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I want to Love this Powertrain

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Re: I want to Love this Powertrain

PostAuthor: faffi » Wed Feb 15, 2017 5:05 am

That sounds like an overly complex solution when you can buy a Kawa 650 cruiser, for instance, that has much more power and revs over the Yamaha 950 :r:
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Re: I want to Love this Powertrain

PostAuthor: CX Rancher » Wed Feb 15, 2017 8:25 pm

faffi wrote:That sounds like an overly complex solution when you can buy a Kawa 650 cruiser, for instance, that has much more power and revs over the Yamaha 950 :r:


:yup: but the Kawa is NOT an AirCooled V-Twinn :r:V :r:
G'Luk !
---Rancher


B Good! GearUP! TwistOn! GearTall RideSmall
Homage to Those We Follow - Rest In Peace Ride At Peace
but Race the Urn, Man

(Corrections to my Speeds and Mileage posted before 5/2014 (-10% above 50mph) and (-1.8%mpg) Your Stock Speedo Variation may vary) Corrected by MoDot and TrailTech on Utah Tour. Truth in Posting Law
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1982 GL500i
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1983 GL650 Std
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Re: I want to Love this Powertrain

PostAuthor: faffi » Thu Feb 16, 2017 5:15 am

But why would you want more rpm? Destroking will result in less volume, meaning less power, especially low-end. And 4 valves actually makes more sense at low rpm than at very high rpm, believe it or not. However, the 950 has a very mild cam and you can get plenty more revs with more lift and a little more duration. And new cams will be far cheaper than designing your own crank and conrods :bg:
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Re: I want to Love this Powertrain

PostAuthor: CX Rancher » Fri Feb 17, 2017 3:12 am

just a mid winter ponderance.
I've always looked at four valve design as a high rpm expense and this twin has a pretty long stroke.

...well having just said that, I suppose the four valve could be better related to piston speed..
hmm its a neato air cooled engine no matter whats inside.

That does it. I have to ride one.
I can engineer a breakfast but that's about it.....
G'Luk !
---Rancher


B Good! GearUP! TwistOn! GearTall RideSmall
Homage to Those We Follow - Rest In Peace Ride At Peace
but Race the Urn, Man

(Corrections to my Speeds and Mileage posted before 5/2014 (-10% above 50mph) and (-1.8%mpg) Your Stock Speedo Variation may vary) Corrected by MoDot and TrailTech on Utah Tour. Truth in Posting Law
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CX Rancher
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Posts: 1116
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Joined: Sat Aug 04, 2012 9:05 am
Location: Ohio, some say Ohiya Flag
Bike year & model: 2006 XV250V 17/41
1978 CX500 - Luv a Maggot with a Twist
1982 GL500i
1982 CX500T
1982 CX500T show winner
1983 CX650C bad-axx
1983 GL650i
1983 GL650 Std
1983 CX650T
1976 GL1000 Old Skins in New Bones(sold)
The only Cure for Obsession is another.
OR a Divorce, que sera sera
Sex: Male

Re: I want to Love this Powertrain

PostAuthor: faffi » Fri Feb 17, 2017 6:39 pm

Yeah, riding would be best.

4 valves are better for high rpm because they are lighter and can be more easily controlled before valve float occur. But for maximum flow, there isn't much difference between two and 4 valves. The biggest difference is when valve openings are small - at the beginning and the end of the open fazes. Then total circumference matter a lot, and 4 smaller valves have more than two larger ones. But at max lift, the area between the two systems are close to identical.

Another benefit with lighter valves is that you can open and close them more rapidly. So you can get pretty big lift and quite long openings with high lift, whereas a two-valve system with heavier poppets will need more ramp time (slower opening and closing) for sufficient lift for high rpm power. This again gives you more overlap, which is good for high rpm power and death for low- to midrange power.

Back in 1983, the Kawasaki GPz750 could keep up with the V45 Interceptor and GSX750E in max power, but it had lost the grunt it had before when it had 10% less max power. So roll-on was slower by quite a bit after it had been tuned, and for the majority of the time for the majority of riders, the GPz was slower than the standard KZ. As well as compared to the Honda V4 and Suzuki inline four, both with 4 valve heads.

Simply put, a two-valve head can be made to perform equal to a 4-valve head at low rpm, but then the 4-valve would make more top-end power. Or it could be made - up to where valve float would become an issue - make similar top end power to a 4-valve head, but then it would not match the low-end power of the latter. Provided, of course, that both types are of equally good designs. Yamaha managed to equal the top end power of the CB900F with their XJ900 and actually produce more bottom and midrange due to a more modern design than the ancient Honda four-valver, as one example.
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