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Old July 16th, 2017, 10:57 AM   #1
Ram Jet
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Top Speed

2007 250 Ninja. Yoshimura slip-ons, stock air box, 110 mainjets, 15/42 gearing. 90 M.P.H. in 6th, 95 M.P.H. in 5th. Does this sound like my bike's running OK?

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Old July 16th, 2017, 11:20 AM   #2
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To save me the calculation, what RPM was it doing at 95 in 5th?
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Old July 16th, 2017, 11:46 AM   #3
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Sounds like overall gearing may be too tall.

110 Mains are pretty big for the stock airbox.

Are you shifting at redline in all gears?
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Old July 16th, 2017, 11:46 AM   #4
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Rider weight will also be a factor.
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Old July 16th, 2017, 11:55 AM   #5
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Weight makes a difference in accelerating time to top-speed. But top-speed itself isn't affected by weight. That's purely a function of cross-sectional area blocking and power required to bore a certain sized tunnel through that air. Cx*Cd, etc...

You'll find removing mirrors, hunched over with chin on tank, arms and hands pulled in with just pinkie-finger exposed to pin throttle will give you a couple more MPH.

I see 98mph at end of front-straight of Thunderhill on my calibrated Vapor dash. Sometimes I can break 100 if I catch a tow, but then I'm over redline for those last couple seconds.
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Old July 16th, 2017, 11:56 AM   #6
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I'm about 220 lbs with gear, and in sixth gear I top out at about same 90~95, just short of doing the ton.

My gearing is +1/-2
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Old July 16th, 2017, 12:26 PM   #7
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Originally Posted by jkv45 View Post
Sounds like overall gearing may be too tall.
I'm not sure why you said that. Maybe you mean too tall for top speed to occur in 6th gear?
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Old July 16th, 2017, 01:29 PM   #8
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Sounds like overall gearing may be too tall.

110 Mains are pretty big for the stock airbox.

Are you shifting at redline in all gears?
I was shifting at 12K. Should I try 14K? I don't feel much power above 12K. To tell the truth I was "white knuckled" at 95 and was only looking at the speedometer which stopped moving at 95 in 5th.

My bike came with 105 mains and was too lean with the O.E.M. mufflers. I was going to increase the main jet size even before I installed the Yoshimura glass packs.

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Old July 16th, 2017, 02:07 PM   #9
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I'm not sure why you said that. Maybe you mean too tall for top speed to occur in 6th gear?
Ya - that's what I mean.
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Old July 16th, 2017, 02:41 PM   #10
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I have my H2 geared like that too. I love the low RPM and low vibration at highway speed, but I'm sure top speed is in 4th now.
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Old July 16th, 2017, 03:35 PM   #11
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I have my H2 geared like that too. I love the low RPM and low vibration at highway speed, but I'm sure top speed is in 4th now.
Maybe not. I only hit 85 M.P.H. today in 4th before it stopped pulling. With the 15/42 gearing, 6th gear essentially becomes and overdrive. I too love the gearing. It feels like you're riding a 750 at highway speed and everything is far more composed and less frantic. I would not change it for all the tea in China.

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Old July 16th, 2017, 03:56 PM   #12
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Ours (6 in the family) all seem to be a touch rich on the mains and a bit lean on the needle with stock air boxes and exhaust, one has stock air box and full Muzzy and is the same. We're at 1300', so maybe that has something to do with it. I've played with valve clearance to adjust the top end power, in the middle of the lash specs mine have more midrange but have a hard time pulling past 12 or 12.5k, but when snugged down to the tight end of specs will pull happily to the rev limiter.
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Old July 16th, 2017, 04:08 PM   #13
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Maybe not. I only hit 85 M.P.H. today in 4th before it stopped pulling.
My 1972 H2, not my Ninja 250. I was saying I'm sure top speed occurs in 4th, where 5th is highest on that transmission.
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Old July 16th, 2017, 04:23 PM   #14
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Ours (6 in the family) all seem to be a touch rich on the mains and a bit lean on the needle with stock air boxes and exhaust, one has stock air box and full Muzzy and is the same. We're at 1300', so maybe that has something to do with it. I've played with valve clearance to adjust the top end power, in the middle of the lash specs mine have more midrange but have a hard time pulling past 12 or 12.5k, but when snugged down to the tight end of specs will pull happily to the rev limiter.
Well, this is an educational point of light for me. I never thought variations in valve clearances would affect power output. Thinking about it I guess tighter valve clearances may have the same effect as advancing the cam timing. Interesting to be sure! My valve lash is set dead in the middle of the adjustment range and that may be why I'm so happy with my bike's midrange torque.

Thank you. See, I'm not too old to learn.

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Old July 16th, 2017, 06:11 PM   #15
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Thinking about it I guess tighter valve clearances may have the same effect as advancing the cam timing.
More likely it's the extra degree or two of duration that picks the top end up and hurts low and midrange.

