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Author Topic: Straight pipes?!  (Read 1589 times)

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Offline Coredozer19

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Straight pipes?!
« on: April 30, 2018, 04:08:24 PM »
We’ve all heard about back pressure and all the other side effects of having straight pipes. But let’s get on the topic. Is running straight pipes on a CB350 bad for the valves?
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Offline tlbranth

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Re: Straight pipes?!
« Reply #1 on: April 30, 2018, 06:31:59 PM »
I'm no expert. Wait for TT & Hondaman or other scientists  to give useful advice. But when I first started messing with car and bike engines in the 60's, the word was that with no muffler, when you shut off the engine cold air could crack the exhaust valves.
That's everything I know.
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Offline Yamahawk

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Re: Straight pipes?!
« Reply #2 on: April 30, 2018, 07:14:07 PM »
Terry, technically, you are rated an 'expert' lol...
I believe that running straight pipes scavenges the cylinder too much, which could lead to oil being sucked past the guides and rings, but that's just my theory lol...no back pressure.
Charlie
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1971 CB750K1 (newest bike), 1996 Royal Enfield 500 Bullet (therapy bike), 1981 Yamaha XV920RH, 2006 Kawasaki Concours (retirement bike), 1975 Yamaha RD350 (race bike), 1989 Honda VTR250 Interceptor (race bike), 1986 Kawasaki EX250 Ninja (race bike in progress), 1985 Honda Elite CH250, 1973 Yamaha GT1 80cc, 1974 Yamaha DT360 project bike.

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Offline TwoTired

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Re: Straight pipes?!
« Reply #3 on: April 30, 2018, 08:37:47 PM »
Quote from: Coredozer19 on April 30, 2018, 04:08:24 PM
We’ve all heard about back pressure and all the other side effects of having straight pipes. But let’s get on the topic. Is running straight pipes on a CB350 bad for the valves?

It can be.  Particularly if you don't retune the carbs.  The lack of back pressure has a leaning effect which can make the cylinder run hotter, stressing the valves.  There is no exhaust sensor, right?  How would the computer know to adjust the mixture?

If you are running straight pipes on the street, might have more risk of annoyed people running your bike over.   I don't think my Excursion would make much of a thump.   ;)
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Online PeWe

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Re: Straight pipes?!
« Reply #4 on: April 30, 2018, 10:57:32 PM »
I had rather open pipes on my CB750. Uneven response from low and jerky behavior on low rpm, city riding impossible to jet correct. Much better low rpm with diffusers in.
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Offline MauiK3

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Re: Straight pipes?!
« Reply #5 on: April 30, 2018, 11:15:28 PM »
Original 4 into 4's run well for a reason. They are properly designed for the engine. Most other forms of exhaust for the CB750 are compromises.
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Offline BobR

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Re: Straight pipes?!
« Reply #6 on: May 03, 2018, 12:02:58 PM »
Quote from: MauiK3 on April 30, 2018, 11:15:28 PM
Original 4 into 4's run well for a reason. They are properly designed for the engine. Most other forms of exhaust for the CB750 are compromises.

  My K4 loves the 4 into 1 on my bike. I mean it must since it runs like a demon when you flog it and purrs like a kitten when lollygagging around. Its not fully straight though- I have a meager baffle in it. Pretty loud. Bob
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