Rephrase?

[chizler62]

I have no experience, other than hearing one, with a XS650 rephased motor. I have seen some pretty healthy claims of power gains that are out in left field. Although, its clear the XS650 community has "vendors" that are fabrictors in the shop and fabrictors in the story telling department. Ive seen claims that'd impress Walt Disney himself on some of their item descriptions. My experience with motors over the years smells marketing and not true performance.

Question is. Does anyone have dyno sheets? Can anyone back these outrageous claims of power gains?

IMO the XS650 was designed with a "vibration" intended. Part of the charm. I can see how the a rephased motor would reduce that if thats your desired intent. But I can not see any actual horsepower gain for the time and money.

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[member3480]

I can only add that I have had two bikes REPHRASED in my shop and I have rode and built many XS650 and there is a difference in vibration at 65 mph on a rephrased motor . Bike feels much better and the sound is a little different. I don't think I read that there is a gain in horsepower . Motors like TRIUMPH BSA NORTON were built like they were and had much vibration and the early YAMAHA-HONDA may have tried to copy that style. Early 450 Hondas have that vibration. I build a lot of race motors and you would have to do more to that crank to get a higher HP gain.
Me I like the vibration it has style and I don't use my XS650 as my 4 hour touring bike . I just like to boop around local with it. If it was my only bike maybe I would do it.

 

[jay760]

I have asked this question several times, there are several threads that cover this, depending on who gives the answers and what you read into this is the only answer you'll get, there seems to be no Dyno sheets with comparable engines,
Last time I asked I was told there would be no power gain in a rephased engine, yet in other threads it says the motor will rev much higher and quicker than a standard engine, how it can do this with no power gain I don't know.

http://www.xs650.com/forum/showthread.php?t=103&page=8
http://www.xs650.com/forum/showthread.php?t=37000&page=3
http://www.xs650.com/forum/showthread.php?t=39214

Here are a couple of threads which briefly go into it, the last one is somebody who didn't get the power expected, coupe of links on that one to times and videos of my 360 engined bike

 

[vsop-dk]

My Rephased 277 is much different than the stock xs650 i rode many years back. The Rephased 277 is much more quiet with minimal to no vibrations at all. The torque is great and in short time, ill have it dynoed and ill get back with a report.

Comparison to my old xs650 is that the older one had 16" rear Wheel and extended forks and 19" front and it were extremely quick in startup.. The Rephased one is quick all way through and it seems the speed doesnt stop, whereas the older one had a speed limit at around 140km/h it were a chopper and legs were beeing stretched

 

[650performance]

When the Yamaha factory was involved in fielding a flat track team in the '70s every combination of the XS engine was experimented with. Mostly this was done in an attempt to replicate the H-D XR750's corner exit traction advantage. There were "twingles", 277, 270 and probably other configurations tried. Ultimately, both the "standard" XS engines that were modified for racing and the final OU iteration were left as-is with welded and trued stock cranks with added weight.
If a rephase offered any more power you can bet it would have been used on race day, especially for the mile tracks. But, it never was. Considering how much effort and money Yamaha put into building the best possible bikes for Kenny Roberts I think it is fair to conclude that whatever advantage(s) a rephase offers, more power isn't one of them. You only get two power pulses in 720 degrees. Apparently, the Yamaha engineers determined it doesn't make any difference where they occur.

 

[member3480]

I owned a Honda Dealership back then and I remember a factory flyer with something about Yamaha changing there crank and got involved with a law problems from Triumph with motors. Honda did some crazy things back then too with there 305 café racer. We ended up owning one and crank and trans were different from stock. One of a kind crank with a 6 speed trans. I sold the bike to a collector in CAL in 2001. Bike was sitting in the warehouse from early 80's and the only people knew we had it was Honda big wigs. We also got two 1969 CB750 300 number bikes that were part of the first 100 off assembly line. Both are still sitting I THINK! in my partners x-wifes garage.
She put up the money for the dealership and he gave them to her. Boy both of those are worth some money. But there was a lot of wheeling dealing back then to be the best at the track.

 

[chizler62]

I have asked this question several times, there are several threads that cover this, depending on who gives the answers and what you read into this is the only answer you'll get, there seems to be no Dyno sheets with comparable engines,
Last time I asked I was told there would be no power gain in a rephased engine, yet in other threads it says the motor will rev much higher and quicker than a standard engine, how it can do this with no power gain I don't know.

http://www.xs650.com/forum/showthread.php?t=103&page=8
http://www.xs650.com/forum/showthread.php?t=37000&page=3
http://www.xs650.com/forum/showthread.php?t=39214

Here are a couple of threads which briefly go into it, the last one is somebody who didn't get the power expected, coupe of links on that one to times and videos of my 360 engined bike

I've read some of those, thanks, and that's what got me thinking about this after a kid in the shop asked for help to do it. "huge power gains for the price of a gasket set"

To meet the claims of the rephrased power gain of 20-30mph over stock I believe you'd need 80hp at the rear wheel, IMO. Ported, big bore even that's a fairy tale for a streetable XS650.
With the money spent I expected to see some outrage on the forums, but I don't see it. So, I was curious if perhaps on this the was some truth.

Basically, correct me if I'm assuming wrong.........

Several hungy to (found results) and hours of labor.
Smooth out the vibration. (turning it inward putting more load on bearings)
Rev freer. (moving power curve forward but not changing it)
and any other bennies?

