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Air intake runners very small??

13K views 38 replies 14 participants last post by  Labratt  
#1 ·
Does anyone know if there is a reason the intake runners are so narrow, apart from clearing the fork tubes.

I'm just in the middle of fitting a K&N filter and the seem so narrow as to be ridiculous.

I'm almost tempted to get some spare runners, saw them off where they screw into the airbox and fit some screens.

I realise I would lose any ram air advantage but I'm wondering how much ram effect you get from such restrictive tubes.

They narrow to about 1' x 1 3/4' and that to me seems SMALL

We all go on about larger and larger exhausts to let the gas out but we dont seem concerned about letting them in. Maybe a slightly restricted intake increases air velosity, does that help? It would seem to be introducing pumping loss into the system

Any bright sparks out there with any ideas??

Cheers
Ross
 

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#7 ·
I would like to see someone bring their bike to the dyno with the bodywork removed. Run the bike with runners, remove the runners completely and do another run. Then we would find out if it helps or hurts.
But you don't get ram air on a dyno, do you? Your experiment would only prove that it makes more or less power without the runners while standing still, rather a moot point. Unless you DO get ram air on a dyno, then I'm just typing out my ass... :eek:
 
#4 · (Edited)
"We all go on about larger and larger exhausts to let the gas out but we don't seem concerned about letting them in. Maybe a slightly restricted intake increases air velocity, does that help? It would seem to be introducing pumping loss into the system"



I agree, that's why I've been considering the Carbonize CF stock replacements.
It'll probably have a bit of an intake honk without the stock sound chambers though.

$375ea U.S.

Image
 
#5 ·
http://www.sportrider.com/tech/146_9910_ram/index.html

I remember reading that intake velocity becomes airbox pressure, and smooth laminar flow would be more important than hogging air. The TLR (being the only twin) has interesting gains.

It might not be a a huge positive pressure gain, but the ramming effect lets the airbox pressure stay in the positive, as opposed to the negative pressure in the non-rammed bike, so making larger intake pipes won't necessarily increase output. the Blackbird doesn't have 3 inch pipes sticking out the front.

Runner length also controls resonance tuning.

I know that for small displacement, high rpm four cylinders (Honda B18C engines) shortening the intake runner length moves the power higher in the rpm range. Increasing the diameter of the intake runners screws up the resonance of the intake ports, and actually decreases output. My money would be on leaving the runners alone. I bet the gains from the tuned resonance are greater than an attempt to haphazardly stuff more air in the box.
 
#12 ·
http://www.sportrider.com/tech/146_9910_ram/index.html


Runner length also controls resonance tuning.

I know that for small displacement, high rpm four cylinders (Honda B18C engines) shortening the intake runner length moves the power higher in the rpm range. Increasing the diameter of the intake runners screws up the resonance of the intake ports, and actually decreases output. My money would be on leaving the runners alone. I bet the gains from the tuned resonance are greater than an attempt to haphazardly stuff more air in the box.
+1. Resonance is important. Tuned length of the intake affects this. Airflow through a duct is rarely intuitive, I'll bet Ducati spent some time and effort on this. MV Agusta and Yamaha are using variable length intake trumpets to good effect, variable length intake runners have been in use on cars for years.
 
#8 · (Edited)
Ya gotta stop 'tweakin' it man!! :stickpoke
Just buy the sprintex and be done with it once and for all. ;) You'll then be happy that the stock runners can vacuum up sparrows and small pedestrians that are untethered to their parents. :naughty:

You've really got a severe case of turbo Busa withdrawal blues?

I'd be loathe to 're-engineer' my own runners because, well, I'm not a engineer learned in Fluid Mechanics.

Two words come to mind: venturi & resonance.
The first I think, you can see evident in those runners and the second happens once the air get into the airbox. I remember reading something about how important it is in the fueling of relatively high performance fuel injected engines.
Cagiva Racing Corporation paved the way for this 'air ram' technology when they were developing the 916's I think and I wouldn't be in a hurry to change their formulas.

