| Author | Message | ||
     Rocketman |
So there's 45 degrees between tdc's? That makes sense. So correct me if I'm wrong but the cylinders are not at 45 deg angle to one another. Rocket | ||
| Blake |
yer silly common crank pin? | ||
| Vonsliek |
by golly bahy! (think eastcoat accent - newfie (ca) & islands off north carolina (usa)) anyhoo .. so, is it 45 deg b/w cyls .. b/w tdc or, b/w timing .. & is any of this same old thing??!! now i know why italian bikes run higher & faster .. 90 deg & - is it - 72 deg?! not to mention austrian KTM ..? deg. matt .. i WILL look into yr comp. wiseco piston setup .. 103 rwhp at 410 #'s = better than our regs 3.8:1 ratio & maybe - just maybe - the ocal HD/buell dealer will front me wome parts for all the $$$$$$$ i spent there?! ;P | ||
| Ceejay |
yep 45 degrees between TDC, which also means they fire at 45 degrees crank rotation, which also means regardless of how far away you measure from the crank they will always be at 45 degrees from one another...also meaning if you want a 60 72 or 90 you might as well go buy one because despite how much money you throw at it, a 45 will never act like a 60, 72, or 90....meaning they can get more revs, but never the same tq...design limitations too much power going in opposite directions | ||
| M1combat |
Torque is all about Stroke and revs... You can make an HD engine a 50 or so degree engine by milling deck planes... You would do this to get more room for the intake manifold... | ||
| Ceejay |
True but while I'm not and engineer, Ima thinking that as soon as you start going longer stroke and further away from a 45 degree piston travel, problems start to arise. I know S&S has that mongo 60 degree but that seems to be tops for a V, L,-twin, in regards to stroke. | ||
| Neb25 |
What are the benefits of lightening the flywheel/crank on a track? Could someone who rides an xb who has had this done describe the difference in how their bike behaves on the track. I am having some work done on my 06 xbr this winter and am wondering if I should have this done. What about knife edging? Thanks | ||
| Hobanbrothers |
Joel, There are a couple of benefits and some get pretty deep in theory, but I will keep it short and sweet: 1) by lightening the flywheel assembly you can get them to spin up faster, getting a jump out of the corners. 2) it also reduces the gyroscopic event and allows you to transition better through tight and twisty corners. There are a couple of things that can be mis-managed when this is done also. We will taylor a flywheel to a given track, Daytona is a track almost on its own aside from maybe Road America for flywheels. Balance factors will come into play depending on RPM ranges. We will typically knife edge XB flywheels where HD Twin cams get a different process done because of crank position sensor. Too light and the harmonics become hazardess to other parts, especially primary components. It will also not give you enertia to complete drafting passes. Hope this helps you in your decision. | ||
| Neb25 |
Hoban, "Too light and the harmonics become hazardess to other parts, especially primary components. It will also not give you enertia to complete drafting passes." Does that mean that by lightening the flywheel assembly that I am decreasing the durability of the motor and drivetrain? Is that why it doesn't come from the factory with a lighter flywheel? Do you do this to your race bikes? Will a heavy flywheel offer more initial traction at corner exit because of the cushioned acceleration? What determines how light to go? | ||
| Hobanbrothers |
If you go too light it beats up other parts because the wheels do not absorb the engine pulses. There is always a fine line, we step over every so often just to see the other side and yes we do to ours and many other race bikes, have for about 10 years now in roadracing applications. I do not believe you are looking at traction issue quite right, I would phrase it like "you do not need as much traction with heavier flywheel because you do not get as much of a hit" and in our racing I would say you need as much hit and go and then get the traction to accomadate it. That can be as simple as the riders right hand, the old fashioned traction control! We had a rider a few years back that would just whack it to full throttle coming out of the corner, there was no in between-no moderation. His wheels needed to be a bit different or he would spit himself off on a regular occassion. Each application determines how light we go, that being motor configuration, what tracks you race, what your level is and how you plan to ride it and how long of service intervals you plan to go. Hope this helps you out? I am sorry, it would be next to impossible to recommend a specific set up without talking to you at some length. | ||
| Blake |
"It will also not give you enertia to complete drafting passes." Very interesting. | ||
| Davo |
Actually the factory firing order is not 45 out. The correct number of crank degrees between fire is 315 and then 405 etc unless you do some serious modifications. It will appear to be 45 out if you put a light on the flywheel. | ||
| M1combat |
