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Author Topic: Intake and exhaust length  (Read 1805 times)

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Offline sebatje

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Intake and exhaust length
« on: October 17, 2010, 11:59:09 AM »
Hi,
Has anybody experimented with different lenths of intakes and exhaust lengths on the CB400? I know that longer intakes should give more top end but what about the exhaust length? (header) Has anybody made a custom header for this type? I'm planning to build a 400 with oversized pistons from yoshimura, webcam and Keihin CR29.
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Offline turboguzzi

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Re: Intake and exhaust length
« Reply #1 on: October 17, 2010, 01:31:09 PM »
it's actually the other way round, rule of thumb is: shorter is better for higher RPM, longer for lower, kind of works for both intake and exhaust.

In 4-1 headers it gets a bit more complex, tuned length depends also on primary (before the collector) and secondary (collector to end can)

checking how your custom setup works would need a free dyno for a day or two and a few sets of pipes to test.... :)

Guess that's why most people, even racers settle down at the end to what's out there on the shelf. supposedly its been dyno tested but for what cam? what carb setup? how do you like your power curve? tricky...

John Robinson's 4-str. tuning book is a good place to start your education on the subject.

TG
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Offline voxonda

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Re: Intake and exhaust length
« Reply #2 on: October 17, 2010, 02:12:18 PM »
And even with a specific state of tuning, depending on circuit you would need another set of pipes and or intake length. You will have to make a compromise.

Rob
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Offline Retro Rocket

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Re: Intake and exhaust length
« Reply #3 on: October 17, 2010, 05:30:43 PM »
Quote
yoshimura, webcam and Keihin CR29.

29's will be too big for a 400 try 26 CR's.

Mick
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Offline sebatje

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Re: Intake and exhaust length
« Reply #4 on: October 17, 2010, 11:36:30 PM »
Well I haven't ordered the carbs yet so they will be 26mm. Are there performance exhaust off the shelf? i've seen Yoshimura and MC-Again. My track will be the street :). Maybe Voxonda and Howell can help me out with this as I live in Belgium.
I know a dealer who has a dyno so that shouldn't be a problem. But for makinf some exhaust to try... I should search for a good welder ;D
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Offline Retro Rocket

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Re: Intake and exhaust length
« Reply #5 on: October 17, 2010, 11:38:50 PM »
Voxonda {Rob} is a very nice guy and i am sure he would point you in the right direction..

Mick
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750 K2 1000cc
750 F1 970cc
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If You can't fix it with a hammer, You've got an electrical problem.

Offline turboguzzi

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Re: Intake and exhaust length
« Reply #6 on: October 18, 2010, 01:23:34 AM »
if you are building a street bike then 26's are a better idea indeed.

Marving.com in italy make some very nice systems in pure 70's style.

Of course that if you build your own system, you are going to need not just a good welder (that's the easy part) but also someone who can bend tubes without squashing them, that requires quite special machinery or sand filling the tubes.... just so you know what you are getting into :)

TG
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Offline sebatje

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Re: Intake and exhaust length
« Reply #7 on: October 18, 2010, 02:02:17 AM »
The marving exhaust looks great!!! And the price is ok :)
I will be removing the alternator and change the iginition to a digital one, crankshaft and rods will be lightned to.
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