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Discussion Starter · #1 ·
Many years ago (too many to mention) I read a book about proformance tuning and it had a formula for the length of the exhaust header from the valves and the relationship to the length of a velocity stack from the valve. If I remember correctly it dealt with being able to vary the torque/horsepower range by increasing or decreasing the ration.
Is there anyone besides me that remembers ever having heard of this and might have the formula?
At the time I had a '66 TT that I experimented on and it actually seemed to make a difference. Of course back then we only had butt dynos.
 

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I know what your talking about, i did this many years ago with my 66 TT, i have a book around here somewhere that has all these formula, in it you tune your intake and exhaust length to work with your cams. I do remember the stock triumph TT pipes fit right in with the E3134 cams one pipe 29 in. the other 28 in. One cylinder would tune a little before the other and the second would carry on when the first started fading, this would spread the power band out over a wider rpm range. I'll try and find the book it had formula for building megaphones also. Gearhead
 

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Did you manage to find those formulas? Im looking for the same thing. I did find this:

d^2=SxRPMxD^2 /108,000

d is pipe diamater
S is the stroke
D is the piston diamater
^2 means squared


and for legnth:


L=TxV/ N

L is pipe legnth

T is camshaft timing in crankshaft degrees

V is speed of wave in exhaust pipe(1,700)

N is RPM desired (500 RPM below peak)

Would love to get one for tuning the velocity stacks as well.
Interesting idea about tuning the 2 pipes to different lengths to broaden the power band!
S.
 

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Thinking about what effect the different length pipes would have on the jetting, my 68 T120R looks to have a shorter right hand side header pipe as do all the 650R's I believe. Maybe that is why the single carb versions run leaner on one side than the other.
 

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Kevin Camerons book "Sportbike Performance Handbook, Vol.II" has this.

This pulse wave tuning is by no means "new", or revolutionary. It has been used in all facets of Motorsports racing and perfromance building since... forever, and yes, it physically moves your powerband up and down the RPM range, widens it, narrows it, whatever you like. As should be, you tune for your particular style of riding or racing.

Excellent stuff, excellent knowledge to gain, proven technology. It doesn't get better than that. You can order this book from Amazon, but Borders / Barnes & Nobles also might have it in stock. About $26.00, but pay back is instant.

Kevin has been involved in successfully wrenching MotoGP style bikes since the 60's, and is a monthly columnist for Cycle World - that is where you remember the name from.

Too lengthy to explain here, but longer, thinner diameter exhausts maintain the pulse waves, and keep the toque peak low, and the power band wide. Short, straight , larger diameter pipes raise the powerband up, increase top-end HP, but slide the torque peak up the band as well. Your choice. Most stock offerings are a compromise, with added EPA and noise restrictions thrown in.

Not necessarily always Velocity Stacks, but lengthening and/or shortening, narrowing or widening your intake tract by any means performs the same phenomina.

Note that you'll need to match the intake and exhaust mods for the best tune. Doing otherwise just throws it all a out of balance and you'll experience LESS performance.

Read up on it, experiment with it, and most of all-have fun. This is fantastic and race proven tuning knowledge.
 

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sharp21; Sorry, I've been up to my ears in other projects and forgot all about it, i've just spent the last hour looking. I've got boxes i haven't unpacked since the move before the last move if you know what i mean. Someone who s been around a few years might have seen it, just a small paper back i picked it up in the early 60s when i lived in Scotland. If i remember correctly it was based on the formula developed by Norton engineers when tuning the manx engines.
 

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Discussion Starter · #7 ·
Thanks Gob-ny-geay. I ordered the book through Amazon.
I also purchased Graham Bell's book "Four-Stroke Performance Tuning" that also discusses pulse tuning.
Most of the information I've found is more about placement of the crossover pipe and exhaust diameter than about exhaust length and the ratio to intake length.
Gearhead, thanks for looking.
 

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Discussion Starter · #9 ·
Thanks, Gob-ny-geay!
Got the book yesterday, started reading last night and learned more about tuning in three hours of reading than I have from all of the so called tuners that have given me advice in the past.
 

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Seablues -

I've always appreciated Kevin's style and approach to the subject, as he is not trying to sell his own personal theories, or validate what he may have done to his own personal rides, but rather he is "reporting" on factual and proven methods, funneling the sifted information to us, and leaving the reader to decide on his own what to do.