 

[650Skull]

When the Yamaha factory was involved in fielding a flat track team in the '70s every combination of the XS engine was experimented with. Mostly this was done in an attempt to replicate the H-D XR750's corner exit traction advantage. There were "twingles", 277, 270 and probably other configurations tried. Ultimately, both the "standard" XS engines that were modified for racing and the final OU iteration were left as-is with welded and trued stock cranks with added weight.
If a rephase offered any more power you can bet it would have been used on race day, especially for the mile tracks. But, it never was. Considering how much effort and money Yamaha put into building the best possible bikes for Kenny Roberts I think it is fair to conclude that whatever advantage(s) a rephase offers, more power isn't one of them. You only get two power pulses in 720 degrees. Apparently, the Yamaha engineers determined it doesn't make any difference where they occur.

Considering there is some toque loss with a 277, the 180 crank would be more suited to a mile oval.

 

[mrriggs]

The trouble with an A-B comparison is that guys typically don't do just a re-phase. At the very least it will get the valves lapped and a fresh set of rings.

To see what effect the re-phase alone has you would need to rebuild the engine with a 360° crank, dyno test it, then tear it down again, re-phase it, put it all back together with the same parts and dyno test it again.

I have a dyno and the means to re-phase the crank and cam. If anyone in the Portland area has a freshly rebuilt 360° that they want to re-phase then we can dyno test it, you can tear it down and bring me the crank and cam. I'll re-phase them and you can put it all back together for another run on the dyno.

 

[650performance]

Mrriggs is correct. It would have to be a direct comparison with as few variables as possible, e.g. same jetting, same total ignition lead, same temperature/humidity, etc. for the data to be of value.
One concern I have is that the cam rephasing has to be dead nuts accurate ... within a degree. That's not a simple task, even for MegaCycle.
I'm not qualified to make a theoretical argument one way or the other, but the answer to these rephasing questions is "out there" in motorcycle engineering land. It's not just Yamaha and Honda who have done this sort of thing (Virago and RS750 flat track bikes) ... the HD factory race team has also fooled around with different cranks with the XR750s. The knowledge exists but only within a very small and select group of engineers.
Where are they and why aren't they participating on this forum?
We can only conclude that these individuals are not sufficiently knowledgeable and sophisticated to be drawn to participate in our learned discussions, hence we don't have the benefit of their input (where's the sarcasm font?).
My guesstimate: If mrriggs finds a donor bike it will be shown to have the same (or less) power and the torque curve will vary very little, if at all. However, as everyone already knows, the sound the "feel" of the engine will be noticeably different.

 

[650Skull]

Every one is obsessed with this power gain and spending 100's if not thouisands to get it.

When Pamco pete done his exercise on MPG and the variations on Coils and spark-plugs, he went from something like 57mpg to over 69mpg going the same route, same speeds, and i think the same time of day to keep each trip as close to each-other as possible.

If he had done each trip to keep the bike mpg at the same as the the original trip then he would have had a steady upward graph showing a power gain and shaved off a lot of time from the first, progressively to last trip.

This is just from a few dollars changing coils and plugs and 1/2 size up on the main.

Cheap power gain. http://www.yamahaxs650.com/test_results.htm

 

[member3480]

I think everyone understands that you can increase power (Horsepower) by doing a bunch of different things. The original question was or is does a REPHASED motor have more HP than a stock bike or is it just intended to take away the vibration.
I agree with MR RIGGS you would have to use the same parts on the same bike to be 100% sure on power. I have DYNOED many of the race bike I built and even though SAME PARTS SAME BORE SAME EVERYTHING the DYNO number are never the same. They a close but not the same and I would never expect them too. You could get close numbers with two different bikes and if there was a 20 to 30% increase in HP on the rephrased motor I would say YES there is a increase in HP.5% is more HP. I would be more worried about CRANK TRANSMISSION CLUTCH BASKET if you did get some real horsepower out of one of these motors. Want horsepower put a bottle on it and hope it stays together.

 

[FLEA]

out of curiosty,has any ever checked engine temps between stock and rephased

 

[hooser]

Question is. Does anyone have dyno sheets? Can anyone back these outrageous claims of power gains?
So is the answers no?

but on another line a guy in a Calgary Alberta Canada needs some basic head work..guides, valves, he is willing to send it to me and I don't like turning work down but if there is shop up there I could point him too to save a lot of shipping fees.. Thanks Gary

 

[Jack]

This debate of whether Repahsing produces more power has been going on for years and the only conclusion that's come of it is it makes for a good conversation. Repahsing doesn't change the volumetric efficiency of the engine,it changes the inner drag and cycling positioning of one piston that assist the other piston through it's upward and downward stroking reducing power and torque demands that would of other wise been absorbed with the 360 firing order. It simply changes the power and torque distribution as long rods do.

 

[hooser]

Jack or anyone what about and good service up in the Canada

 

[Jack]

Jack or anyone what about and good service up in the Canada

There use to be a guy in Canada that ported but it's been years ago,don't recall his name. Gary ,you're about the only game in town porting the XS head. There's Schumann Motor Work's,don't know much about him,looks like he's ported a few, Chris is closer to the Canadian border.

 

[650performance]

In addition to Gary there are ...
California: Check out enginedynamics.com in Petaluma, CA. They have lots of experience and a proven track record. They've ported the heads on successful XS-based race bikes among many others. They have a national reputation for getting power out of large Honda, Yam, etc. singles.
Connecticut: And, you can get a "port only" Harry Lillie CNC head from Michael Morse at 650central.com that works very well on both hot street engines and 70+ RWHP race engines.
I've heard of others, some of which may be good, but these are the only ones I have personal knowledge of that perform as claimed.

 

[hooser]

Thanks but just need a good shop to install valve guides and cut seats.

 

[jay760]

I've just run 12.31 at 104mph on a standard crank, 750cc with JE pistons, unknown cam and ported head, this was with a strong head wind, another guy there who holds the record in his class at 11.65 put in the same time as me on the day due to the wind, biggest thing against me is my weight at over 200lbs.