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Author Topic: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt  (Read 748 times)

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Offline DrM

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Just watched this YouTube video: HARLEY Iron vs INDIAN Scout vs YAMAHA Bolt DYNO BATTLE! (Pt 02) --
https://www.youtube.com/watch?v=ochaC8xS60Y&ab_channel=BLOCKHEAD

The Dynometer doesn't lie -- Does Yamaha overly restricts the Bolt?



Offline lunkhead

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #1 on: December 13, 2020, 03:36:56 pm »
Some of worse mechanics we've had came from MMI. NONE have lasted more than a few weeks and they've all had trouble with actually fixing motorcycles. Those guys talk about that Scout like it's the big model but the data seems to indicate it's the Sixty. They try to explain why it went from the claimed 100 crank HP to 70 when the claimed HP is actually far less and more in line with the Sixty specs and transmission losses. Maybe it really is the bigger Scout but the numbers just don't add up unless there's something wrong with it.

There's no doubt the Bolt has a restricted intake but comparing to a slightly bigger, liquid-cooled, high compression engine that runs on high octane isn't fair. They should compare the Scout to a Ducati 950 if they want an apples to apples comparison. The Harley comparison isn't fair either but it does have to keep temps down by using low compression just like the Bolt. It's smaller displacement, long stroke, pushrods and only 2 valves per cylinder put it at a disadvantage.
C-SPƎC

Offline DrM

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #2 on: December 13, 2020, 04:38:45 pm »
That video was the first dyno-run I've ever seen on the Bolt.  I guess they could have doctored what was supposed to be stock bikes to get the results someone paying the bills might have wanted, or it could be honest -- no way for me to know.  I have seen even degreed professors lie in research, so nothing is beyond reproach or examination.  Too bad Yamaha doesn't give us a dyno-run on the Bolt. 

I agree the comparison is not really apples to apples.  Liquid-cooled engines have (should have) a definite advantage over air-cooled, given the same displacement.

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Offline lunkhead

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #3 on: December 13, 2020, 06:38:44 pm »
One poster said his EU Bolt specs at 40 kW (53.6 HP) on his passport which is a reasonable 3-5 HP difference from known RWHP. CW got 50.8 HP, Ivan got 49.4 and DJ 48.4.

Here's what the difference in removing intake restrictions looks like. There's only so much that can be done for peak HP without internal mods (high CR pistons, cams, etc.)


And what just correcting AFR and ignition timing looks like.
C-SPƎC

Offline Sdaniels

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #4 on: December 14, 2020, 09:13:05 am »
Chain drive would add a few more hp.   I knew shaft drive kills more power than chain but I was very surprised to read a belt was quite a bit less efficient than the chain.  Article I read said well maintained chains average a 3% loss where a belt is about 9%. 
« Last Edit: December 14, 2020, 09:55:52 am by Sdaniels »
2015 C-spec

Offline lunkhead

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #5 on: December 14, 2020, 10:48:45 am »
A non o-ring chain would be way more efficient than a belt but belts have been getting narrower and better. They used to be wider and had more friction which is where those numbers came from. An o-ring chain and a current narrow belt are real close. I won't quote any figures but chains still win.
C-SPƎC

Offline YAMAHAULER1

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Re: Why You Might Want to Modify The Exhaust and the Air Intake On The Bolt
« Reply #6 on: December 15, 2020, 01:59:53 am »
A big O'l 10-4 And a +1 on lunkhead's evaluation of MMI students "grads maybe", "mechanics not". A lot of wasted money going down the oil drain hole there. Love the "actually fixing motorcycles" line.