Lone Trumpet
Street Tracker
My head hurts... :crazy:
Airbox flow testing
- Thread starter Aussie_T100
- Start date
Sal Paradise
Hooligan
Chris,
Aussie gives us yet another comparison of the airbox mods vs pods, thats all. Nothing wrong with choosing to keep your airbox and snorkle, and , yes you are correct, Aussie was testing vacum at max or above max rpms. Guys modifying the airbox or putting pods on Bonnies are clearly looking at upper rpms...thats what they want. Thats no surprise, is it? I have seen Piemans chart many times.
I didn't hear Aussie making a recommendation for your bike or mine, and to take your argument to its logical next step, at 3k rpms there is virtually no difference and if you ride really slow you should leave the whole intake stock if thats your choice.
All of which we agree on. But most who mod airboxes like to use the upper rpms and I personallly go over 7k regularly as do many and for us its good information.
Aussie gives us yet another comparison of the airbox mods vs pods, thats all. Nothing wrong with choosing to keep your airbox and snorkle, and , yes you are correct, Aussie was testing vacum at max or above max rpms. Guys modifying the airbox or putting pods on Bonnies are clearly looking at upper rpms...thats what they want. Thats no surprise, is it? I have seen Piemans chart many times.
I didn't hear Aussie making a recommendation for your bike or mine, and to take your argument to its logical next step, at 3k rpms there is virtually no difference and if you ride really slow you should leave the whole intake stock if thats your choice.
All of which we agree on. But most who mod airboxes like to use the upper rpms and I personallly go over 7k regularly as do many and for us its good information.
Speed3Chris
I like Dick
Nothing wrong at all as most that buy bonnevilles will keep their airboxes.
The point is...Aussie's flowrate testing was performed about 20% higher than most will run at redline. What Pieman's testing shows is just how capable the airbox is with some modifications versus removing the airbox, not only at maximum RPM...but also at the full range of RPM where most ride.
The other important point Sal is one can't possibly know what hp difference throughout the RPM range is without dyno testing with and without an airbox. Ventura's testing will not show this either. One can't correlate de-restriction to hp even with an established correlation between AFR and de-restriction which is the point of Ventura's testing which is helpful to those who want to jet their bikes against a particular airbox and pipe configuration. The same can be applied to Ventura's testing against Aussie's tests. You can't glean jet size from Aussie's testing. You can however glean jet size on the dyno like Pieman did with an EGA and what most do when they go to the dyno to maximize hp. I am not disparaging Aussie's testing. More data contributes to an informed decision and Aussie's testing even though it is specific to a particular RPM well above redline does show that the largest gains are achieved by removing the snorkel and the restrictor plate which agrees with Pieman's dyno testing. I am just adding Pieman's results to show others what the real world results are of opening up or removing the airbox. This can't be deduced by inches of vacuum and in particular throughout the RPM range where most ride unless the test is re-run accordingly.
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Aussie_T100
Banned
It is good to see a lively discussion has been generated by my results.
Regarding flow rates, the manufacturer quoted flow rate for the vacs I used can only be considered as a nominal figure and no doubt would have been measured at a restriction level of zero. As soon as you add any restriction that flow rate will drop so it must be taken into consideration that the flow rates from one test to another are not the same.
If I had been able to stabilize flow rate for all tests the result would have covered a broader scale, that is, if the flow rate at the highest restriction level (stock airbox) had been maintained for all tests restriction levels would have been numerically lower for all subsequent tests. It is only a primitive device after all.
Another factor to be considered is that the actual intake airflow in an operating engine is a pulsating airflow not a smooth constant airflow. Intake cam timing plays a part here, if you consider a camshaft with an intake duration of 242 degrees air is flowing into each cylinder for only 33% of the time (720 degrees divided by 242 degrees) so for the other 66% of the time no air is flowing in that intake tract.
This means that, with our 2 cylinder engine, there is no flow through the airbox for 33% of the time - in theory at least. To compensate for this in a steady flow testing scenario flow rate should be increased by 33% in my opinion.
Regarding flow rates, the manufacturer quoted flow rate for the vacs I used can only be considered as a nominal figure and no doubt would have been measured at a restriction level of zero. As soon as you add any restriction that flow rate will drop so it must be taken into consideration that the flow rates from one test to another are not the same.
If I had been able to stabilize flow rate for all tests the result would have covered a broader scale, that is, if the flow rate at the highest restriction level (stock airbox) had been maintained for all tests restriction levels would have been numerically lower for all subsequent tests. It is only a primitive device after all.
Another factor to be considered is that the actual intake airflow in an operating engine is a pulsating airflow not a smooth constant airflow. Intake cam timing plays a part here, if you consider a camshaft with an intake duration of 242 degrees air is flowing into each cylinder for only 33% of the time (720 degrees divided by 242 degrees) so for the other 66% of the time no air is flowing in that intake tract.
This means that, with our 2 cylinder engine, there is no flow through the airbox for 33% of the time - in theory at least. To compensate for this in a steady flow testing scenario flow rate should be increased by 33% in my opinion.
BlueJ
Blue Haired Freak
I don't think there's any relevance to a discussion of flow rate here. Aussie's experiment was only measuring the *resistance* to flow - certainly even the stock airbox with snorkle intact (and perhaps even a squirrel nest) could support a fairly substantial flow rate under sufficient pressure. The experiment "only" (and I use quotes because it was a beautifully done experiment and there's really no justification for anyone critisizing it) showed what relative resistance the various airbox configurations would offer to some given flow rate.
And the bottom line is clear: The less crap and convoluted pathway for the air to follow, the easier it is for the air to get to the gas for bang time. That means the less power being stolen from the engine to suck the air in and more available for turning the wheels.
