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Discussion Starter · #1 ·
OK, I have been getting quite a few questions about air filters and performance, so I will try to clear up some of this.

The stock air filter is pleated paper and does a great job of filtering. The BMC, K&N, and DNA filters are pleated cotton gauze that filter less, but flow more. How much more? I don't know, I have not compared them on the flow bench. As a result, I don't know which is "best". I use the BMC because it was released first. The K&N has pleats running 90 degrees to the BMC, I don't know if this means anything - it is just different.

FLOW:
It takes roughly 1.5 cubic feet of air per minute (CFM) to produce 1 horsepower in a good four-cycle engine. A less efficient engine will require more airflow. An engine is a pump that fills with air at different rates and amounts at different speeds. It fills most efficiently at peak torque rpm. It requires more flow at higher rpm. an engine making 120 hp requires roughly 180 cfm of flow. 130 hp requires roughly 200 cfm of flow.

If an air filter flows 250 cfm, and the engine only wants 200 cfm, then changing to a filter that flows 1000cfm will do NOTHING.

If the filter flows 180 cfm, and the engine wants 200 cfm, adding a filter that flows 250 cfm will only help at higher rpm - where the flow is needed. Until the engine's airflow is restricted, it will make the same power.

The air filters for the Daytona 955i engines has a good amount of filtering area and flow. The flat filters on the 1050 Speed Triple have less area and thus, less flow. Does that mean the 1050 engines need a better flowing filter? I am not sure, and won't know for sure until I test back to back on a flow bench or on a dyno. Only then will we know IF and HOW MUCH the aftermarket air filters help power.

Even then, the additional airflow will ONLY be at the top end of the powerband. You spend little time in this area, and even then, only see it briefly.

But the stock paper filter DOES filter better than the cotton gauze aftermarket filters. This is something you need to keep in mind.


For a good idea of how much flow and engine needs:
engine size in cubic inches X RPM X efficiency /1728 = CFM

For a 1.05L engine at 9100 rpm:
64.075ci X 9100rpm X .75 / 1728 = 253 cfm

For a .955L engine at 11,000 rpm:
58.278ci X 11,000rpm X .75 / 1728 = 278 cfm

I hope this helps.
 

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Discussion Starter · #3 ·
Ballpark.
Efficiency is higher at peak torque rpm, but cycles (rate) is less.
It may actually be optomistic for a stock engine.

But it gives a reasonably accurate idea of what is happening.
 

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10-4 buddy, I just thought you used a portion, no, ALL of your cunning, to come up with an efficiency constant. Just craving more knowledge.
 

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Discussion Starter · #5 ·
It just dawned on me that if I take the fuel corrections in the cells in TuneEdit, I can probably calculate an aproximation of BSFC based on rwhp. This might give a close idea of efficiency.

Not that it really matters. ;D
 

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Discussion Starter · #6 ·
OK, let's try this again, and try and slow down the number of PMs and e-mails asking about this.

NO. I do not know if aftermarket air filters make a single hp on stock or near stock bikes. I doubt I will ever know, my bike is not stock anymore. And each day it gets farther from stock.

I didn't bother putting on the BMC filter that I am using until after I had an aftermarket exhaust, ported header with precat/silencer removed, TuneBoy, and some intake work. I didn't think it would matter much until I had broken 125 hp, and then only at higher rpm.

When I tested the BMC with these mods, I had to add more fuel to the upper midrange and top end of the powerband. This means that I had more airflow in these regions of the powerband.

Please do not think just because I use one, that I think they are needed. For the money, I think header work should come first.

I hope this helps.
 

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Devious said:
The BMC, K&N, and DNA filters are pleated cotton gauze that filter less, but flow more. How much more? I don't know, I have not compared them on the flow bench.
Someone tried it there: CLICK
 

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bmc's are sometimes so thin you can see through the bends. it's the same with K&N, they loose oil and after the oil has gone the filtration goes down dramatically.

I think the best aftermarket filter is probably pipercross, as it's thick foam like motocross bike filters.

but even that is pain in the ass to clean. you get probably 20thou km with one original paperfilter, so the cost is hardly an issue.
 

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Anyone have a pipercross filter?

I wasn't looking at an aftermarket filter because I had one on the SV1000 (k&n) and the inside of the 'clean' side of the airbox would have a thin layer of fine dust on it.

But if the Pipercross filters as well as stock then I might be interested.

Cheers,

Daniel.
 
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