Mind you, a lot of this is related to racing, but you can also study it thoroughly and easily translate the data to conform to a practical street ride.

So many of these style books present well initially, but once you begin reading, you suddenly realise that it merely a self-absorbed treatise by the author to push his personal opinions, tribal knowledge, and theories on the hopefully gullible reader. Others unveil themselves as poorly hidden attempts to sell a particular product or name brand. None of that style behaviour in Cameron's Manual.

With respect to our bikes, I would suggest reading the facts about Airflow - Intakes, Airbox Applications, Carburation, Cylinder Head Gas Flowing, and Exhaust Flow. This is where we get the most bang for the buck, and the most seat of the pants return, and as you so rightly stated, very uncomfortably contrary and counter to what many "Experts" have been blarting about all these years!!

As you will read, Step 1 is to decide what type of rider you are, and what style end result you wish to achieve. Excellent advice.

Have fun!
 

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Kevin Cameron's book is really excellent, but he doesn't talk much about crossover pipes, which are essential for developing maximum low speed torque (highly desirable for street riding). The closer the crossover is to the exhaust port, the lower in the RPM range the torque boost occurs.

Also, current practice for automobile engines is to step-down the diameter of the header pipes a couple of times prior to the collector to keep the gas flow speed high. Thermal barrier coatings on the inside of the pipes also help retain energy in the exhaust flow.

On the intake side, the longer the trumpet, the lower the RPM at which the boost is produced. Generally this is tuned to "fill-in" the dip in the torque curve produced by your exhaust system. The intake is easier to tune on a dyno because it isn't hot (i.e. you are likely to burn your hands swapping exhaust pipes)!

A really excellent discussion of all this can be found in "Gas Flow in the Internal Combustion Engine" by Adnand and Rowe, which I believe was published by Cambridge University Press in about 1974. I loaned my copy to someone in about 1975 and never got it back. It is long out of print now, but a good read if you can find it. These two guys designed the Mk III Norton Commando mufflers that were very quiet without losing any power over the old reverse-cone megaphones.
 

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So, if I fit 3" velocity stacks with standard downpipes, will it be better or worse?
Even if there`s no apparent improvement, I`d still prefer them to the air boxes.
 

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So, if I fit 3" velocity stacks with standard downpipes, will it be better or worse?
Even if there`s no apparent improvement, I`d still prefer them to the air boxes.
...funnily enought,I was up at thje National M/C museum friday and here's a photo of the 1969 works 'Thruxton'... So I might take my 3" stacks off!Cheers!
 

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'Tuning for speed' by Phil Irving(Vincent engineer)is VERY good but one on amazon is at £59(another £159)!!!Worth a look in your local library?Cheers!
 

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read the devolopement history of the triumph bonneville and it will show on page 24
the racing kit -specific lenghts /diameters of ex and megaphones to suit rpm range
i've got a engine analyzer program to sort it all out on,
 

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...I think 'seablues47' has an '04 bike so the earlier tech stuff for a bonneville won't be applicable mate?Cheers!:)
 

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There are alternative intake lengths that will work.The longer alternatives work better,but can be impractical.Longer alternatives can make more power at any speed than the shorter alternative.
"Vs" is the speed of sound in ambient air ,346m/sec @25 degrees C, 340m/sec @ 15 degrees C.

Long alternative (mm)= Vs x 8900/rpm
2nd alternative = Vs x 6600/rpm
3rd alternative = Vs x 5150/rpm
4th alternative = Vs x 4150/rpm
These lengths are measured from the valve to the end of the bell-mouth.
If you used the 2nd alternative at 6500rpm,it would also work as the 3rd alternative at 5072rpm ,etc.

The common formula for exhaust length in inches from the valve is
L = 850 x (Exhaust opening timing + 180)/rpm
The exact exhaust opening timing will not be the figure you use to set cam timing at 0.020" lift.you can add about 10 degrees to that figure.

You don't use your maximum rpm,or even peak-power rpm, in these formulae.The rpm you use will be closer to your maximum torque rpm,for best all-round results.
You could set up the exhaust at peak torque,and have the intake working a little below and a little above that.
 
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