| Author | Message | ||
     Jakecheez |
So I spoke with a pretty educated Buell mechanic at Bumpus HD/Buell in Memphis, TN. I was asking about tuning option for my bike and he wanted to know what mods had been done. I told him about the 1200cc big bore kit on it. He explained to me that the xb9 and xb12 have the same bore and pistons. The only difference between the two is the crank (giving the two bikes different strokes). Since this is the case, why does the 1200cc big bore kit from nrhs.com claim to give a bigger bore to the stock 9 case? | ||
| Augustus74 |
Does the kit your looking at have a new crank? If not then doesn't the extra displacement have to come from somewhere ie. larger bore? Not sure how true it is but I've heard that putting 9 pistons in a 12 raises the compression pretty high with no other mods so not sure if the pistons are the same height??? Alas, I am also not a mechanic  | ||
| Froggy |
Everything you posted is correct. The XB12 is the same as the 9, just different pistons and a longer stroke. (few other minor related parts too) It sounds like your bike was bored out to 1200cc instead of stroking. | ||
| Jakecheez |
Thanks guys It says that the stock 9 cases are bored out to the largest safe size. That gives it a different displacement. I was just not sure that boreing it out could change it to a 1200cc after what the mechanic told me. But the end result is a case that is bored out to a 1200cc but is a larger bore than the stock 1200cc case and has the same stroke as a 984cc? | ||
| Ourdee |
What if you stroke it now? I know the piston would have to be changed to keep the compression right. would you get a 1600? | ||
| Froggy |
Jake, that sounds correct. | ||
| Augustus74 |
You need to get definite specs on your bike. I was kind of looking into bigger motor options and it seems a 9 can be stroked into a 12 but being that the 12 cases(lower area around crank) are a little different, they can be clearanced to go even bigger(stroke). OR you can put 12 jugs(cylinders/pistons) on a 9 to get 1200 but if you bored out the jugs and got different pistons you would also be bigger(bore). | ||
| Pogue_mahone |
the other option for more HP is forced induction or 4 valves per cylinder. any one making/doing 4 valves? for the HD based engines? airflow is HP and cubes dont hurt either. | ||
| Pogue_mahone |
and also... long stroke gives more time to get the fuel/air in place for the burn. | ||
| Rsh |
The bore is 3-13/16" which makes the motor 1170cc's basically a short stroke big bore 1200. You have the best of both worlds, a big bore that can rev. | ||
| Jakecheez |
I'm beginning to understand....to thicken the plot it has stage 3 porting and according to NRHS that means differnt pistons altogather. But if it is bored out, it would have bigger pistons, anyways, right? And with casted millennium big bore heads it wouldn't NEED porting.....I think? Now I'm confused again. The big bore heads do allow for better air flow to the combustion chamber.....I think.....also, it has 585 cams which will just change the valve timing, correct? Oh man- forgive me here I'm just starting to barely grasp all of this information and how all of the engineering works..... | ||
| Slaughter |
I run my 03 XB9 with the 3 13/16 bore, 3 1/8 stroke (1169cc) motor with stage 3 heads, 585 cams, roller-rockers, semi-solids... and a few other goodies. I've kept compression to 10.5 so I can still run pump fuel. The short-stroke, big-bore motor is really sweet. Quicker revving... a bit more "peaky" but for a sportier ride, it's excellent. On the last rebuild, I took a few deep breathsd, opened my wallet, called Dahmer at DarkHorse Crankworks and picked up a 2008 XB9 crank and had it lightened/balanced with the new pistons and the cases bored to accept the bigger bottom end bearings. Is much more rugged with the new BIGGER bottom end (good reason they've made that mod for all since 2008). (don't let my ex-wife know I'm saying that bigger bottom ends are more rugged, she STILL knows where I live!) | ||
| Slaughter |
By the way, I think the biggest "bolt-on" big bore kit for the XB9 worked out to 1050cc... something like that. Sounds like you have the truly deluxe big bore at 3 13/16! (SCHWEET!) | ||
| Rsh |
Just the cases have been bored to allow for the larger diameter of the big bore cylinders. Stage 3 heads are ported and polished for high flow, they are milled and matched to the chosen piston to achieve the desired compression ratio. Larger valves may also be installed depending on the application. High performance valve springs may be installed as well depending on what cams are used. Yes the cam's change the valve timing | ||
| Sloppy |
The XB9 stroke is very conservative on piston speeds. With a short (er) stroke you can raise the rpm of the engine which equates to more horsepower as long as the cams & heads are matched. Sounds like NHRS put together a great package for you. The higher reving capability of the 9 with the displacement of the 12. That's a win / win! | ||
| Steve_mackay |
