Mickrick wrote:
So Pash, what difference would it make between a 10 degree and 30 degree squish?
Maybe my crank could be modified? Offset the larger pin for a longer stroke mebee?
So Mickrick, here's my opinions...
Squish helps combustion by introducing turbulence by forcing the mixture into the centre of the combustion chamber, the turbulence results in a more disordered flame front (or reaction zone) which enables more fuel and air to react and hence burn quicker. This means you can reduce the advance and reduce the fight against the piston as it comes up to TDC.
What is the best squish angle? 10? 15? 30? It depends on combustion chamber design and as ever there is always a design point, the general rule of thumb is that the higher the target engine speed for peak performance (torque), the higher the squish angle.
You will read in lots of places how poor the squish band is on the Thunderstorm heads, they are roughly cast rather than machined to match the piston, and more interestingly, the squish bands are nominally 15 deg in the head whereas the piston has a 10 deg squish angle.
The XB heads have a zero squish band angle, but as the squish band is machined (the deck of the head) you can set this up quite accurately, and following advice from those that know, the target clearance is 0.03 inches or 0.75mm.
My two S1s have XB heads (you need a different front engine mount), the black one has done around 15k miles in the configuration. It was a very clear improvement over the Lightning heads (pre-Thunderstorm) and doing top gear roll-ons with another forum member with his well set-up carbed X1 (Mukuni, Forcewinder plus Pro Race exhaust on both bikes), the S1 clearly accelerated faster.
The black S1 and I spent an afternoon with Tubbs on his dyno, where we actually ran out of main jets (I am a size up on when we left the dyno). I am using a Dynatek 2ki ignition unit on curve 4 and I'm pretty sure I am a little way away from optimising the ignition timing.
The bike made 95hp (corrected), which isn't that much really. Beef's, with the 1250 kit made 105 IIRC, and there are plenty of other people on here who have reliable engines with big bore kits and big numbers. Indeed, our very own Tubbs is no stranger to tuning Buells.
My X1 runs like a dream, I'm pretty sure the S1 is faster, but what I did do was lop 0.9mm off the head (not much thought at the time as I was feeling no love for the bike) which was the depth of the step in the head from the face to the squish band. Still using standard push rods. Again, I am pretty sure I could make it run better but it runs very sweetly indeed so no rush.
In terms of cranks and pins and stuff, I have not touched the bottom end (apart from change the oil pump gear and my other S1 has SE536 cams but I have not ridden it much).
What would I do? If I concentrated on the X1, I would machine a set of XB heads to match 10 deg squish pistons, maybe put some SE536 cams in and then play on the dyno for a day tinkering with ignition timing and fueling. I would be welding slave lambda bosses on the headers.
The SE536 cams have quite a high lift at TDC on the exhaust, however they appeared to be favourites with NRHS (pre-Hammer Performance) and didn't give much away to the 575s however the beauty of the 536s is that they have less lift than the XB cams and they have a longer overlap, which suggests that the valve acceleration is lower hence the valve train gets an easier time so should be more reliable than on an XB. Maz doesn't like XB heads as (amongst other things) they have a beehive spring (rather than a pair) which he has seen fail (but the dual springs fail too) and the valve stem is 6mm rather than 1/4" IIRC.
Register
Login
FAQ
Search
reliability is a must, but a bit of extra poke wouldn't be missed, and if I pull it apart, I may as well spice things up a bit, it's just a toy 
