| Author | Message | ||
     Cvc |
Will a xb12 piston work in a blast? Will the piston sit too low in the bore? The short stroke xb9 and blast parts seem interchangeable based on the opinions here. I just need to know if the rod is longer on the 9's and the piston the same height or same rod short piston? thanks CV.... | ||
| Jsracer |
The 9's rod is 7.270", the 12's rod is 6.926". The difference between those two numbers happens to be half the difference between the strokes of the 9 & 12. Therefore the pistons of the two engines have the same compression height (distance from the wrist pin to the top outside edge of the piston). But that doesn't make it a good idea to put an XB12 piston into a Blast. First, you'll drop the compression ratio down to about 8:1. You're talking about a piston that's made to give 10:1 compression under a 62cc chamber when you've got 600cc of displacement. Dropping that displacement to 492cc causes the compression ratio to drop proportionally unless you also put a dome on the piston. The factory stock Blast piston has more of a dome than the XB12 piston and yet only manages 9.2:1. Second you'll lose your squish band. A Blast head has an angled squish shelf which is made for an angled dome piston. An XB12 piston is a flat top with a small button dome in the middle. So while there won't be any mechanical interference, there won't be any squish band either. In the end, if you do this swap you'll have a much worse running engine. Aftermarket pistons are readily available for Blasts. They have the proper size and shape dome for the application. Plus they're forged, where all the factory stock pistons are castings. | ||
| Cvc |
Thanks for the info I have a low mile blast that needs a crank (due to my error...12year old Scotch is good but not 12year old locktite) so while its down I have been contemplating a big bore kit and using a lightning head. I would be interested in stroking the motor while it is apart any possibility of using an X1 or sporty 1200cc crank? I used the top end on a blast with a bad boot that leaned out until it burned the head and piston. |
