| Author | Message | ||
     Saintly |
Ok, here's something that has been bothering me for quite some time. There are at least three manufacturers of big bore cylinder/piston kits for the Buell XB series bikes. I believe that all 3 companies AND everyone on this site constantly refers to these kits as follows: The smaller of the two kits is called the 1050 kit when used on an XB9 and its called the 1250 kit if used on a XB12. and: The larger of the two kits is called the 1200 kit if used on XB9, but its a 1430 kit if used on a XB12. The difference in displacement created by the kits is due to the different stroke length of the two engines (ie. XB9 stroke = 3.125" {or 3 & 1/8"} and XB12 stroke = 3.8125 {or 3 & 13/16"} ) My problem is that these kits DO NOT produce the "descriptive displacement" when installed in an XB9! They come real close in an XB12, however. (and I realize that displacement figures are commonly rounded up) Let me show you what I mean: The area of a cylinder = pi x (radius)² x Length which in our application equates to: displacement = [pi x ( 1/2 bore)² x stroke] x 2 ( for TWO cylinders, which is how many most buells have) Let's test it for a stock( 3.5" bore) XB9, shall we? XB9 displacement = [ 3.14 x (1.75)² x 3.125 ] x 2 = [ 30.05 ] x 2 = 60.1 cubic inches or 984.85 cc ( at 16.387 cubic centimeters per cubic inch ) What do you know! the XB9 is indeed listed as being 984cc's or 60 cubic inches ! Shall we try the stock(also 3.5" bore) XB12? XB12 displacement = [ 3.14 x (1.75)² x 3.8125 ] x 2 = [ 36.662 ] x 2 = 73.324 cubic inches or 1201.56 cc's Alas, the XB12 is reffered to as having 1200 cc's or 74 cubic inches! Now lets calculate the displacement for the XB's using the smaller (1050/1250) kit which uses the 3 & 9/16" bore : ********* note 3 & 9/16" bore = 3.5625 ********* So, HALF of the bore( the radius) is 1.78125 ****************** Bigbore1 XB9 displacement = [ 3.14 x (1.78125)² x 3.125 ] x 2 = [ 31.1336 ] x 2 = 62.2672 cubic inches or 1020.3726 cc's ? ( Where's my other 30cc's ? ) Bigbore1 XB12 displacement = [ 3.14 x (1.78125)² x 3.8125 ] x 2 = [ 37.9830 ] x 2 = 75.966 cubic inches or 1244.855 cc's (this is pretty close to 1250 cc's) And finally the bigger kit for XB's Which is called the 1200/1430 kit and uses a 3 & 13/16" bore : *********** note 3 & 13/16" bore = 3.8125 ******** So, HALF of the bore( radius ) is 1.90625 ****************** Bigbore2 XB9 displacement = [ 3.14 x (1.90625)² x 3.125 ] x 2 = [ 35.6566 ] x 2 = 71.3132 cubic inches or 1168.6094 cc's ? ( Nearly 32 cc's short !) Bigbore2 XB12 displacement = [ 3.14 x ( 1.90625)² x 3.8125 ] x 2 = [ 43.501 ] x 2 = 87.002 cubic inches or 1425.702 cc's ( again, pretty close to 1430 cc's) So what gives? XB9 riders are getting screwed. Why call it a 1050 kit if you only get 1020 ? And why advertise a 1200 kit if 1168 is all you net? At least the guy who punches out his XB12 gets pretty damn close to the advertised displacement of the kit! Ok, my rant is over. Any feedback? Check my math, I know I did! | ||
| Bigblock |
well, i'm too lazy to check the math, but that sounds about right! Are you doing any riding? How's the weather up there, I'm thinking about taking my bike out of storage next week. I haven't heard anything from you "upstate" guys for quite some time, I'm definitely chomping at the bit for the riding season to start. Ray | ||
| Hammer71 |
Very soon Ray...Very soon. Fritz you have way too much time on your hands. | ||
| Crusty |
O.K. Food for thought. The late '60s/ early '70s Suzuki 350 twin actually displaced 315cc. The first Honda 750 was actually 736 cc. The Norton 850 Commando was an 830. It's called Marketing. | ||
| Gentleman_jon |
Hey Fritz, Excellent mathematics. Can't believe you got that all figured out without taking any motors apart  Have you given any thought to going to March Badness in Georgia at the end of March? I am going. Going to be some very excellent road riding, or so I am told. You ought to try to make it. It will definitely take you mind of all that pi r squared stuff. | ||
| Essthreetee |
Being a math teacher I come across this all the time...here is how I explain it.... Pi are NOT squared...Pi are ROUND. CAKE are squared.... That is all. | ||
| Bigblock |
too bad it's 19 degrees today, because methinks riding needs to happen SOON! We ALL have WAY too much time on our hands... | ||
