277 degree rephase experience good or bad

[swbill]

I used the search and wasn't satisfied with all I found so I asked a simple question. At the time I was reading about rephasing, 4 or so years ago, it seemed like a fad or "craze".
If you'll re-read my first post you'll also see I asked for replys that actually have something to do with the question I posed. See Punkskalar and Mr. Riggs' replies for examples of what I was seeking.

Sporty to hell with those guys, if people didn't ask questions this would be a pretty boring forum. I to am considering all this work so the more conversation the better. I guess if all the knowledge is in the "search" button then Travis might as well lock the site and archive all the info lol.

 

[pregrid]

I used the search and wasn't satisfied with all I found so I asked a simple question. At the time I was reading about rephasing, 4 or so years ago, it seemed like a fad or "craze".
If you'll re-read my first post you'll also see I asked for replys that actually have something to do with the question I posed. See Punkskalar and Mr. Riggs' replies for examples of what I was seeking.

My apologies, sir. I, too have asked a lot of questions on this site and couldn't have gotten to where I'm at on my project without answers to those questions. I'm an idiot sometimes, and then again sometimes I'm an asshole.

 

[sportyrider]

apology accepted, we all have our days

 

[pregrid]

 

[Highside]

I own 2 bikes with a rephased engine, and have built 10 or so engines rephased. But, I'm gonna be a bit biased - might as well go ahead and get that our there

Vibrations are WAY less. You can now ride sustained higher RPM without having your legs, hands or ass fall asleep.

Torque is up - just a matter of physics.

What are the physics behind that? I can't think of anything.

HP - No telling, I've never dyno'd one...

If torque went up then HP should've gone up to, or am I missing something.

 

[sportyrider]

Inertia is reduced by having the pistons not moving up and down together. In theory, motion stops at top dead center and bottom dead center. Having the pistons offset means only one piston is at rest at those points. So, just as removing the fan belt from your car's AC makes move hp available to the rear tires, so does making the engine work less hard overcoming inertia make more power available to the bike's rear tire.

At least I think that is how physics comes into play.

 

[DirtyErnie]

Sporty's got it right. Check the www.xs650.com homepage, scroll down about half way. Keep scrolling past the punkins and hot girls, there's a real nice animation showing the motion and the force vectors.

 

[Highside]

^^^ I looked at the animation. read the article linked to it, and have yet to read an explanation that makes sense.

Here's why I'm not buying the "more torque" claim. Although the pistons are no longer moving together, you still have the same amount of mass going up and down. The power loss due to reciprocating mass is still the same, the only way to reduce it is to reduce the mass. Changing the phasing only changes when the power losses are occuring, not the total amount.
Re-phasing the power pulses has the same effect, you gain in one area and lose in another. The net result is no change.

Untill I see data and some more solid science behind this, I relegating this to a "paper napkin hypothesis".

 

[Rexxis]

I figured this out by doing mind experiments not by owning a rephase but when I asked it was confirmered by rephase owners.

Mind experiments FTW

 

[C-Los SD]

^^^ I looked at the animation. read the article linked to it, and have yet to read an explanation that makes sense.

Here's why I'm not buying the "more torque" claim. Although the pistons are no longer moving together, you still have the same amount of mass going up and down. The power loss due to reciprocating mass is still the same, the only way to reduce it is to reduce the mass. Changing the phasing only changes when the power losses are occuring, not the total amount.
Re-phasing the power pulses has the same effect, you gain in one area and lose in another. The net result is no change.

Untill I see data and some more solid science behind this, I relegating this to a "paper napkin hypothesis".

I don't know about the science involved, but I have one XS with a 750 big bore 17/32 gearing and 700cc rephased 17/32 gearing, both bikes have mikuni VM34 carbs. The rephased gets up to speed a lot faster then my 750. I'm still breaking the motor in, but I have been on CA freeway's going 85-90 mph easy with very little vibration. My butt tells me the rephased has a lot more torque.

Hugh, what's the max RPM for a rephased motor?

 

[Punkskalar]

I don't know about the science involved, but I have one XS with a 750 big bore 17/32 gearing and 700cc rephased 17/32 gearing, both bikes have mikuni VM34 carbs. The rephased gets up to speed a lot faster and the 750. I'm still breaking the motor in, but I have been on CA freeway's going 85-90 mph easy with very little vibration. My butt tells me the rephased has a lot more torque.

