Smaller Header Pipes

[Coyote]

I was watching Performance Car TV yesterday and they had an overview of what they had done to this car they were preparing for a competition. They mentioned how they made custom extracters that were slightly smaller than the stock system which resulted in the exhaust having to travel faster giving the engine more power. Homies think making bigger extracters is good for performance but it only makes the exhaust fumes travel slower making the engine more sluggish.

This got me wondering about doing the same to the CBR. Could I improve performance by making header pipes that were made of smaller tube metal or is there a lot of other things you would have to modify to benefit from this that they didn't mention?

[onearmedbandit]

Exhaust science is quite complicated, tuned length headers, opitimum diamater, etc. A lot to do with scavenging from exhaust pulses etc, ie as one cylinder has completed it's compression stroke and expelled the gases, the vacuum created by the leaving pulse sucks the next cylinders (in the firing order) 'pulse' out as well, making the engine more efficient. Reducing the diamater will speed up the flow of the exhaust, but it maybe at the expense of another area of its performance. More so than a lot of other mods, exhaust systems need to be designed as a complete unit to get noticable gains, from what I understand (correct me if I'm wrong) this even includes the shape of the airbox (induction side).

But, if you've got the time and ability it would be a good experience for you to try something.

[Coyote]

Thanks for the response. I was thinking of making header pipes for a metalwork project at school (currently making a rear stand for a sportsbike), if they didn't work out I could always revert back to stock anyway

[onearmedbandit]

Nothing to loose by trying as you can always revert back to standard as you say. I must say though the Japanese are very good at getting the whole recipie right the first time, but I'd be interested to read of your results. You'll definately want to do some dyno-testing though, as even a change in exhaust note and feel can make a bike 'seem' faster or slower. Good luck.

[Motu]

There are formulas for pipe diameter and length,I've posted them here before I think,but as my books are still packed away I can't find them (sunday afternoon project,unpack my books?) The exhaust gases and the exhaust noise are two different things,one travels down the pipe at aproximatly the speed of sound,the gases are needed to move at around 300 ft/sec at max rpm,the smaller the dia the faster they move - most stock pipes are about one size too small as this boosts bottom end HP.Very early Triumphs had huge fat pipes because they thought that was a good idea,but the gases traveled too slow - so later models,say 60s models,actualy stepped down in size from the exhaust port....check out a 69 Bonnie.I'll post some formulas when I find my books later.

Found them - exhaust pipe length...L=V 120/N
L=length of pipe
N= engine speed in rpm
V= velocity of wave in ft/sec

Velocity of the wave is variable to some degree,if you use a figure of 1700ft/sec it'll get you close enough.

Pipe dia formula is - V=piston speed/60 X D squared/d squared
V=gas velocity in ft/sec
D= piston dia
d=inside pipe dia.

piston speed=Stroke X 2/ 12 X rpm,this gives ft/min so divide by 60 for ft/sec.

It all sounds pretty complicated but it's fun to play around with - I used to do this stuff before calculators....and I didn't take maths as a subject at school.Enjoy yourself,I do.

[onearmedbandit]

Did you mean this one Motu?

http://www.kiwibiker.co.nz/forums/sh...xhaust+formula

Look for Motu's post.

[Coyote]

Mustn't forget installing a flamethrower system as well

[WINJA]

I was watching Performance Car TV yesterday and they had an overview of what they had done to this car they were preparing for a competition. They mentioned how they made custom extracters that were slightly smaller than the stock system which resulted in the exhaust having to travel faster giving the engine more power. Homies think making bigger extracters is good for performance but it only makes the exhaust fumes travel slower making the engine more sluggish.

This got me wondering about doing the same to the CBR. Could I improve performance by making header pipes that were made of smaller tube metal or is there a lot of other things you would have to modify to benefit from this that they didn't mention?

AT FULL REVS THOSE SMALL 250 LIKE YOURS HAVE OVER 100% VOLUMETRIC EFFICIENCY , ID TAKE A $20 BET THAT YOULL ONLY MAKE IT WORSE

[Jamezo]

AT FULL REVS THOSE SMALL 250 LIKE YOURS HAVE OVER 100% VOLUMETRIC EFFICIENCY , ID TAKE A $20 BET THAT YOULL ONLY MAKE IT WORSE

over 100% efficiency, cor blimey!

"Lisa, in this house we obey the laws of thermodyNAMICS!" - Homer Simpson

[marty]

i think he meant that it was as volumetrically efficient as it was going to get, therefore it was, for all intents, operating at 100% of its ability.

[Coyote]

AT FULL REVS THOSE SMALL 250 LIKE YOURS HAVE OVER 100% VOLUMETRIC EFFICIENCY , ID TAKE A $20 BET THAT YOULL ONLY MAKE IT WORSE

Always room for improvement though

[marty]

the engines i work on are allowed to run go 105% for short periods of time, with 100% being around 32000rpm, 3750 ftlbs of torque. they can sustain 5000 ftlbs in an emergency though

[NordieBoy]

Have a look at MotoMan's website.
If you can get past the garish colours etc then you'll find out about "velocity porting" etc etc.

See what you think.

[HDTboy]

I'd also vote for over 100% volumetric efficiency, and also think you'll only make things worse by putting smaller headers on. You may make a bit more torque down low but I'd say you'll lose the need for a 19'000 redline

[WINJA]

Always room for improvement though

IF PEOPLE LIKE 2 BROTHERS ARE FUCKING UP EXHAUSTS ON 250S YOU HAVE NO
CHANCE.