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 Tight curves!

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Trevor Amos



Number of posts : 860
Registration date : 2010-08-13

PostSubject: Tight curves!   Thu Dec 18, 2014 6:43 am

The exhaust pipe should not feature a tight bend too close to the cylinder, especially if it is bent in any direction other than the vertical plane relative to the cylinder. Gas flow is at its highest velocity at the roof of the exhaust duct during the blow-down phase, and should follow the duct and pipe straight out with no impediment to gas particle flow. If not, a returning plugging pulse will adopt an asymmetric path from a left or right pipe curve, and in turn will adversely affect the "loop" of the scavenge flow.
All of that sounds very plausible and is said to have originally come from a head techo at Yamaha. I can also see the implications for a biased pulse running up one side of the duct into the cylinder. It does also suggest that research was going on into this as so many exhausts on the Japanese 4 cylinder engines usually had one or more serpentine pipes snaking through the frame work. So there must have been something worth checking out.
I guess the only way for us Bantamers to corroborate this proposition is to construct some pipes and spend a day at the dyno investigating?

Trevor
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dansofield550

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Number of posts : 362
Localisation : gravesend kent
Registration date : 2011-10-23

PostSubject: Re: Tight curves!   Thu Dec 18, 2014 7:46 am

I was gonna say that ! All I know is it goes well as it is but I'll be changing the front section when time and Brain power permit, more power is always welcome
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Trevor Amos



Number of posts : 860
Registration date : 2010-08-13

PostSubject: Re: Tight curves!   Thu Dec 18, 2014 9:32 am

Yes, I`m sure you were Dan? Achieving more power is always the raison d'étre of development work, but not wasting the power that you have already made is equally important, as is fully exploiting the wealth of information that is readily available to enable improved performance!

Trevor
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nigel breeze

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Number of posts : 341
Registration date : 2007-12-23

PostSubject: Re: Tight curves!   Fri Dec 19, 2014 7:26 am

Evening Trevor/ Dan, do we have a bantam friendly dyno man ?
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Trevor Amos



Number of posts : 860
Registration date : 2010-08-13

PostSubject: Re: Tight curves!   Fri Dec 19, 2014 10:27 am


Throw enough cash at it and you can take your pick of the dynos, friendly or otherwise, plenty of money sloshing around Bantam racing these days, isn`t there ?

I know of a couple of dynos that would cater for Bantams, they work with scooters so they should know what is what. But as to the efficiency of their respective bits of kit, I have my doubts! Some of the gorillas operating these rolling roads ought not to be let loose on anything more complicated than a concrete mixer!

Think I`ll stick to my calculator and computer software, numbers on paper are far cheaper.

I have attended a few "tuning" sessions, but some descended into farce with no organised plan, or systematic approach, just chasing the biggest power number but going around in circles. The only winner was the proprietor of the tuning emporium with his burgeoning takings.

The guys at Aprilia had two engine dynos working five days a week, power went up each year by an average of less than 1hp to peak at 54 at the gearbox. I can`t see too many Bantam tuners sticking with that level of dedication.

Trevor
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