# Lightened Flywheel - Waste of Money?



## elelegido (Sep 24, 2014)

A few "experts" in the engine tuning forums claim that a $500 lightened flywheel is a worthwhile mod for decreasing 0-60 times. I've run some numbers and it looks like going from a 6kg to a 3kg flywheel would provide a horsepower increase equivalent at max. acceleration of only around 3bhp at best in first gear, with the HP increase equivalent obviously declining with each upshift.

There are a few gearheads on here - has anyone done a 0-60 comparison of before and after comparison with a flywheel mod?


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## Atavar (Aug 11, 2018)

No, but I know what I’d does for motorcycles. Decreasing flywheel mass increases responsiveness (by decreasing the time it takes to change rpm). At the same time it decreases the torque applied to the rear wheel. 
What this means is that it can actually hurt your 0-whatever time by removing torque, which is what gets you off the line. 
It will also make your engine less smooth. The flywheel mass is what keeps your engine spinning smoothly in between power pulses from the pistons. 
Another thing to consider is that your engine is balanced by balancing the flywheel _after_ it is installed on the engine. This is not a trivial task. 
If you are serious about reducing 0-60 times you would be better served by pressurizing the intake and opening up the exhaust and valves and remapping. All of these need to be done together. Doing only part will cause more problems than it will solve. 
There is no single piece magic bullet. Car manufacturers pay teams of highly educated engineers millions of dollars to design a well balanced engine. No shade tree mechanic is going to improve that. 
Spend your money on a faster car. Lol


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## elelegido (Sep 24, 2014)

Decreasing the mass of the flywheel improves vehicle acceleration time (because more of the torque of the engine is used to accelerate the vehicle and less to accelerate the flywheel); my question is by how much. I don't think that the rotational inertia of the flywheel over the linear inertia of the vehicle is going to be that great, meaning only a small increase in acceleration.

It would be possible to model it on a computer but I can't be bothered. It's much easier to just ask someone who's actually measured acceleration before and after the mod.


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## tohunt4me (Nov 23, 2015)

elelegido said:


> A few "experts" in the engine tuning forums claim that a $500 lightened flywheel is a worthwhile mod for decreasing 0-60 times. I've run some numbers and it looks like going from a 6kg to a 3kg flywheel would provide a horsepower increase equivalent at max. acceleration of only around 3bhp at best in first gear, with the HP increase equivalent obviously declining with each upshift.
> 
> There are a few gearheads on here - has anyone done a 0-60 comparison of before and after comparison with a flywheel mod?


Have you tried a K&N air filter ?
$50.00 & more H.P. & FUEL ECONOMY INCREASE .


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## Atavar (Aug 11, 2018)

tohunt4me said:


> Have you tried a K&N air filter ?
> $50.00 & more H.P. & FUEL ECONOMY INCREASE .


Opening up the intake without opening the exhaust and valves is going to cause issues. 
Besides, K&N’s aren’t really filters. They increase airflow precisely because they filter less.


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## Atavar (Aug 11, 2018)

elelegido said:


> Decreasing the mass of the flywheel improves vehicle acceleration time (because more of the torque of the engine is used to accelerate the vehicle and less to accelerate the flywheel); my question is by how much. I don't think that the rotational inertia of the flywheel over the linear inertia of the vehicle is going to be that great, meaning only a small increase in acceleration.
> 
> It would be possible to model it on a computer but I can't be bothered. It's much easier to just ask someone who's actually measured acceleration before and after the mod.


If this were true you could just remove the flywheel entirely for maximum mass reduction. The result would be your engine would run like crap and probably not be able to idle. 
You flywheel has already been engineered to have the optimum mass for your engine by people much smarter than you or I. 
If you want a faster car buy a faster car.


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## elelegido (Sep 24, 2014)

tohunt4me said:


> Have you tried a K&N air filter ?
> $50.00 & more H.P. & FUEL ECONOMY INCREASE .


Freeing up the intake and putting on a better manifold / free-flow exhaust would be within budget but all that would increase the noise level too much. If I did go down that route then I'd have to increase the soundproofing in the car.

I've had turbos before so I might just get a a turbo kit for it.

I'm not considering a flywheel swap; I was just wondering if anyone has done a before and after timing.


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## Atavar (Aug 11, 2018)

You can get a free flowing quiet exhaust. Bigger tubes with a good muffler tuned to the tubes. 
This still leaves the valves. Without enlarging valves and increasing their dwell if you open intake and exhaust you are going to have a bottleneck at valves and mess with scavenging. 
There are tons of kids here that put tons of money in their import pocket racers. Sure they sound nice but my big heavy stock minivan still beats them stoplight to stoplight. 
Going the shade tree tuning route is a money pit with diminishing returns. When it’s all done buying a faster car would have been cheaper and easier and you’d have a faster car. (With a warranty)


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## elelegido (Sep 24, 2014)

Atavar said:


> If this were true you could just remove the flywheel entirely for maximum mass reduction.


No, it wouldn't be possible to remove the flywheel entirely - it's a kinetic energy storage medium necessary for powering the engine through the compression strokes of each cylinder at low rpm.


> You flywheel has already been engineered to have the optimum mass for your engine by people much smarter than you or I.


Manufacturers build cars to be compromises that will appeal to and suit the widest number of consumers possible. For example, they build cars with modest states of tune with relatively low bhp/cc outputs because they have to cater to those customers who never service their cars or even change the oil. The manufacturer therefore selects the best compromise between output and longevity. However, drivers who regularly change the oil & filter and maintain their engines can comfortably increase their engines' state of tune without affecting reliability.

