the combustion chamber and retarding the timing sorted it out completely.

Hang on,that's what you said.

Sorry,it's Sunday,and I'm half pissed.

I'm with you an Greg,pissing about with fueling and such is a complete waste of time,unless you had it so rich to cool the chamber that you'd be as well throwing a bucket of petrol at it.

Ratchet,why didn't you pull the heads and have a look?Surely any "road geez" worth their salt would have spotted any problems like hot spots,squish problems right away

[Guest ratchethack]

Ratchet,why didn't you pull the heads and have a look?Surely any "road geez" worth their salt would have spotted any problems like hot spots,squish problems right away

Big J, I assure you that if the bike belonged to me, it'd have been out on the road and out of its break-in period nearly 2 years ago. I'd have started with a heads-off inspection on day 1 before the end of the first tank of race gas. Depending on what I found, I'd more'n likely have had 'er buttoned back up within a week with a permanent solution. My best expectation at this point would be a set o' stock pistons, but if it looked like there could be a reasonable return on investment, I might've at least measured, and if indicated, re-set the squish to see if I could thereby find a way to live with the FBF's.

 

BAA, TJM & YMMV

. . . it's Sunday,and I'm half pissed.

Wot's y'er favorite local swill?

[dlaing]

That implies that there is something wrong with this particular machine that prevents use of high-comp pistons. I'm suggesting that it's mechanical and fixable, but will require a skilled builder/machinist, not a progammer.

So if adding fuel did not fix it, you think retarding the ignition would NOT help and only one of the mechanical solutions would work????

Or retarding the ignition enough to help would have undesireable consequences???

[big J]

Drink.Any kind

[Guest ratchethack]

Drink.Any kind

A capital idea! Methinks y'er got a bit o' lead on me now. . . .

[Greg Field]

If you get the squish right, you can eliminate pinging.

 

Jason at MI built a monster motor from a 98 EV engine. He used V11 Sport pistons with the medium-valve heads from the EV. He carefully set it up for squish and proper clearance. Compression ratio was way higher than with FBF pistons in a V11 Sport. Horsepower was very near 100, by my seat dyno. I'd pull like a freight train from 1200 rpm on up, with no pinging.

 

One moral of the story: A properly set up engine with higher compression can actually be far less prone to pinging than a poorly set up lower compression engine, on the same gas.

[Guest Rocker]

Has anyone fitted FBF high compression pistons to their V11? I am looking at doing this and would be interested to hear any thoughts on the topic, please?

 

Richard

V11 Rosso Corsa

 

I'm intrigued to know why you should want to do this. You must have a valid reason. Please share it with us all.

 

Rockerob.

[luhbo]

....

One moral of the story: A properly set up engine with higher compression can actually be far less prone to pinging than a poorly set up lower compression engine, on the same gas.

 

Yes, that's the point. It's the proper set up that makes the difference. What he did was reduce the roof height instead of overstretch the piston dome height.

If it was rising the dome height only it might eventually work, but usually you cannot make them higher without enlarging the valve pockets. That's the point where the crap begins. High domes and deep valve pockets make everything else but a compact combustion chamber.

 

You can top all this only by one thing: trying to drown the resulting ping and knock centers. That's like drowning all the little kitties your cat might bring home every year. That's not an intelligent solution and only the real dumb minded butcher will find some satisfaction while doing such.

 

Hubert

[Alex-Corsa]

Moral of the story is, that higher compression pistons reduce engine's life and money of your pocket...

I don't think that Guzzi's mechanics were so stupid of instaling the pistons and making the motor as is now.

Every now and then I hear people messing their bikes with racing parts , well where you hear racing =less engine life, or much less engine life.

Few mods can actually make the engine work real better or last as long , one has to ask people that have made them and tested them for long,perhaps Dynotec or Daes have a good 'bag of tricks' (here in Europe)on the line for that purpose.

As far as I am concerned I am just into having a better fuel map suited to my needs and perhaps latter do that twin spark and some other essensial works done ,from a real specialist of the kind but there are another 40- 60k to go.