"Doing it Right" or "How to Build a Functional Café Racer"

Sideswipe

Active Member
Hey mate really loving this article especially the mathematical proofs behind it (like working out how long my intake should be and such) really will be a brilliant resource when i start planning to beef up the CB900

love it mate keep up the good work.
 

stroker crazy

crazy as a fox
Sonreir, I know this is a bit of a step back in this thread, but I've just read and re-read your post on exhaust design and I would like to ask a few questions.

I am in the process of improving the breathing of the SkyTeam 'Áce': http://www.dotheton.com/forum/index.php?topic=43357.0
The intake side is fairly easy to deal with but the exhaust appears to be severely restrictive. After getting my head around converting your mathematics into the metric system I think I now have some understanding of general principals.
I have only worked with two-stroke bikes for the last thirty years so items like 2cat and EGR came as something of a surprise!
Calculations indicate quite a long pipe so I was wondering if it would work if the pipe diverged in two after the header, and shorter secondary tubes were used? This would also allow the use of two minimally unrestrictive mufflers, hopefully making the resulting noise less obvious.
Incidental to this, I was wondering if there was any appreciable gain to be had by blanking of the (external) EGR?

Would much appreciate your input on this.

Crazy
 

stroker crazy

crazy as a fox
Ignore the previous post - its lateish and I've had too many beers!
Obviously splitting the pipe increases its effective diameter, not the length.

I think I should go to sleep now!

Crazy
 

teazer

Over 10,000 Posts
DTT BOTM WINNER
Crazy, the issue is that most times the calculate intake and exhaust lengths are too long, so we use 1/2 or 1/4 of the calculated length to take advantage of second, third or even 4th order reflections. In the real world, those lengths are only "ideal" for a certain rev point plus or minus a bit., so I wouldn't sweat it.

You can use the same calculations as a 2 stroke but arranges slightly differently to allow for different timing of events.
 

stroker crazy

crazy as a fox
teazer, my current intentions for the 'Ace' exhaust are these:

Cut the original pipe at start of CAT and at silencer
Weld in new straight section about 6 inches longer than original (I will probably be shunned for going against the trend for short pipes!)
De-restrict silencer internals
Make a combined clamp/mount to join silencer to pipe and attach both to bike
Make a strut to connect rear of silencer to frame under seat hump

Might do a Photochop later to illustrate the result.

Thanks for the inspiration provided by this thread,

Crazy
 

teazer

Over 10,000 Posts
DTT BOTM WINNER
I like that plan. Pipes that are too long peak early but that extra length doesn't hurt too much unless they are excessively long. So a long pipe means potentially slightly more low down, slightly less up top but the same rev range as before. It should (hopefully) tip the power curve a little to make for more fun on the street.

That all assumes that there are no obvious restrictors built into the head or pipe that also need to be addressed.
 

Texasstar

Can't is a four letter dirty word
teazer said:
It's an optimization exercise and not a maximization trip.

I will be passing that wisdom to my son Teazer. I can't believe this doesn't have more views! Y'all are great!
 

Texasstar

Can't is a four letter dirty word
Sonreir what about application streamlining? Going fast? What fairings have worked best for different sized bike historically, race application, etc?
 

crazypj

Split personality, I fake being smart
The 'best' streamlining doesn't usually look so good, Hayabusa is very efficient but makes bike look like a tank.
Yamaha R1 is far less efficient but 'looks' faster
 

Sonreir

Oregon
DTT SUPPORTER
For ideal streamlining, look no further than mother nature. A fluid of higher viscosity passing through a fluid of a lower viscosity at a high rate of speed will take a very familiar form:

water_drop.png


The reason for this shape is that this is the path of least resistance. If the wind resistance were to increase any further, the rain drop would be forced to change shape and/or break apart.

Chances are, the only rain-drop shaped fairing you're going to get is one to make yourself. For a bike, you're looking for a full fairing that covers as many exposed parts as possible (including the rider). It should come to a taper at the back and at no point should there be any jagged edged or exposed machinery.

As you can probably imagine by now, that's not likely to be possible.

For flat-out top speed, you want something looking a bit like this:
speedweek-3.jpg


You can see that the rider is fully encased by the fairing and the fairing comes to a point in the rear. Though you can't see the front side, you can bet it's as circular as possible (including around the forks and front tire). There's likely to be an air inlet for the engine, but that's about it.
 

Texasstar

Can't is a four letter dirty word
Airtech says of the 3 the VsF1 is the best and it looks like your water drop.
 

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Sonreir

Oregon
DTT SUPPORTER
I'd pick the TD32, personally. Obviously, I've never taken any of them into a wind tunnel or done any other sort of empirical tests, but I like how it has mountings for a windshield which will help the rider get down into the "bubble". A clever father/son team with some fiberglassing materials could probably modify it to close up the bottom gap. ;)
 

cyclefreak

Over 1,000 Posts
Aerodynamics is nothing new. Back in the day going fast was much more important than "looking" fast like many bikes today.
e8y3aqaz.jpg
 

crazypj

Split personality, I fake being smart
Sonreir said:
I'd pick the TD32, personally. Obviously, I've never taken any of them into a wind tunnel or done any other sort of empirical tests, but I like how it has mountings for a windshield which will help the rider get down into the "bubble". A clever father/son team with some fiberglassing materials could probably modify it to close up the bottom gap. ;)

By the look of things the TD32 comes with pieces to infill the center section
 

Texasstar

Can't is a four letter dirty word
Oh We love those Fibonacci curves are so beautiful...we don't give a rats ass how it looks we want to go fast! If we want Lucky to look good we will take off her bra and take her for a romp in the country.
 

teazer

Over 10,000 Posts
DTT BOTM WINNER
Sonreir said:
For flat-out top speed, you want something looking a bit like this:
speedweek-3.jpg

.

That would be Brett deStoop and his 232MPH GT750 Suzuki triple two stroke.
 

Texasstar

Can't is a four letter dirty word
Kop made some calls to airtech for us.


I got an email from Dutch that said " I spoke to Kent about the bike and we've narrowed it down to 2 choices:

Cool looks + some streamlining: CR931 http://www.airtech-streamlining.com/hondaz/CR931962-63.html
All out high speed attempt: PEEL1 http://www.airtech-streamlining.com/ducati/250350SINGLE.htm

So we love the peel1! All out speed! He also said we need to go with a taller Vesco tail to keep the air on longer.
 

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