| Author | Message | ||
     Purpony |
Just wondering what type of hp/tq gains you get from upgrading to XB pistons and jugs? And after asking that question, is it XB9 and/or XB12 parts that are used? Is there any gains going XB pistons/jugs and keeping the Tuber heads, or are XB heads needed as well? thanks | ||
| Xl1200r |
I can't answer the gains question, but I think guys like to use the XB9 pistons because they're a flat-top design and will give high compression. As for the heads, they are the same between the two (XB9 & 12). Not sure if you can use XB9 pistons with Tuber heads - might have some valve interference. The XB12 pistons are dished (from what I've heard) and won't cause valve contact issues. | ||
| Hootowl |
The xb jugs also have more fin area. Heads do too probably. The XB heads also flow better. And while I have no direct knowledge, I too am under the impression that the XB9 pistons yield higher compression. | ||
| Ratbuell |
Yes, XB9 slugs are higher compression. XB heads flow better than Thunderstorm. You do have to have matching heads and pistons - XB to XB. You can NOT use tuber heads with XB pistons. And a warning on XB9 pistons - aside from fighting detonation and having to have fueling correct, you're gonna put a HUGE strain on your starter. Just to bear in mind... | ||
| Jsracer |
XB9 pistons are domed, not flat top. They give about a 10:1 compression ratio under 62cc chamber XB heads at the XB9's 3.125 stroke. At the 3.813 stroke of an XB12 or a tuber they give around a 12.1 compression ratio under XB heads. The dome is shaped to fit the chamber on an XB head and really can't be put under a tuber head as you'd get mechanical interference. Even if you could solve that problem, you'd lose your squish band. XB12 pistons are almost flat tops. They have a round "button" of a dome in the middle of them about the diameter of a quarter. They give around a 10:1 compression ratio under an XB head with the 3.813 stroke of an XB12. They could be put under a tuber head but it wouldn't be a good idea. Under a Thunderstorm head you'd lose about a point of CR versus the proper Thunderstorm piston and you'd also lose your squish band. Under a Lightning head as a replacement for the stock flat tops they'd work OK and give a small bump in CR but you'd be better off with an aftermarket 10 degree domed piston to give you a squish band. The stock starter is plenty strong enough to support 12:1 CR. CR is only one component of compression by the way, the cam's intake close event timing also has a lot to do with it. But even with the stock cams 12:1 should be no problem with the stock starter. There are many many race motors with cranking compression north of 220psi that start fine using a stock starter. Both of these pistons are castings. Cast pistons are not as strong as forgings and don't resist detonation as well. You might get away with using a cast piston at 12:1 if you use race gas but if you try to use pump gas personally I think you're taking a big chance of a very expensive detonation related failure. Cast pistons are also heavier than forgings. Aftermarket high compression forged piston are readily available for any of the XL/XB/Tuber heads and they would be a much better choice for a high compression application. Personally I can't see doing all that work and putting in pistons that are at risk of breaking just to save a couple hundred dollars. One single failure will cost you much more than that. Another advantage to an aftermarket forging is that you can bump the displacement up at the same time with a big bore kit. | ||
| Ratbuell |
I wasn't saying higher CR would kill the starter... Maybe I've been spending too much time on the 1125 board lately, but with all the talk about "my stator is going" and "my battery is junk", my comment was more along the lines of "your battery will use more juice to start the bike with higher CR". All the more reason to take longer rides  |
