Lone Trumpet
Street Tracker
My head hurts... :crazy:
Nothing wrong at all as most that buy bonnevilles will keep their airboxes.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.
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: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.
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.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.
You just don't get it. I explained it previously but it went right over your head.
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.
Aussie, you are to be commended , really really interesting work and very well presented. Thanks.
Wanna fight about it?