| Buellin_ri |
I hear that Big Block. | ||
| Saintly |
I wouldn't say I've got too much time on my hands. What's it take to do a simple algebra problem? 5 minutes is all it took me, It took longer to type it on this forum than anything else. I've seen hundreds of posts about non-bike related B.S. on this board over the last few months. Thats why I've been scarce around here lately. Too much mindless drivel & hardly and bike related posts. B.T.W. Ray(Bigblock) It's 19° in brooklyn today? It's much warmer than that up here in OC. I rode for about 3 hours yesterday, & I'm planning to go out for a putt this afternoon too. P.S. Crusty, I understand the concept of marketing, you'll notice in my post that I said: "and I realize that displacement figures are commonly rounded up" for instance, the old 900cc iron head sportsters displaced 883cc's But, that practice has not been as widely accepted in the past 20 years. (ie. 883 sportser, 1340 evo, 1450 twin cam, & 984cc Buell) Besides these are bigbore kits, clearly the cunsumer who installs these kits is concerned with the "displacement increase" that he/she will be getting. I think that it's deceptive to "market" these kits this way. The whole reason that I bought this subject up is that I've sold/installed two of these kits now. One of the major factors when deciding between the two kits is the gain in displacement vs. the complexity of the job. The smaller of the two kits DOES NOT require that the cases be bored out larger to accept the cylinders. This would seem like a real plus IF you think your gaining nearly 70cc's with this so called 1050 kit. BUT, when you discover that your only gaining 36cc's it doesn't look so appealing does it! Now it seems like it's not worth the effort for such a small gain. The larger kit, while requiring MUCH more labor & machine work, seems like the only way to get a substantial gain on an XB9, but still you're NOT getting to 1200cc's like you might think. And, if marketing is the reason, then why do the displacement figures for the XB12 come so close to the "adversised" values? | ||
| Bigblock |
Cold here, way too cold for my riding tastes today, esp. without that nice 1 piece suit I was borrowing. Not all of us have heated gear ! I think I know what my tax return is going towards...(maybe a heated vest,too) It was a lot warmer yesterday than it is today. Cold in the morning, but downright riding weather yesterday afternoon! I hope to get the bike out of it's niche in the shop this upcoming week, and I may have a nice space in a garage just a couple blocks from home. And for a lot less than the parking garage was charging me! Love the pic in your profile Fritz! | ||
| Bigblock |
Sometimes that little bit of overbore can make a big difference in the way a motor runs. When I was racing bigblock chevys, we learned real quick that you bore a 396 .030 over to a 402, it makes it run like a whole new beast! They even list the cam grinds differently for a 402 as compared to a 396 these days, the 402 is usually reccomended to run the same grind as a 427, as compared to a 396. It's not like this for all motors, of course, so go figure. When you punch that "1200" out to "1250", though, I think that you are upgrading to an unlined aftermarket barrel, and perhaps this is part of the appeal? Might be worth a bit of power in reduced combustion chamber temps, possibly? Ray | ||
| Bigblock |
Hi Hammer, how's things? Been riding lately? Or are ya chompin' at the bit like me? I'm really looking forward to a nice view of something other than concrete, glass and brownstones! | ||
| Panic |
"you bore a 396 .030 over to a 402, it makes it run like a whole new beast" Why? Adds 1.5% to displacement, about 1/10 point to compression. Same as going from 984 to 999 - I'd be surprised if you noticed without being told. 1.5% is less than the average difference in cylinder pressure bwteen 2 cylinders. Easier math: bore^2 * stroke * 1.5708 = inches. Inches * 16.3871 = CC. | ||
| Diablobrian |