How much hp do you think there is to gain? Enough to satisfy that hole left by the beloved Busa?

Lenny - good point about the dyno. I think the 'better' operators/manufacturers are catching on with huge ass fans etc but I don't think it would replicate the ram effect that well, but it must be more realistic I guess. Or...... I could be just typing out my ass as well. :eek: :laughing:
 
#11 ·
I'm totally guessing here but I thought the venturi effect of the runners was all made irrelevant because of the airbox needing to maintain positive pressure? The runners and ram air's function is to positively charge the airbox and the all the resonance and turbulance and insufficient air flow problems are airbox shortcomings. No?

When there's talk of putting a Turbo on I'm suddenly reminded of those one shot toilet paper tube sized Nitrous kits they sold on Ebay for Bikes a few years ago.

Translation: Sprintex = Hoover
 
#13 ·
I'm totally guessing here but I thought the venturi effect of the runners was all made irrelevant because of the airbox needing to maintain positive pressure? The runners and ram air's function is to positively charge the airbox and the all the resonance and turbulance and insufficient air flow problems are airbox shortcomings. No?



Translation: Sprintex = Hoover

This may be true when the speed of the bike is high enough to create meaningful positive pressure in the airbox. The pressure waves in the intake tract are very powerful, acceleration from low speed is when resonant frequency of the intake tract comes into play.
 
#18 ·
At low rpms there is reversion past the intake valves that pressurizes the airbox. Opening the runners may negate that effect.
The reversion occurs at all rpms, not just low rpm. That's the point of tuned intake runners. When the pressure wave travels through a duct and reaches an opening, a reverse signal is sent back down the duct. Optimizing this signal (through tuned length) can "ram" the fuel charge into the cylinder if the wave hits when the intake valve opens. This in effect "supercharges" the cylinder. The tuned length will only work at certain rpm though. At high speed, the ram air may pressurize the airbox enough to overcome any tuning of the intake runner.

As I mentioned, intake tuning is a science and also requires some iterative experimentation. As Vic_Ducfut mentioned, the factory engineers are also constrained by noise regulation, package confinement etc.
 
#19 ·
Well, it looks like intake theory is just as complicated and contorversial as exhausts.

It would be nice if we all could afford to have dyno's at home so we could say "Hey guys, I did THIS and THAT happened".

Thanks for all the input. It looks like only trial and dyno will ever put this one to bed.

Cheers
Ross
 
#20 ·
You guys are barking up the wrong tree. It has nothing to do with the runner length on this bike . All you have to remember is that when air speeds up ( going through the narrow section) it looses pressure and when it slows down (in the air box) it increases pressure right above the throttle bodies. This adds up to a pressure greater than normal atmosphere. Runner length only applies with velocity stacks, length of intake manifold and exhaust system. Air going over the aircraft wing is faster than the air going under, this is what lifts the wing.
 
#21 ·
You guys are barking up the wrong tree. It has nothing to do with the runner length on this bike . All you have to remember is that when air speeds up ( going through the narrow section) it looses pressure and when it slows down (in the air box) it increases pressure right above the throttle bodies. This adds up to a pressure greater than normal atmosphere. Runner length only applies with velocity stacks, length of intake manifold and exhaust system. Air going over the aircraft wing is faster than the air going under, this is what lifts the wing.

Hmmm...not exactly. The airbox is a Helmholtz Chamber. Google it and you'll likely find better explanations than I can give here.
 
#27 ·
Ah the good ol Helmholtz chamber - the same as the expansion chamber on the exhaust of a 2 stroke 'rock hopper' (dirt bike), same principles but on the inlet side of things.

I was probably a bit off track before with the venturi yap about the runners and after consulting a 'bible' I don't think the runners are as important as the airbox itself. They found on the early 851/888's that they actually got more performance from leaving the top off the airbox to the demise of air quality (bypasses the filter effectively) and what they learnt from that was the bigger the airbox the better (resonance). They made the airbox bigger for the testastrettas apparently and adjusted the frame (996/8) for a bigger airbox (dubbed the 'Kyalami' frame) but didn't employ the larger airbox until the 2001? 748R which enclosed the throttle bodies as well.