So I spoke with a pretty educated Buell mechanic at Bumpus HD/Buell in Memphis, TN He explained to me that the xb9 and xb12 have the same bore and pistons. If he did indeed tell you the XB9 and XB12 have the same pistons, he's not all that educated. The XB9 pistons will yield higher compression ratio(1 point IIRC) on an XB12. They share the same bore, but not the same pistons. | ||
| Jakecheez |
The higher compression ratio is not due to the different stroke? | ||
| Jakecheez |
From my last post - I wanted to add that I was talking about the difference between the stock 9 and stock 12. If they have the same bore and same pistons (not necessarily true) then would the compression ratio be different due to the different crank (giving it different stroke)? Or does the stroke not effect compression ratios? | ||
| Rsh |
The stroke does not effect the compression ratio. XB9 pistons are domed, XB12 pistons are flat. Both piston's have the same diameter. Installing a domed XB9 piston's in a XB12 motor will yield a higher compression ratio because of the dome. | ||
| Jeffreyh |
Stroke does affect compression ratio or more accurately, displacement affects compression ratio. Both the XB9 and XB12 have 10:1 compression in stock form. Both use the same bore size and same heads. Since the 9 has less displacement and an equal sized combustion chamber it needs more dome to get to that 10:1. So the 9 piston has a bigger dome than the 12 piston. Since the 9 piston has a bigger dome than a 12 piston, you can put a 9 piston into a 12 and it will raise compression ratio. It ends up over 12:1. I question the wisdom of a 12:1 compression ratio with a cast piston but to each his own. | ||
| Jakecheez |
Amazing the knowledge you guys have- thank you so much!!! I might be crossing the line, asking this, so ignore it if I am- I apologize in advance. I have a Power Commander III to help with AFR. It has been the thorn in my bikes side. I need to remove it. I just got an ecmspy cable and a copy of the program. Is there a way to progam the ECU to run the bile correctly with the mods I have on it? Would it be better to just have it dyno tuned? Is dyno tuning possible with the current mods? I've asked similar questions in past posts, but now that you guys have educated me a bit, I understand more of what has been done and how the engineering of the engine works- thanks again! | ||
| Steve_mackay |
I have a Power Commander III to help with AFR. It has been the thorn in my bikes side. I need to remove it. Yup. Is there a way to progam the ECU to run the bile correctly with the mods I have on it? Yup Would it be better to just have it dyno tuned? Yup Is dyno tuning possible with the current mods? That's a stickier question.... The problem being, is there anyone up in your neck of the woods that is competent and capable of such a task? | ||
| Jakecheez |
I do have buddy with with a twin turbo highly modified v-rod with lots of dyno time. He says that Jason at Fairibult HD is the only guy he will let touch his bike (on the dyno). I know the two bikes are two different beasts, but I think he is capable. I'll ask Jason and see if he feels confident about it. As for everything- I can't thank you guys enough. So I'll start by saying thank you- | ||
| Krueger08xb12s |
a question for Jeffreyh's statement above- has anyone here done or heard about 9 pistons in a 12. Is it very dangerous to our xb's to raise the compression ratio to 12:1? Thanks | ||
| Steve_mackay |
Yup, Hals does 9 pistons in XB12s quite a bit. It's not 12:1 either... It's closer to 11:1. | ||
| Boltrider |
The guy doing the Red, White, and Buell article in Trackday Mag had 9 pistons put into a 12. Lots of good info on the motor build. It's part 4 of a 5-part article. http://www.trackdaymag.com/Search.aspx?searchtext=Red,%20White,%20and%20Buell http://www.trackdaymag.com/Articles/Red,-White-and-Buell-Part-4,-More-Power!.aspx (Message edited by boltrider on July 24, 2009) | ||
| Boltrider |
http://www.trackdaymag.com/Search.aspx?searchtext= Red,%20White,%20and%20Buell (Message edited by boltrider on July 24, 2009) | ||
| Fast1075 |
If you go the 9 in 12 route, pay close attention to the quench and make sure EVERYTHING in the combustion chamber including the piston domes are smooth and free of burrs or sharp edges...tune CAREFULLY and run good fuel....especially if you run short duration cams. | ||
| Teddagreek |
Track day mags buell chronicles have been great.. I'm curious what type of gains would get by raising your compression to 12:1 Sporty guys seem to do this a lot.. Now a stock 12 can be safely bumped to 12:1Cr That being said could a big bore 9 (1169) be raised to 12:1 Or could a tired 9 be bumped up to 12:1 Isn't a 10% ethanol blend better suited than the old MTBE blend... | ||
| Jeffreyh |
"It's not 12:1 either... It's closer to 11:1." Sorry but you're wrong. I got my information from a very knowledgeable person who was running NRHS at the time. | ||
| Fast1075 |
Jake...your buddy with the bad V-rod has a modern 4 valve liquid cooled engine...your air cooled pushrod two valve engine will share nothing in common regarding build or tuning strategy. | ||
| Jakecheez |
I know that and that's why I'm sketchy about usingthe same technician. The complexity of the bikes are similar enough that if the dyno tech can understand both sides of it, he is the guy I want tuning my bike. |
