View Full Version : K&N airfilter and dyno on St1300

Red Brown
01-17-2006, 10:22 PM
Hi Folks,

I read the following...

"Before installing the filter, Tissen made several dyno runs with the stock configuration to get a baseline for comparison. In stock form, our long-term ST1300 belted out 111.7hp at 7750 RPM on K&N's Dynojet. After installing the K&N replacement filter, we were amazed to see peak power jump to 117.74hp at 7500 RPM, a solid 6hp gain. The ST1300 picked up power everywhere, gaining 2.5hp at 2500 RPM, 2.8hp at 4000 RPM, and 5.2hp at 5500 RPM."

I am considering using a K&N but have heard from quiet a few riders mentioned the filters tend to also allow more dirt particles to pass through due to increased air-flow.

Is this a problem with K&N and other high-permance air filters?


01-17-2006, 11:24 PM
You will find most of us are running with the stock filter on the ST1300. Mark has some good feedback on filters on his site. (http://motorcycleinfo.calsci.com/Consumables.html#AirFilters)

Post this over on ST-OWNERS, I'm sure Rob or someone else will have some excellent input.

In my opinion, don't waste your money, but that just my opinion.


01-17-2006, 11:44 PM
:tab For a street bike, I think the more dirt argument is a red herring (something of a distraction from the real issues). Of course, the only way to know for sure would be to test the oil in two bikes ridden in similar conditions, one with the K&N and one with the OEM filter. I have used K&N on ALL of my street bikes and have put lots of miles on them (60K, 47K, 45K) and have NEVER had any problems with the K&N's. On the plus side, they have always improved throttle response and made the bikes run a little better. I dyno'd both VFR's and it does help with the dip around 5500rpm and adds a few HP across the rev range.

:tab Now lets talk about DS and dirt bikes... Maybe more dirt gets through, although I would still have to see something serious to convince me. I ran a K&N on the GS and that bike saw some MAJOR dusty/dirty conditions, yet when I cleaned the filter, everything downstream of the filter was totally clean and dirt free. The kicker is that the filter would have dirt literally caked up on the outside of it!! Often times this was the case even after only a few days of riding. Obviously the filter has to be cleaned a LOT in dirty conditions. This is why I use the K&N. Replacing the OEM filters on the GS would cost a fortune as they are more expensive than the K&N!! I can pull the K&N and clean them to my heart's content, over and over...

:tab Sometimes I think things like this boil down to those people that have to eek out that tiny teeny last little ounce of perfect performance. It does not matter of they have long since gone past the point of diminishing returns compared to the cost put into getting that last little bit. All the places where dirt small enough to get through a K&N can go are pretty big and the likelihood of something that small causing serious damage to an engine is very remote. Worst case you might have something that could melt and build up over a LONG time somewhere like a valve seat and you'd lose a tiny bit of compression, probably not much worse than having your valves too loose. Most bikes are more likely to build up carbon deposits that will cause more problems before something like this became an issue.

:tab Anyway, that is my nonexpert empirically based opinion :-P

Red Brown
01-18-2006, 09:41 AM

Thanks for the feedback. I get a faster response on the TWT site than on others ;-)

Anyway, the dyno checked article in favor of the K&N seems to oppose the other article that indicated very little performance improvement. The first article indicated a 6 HP gain using K&N on a ST1300.

I think dyno runs can vary based on a number of factors just beyond the add-on improvements. The dyno can also differ based on the individual's knowledge conducting them.

Oh well....stick with OEM. I can still get to 145 MPH with stock :trust:


01-18-2006, 09:47 AM
I had a discussion about filters with a friend who operates heavy commercial equipment. He says that it's not the dirt you see that does the damage, but the dirt you don't see - the very fine particles that get through. So, if a K&N or other aftermarket filter will capture particles as small as the OEM filter, then you're doing no harm. His other observation was that a dirty filter does a more thorough job of filtration than a clean filter, because larger particles will obstruct paths that the smaller particles might have gotten through. Of course, engine performance begins to suffer at some point because the air can't get through either. ;-)

01-18-2006, 01:41 PM
He says that it's not the dirt you see that does the damage, but the dirt you don't see - the very fine particles that get through.

:tab Right, and that is why I mentioned oil analysis. Anything small enough to not be seen is not going to score pistons, tear piston rings, obstruct valves, etc,... However, if there is build up in the oil, then perhaps it might start doing some damage over time. This is part of the reason why dirt riders change their oil so frequently as compared to street bikes.

Cagiva 549
01-18-2006, 04:16 PM
when I first started running diesel engines in my trucks I ordered K&N filters to the tune of $60 each I thought this is the ticket . I ran oil anylises from the begining . My first service with the K&N the dirt levels in the used oil had quadrupled , I left it on for the next service ,dirt was still high , after the third service and no change the paper filters went back in . one of those engines was parked at about 300,000 miles the transmission got tired the other one was still running good at 250,000 the body crapped out around it . 2 K&N filters for 6.9 ford diesels for sale , cheap . SEYA

01-18-2006, 04:21 PM
:tab Dave, just curious. Obviously, with any filter, some stuff gets in. Is there an accepted level of contamination? Also, what type of problems would you see with more dirt in the engine? Buildup? Scoring of surfaces? Bearing failures? Like I said, I am no expert, but I am surprised that any great quantity of dirt entering the engine through the air/fuel mixture would so easily find it's way into the oil system :scratch: Wouldn't that mean it was getting by the piston rings? Or is there another path for it to get to the oil? Perhaps a crankcase breather?

Cagiva 549
01-18-2006, 05:35 PM
Dirt going into the engine with the air will stick to the cylinder walls on the compression stroke and end up in the oil . It works like valve grinding compound on the rings and cylinders in the process. When enough dirt is in the oil it will wipe out the bearings as well . We are talking very small particles here , The oil filter will trap any thing bigger than 30 microns . Once the process starts it accelerates rapidly , more ring wear , more dirt bypass . Most big engines use bypass oil filtering , That filters oil down to 3 microns but the filter process restricks oil flow so much that only a small amount of total flow can go thru the bypass filter, but what goes thru comes out very clean. The air intake has to balance the amount of air it can flow with the amount of restriction to trap contiaminats . the only way to increase flow with out increasing dirt is to increase the size of the air filter . My old Husky had a three stage foam filter about a foot long and 8 inches high , I could race a month with out cleaning the filter while some other brand bikes had to change filters at pit stops in a dusty race. I have never seen specs or micron ratings on air filters but would like to . but I have seen the results of improper filtration . One of our backhoes that I serviced this week is headed to the auction , The nut that holds the filter inside the filter housing broke since the last time it was serviced . I dont know how long it was broken but the engine is gone , the compression is so low it is hard to start, and that all happened in 250 hours . I tend to go to the excess to make my engines last a long life , I dont work on stuff for a hobby . Now if you are racing an engine you will probably fresh it up every few races in that case toss the filter and run V stacks , after all more air = more power and thats what it's all about . The most efficient air filter I have seen were the old oil bath filters used back in the 50's , Very low air restiction , no replacment , just clean it and add new oil, They had to be serviced though . If not the dirt and oil would turn to a solid block in the bottom and it would no longer filter. I love bikes with big air boxes , The bigger the element the less you have to service it . SEYA