Scooterotica

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Just got my Pro Porting 218 stage 4 running this week, and went out for a ride yesterday to get some miles on it and work out the jetting.

Specs are............
60mm crank (cut increased inlet)
2.0mm squish (-0.6mm in cylinder + 1mm head squish + Malossi head gasket)
18 deg iginition timing
Revolver RH pipe
Standard gearing and clutch with Malossi springs
SCK fast fast flow tap
Si 24/24e carb with cosa carb top and needle valve, main jet fuel passage drilled
Running in at moment with 52/140 pilot, 160 AC, BE3, 125 main, drilled air filter.
Stage 6 EGT (recommended)

Initial feelings are its strong and torquey, but also revs, just like it says on the box !! I'll update this when it's run in and the carburation is set up, running a bit rich at the moment.

Why have you gone for such a big squish?

he,s probably running a standard head, to acheive 1.2 he'd need to reprofile otherwise incur heat! i've spoke to harry and for all out high speed touring, in his words "f@@k squish" harry swears by 2.4 and 4-5 thou piston to bore...he's some guy!!!!

H,POOL GADGE wrote:he,s probably running a standard head, to acheive 1.2 he'd need to reprofile otherwise incur heat! i've spoke to harry and for all out high speed touring, in his words "f@@k squish" harry swears by 2.4 and 4-5 thou piston to bore...he's some guy!!!!

and there are loads who call him huge jet harry lol

The head has been reprofiled by Harry, has been built as a high speed tourer, so the large squish is to avoid 'pinking'.

Nearly completed the run in period, and currently spec'd as above but with a 130 main. The main problem at the moment is the new filter is not letting the carb breathe, seems very restrictive. It's new, came in piaggio branded packaging, but not guaranteed to be OEM.
I'm going to try an original air filter and hopefully that will cure the richness.

Ok now I'm lost........ thought that the theory was to get the squish as close to 1mm in order to prevent pinking or does having ridiculously low compression also do the job?

LINK TO SQUISH ARTICLE

Also my understanding is low compression = low power...........

For example, a 207 with 60mm crank and 22cc head (inc 1.2mm squish,) = 9.9/1 compression (uncorrected.)
By adding another 1.2 mm to the squish you're increasing head volume to 26.36cc which gives an uncorrected compression of 8.26/1.

With an uncorrected ratio of 10/1 being considered "safe" (unless I've misread some of the articles on here,) why would you want to go much lower?

By the way I'm not being a knob and doubting anybody, I'm honestly interested as there seem to be so many variables that people seem to say work and swear by.........

to get the squish action working the squish bands width combined with clearance and compression ratio is calculated together to create an appropriate squish velocity ,so 0.6 on a narrow band width or 1mm on a medium width or 1.5 on the widest band can all be effective,the requirement for an effective squish is very important on higher comp ratio,s,high performance motors but hardly required on low comp ratio,s
once above around 1.8 its hardly effective
squish clearance can be used to adjust compression ratio so the 2.5 squish is probably used as a cost effective method to obtain the correct head volume without the need or cost to machine the head

Darrell Taylor wrote:to get the squish action working the squish bands width combined with clearance and compression ratio is calculated together to create an appropriate squish velocity ,so 0.6 on a narrow band width or 1mm on a medium width or 1.5 on the widest band can all be effective,

Now this is something I've read before (another variable,) what difference do the different widths have on a motor, or rather when would you employ a narrow, medium or wide band?