More power with more intake length

With tuned length intakes the longer they are the less laps the pressure signal in them makes and the stronger that signal is. So short of long can tune for the same rpm but there is a calculator for that, to get best length if you input all the data on your engine. And on this calculator, there are many different lengths for different calculations from different formulas. They are basically around the same length and one is very long and impractical. We used 12" from valve to atmosphere on this BSA. And it seems a great length for it.

mark parker said:

With tuned length intakes the longer they are the less laps the pressure signal in them makes and the stronger that signal is. So short of long can tune for the same rpm but there is a calculator for that, to get best length if you input all the data on your engine. And on this calculator, there are many different lengths for different calculations from different formulas. They are basically around the same length and one is very long and impractical. We used 12" from valve to atmosphere on this BSA. And it seems a great length for it.

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Really nice. How many bikes is that made up from?

Heck of a good idea using that frame with all the open space under the tank. Plus I know it wouldn't be like riding a classic British wet noodle frame at speed. I wish I were 25 years younger. You're giving me bad (good) ideas an old man should not be chasing.

mark parker said:

With tuned length intakes the longer they are the less laps the pressure signal in them makes and the stronger that signal is. So short of long can tune for the same rpm but there is a calculator for that, to get best length if you input all the data on your engine. And on this calculator, there are many different lengths for different calculations from different formulas. They are basically around the same length and one is very long and impractical. We used 12" from valve to atmosphere on this BSA. And it seems a great length for it.

Click to expand...

Very well done - I like it.

Would this work with a single mikuni?

I just added 1/4" to my P11 intakes. Now have a whopping 8" from the bottom of the intake guide to the back of the carburetor bellmouth. A little over 10" to the back of the filter housings. It is a PITA to get the filters on now. I can't go any further in my frame and still have relatively easy to maintain filtration. Not sure why I'm mentioning it. It don't mean squat other than the P11 shipped with 1/2" intake manifolds and 930 carburetors. Intake is a lot longer now and the carburetors are a lot bigger and vastly better than 930 Amals for tuning. Engine spins up really quick. Al would hate it.

A tuned length only suits one frequency and multiples of it. A rule of thumb for inlet lengths in inches used to be 28,000 divided by the revs . But in effect the length usually operates well over a wide rev range. My exhaust system has the same lengths which were successfully used for Kawasaki Z900 aftermarket 4 into 1 exhausts. My two header pipes are the same length as the tail pipe. The tail pipe has big enough diameter to offer no restriction. In theory it resonates at twice the frequency of one of the header pipes. Many years ago, I spent time modifying exhausts and cam timing trying to get more torque. Not much made any difference,except for a restriction at the collector of the exhaust. That can cut 2000 revs off the top of the usable rev range,
When we change things we usually only change one thing at a time. However the variables often interact with each other. We need to change one thing and adjust everything else around it, and try to recognise the pattern.
So with inlet lengths - make the change then use the dyno to see what gets the best out of it when you adjust all the other things.
Even then, proving you have gained can be elusive, until you ride the bike.

The revs you use when you race usually varies with the type of circuit, it's lengths of straights and corners and whether it has hills. I sometimes changed the overall gearing between circuits, then find out what my bike is doing when I get there. I don't need loads of top end power, but more is always useful. Torque is a very strange thing, the only way of knowing you have improved is by raising the gearing to make the motor pull harder. I use close ratios with very high overall gearing. A good gearbox can make a slow bike become much faster. In a race, my motor never drops below 5,500 RPM and never goes over 7,300 RPM. I get a good surge of power on very up-change.