Agree with posts before - nothing is ideal but as 'retailers' the engineers need to balance noise emissions & regulations into their designs in order to get their 'product' sold in the marketplace.
 
#30 ·
Agree with posts before - nothing is ideal but as 'retailers' the engineers need to balance noise emissions & regulations into their designs in order to get their 'product' sold in the marketplace.
Engineering, after all, is described as an endless series of compromises...
 
#29 ·
It seems to me you're all over looking the obvious.........racers don't use stock runners. Last i heard people that race things don't add parts that make them slower.

No one here has yet to mention the resonance chambers stuck on the side of the damn things. Nothing more that a way to get by sound regulations.

With a stock bike you probably wouldn't see much difference with after market runners, but once you add a free flowing exhaust and air filter, PCIII, etc. etc.....it all adds up.
 
#31 ·
There is NO ramming effect until the bike is doing around 130 mph. This has been proven on the Bonneville flats. In my opinion there is adequate area in the "necked" down portion of the runner. Don't forget that both those runners are feeding the airbox and only one cylinder is sucking at a time. If there's anyone who's a freak about performance and altering stuff that seems inadequate it's me, and I'm not going to mess with them. Also, fwiw, my runners do NOT have that goofy looking chamber. They're just straight and plain like the pics of the aftermarket ones seen on here.
 
#32 ·
Also, fwiw, my runners do NOT have that goofy looking chamber. They're just straight and plain like the pics of the aftermarket ones seen on here.
How is that? Did you cut them off? What bike do you have? What year bike do you have? What model...Tri, "S", Base? Come on man, you can't say stuff like that and not explain you'll make my head explode, I'm all about details.
 
#34 ·
Ten Baby,

I have a 2007 Tricolore, last five digits 01431. Full Termi, etc. My runners mount with three screws to the air box and a rubber sleeve connector which is stapled to the runner and slides over the air inlets. Made of CF. That's it, no chamber and no other mounting points. They look exactly like the aftermarket ones except have a slightly smaller waist. And it does growl when I get on it. I must be living right or something because that's what was on the bike when I picked it up.
 
#36 ·
Ten Baby,

......... My runners mount with three screws to the air box and a rubber sleeve connector which is stapled to the runner and slides over the air inlets. Made of CF. That's it, no chamber and no other mounting points. They look exactly like the aftermarket ones except have a slightly smaller waist. And it does growl when I get on it. ......
I'd like to see a photo of that Lee, sounds sweet. Next time you're 'in there'.

Do you need to change the mesh guards for the runners as well Ten-6??? Or are they the same for the Tri as the S ??
 
#35 · (Edited)
Thanks for humoring me man.............

It sounds like the issue might be solved. Evidently Tri's not only come with a better breathing exhaust but a free flow intake to back it up. I guess that effectively ends the "different/modified runners will ruin HP" debate. Now we need to find the part number and call for the prices........hold on to your wallets.
 
#37 ·
I don't know, I'd like to see some pics as well. We need some more people with Tri's to check and see if they have the performance(DP?) runners also.
 
#38 ·
I have no more reason to go in there now but one never knows. If I do I'll post a pic or two.

I don't know why I have these and I can't imagine they'd change the runners because it's a Tri. I don't remember reading anything about it in the Tri specs. But I'm not bitching 'cause I love the roar. Like an animal or some such, you know?
 
#39 ·
As much as I hate to resurect this post I will anyway..:laughing: A mate of mine runs his own workshop and they have seen gains of up to 7 hp by modifying the stock intake runners. This involves removing the resonant chamer and increasing the volume of the runners. Not giving any names or data as yet as I'm trying to get some dyno info to back up the claims as am planing this for my 1098 as well. At the end of the day its all about improving the breathing of the engine to improve cylinder filing and hence power. Resonators on airboxes are mainly to reduce intake noise and disrupt the intake airflow. Removing them can only be a plus...