""It will also not give you enertia to complete drafting passes." Very interesting." Heavier flywheels tend to produce higher peak HP and a slightly broader upper RPM power curve. I'm pretty sure it has to do with having more inertia useable to compress the charge. That said... It also takes more to spin the wheel so I really don't know exactly where the extra power comes from, but I've heard it's there  . | ||
| Diablobrian |
It has a lot to do with how we measure HP and torque. We measure them by Accelerating a drum of a specific weight. So inertia of the drum and inertia in the crank and drive line have to play a part in the results, however, driveline inertia is not taken into account during dyno testing. I'm not sure what sort of mass compensation could be done to account for it other than instituting another formula on the output using the ratio of drum mass:drive line mass and even possibly crank stroke because of the difference in flywheel effect between a larger and smaller diameter crank. Primary drive ratio, transmission ratio and final drive ratios could also have an effect. Maybe the reason it isn't taken into account is the level of complexity of calculations would be much greater. How many owners know what their crank weighs? what their primary ratio is? what the various gear ratios are? final could be counted on the spot. At best dyno numbers should be taken as approximate numbers (except the rpms  ) but people tend to read WAY too much into the numbers and not enough into the shape of the curves and locations of the peaks. Of course I could be wrong | ||
| Jimidan |
If you take a look at the XBRR flywheel, these engines can run successfully with a much lighter flywheel. I wonder how much it weighs? jimidan | ||
| M1combat |
Ummm... I'm thinking there's probably some significant difference in the engine cases Jimmy. | ||
| Jimidan |
True, there are some differences in the engine cases, but what do these changes have to do with what the flywheel weighs? It was my understanding that the cases were expanded to have more deck height (more room for those intake manifolds) and wider stud spacing for bigger bores. How would that affect the primary and secondary imbalances, absorbing the power pulses, etc. jimidan | ||
| M1combat |
Different engineering goals would be the best way I can put it. You can make small "visual" changes that have huge impacts on what the structure can and can't do. That said... I'm pretty sure the XBRR cases are "significantly" different. | ||
| Jimidan |
M1combat, So what you are saying is that you don't know? I mean it is OK not to know something...there are plenty of things I don't know. The question is not whether the cases are "significantly" different (that is acknowledged), but rather what effect that these differences have on flywheel weight? If you will harken back to Hobanbrothers statement: "If you go too light it beats up other parts because the wheels do not absorb the engine pulses. There is always a fine line,..." and then at mine, "If you take a look at the XBRR flywheel, these engines can run successfully with a much lighter flywheel. I wonder how much it weighs?". What does the acknowledged differences in the cases have anything significant to do with this? | ||
| Glitch |
This one looks pretty light.  | ||
| M1combat |
Well that's pretty much what I was saying . I don't know "what" the differences are, but given the fact that they seem to survive with significantly lighter flywheels at significantly higher HP and RPM levels I think we can assume that the changes are such that they allow lighter flywheels . The effect these changes have on flywheel mass? None . That's all in the design of the flywheel . | ||
| Davo |
Glitch, Do you know what that flywheel weighs? Pretty cool rods as well. I wonder how that flywheel will do if the sump gets loaded up with oil? I assume its a drag racing crank? (Message edited by davo on January 17, 2007) | ||
| Jimidan |
Isn't that the XBRR flywheel assembly? jimidan | ||
| Glitch |
Isn't that the XBRR flywheel assembly? Yep. Here's the crank case. Thought these might help, being able to see what's being talked about.  | ||
| Jimidan |
Hmmm, you can't even see the line where the cases split...I know they have to. Why doesn't Buell use those cases on all of its machines? | ||
| Glitch |
M1, did you get my e-mail reply? | ||
| Crusty |
Hmmm, you can't even see the line where the cases split...I know they have to. Why doesn't Buell use those cases on all of its machines? Give them time, they will! | ||
| M1combat |
Yes Glitch . Thank you. | ||
| Panic |
"These cranks will only save you 3lbs over the stock item though, as their main advantage is about saving reciprocating mass rather than just dead weight." I'm confused. $950.00 to remove 3 lbs.? That's about 1 hour of shop time - and if the lathe operator knows what a flywheel is rebalance shoudn't be necessary. Where did the other $875.00 go? What part of the crank is reciprocating mass? | ||
| Panic |
"a 45 will never act like a 60, 72, or 90....meaning they can get more revs, but never the same tq...design limitations too much power going in opposite directions" The V angle has no effect on either RPM or torque. |