And the bottom line is clear: The less crap and convoluted pathway for the air to follow, the easier it is for the air to get to the gas for bang time. That means the less power being stolen from the engine to suck the air in and more available for turning the wheels.
Speed3Chris
I like Dick
There is a lot of science to airbox design as it relates to the IC engines and you touch upon some of the reasons why a simple laboratory test like you performed, while interesting, doesn't capture all variables involved. One element you mentioned is the pulse and compressiblity of air and its potential energy. Air has mass and velocity and therefore momentum and can even be stored and then released. The inventor Helmholz discovered this many years ago. So restriction can have a purpose...the same tradeoff with muffler design if the resonance of airflow based upon volume and RPM can be matched to the part of the torque curve where cam timing in particular doesn't flatter torque:
http://www.phys.unsw.edu.au/jw/Helmholtz.html
http://www.thunderproducts.com/AirboxesDynotech.htm
The magic is finding the balance of restriction for maximum of helmholtz effect for optimum torque and not too much restriction to rob maximum horsepower. No coicidence that Helmholtz is about sound and a large part of the tuning knob for designers when it comes to airbox design.
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Speed3Chris
I like Dick
You just don't get it. I explained it previously but it went right over your head. It is all about flow. Restriction and flow are exponentially related. That is why for sake of an experiment it is critical to match flow set up to what the engine flow is. Further this is why one airbox does not fit all. A major thrust of Aussie's test is to determine if the airbox on the Hinkley bonnie is the right size. Pieman's dyno testing proves that up to about 4500 RPM it is very unrestrictive. Most airboxes have this kind of threshold incidentally...limiting factors being space, tuning for torque and sound. Above that it becomes restrictive without modification. This is because of higher flow at higher RPM. The airbox doesn't change at that RPM but the flow does.
If you put the Hinkley airbox on a lawn mower engine, the lawn mower engine because of its relatively small stroke volume and governed RPM would be virtually unrestricted. If you mounted the Hinkley airbox on a Dodge Viper it would be hugely restrictive. This is because of the radically different flow requirements of each engine. Restriction is all about flow and why a critical ingredient to any airbox test.
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Aussie_T100
Banned
Steady up Speed3Chris, lively discussion is great but let's keep the tone friendly eh?
Any subject can be as complicated as you want to make it but I think what has appealed to most is the simplicity of my testing procedure which helped make the results more understandable to those of us without an engineering degree (myself included).
Speed3Chris
I like Dick
If you don't think what I added to your thread was helpful, I am sorry. It is your thread afterall. You and others remind me that I really shouldn't attempt to stimulate further discussion or complicate discussion with facts especially if it goes against the grain of urban legend.
Have fun Aussie.
Have fun Aussie.
Sal Paradise
Hooligan
Chris - You are right, you are so far above us, we can't possible comprehend so just leave us to our foolish ways now.
Aussie, you are to be commended , really really interesting work and very well presented. Thanks.
Aussie, you are to be commended , really really interesting work and very well presented. Thanks.
Aussie_T100
Banned
If you don't think what I added to your thread was helpful, I am sorry. It is your thread afterall. You and others remind me that I really shouldn't attempt to stimulate further discussion or complicate discussion with facts especially if it goes against the grain of urban legend.
Have fun Aussie.
I started the thread but I wouldn't claim ownership of it - it's a community forum after all. I have no objection to your "attempt to stimulate further discussion or complicate discussion with facts" in fact I welcome it. My only objection - if you could call it that - was the slightly unfriendly tone in your reply to BlueJ.
Aussie_T100
Banned
Thank you for the kind words it makes the effort worthwhile.
Aussie_T100
Banned
outwestrider
Scooter
HuH?
Ok - so here's the simpleton asking a silly question, how do you get the "restrictor plate" out? - that is - which side of the air box should you take apart to get the thing out! - or does it require the total removal/reinstall of the air box to accomplish the goal? And ... my new to me 06' Bonnie appears to have the a/i removed, snorkel removed and after market pipes - which leads me to believe it has been jetted - will removing the "restrictor plate" to achieve the gains Aussie T, pieman and Chris have so far explained require different jetting or just carb adjustment? Ok - that's enough for one paragraph ...
Ok - so here's the simpleton asking a silly question, how do you get the "restrictor plate" out? - that is - which side of the air box should you take apart to get the thing out! - or does it require the total removal/reinstall of the air box to accomplish the goal? And ... my new to me 06' Bonnie appears to have the a/i removed, snorkel removed and after market pipes - which leads me to believe it has been jetted - will removing the "restrictor plate" to achieve the gains Aussie T, pieman and Chris have so far explained require different jetting or just carb adjustment? Ok - that's enough for one paragraph ...
Aussie_T100
Banned
The right side of the airbox must be removed to get the baffle out, the side can be removed insitu but a couple of the screws are difficult to get to. I believe that if you unbolt the airbox from the frame and loosen the boots on the carbies you can move the airbox to the rear enough to make it easier to get to the screws. The baffle just slides out once you have the side off. You'll need to reseal the side of the airbox when you refit it. Why don't you enlarge the inlet opening while you are at it?
Ventura's suggested jetting for the scenario's you are looking at are:-
Open exhaust + no snorkel................115 / 40 / no shims / 2.0 turns
Above + Restrictor gone....................120 / 40 / 1 shim / 1.0 turns
Above + enlarged filter inlet...............130 / 40 / no shims / 1.75 turns
Ventura's suggested jetting for the scenario's you are looking at are:-
Open exhaust + no snorkel................115 / 40 / no shims / 2.0 turns
Above + Restrictor gone....................120 / 40 / 1 shim / 1.0 turns
Above + enlarged filter inlet...............130 / 40 / no shims / 1.75 turns