Hugh, what's the max RPM for a rephased motor?

I seem to spit out valves and break valve springs around 9500-10K RPM

I love the folks who say "I'm not buying it" when the proof is in the bikes themselves that have been rephased... If you wanna see dyno numbers and other High School kid mentality figures, then you might as well go get a different bike. The proof is in the science and physics, and also in the hands of the owners of numerous rephased bikes across the world

I've offered numerous times to build a bone stock rephased engine, have someone dyno their stock bike, swap in the engine, and dyno again (they get a free rephased engine!) and no one to date has taken me up on it. Now I'm just to busy building engines to mess with it, go figure

I'm building a BONE STOCK 80' Special II soon, with bone stock internals that will be rephased. Folks can come to any show I attend or come to the shop and ride it. If you aren't convinced at that point, I'll buy you a cookie

 

[Punkskalar]

If torque went up then HP should've gone up to, or am I missing something.

Of course. Like the old racer friend of mine says "HP Sells Parts, Torque Wins Races"

 

[BoBDoG]

Got on this forum cus i just bought a 650 to do a cafe project on. The rephase sounded really cool. I have a weak attempt at the torque issue, here goes and PLEASE DON'T FLAME ME!!!

Here is the formula used for determining torque on engines.

T = HP x 5252
----------
rpm

That 5252 number means a lot. it explains why dump trucks, etc(diesels mainly) make more Ft/Lb than gas engines, because they don't rev past umm maybe 2500 or 3000 rpm before they don't squirt out more power. if the peak hp comes before 5252rpm then it will make more torque.

I think part of the torque question was really found with a previous post. And that would be that the red line is now at 9,500 to 10,000(I know thats a joke). The change in inertia movement may have made it easier for the crank to turn faster while staying balanced.

Just my two cents.

 

[CoastsideXS650]

I'm an idiot sometimes, and then again sometimes I'm an asshole.

I have this same problem. Usually more of the latter than the former.

 

[CoastsideXS650]

I found this information on this site here. http://www.vettenet.org/torquehp.html

"First of all, from a driver's perspective, torque, to use the vernacular, RULES . Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*."

 

[bobadame]

Just a guess, I'm not a scientist. If the entire bike shakes less with a re-phased engine then less energy is wasted. Takes a lot of power to make an entire motorcycle shake as much as these do.

 

[mrriggs]

Torque is a measure of work, horsepower is a measure of work over time. More horsepower means you can do more work or do it more quickly.

The torque of the engine is actually pretty meaningless since you can make the torque at the wheels whatever you want with gearing. The horsepower is going to stay the same regardless of gearing (ignoring losses from friction).

For example, you can take a weed whacker motor that makes 1/2 hp @ 10,000 rpm and make 200 ft-lbs at the wheel by running it through a 762:1 gear reduction. Compare that to a motorcycle engine that makes 50 hp @ 7,000 run through a 5.3:1 gear reduction. Both will put about 200 ft-lbs at the wheel, both will do the same amount of work, but the motorcycle engine will do it much faster.

A re-phased motor is not any more balanced than a stock motor. It is a parallel twin with no balance shaft which means that it is impossible to truly balance it. All you can do is move things around to change the way it vibrates. The vibration of the re-phase is less intense than the stock configuration but it vibrates at twice the frequency. Plus, in addition to the normal up-down and front-back vibration, you now have a side-to-side vibration since the two halves of the motor no longer mirror each other. To some people this is an improvement to the stock design. I personally prefer the throb of the stock vibe to the buzz the re-phase produces.

 

[LilMoney]

I think what's amazing is that we've got one of the least expensive motorcycles out there, but it still aint cheap to rebuild an engine.

Posted via Mobile

Compared to the modern BMW engines I work on, Thats pocket change !!!!!!

 

[BoBDoG]

I found this information on this site here. http://www.vettenet.org/torquehp.html

"First of all, from a driver's perspective, torque, to use the vernacular, RULES . Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*."

Thanks for the great reply without any flames....

I love this forum allready.

 

[AussieHard]

I'd just like to say this site has a wealth of knowledge and debate is always good.

As to earlier comments as to use the search function, well if you do you get complaints for necroposting (posting to old threads)………So don't really matter if you ask new or ask on the old someone well be a party pooper!

Overall the majority will helpful either way!