UPDATE ON SKUNKWORKS

[al_roethlisberger]

What should it be? Crossover or no crossover?

I don't know much about this but I did run my 950 tonti w/o any balance pipe for a while & it killed the top end. I think it's about scavenging. they were wide diameter headers too which probably didn't help...

 

Captain, I still think you were good on the white ....blue???

 

KB, Cymru

 

....that's correct, and is the humorous fallacy of most American HD riders that immediately remove the "restrictive" stock exhausts and go with individual "straight pipes" only to find that they've actually lost power in holes all across the band.... although they think it's more powerful bacause it's now so damned loud

 

Exhaust tuning, length, diameter, and crossovers are a complicated affair.

 

Crossovers are tuned for scavenging(hence different locations on the headers as needed for a particular power goal - compare the '02 and '03 bikes), and in combination with header length tune exhaust pulses to clear/charge the combustion chamber.

 

Of course, I don't pretend that my exhaust is so precisely tuned, or that I'm an expert exhaust tuner myself.... as I haven't taken the time to so closely design and evaluate my own ...but at least it's based on standard products that are supposed to have been to some degree

 

I would be leery of "straight pipes" as there is a reason manufacturers and racers include collectors and crossovers to maximize performance.... and unless you are drag racing ... well...

 

al

[Guest Fonzarelli]

The purpose of the exhaust crossover is to give one cylinder double the exhaust escape area.

 

Whaaaat?

 

That is because both cylinders do not fire on the same stroke, so the exhaust is only used by one cylinder at a time, so you can use BOTH sides of the exhaust system for each cylinder!

 

There might be some type of scavenging going on, but I believe that the crossover lowers restriction moreso than increase the exhaust gas pulses.

[Baldini]

...but...that old 950 ran great on a set of straight thru pr type (crossbow) pipes, w/ simple balance pipe under the gearbox for years even as it threw out the inside perforated tubes & packing bit by bit - at my level it's not an exact science...it was easier for simpletons like me when we had carbs...but so long as you don't let it run too weak full speed ahead captain...pioneer spirit...it's what America was built on... really tho...stick to the white!

 

KB, Cymru

 

...& let's not kid ourselves...it's noise we want...noise IS power eh chaps! but remember...they'll always hear you coming

 

....the tinnatus'll tell you when to quiet it down a bit!

[Guest J.R.]

I won't even pretend to know anything about exhaust tuning

But,I've often wondered at the effects of longer tubes and less diameter.

Think of the brilliant Britton motor,and how the system went a looong way in a short distance by multiple bends.

What was the gain as apposed to straight out,more mid range,or just for better ground clearance

Any thoughts?What a shame such a brilliant mind died so early.

 

J.R.

[callison]

noise IS power eh chaps!

 

Not quite. Power tends to make noise, but noise is not necessarily power. If it were, all of those Harley's blatting around my neighborhood with straight pipes would be putting more than 50 horsepower to the ground.

[Murray]

To the no cross over I think you will slow your bike down. The previous owner of my carbed 1100 sport had way too much money and fitted the full Terginoni race system. It has a crossover very similar design to the curren v11's in the same spot Raceco tested a few cross overs and found that the stock V11 flowed best of all. Have fun with your experiment but I think you will find you definatly need a cross over of some description.

[Guest captain nemo]

Yes, I've decided to keep the stock crossover. All I will do is cut the pipes that lead back to the stock cans. The Supertrap horns will be welded right onto the crosover so that they will be jetting out only slightley from the wheels. Next Tuesday I get my other Surpertrap parts and then it is all packaged and off to Jet Hot.

 

In the mean time I disconnected all the rear electricts and I am open for ideas to use l.e.d.or other lights and get rid of that big piece of plastic. Any threads on this?

[emry]

Check this guys.

 

Tuning Calc

 

Exhaust explainations

 

or this..

 

Header Design

 

[dlaing]

Check this guys.

 

Tuning Calc

 

I ended up with a seven inch header being optimum.

Maybe for a white girl

 

This formula from one of the other links that Emry provided seems to work better:

Length (in inches) = (CID x 1900) ÷ (rpm x pri.OD2)

What is our headers OD?

Each cylinder is 32.452 CID

Edited December 14, 2003 by dlaing

[al_roethlisberger]

In the mean time I disconnected all the rear electricts and I am open for ideas to use l.e.d.or other lights and get rid of that big piece of plastic. Any threads on this?

 

Here are some fender eliminator threads after searching:

 

http://www.v11lemans.com/forums/index.php?...9&hl=eliminator

 

http://www.v11lemans.com/forums/index.php?...0&hl=eliminator

 

http://www.v11lemans.com/forums/index.php?...4&hl=eliminator

[Guest captain nemo]

David, I'm trying to calculate the length of my two inch header runing my 33 inch head at 4000 prm and I get 39 inches. This seems about right. I'm imaging that is about the length of pipe that runs into the crossover. In fact, I'll go check - hold on.....they are 32 inches into the crossover - HOWEVER. if you then measure the length of the crossover where the sound wave will first bounce back, it is 6 inches - which is about wrere the calculation says is perfect for 4000 rpms. Actually 4125 would be a sweet spot - and then probably all harmonics off of that.

[dlaing]

sorry, I am confused. I keep getting about 3 or 4 inches instead of about 30 or 40.

Am I reading the formula wrong?

I took CID of 32.45 x 1900 and got 61655.

I took 61655 and divided by the rpms times 4. (I got the 4 from 2 inch diameter squared.)

So if we used 5000 rpms we would divide 61655 by 20000 and got 3.08275.

This can't be right, can it?

[Guest captain nemo]

Oppps. I see what you mean. I was using 19000 instead of 1900. Perhaps there is a typo in that because a 3 or 4 inch header pipe makes no sense. With my 'mistake' it came out exactly right - what you would expect. The other box the Emry gave us also comes up with the very short pipe. I don't get it.

 

Emry - is it possible that the 1900 figure should be 19000? Our headers are over 30 inches long.

 

 

Al - I liked the very clean look of your backend, but I ordered one from Fast by F. I was looking for some feedback on it, but didn't see any. I wonder if they are bright enough. Also, I noticed in both his and yours that I didn't see the overhead plate light. Gone?

[al_roethlisberger]

Yeah, the light from the tail-light is plenty to illuminate the plate... although it is red.

 

However, since it is exactly the same light as used on Ducacti Monsters, you could always get that option with a clear underside for illuminating the plate.

 

FBF's replaces the OEM tail-light with a different unit, so I don't know about theirs.

 

al

[emry]

The formula is correct. But it is a simplified version optimized for V-8's and peak Hp. The pipes on own bikes unfortunatly were not designed for that. Their length is set by the availizblity of space, i.e. the exhaust port + the short radius of the header to the crossover.

 

If you use the formula CID is the displacement of the entire engine. This formula is to optimize header to collector length. This formula produces a very good result for a very specific RPM range. Great for constant throttle position engines, i.e. planes, drag racers, 4-stroke boat engines, not street bikes

 

Our headers also have a 1.75 OD. Actually 1.7786 on my Scura. With a header length of 31" and OD dia. of 1.75 our bike are tuned for 1250 rpm give or take. Explains the big dip at 4000g eh? (stock parts suck, or blow, your preference. )

 

Those of you that feel really in to number crunching.....

 

Primary Pipe Length " = (850 * (EXO@0.001"+180))/RPM

 

Primary Pipe Diameter " = SqRt ((cc per cyl./(Primary Pipe Length * 25)) * 2.1