Squish band? on a 250 nc m3

[Bevel bob]

Is it possible to incrporate a squish with the standard borgo piston and what needs to be done?

[DewCatTea-Bob]

Is it possible to incrporate a squish with the standard borgo piston and what needs to be done?

____ I must not understand what you actually mean to be asking... cuz you shouldn't need to do anything (other than make sure that your piston's top-edge is reaching near flush with the top of the cyl.sleeve). _ As all stock DUKE pistons & heads have included a squish-band since the 200s were discontinued !


Dukaddy-DUKEs,
-Bob

[ericpritchard]

The Ducati squish is one (of many) reasons for good power from the engine. I try to get the squish clearance (piston to combustion chamber) down to 0.030" - not less (very important!). Likewise, I've used 0.060" clearance between piston and valves - I know some folks use less, but this works for long tracks like Daytona etc. Using these clearances, my current motor makes 30.5 bhp (10,000 rpm) at the rear wheel on the dyno and is reliable with a good spread of power.
Eric Pritchard

[DewCatTea-Bob]

" Is it possible to incrporate a squish with the standard borgo piston "

____ After reading Eric's post, I now assume that what BevelBob had meant by "squish", is: 'optimumized squish-effect' . _ And to that the answer is then yes, as the stock piston & head already have a matching 'squish-band' (which is about 10mm wide).
__ I've never played-around with altering the space of the 'squish' to check-out how it may alter the 'squish-effect' (as it seems Eric has done), but I do realize that the greater the spacing/clearance between the two squish-band surfaces, the less it's positive effect ought be. _ So I always reasoned that the closer/smaller the clearance/space, the better,, and usually tried to end-up with no less than about 15 thousandths of squish-space/clearance.
__ Anyhow, Ducati already has their own squish-band employed (in 250s & newer) as they had wished it, and messing around with it's spacing is a heck of a lot of fussing-around for next to no improvement for all your trouble !
It's certain that the squish-effect can be made much less effective but, likely not any better (to make any noticeable positive-difference, even on a dyno).


Dukaddy-DUKEs,
-Bob

[Bevel bob]

Thanks Eric. 30 thou is what I needed to know, I will plastecine the clearance on head and valves , I understand the liner will have to be removed and jug base machined also top of bore cleaned up. I will also be checking CR as i understand its a lot lower than the specs say.

[DewCatTea-Bob]

" 30 thou is what I needed to know, "

____ I doubt that there's anything magic resulting from that exact figure, and that it's "very important!" to avoid 29-thou or less. _ I'm reasonably sure that anything between 15 & 40 thousandths is close enough to optimum, that any alteration within that range would make no worthwhile difference.


" I will also be checking CR as i understand its a lot lower than the specs say. "

____ It ought be considered that the Compression-Ratio 'specs' are based on 'calculated' measurements and that an actual CR can only be a (varying) amount less (than a calculated-figure), depending on the valve-timing (of the cam employed). - (Wild-cams will produce somewhat lower 'actual'-CRs than milder cams do.)
__ The stock n-c small-valve Mk3's CR-spec is 10:1, and the large-valve Mk3's figure is 9.8:1 -(due to larger valve-pockets in it's piston), and the w-c Mk3's CR-spec is 9.5:1 -(due to it's taller cylinder -[which isn't merely the jug!] ).


Dukaddy-DUKEs,
-Bob

[ericpritchard]

Hey, Bob,
I am sure you are right in your comments, and maybe I should elaborate on my specs. I am talking about NC Ducati's for the track/racing - not for the road - and only relate what I have found by experience on the race track. If you are not going to take the motor to its limits then the precise value of the squish or piston to valve clearance is pretty academic - but if it's continued race use - then that''s another matter. I hope I didn't confuse anybody!
Regards
Eric Pritchard

[Bevel bob]

Hi Eric, yes this is a road bike, but I dont ride it like my other old classics.!! I have other bikes for pootling around,or going really fast, I take the 250 out when the roads clear and thrash the nuts off it,frighten myself silly and stir up the blood. I have set myself a challenge to get the bike over 105 and its prooving a lot harder than expected as I dont have the roads for a good run up. Riding a modern is no challenge to go fast.I think i need around 26 bhp?.

[DewCatTea-Bob]

" I am talking about NC Ducati's for the track/racing - not for the road - and only relate what I have found by experience on the race track. If you are not going to take the motor to its limits then the precise value of the squish or piston to valve clearance is pretty academic - but if it's continued race use - then that''s another matter. "

____ Well Eric, I certainly had not meant to indicate that there's not a precise most-optimum setting for producing the absolute best results from the squish-effect, or that .030" is not that particular setting !! ...
However I did mean to indicate that if an existing clearance-setting is not too far off (from whatever the precise best-setting actually is for optimum squish-effect), then it's not really worth all the trouble to go-about dialing-in the clearance-setting to achieve that setting, even for racing purposes. ...
For instance if the existing squish-clearance is already just-under .045" and somebody bothered to complete all the work needed to reduce that clearance about .015",, while there may be a genuine improvement in the 'squish-effect', it surely wouldn't provide an increase much greater than 1/10th of a horse-power, (which wouldn't even make-up for a couple pounds difference in rider-weight).
__ If there were any confirmed research which indicated that any change in squish-band clearance under .020" can result in over a half a HP (for a single-cylinder), then I wouldn't have chimed-in on this subject.
And unless someone has a non-stock Duc.single which has an incorrect model of cyl.jug / piston combo, the std.squish-clearance should not be much off (from whatever the optimum squish-figure) by more than the thickness of a cyl.base-gasket.


Dukaddy-DUKEs,
-Bob

[DewCatTea-Bob]

" I have set myself a challenge to get the bike over 105 and its prooving a lot harder than expected "

____ If by "bike" you mean a stock large-valve 250-Mk3, then (without a tail-wind) it's not possible to reach it's 110-MPH top-end speed if ya weigh much over 150lbs. _ Not because of the actual weight, but because of such a rider-body's shoulder-width trying to slice too large of a slot through the air, (creating too much wind drag!).
So if your body-size is over 5'8" & 150lbs, ya can forget getting over 105-MPH without at least a 5-MPH tail-wind, (or a long down-hill stretch).


Dukaddy-DUKEs,
-Bob