Mak's step-by-step guide to building an un-original, but still fun, cafe bike

doc_rot

Oh the usual... I bowl, I drive around...
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Ive never heard that dual exhaust makes for quicker throttle reponse. I think throttle response has more to do with the rotating assembly and the intake system. There is a ton of info on cross overs/x pipes/ or 2>1 making more power than single tubes because of exhaust scavenging. If you dont have a cross over or something you are leaving HP on the table. What size primary tubes did you use?
 

makenzie71

Been Around the Block
Ive never heard that dual exhaust makes for quicker throttle reponse. I think throttle response has more to do with the rotating assembly and the intake system. There is a ton of info on cross overs/x pipes/ or 2>1 making more power than single tubes because of exhaust scavenging. If you dont have a cross over or something you are leaving HP on the table. What size primary tubes did you use?
And if this was a 200hp bike gaining an extra pony or two might be worth the personal sacrifice of something I love the feel and sound of...but the CX500 is doing good to be putting 45hp on the ground and the affect any exhaust has on that number is negligible :D
 

doc_rot

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And if this was a 200hp bike gaining an extra pony or two might be worth the personal sacrifice of something I love the feel and sound of...but the CX500 is doing good to be putting 45hp on the ground and the affect any exhaust has on that number is negligible :D
The cylinders fire 180 from each other making the exhaust pulses alternate. By feeding them into a common tube, the effect is that during a exhaust pulse, the velocity of one tube rushing out past the other produces vacuum pulling the opposite tube when its not pulsing. Additionally, the more opportunities for pressure waves traveling backwards, created by steps in the header, the larger the spread of the torque curve. thats why the 4>2>1 is prefered over a 4>1 for a inline 4 street bike, and the increasing appearance of "stepper headers". Single tube collectors make for a narrow powerband. Depending on the application you can see significant gains and it will be most noticeable in the low and mid range when the vacuum is weak- street bike territory. This is why most factory exhaust systems of this era usually have a crossover hidden underneath somewhere, its free power.

BTW the exhaust looks great, I wasn't trying to infer that there is something wrong with it. Not everything has to be built to 100% performance. but using separate exhaust tubes is usually not a performance upgrade for a street bike. You could tuck a cross over under the oil pan and no one would notice.. just saying.

Party on
 
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makenzie71

Been Around the Block
It no longer has one and it's okay. I've done this before and I was quite pleased with the results the first go round.
 

CarbsAndCylinders

Careful With That Axe Eugene
I think a crossover pipe is used to increase power at lower revs, so it would not increase horsepower at higher revs but a 2 into 1 (or 3 into 1, or 4 into 1) can increase maximum horsepower if the pipes are of the correct length and are joined at the right length. It will increase power in the rpm range that the pipe lengths and the join affect but not outside of that range and in fact will probably reduce power outside of that range. This is how I understand it at least.
 

doc_rot

Oh the usual... I bowl, I drive around...
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Cross over for low and mid power. I have no doubt your exhaust will work.
 
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pidjones

Over 1,000 Posts
You like the sound and I think we all like the look. With performance not a necessity (other than make you happy when you twist the right grip), I think it's fine. If performance was the goal, a different power train all together might have been better.
 

hermanzini

New Member
Interesting !
i’m about to buy some roadriders for my 550 project, can you explain the cable ties and how they help please?
For me it was a much faster way to get the tire on/off, as it was done in one operation instead of two. Also nice to have full control on the tube.
 

teazer

Over 1,000 Posts
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That's interesting. I wonder why.

Back in the day when Slater brothers were racing Laverda SFC's they added an X pipe double crossover for a wider powerband and more top end. On a CX500 it's less of an issue.

With the over under pipes, I'd modify the upper header to bring that pipe slightly forwards and down to tuck them together a bit tighter. The look is important and attention to those sorts of annoying little details make all the difference between OK and excellent.
 

doc_rot

Oh the usual... I bowl, I drive around...
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After checking out the Murray Carb site, I wonder about the efficacy of removing the crossover because he is using 1 3/4"OD tube for the primary which is way too big for 250cc cylinder displacement. Perhaps this is why the crossover is elminated as more exhuast tube volume would be even more detrimental and hurt velocity even more since the primaries are too large for the application.
 

makenzie71

Been Around the Block
I have done pretty poorly at keeping these threads updated...but I've got 99% of the paint done and started reassembly.







 

makenzie71

Been Around the Block
I share the progress of this bike with a lot of facebook groups and a lot of other forums and I've been really surprised the last couple of days by how many people actually know who Pollock is haha
 

makenzie71

Been Around the Block
Not much of an update but all the same...getting wiring down, trimming what doesn't need to be there, adding what needs to be there, wiring up and testing an improvised coil on plug setup that seems to be working great

 

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