| Author | Message | ||
     Xbolt12 |
I was just thinking, now that you have the tool and knowledge for tweaking the ECM maps, and hearing on Friday that you cannot raise the rev limit, I wonder how a retuned xb9 ECM or race ECM would work on a built xb12?? If you could get the fuel maps dialed in, it would then give you over-rev to 7500. All without dealing with the competition only ECM. Hmmm, interesting..... | ||
| M1combat |
I have an XB9 ECM just for that specific purpose  . I've had it for over a year waiting for a proper tuning tool so I could check it out . That said... I don't think anyone with a 12 crank should go past 7200. At all. Unless of course you have MUCH more than just the twelve crank . That said... If I can't adjust the rev limiter... Maybe I just won't do it. I have accidentally bounced off the rev limiter a few times and I HATE to think what would happen if it had been at 7500RPM. My bike is only run on the street. I haven't even taken it to a track day yet.. | ||
| Xbolt12 |
Yeah, but what if you want to build a big-bore, short stroke using the xb9 crank.... | ||
| Alex |
If You use the XB9 crank it isnīt a XB12 any longer but a XB9. If You big bore it it is a big bore XB9. For any XB9/big bore XB9 You certainly use a XB9 ECM. If You use a XB9 ECM in a real XB12 I would do what M1combat says. Best regards Alex | ||
| Buelldyno_guy |
It can be done and it appears that using a stroke of 3.8 or longer (stock 1200 cc length) you need to limit RPM to about 7200 max due to piston speed, If you shorten it up just .200 or a approx.. 3.6 you can turn it up to your valve train limit. We spin our 1210 cc engine to 8200 and could go up to 9K but it would need more valve care between races. Some of the early Thunder Bikes had a shortened stroke with a large over square bore. However there are a few new ultra short stroke 3.125 engines with the same over square bore at 1197cc that with good heads could go to 8K+ and make 120 hp easily. We use a S&S 3 5/8 crank with Temkin bearings but Brian can make you a 3.6 crank using your 3.125 XB9 as a start and roller bearings. ... Terry | ||
| M1combat |
I assume you're referring to 3-13/16" bore for all of those. Also... What does a good 3.6 crank cost? What about machining a set of cases for Temkin bearings? Why couldn't you get a larger bore by using longer rods and just running the pistons farther up in the jugs? It would have the benefit of less side loading too right? Maybe I'm just dumb and missing something . | ||
| Ezblast |
Great question! - I wonder also! GT - JBOTDS! EZ  | ||
| Xbolt12 |
Alex, you are only partly correct. The xb12 has a larger throttle body and probably a different ignition curve, a different primary gear ratio, etc. Buelldyno, Thanks for the info. Also thanks for doing 186 dyno runs or whatever it was for you and Al to get the maps figured out. Wish Al had a dyno or you were down in San Diego... | ||
| Alex |
XBolt, I know the differences between the 9 and 12 engines as I have them in my engine shop all day long. You were talking about using the 7500 rev limiter of the 9 ECM. As piston speed as well as forces acting upon the rods are mainly linked to the engine stroke it is the crankshaft that the rev limit should be addressed to not the throttle body size or the primary gear ratio. Thatīs what Iīm saying. If You "short stroke" Your engine You can go up with revs (read: You can use the 9 ECM), if You leave it "long stroked" keep revs down (read: stay with the 12 ECM). Best regards Alex | ||
| Xbolt12 |
Got it. But my real question had do with other differences between the ECMs and whether the 9 ECM would get enough fuel to a short stroke 1200 built out of a xb12 motor using the xb9 crank and the big 88 or 90 cu cylinders and also if the advance curves would work well. | ||
| Buelldyno_guy |
Donald as I came back to see this I realized my post might have just confused things. Stock XB9 Stroke 3.125 with racing mods can rev to over 8K. Stock XB12 stroke is 3.8125 and is limited to about 7200-rpm. The short crank can be lengthened by re-pinning to 3.625 the longer stroke creates more mechanical advantage thereby more torque. At 3.6 the piston speed is still within acceptable limits. As pointed out, you will have to use a ECM that allows a higher rev limit. Give Brian a call about the crank mods including the bearings, or you can order a 3.6 race ready crank from S&S, but it will come set up for the tapered bearings. | ||
| Alex |
Buelldyno_guy, how do You re-pin a XB9 crank to 3.6"? Best regards Alex | ||
| Buelldyno_guy |
You can take the short stroke and make it longer by moving the pin. You can not shorten the long stroke down. Give Brian a call he can give you the details and cost. You can buy the S&S 3.6 crank off the shelf also . ... Out race bike started life as an XB9 and to get to the 1210-cc +1 mm limit we used the 3 5/8 S&S crank with a 3 5/8 bore. Brian is one of our major sponsors and helped make the tapered roller bearing crank fit in the new style XB cases. Terry | ||
| Diablobrian |
Terry, That sounds identical to what hal's did with my motor. I was getting 100 rwhp with mild porting, stock air box, race ecm, and Jardine slip-on. what kind of rwhp are you getting on your race bike, and what other mods does your motor have? | ||
| Whodom |
Along the same lines- I got a brochure in the mail last week from Confederate Motorcycles. Their "Wraith" model uses what appears to be a Sportster-derived powerplant with a 4 inch bore and 3.6" stroke, which works out to ~90.48 cubic inches or 1482 cc (!!). They don't provide any performance figures for the engine. It would be interesting to see how it compares to the Buells. | ||
| Diablobrian |
I thought they took a wraith out to Bonneville. It should be fairly easy to derive their HP number if we know the top end speed. | ||
| Whodom |
Evidently it only did 131 MPH which isn't impressive at all. OTOH, it doesn't sound as if this was a serious speed attempt and the plant was evidently a 100 cubic inch S&S engine rather than the in-house built unit described in the brochure. | ||
| Diablobrian |
Wonder why they wouldn't make a real run at it, unless they had mechanical issues. They probably wouldn't admit it if they did for fear of negative stigma. | ||
| Alex |
Terry, I know that the crank pin needs to be moved to the rim side but I was wondering how You do it. Do You close the pin bore in the flywheel and re-bore it? Best regards Alex |
