How much power will it make? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 03-03-2014, 06:21 PM Thread Starter
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How much power will it make?

I know dead stock the vn750 makes ~65-70 HP and ~45 ft pounds of torque. My question is does any one know approximately how much increase in power you should see by doing an ear shave with jetting and removing goat belly and stock mufflers and putting on some decent slip on pipes? Any body ever dyno their ride afterwards?
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post #2 of 12 (permalink) Old 03-04-2014, 07:58 PM
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Im actually gonna be bringing mine to Cycle City in Sloatsburg, NY this season. They have a dyno there, and I wanna see what my mods have done.
Someone here posted some earshave dyno graphs, but it more changed the torque curve than anything else. After an earshave and an exhaust mod, Id expect somewhere around an 8-12% increase in HP though...I'll find out, lol...

If you really want more HP, then look into high comp pistons...our bikes are 10.xxx to 1...going to a 12:1 would make it kick....only company I know of that "might" be able to have em is Wiseco.




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post #3 of 12 (permalink) Old 03-05-2014, 06:28 PM Thread Starter
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I would say torque would be better a healthy torque curve brings you to the HP. Just hoping it will be worth the effort. Exhaust is done (still have to make brackets) sounds gnarly but she is definitely lean now. I'm pretty sure she was lean to begin with but withe new exhaust you hear it better. I knew I had to clean carbs so I figured if I was going to pull it apart it only made sense to do the mods. I was also thinking about putting some 3.5 risers on the bars I should not have to worry about cables? I thought I read one of your posts saying you could go with 11" bars without mods to cables.
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post #4 of 12 (permalink) Old 03-05-2014, 08:51 PM
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Our bars are 7.5" stock...so with 11's (3.5 more) depending on the bend now, you can probably squeeze by...if you keep em narrow....I order a pair of wide 11.5s....more than likely, Im gonna need longer cables (I went wide mid apes)...

Also, for more HP, I forgot....polishing and matching the intake and exhaust ports can add up to a 6% increase....that needs to be done properly though by somebody that knows how....Ive done it on other bikes, but never on this one....although I will be....



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post #5 of 12 (permalink) Old 03-05-2014, 08:55 PM
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It's generally agreed that you can add about 3" of rise before the cables become a problem. I added a 1" riser and the cables still have plenty of slack.

I'd have to agree that with these high rev loving engines adding torque is more important than just looking at the hp readings. With an good earshave, a slightly less restrictive exhaust, and the carbs properly set up I'd expect to see 6-7% power increase. Please remember that 7 % on an engine that already makes about 55 hp at the rear wheel (dyno tests previously published here around 2006) is only about a 4 hp increase.

At the same time it's really easy to get things out of balance and actually loose power.

With my stock exhaust after my earshave and a bit larger jets the bike starts easier and feels like it is a tad stronger but in my case it's only a "seat of the pants" test.

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post #6 of 12 (permalink) Old 03-05-2014, 09:26 PM
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post #7 of 12 (permalink) Old 03-05-2014, 09:36 PM
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I remember someone putting their bike on a dyno, but they did it after they did the earshave. No testing was done before so there was nothng to compare it to.

Dynos give HP readings from the rear wheel. Bike makers always list HP figures from the crank. The bike I believe after the earshave put out 56hp. Comparing this to other shaft drive bikes we estimated the crank HP was about 67. So if you believe Kawasaki claim of 65 HP, then doing just an earshave gain you about 2 horses.
Add a lighter weight better flowing exhaust you'll likely get one or two more and gain some advantage in accelleration just do to the lighter weight.

I doubt seriously you could gain more than 5 HP doing what you plan.


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post #8 of 12 (permalink) Old 03-05-2014, 11:31 PM
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I'll find out in a month or so....then again, I never tested prior...so results would almost be meaningless except to me...and Im all that matters....lol

I know when I was running all stock, with a tiny hole in the goat, it was..."meh"....soon as I earshaved and modded my exhaust by MY standards, I was poppin the front wheel goin into 3rd (when gettin on it)....

Being around hotrods and dragracers since the late 70s, I would think all the same principles to increase performance would apply....no ?....basically the same engines (vs a 2 stroke)....sooooooooooooo.....same principles....

Increase air intake, and alleive exhaust.....no brainer.....added stuff would be the port polishing and cam work.....and to an extreme, getting high compression pistons made up.....if ALL was done, and was yin/yang with each other, I can see this motor pushin 90hp or more....its just sad that its a short stroke. Then again, if one could/would fab a new jug, longer....also a new conn rod, you'd increase the displacement....easier to get a Kawi 800 engine and work that....unless one decides they wanna have the fastest VN7xx on the planet....Ooooooo....just had a Bonneville flashback, lol....

Think...we're at a 10.xx:1 comp ratio....increase that to 12.5:1....instant HP....but needs to be balanced with carburation etc....lotta guys dont get that....



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post #9 of 12 (permalink) Old 03-06-2014, 12:36 PM
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Quote:
Originally Posted by Wolfie View Post
Im actually gonna be bringing mine to Cycle City in Sloatsburg, NY this season. They have a dyno there, and I wanna see what my mods have done.
Someone here posted some earshave dyno graphs, but it more changed the torque curve than anything else. After an earshave and an exhaust mod, Id expect somewhere around an 8-12% increase in HP though...I'll find out, lol...

If you really want more HP, then look into high comp pistons...our bikes are 10.xxx to 1...going to a 12:1 would make it kick....only company I know of that "might" be able to have em is Wiseco.
x2 on Wisseco that's what i used, got 12.5:1 ratio,shave the heads and using a thinner flange(done that too) would also increase hp with out major work
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post #10 of 12 (permalink) Old 03-10-2014, 03:21 AM
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I did calculations on the cross-sectional area of Keihin jets at one point. Ear shave alone will help a bit, probably less than 5%.

If you re-jet to add more fuel, you'll gain power roughly proportional IF you have intake/exhaust modification to support that flow. I jetted and ear shaved and felt a small increase, probably ~5-8%. After swapping to de-baffled HD pipes on the same jets/intake, I picked up a little more and found the back tire breaking loose on me easier. Calculation on my jets puts me at an extra ~8-9% cross sectional area. Taking into account restriction is increasingly lessened with cross sectional area of fluid flow, I wouldn't be surprised at 10%. Maybe up to 12% increase if it was running leaner with all the air flow.

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