what looks like a small percentage in the displacement can have a larger overall affect on a motor. The bore:stroke ratio is a delicate balance that changes the character of a motor dramatically. The Japanese constantly play with this ratio on their il4s. To make the motor rev faster and build more high end power they go oversquare, the piston is larger than the stroke is long. For a torquey slower revving bike they go under-square, the piston is smaller and the stroke is longer. On paper the difference between a 350 small block and a 383 (350 with a 400 crank) is what 8%? These stroker motors are serious azz kicking small blocks. It can be easy to dismiss the effects of relatively small overbores on paper, but the dyno tells the tale. The other question to consider is whether the new pistons change the effective compression ratio? (Message edited by diablobrian on February 27, 2006) | ||
| Saintly |
Easier math: bore^2 * stroke * 1.5708 = inches. Inches * 16.3871 = CC. That's not easier math, it's the SAME math. My equation began with the simplest & most accepted formula for area of a cylinder: A = pi * r² * L(ength) so: D(isplacement)= [pi * (bore ÷ 2)² * stroke] * 2 so: D = 2pi * r² * L Your equation is a "derived" equation (derived from mine actually) you said: D = d² * L * (pi ÷ 2) where d is diameter/bore and your 1.5708 IS half of pi(3.14) so if you set them equal: d² * L * pi/2 = 2pi * r² * L first, cancel the L's: d² * pi/2 = 2pi * r² but d(iameter) = 2 * r(adius) so: (2r)² * pi/2 = 2pi * r² which becomes: 4r² * pi/2 = 2pi * r² or: 2 * 2r² * pi/2 = 2pi * r² so: 2r² * pi = 2pi * r² Finally: 2pi r² = 2pi r² Also you'll notice in my original post, that I DID say: " at 16.387 cubic centimeters per cubic inch " which is the same as you saying: "Inches * 16.3871 = CC." (Message edited by Saintly on February 28, 2006) | ||
| Bigblock |
What Diablo Brian said, plus, the timing lights at the dragstrip don't lie, either. | ||
| Mikexlr650 |
fritz, you keepin that 9R for this season? did you feel that the kits made a real change in the bikes overall power output (regardless of actual displacement change)? | ||
| Mikexlr650 |
bigblock, warm weather is very close now. did a fair bit of off roading this winter. snow can be a lot of fun on bikes, quads, & buggies. if you're lookin to save some pennies you can always store your bike in my barn (for free) for the coldest part of the year. | ||
| Bigblock |
Thanks Mike, but I have free cold weather storage here in Bklyn, my brother's shop. But, it is almost an hour away on the subway, so it's not a good place to keep it when riding... Winter quadriding or buggying sounds like fun... | ||
| Mikexlr650 |
the snow provides just enough traction for the odyssey to get up to speed. grab a handfull of rear brake cut the wheel and it's an ear to ear grin as you go totally out of control. never gets old! | ||
| Saintly |
fritz, you keepin that 9R for this season? Yes, unless it sells first. It'll have a 4-sale sign on it this season. I'll just ride it till someone waves cash my way. did you feel that the kits made a real change in the bikes overall power output (regardless of actual displacement change)? I sold a "1020" kit to a one guy who planned on installing it himself. I also sold & installed an "1168" kit to a fellow named Gary Linguisky who pulled his own engine from his "03" 9S. Gary also got headwork done, roller rockers, Force header & can, and a Power commander. I outsourced the bore job and he supplied the finished heads. I never got to ride it when he re-installed the engine, but you should hear him rave about it! Hard to tell what woke it up when you do all that stuff at once. | ||
| Panic |
"That's not easier math, it's the SAME math." 10 X as many steps to do the same thing = the same, not easier? And you used 10,000 words to explain multiplication? What do you do for a living, Federal employee? "To make the motor rev faster and build more high end power they go oversquare" Has nothing to do with it. "Rev faster" is a fuction of inertia, not stroke. Bore to stroke ratio was considered the pinnacle of design parameters... in 1920. You're mistaking similarity for causation. | ||
| Saintly |
"What do you do for a living, Federal employee? " That's actually quite funny! I was just pointing out that your equation and my equation were one and the same. I wasn't solving for actual displacement with those steps. You divided pi in half and then used diameter. I divided diameter in half and then used pi. It's all good though! And I suppose it is just a tad fewer words to say: "Inches * 16.3871 = CC." Rather than: "at 16.387 cubic centimeters per cubic inch" My bad, now I've got to get back to sorting all these letters. |