And it gets a teeny, tiny bit more lift.
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Old July 16th, 2017, 08:24 PM   #16
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More likely it's the extra degree or two of duration that picks the top end up and hurts low and midrange.

And it gets a teeny, tiny bit more lift.
Yes, duration also. I thought of that after my last post. And lift, I didn't think of that.

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Old July 16th, 2017, 11:40 PM   #17
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Same effect as more duration. Timing remains the same as lobe-center doesn't change.

Or if you're taking about increasing overlap with the same cams, you'd retard the exhaust and advance the intake cam.
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Old July 17th, 2017, 12:05 AM   #18
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Same effect as more duration. Timing remains the same as lobe-center doesn't change.

Or if you're taking about increasing overlap with the same cams, you'd retard the exhaust and advance the intake cam.
Jac Cammeister Ryann you're right again duration not timing. The toe of the cam is passing the rocker at exactly the same time regardless of valve lash setting. Can you imagine designing the profile of a camshaft AND setting-up the machinery to grind it accurately. My God given brain is too small. I'll settle for adjusting valve clearances.

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Old July 17th, 2017, 06:24 AM   #19
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Bill, I had an automotive machine shop grind my boat's reverse rotation engine's cam for more lift and duration. It was cheaper than buying a new reverse rotation cam. The small block Chevys have different rocker arm ratios, so they have more lift at the cam than the Ford 289 in my boat. So the shop ground my 289's cam to Chevy specs. I plotted the profile before and after, and it was like the lobes grew taller and wider. The funny part is how you grind a cam so the lobes get taller.
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Old July 17th, 2017, 06:37 AM   #20
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Bill, I had an automotive machine shop grind my boat's reverse rotation engine's cam for more lift and duration. It was cheaper than buying a new reverse rotation cam. The small block Chevys have different rocker arm ratios, so they have more lift at the cam than the Ford 289 in my boat. So the shop ground my 289's cam to Chevy specs. I plotted the profile before and after, and it was like the lobes grew taller and wider. The funny part is how you grind a cam so the lobes get taller.
Could they grind down the heel of the cam so when you adjust your valve lash at the heel of the cam the toe height staying the same (+ or -) the rocker sees that as additional travel from heel to toe and that would increase lift at the valve? Ouch, that hurt.

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Old July 17th, 2017, 06:45 AM   #21
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Exactly, lower the base circle and the lobe gets taller. It just sounds funny when you talk about grinding more lift into a cam.
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Old July 17th, 2017, 06:52 AM   #22
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Maybe not. I only hit 85 M.P.H. today in 4th before it stopped pulling. With the 15/42 gearing, 6th gear essentially becomes and overdrive. I too love the gearing. It feels like you're riding a 750 at highway speed and everything is far more composed and less frantic. I would not change it for all the tea in China.

Bill
It certainly does help calm it down on the highway, but has made the top gear too tall to pull to redline for max speed - a fair trade for a street bike. I have geared my SV up for the same reason.

You would gear it differently if it were a race bike and you needed top speed.

By saying the overall gearing was too tall I was just pointing out the reason for the higher speed in 5th than 6th.
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Old July 17th, 2017, 07:03 AM   #23
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Exactly, lower the base circle and the lobe gets taller. It just sounds funny when you talk about grinding more lift into a cam.
I really never heard of "grinding more lift" on a cam. I would have thought they would start with an unprofiled bilit and start from scratch. I never knew they could do that. I KNOW I don't have the brains set-up the equipment to do it.

Boy, I'm grateful for this blog. I learned about valve clearance and duration and know about making a silk purse out of a sow's ear.

Bill
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Old July 17th, 2017, 07:13 AM   #24
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I could have had them start with a cam blank, but the non-standard marine cam for reverse engine rotation runs the price way up. Since I already had a running cam, modifying it was cheap. It was the mid '80s and it was $60 to do the cam and $50 to grind the crank 0.010" under. Even if you account for inflation, that's still pretty economical.
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Old July 17th, 2017, 09:29 AM   #25
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Wow... wish I could get cams ground for that price!

Depending upon the drivetrain layout, you'd insert a shim of same thickness as reduction in base-circle. This would prevent your hydraulic lifters or rocker adjusters from running out of range. Extra lift comes from thickness of this shim + original cam-lobe height.
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Old July 17th, 2017, 09:44 AM   #26
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Wow... wish I could get cams ground for that price!

Depending upon the drivetrain layout, you'd insert a shim of same thickness as reduction in base-circle. This would prevent your hydraulic lifters or rocker adjusters from running out of range. Extra lift comes from thickness of this shim + original cam-lobe height.
With the small block Ford, the small reduction of base circle was not enough to make much difference to the pushrod and rocker arm geometry. I can't remember... I may have bought a set of slightly longer pushrods when I replaced the old ones.

$60 in 1985 when I had the V8 cam ground is about $140 in 2017 dollars. Still a good deal, and I suspect I could get one done for about that around here.
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