In the case of flywheels, the balance/compromise is between engine smoothness and efficiency. Average Joe Driver isn't going to want an engine with a slightly lumpy tickover or one that has a super-sensitive acceleration from idle to redline, so a heavier flywheel is specified. However, for the performance-minded driver who doesn't mind a slightly uneven idle or a super-responsive throttle, there are gains in efficiency to be had.


> If you want a faster car buy a faster car.


No, I'll be modding the engine of the car I have for more power. Partly because I like the car, partly because it handles like a go-kart and partly because I like wrenching.


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## Ted Fink (Mar 19, 2018)

Due to inflation speed is out, efficiency is the new trend... LOL

Do you race? Or just have a personal need for speed?


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## elelegido (Sep 24, 2014)

Atavar said:


> You can get a free flowing quiet exhaust. Bigger tubes with a good muffler tuned to the tubes.


True, although a K&N would still be loud


> This still leaves the valves. Without enlarging valves and increasing their dwell if you open intake and exhaust you are going to have a bottleneck at valves and mess with scavenging.


If I went this route, I'd just change the cams. Too much money, for me, to change the head and mess with valves.


> There are tons of kids here that put tons of money in their import pocket racers. Sure they sound nice but my big heavy stock minivan still beats them stoplight to stoplight.


Just depends where one is located. In the States, straight-line drag racing from light to light is important. This is why cars in the US weren't traditionally able to corner very well - they don't need to. The kind of driving I do includes a lot of canyon carving, where handling is as important as power. A big v6 minivan will be quick off the line, but a well-sorted rice rocket will leave it for dead in the twisties.

Plus, I think that a lot of the kids with Civics etc just put a fart cannon back box on the car and call it job done. Lots of noise but no go.


> Going the shade tree tuning route is a money pit with diminishing returns. When it’s all done buying a faster car would have been cheaper and easier and you’d have a faster car. (With a warranty)


There's not much challenge in that, though. For me, part of the fun is in the build. Each to his own.


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## elelegido (Sep 24, 2014)

Ted Fink said:


> Due to inflation speed is out, efficiency is the new trend... LOL
> 
> Do you race? Or just have a personal need for speed?


It's just a hobby. I've got this little Japanese car project that's worth less than $1,000. It's had some work done on the suspension and it's hilarious to drive. When I'm driving through the curvy back country roads and come up behind a Golf Gti or a $40,0000 BMW or Audi etc, they see this little old shitbox in the rear view mirror and accelerate away to try to shake it, but they can't. The car sticks to the road like glue in the corners, but it needs more power to reel them back in on the straights.


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## tohunt4me (Nov 23, 2015)

elelegido said:


> True, although a K&N would still be loud
> If I went this route, I'd just change the cams. Too much money, for me, to change the head and mess with valves.
> Just depends where one is located. In the States, straight-line drag racing from light to light is important. This is why cars in the US weren't traditionally able to corner very well - they don't need to. The kind of driving I do includes a lot of canyon carving, where handling is as important as power. A big v6 minivan will be quick off the line, but a well-sorted rice rocket will leave it for dead in the twisties.
> 
> ...


It's only loud ( er) when you stick your foot in it .


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## Atavar (Aug 11, 2018)

Go with a supercharger. Best bang for the buck horsepower wise.


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## CarpeNoctem (Sep 12, 2018)

From the simulations I have seen, a lighter flywheel would be good on tracks with tight corners as you get a faster response in accelerating/decelerating and also less weight being slung in the corners. I would look into it more if I had a dedicated track car but I wouldn't do it for a modified daily driver. In some situations, there are advantages for a heavier flywheel. So, YMMV.

I'm not a engine mechanic but play one on TV. I also stayed at a Ramada Inn last night so...


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## elelegido (Sep 24, 2014)

CarpeNoctem said:


> From the simulations I have seen, a lighter flywheel would be good on tracks with tight corners as you get a faster response in accelerating/decelerating and also less weight being slung in the corners. I would look into it more if I had a dedicated track car but I wouldn't do it for a modified daily driver. In some situations, there are advantages for a heavier flywheel. So, YMMV.
> 
> I'm not a engine mechanic but play one on TV. I also stayed at a Ramada Inn last night so...


Right, on a track car a difference of a tenth of a second per lap might be worth having. On a road car I would say the benefit per dollar is negligible.


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## tohunt4me (Nov 23, 2015)

Atavar said:


> Go with a supercharger. Best bang for the buck horsepower wise.


You need a computer to run the supercharger . $$$
( I only own 1 car that is supercharged. From the factory.)


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## elelegido (Sep 24, 2014)

tohunt4me said:


> You need a computer to run the supercharger . $$$
> ( I only own 1 car that is supercharged. From the factory.)


A lot of guys use a piggyback ECU on the main ECU for fuelling and ignition timing. They're not all that expensive to buy but the dyno time to set the map up properly could be.


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## TomTheAnt (Jan 1, 2019)

While you're in the modding mode, don't forget the Tornado. 









Tornado Air™ — More Power, More Mileage!


Drive 30-60 extra miles or your money back. Order online now!




www.tornadoair.com


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## UberBastid (Oct 1, 2016)

I used to have a Jeep CJ5, mid 70's I believe.
It had a 226 V6 "Dauntless" engine.
The flywheel was actually HEAVIER than the usual 226.
Why?
I was told that once you got that flywheel spinning, it was very difficult to stall the engine.
When climbing a steep hill, (very steep) in compound low, you could take your foot off the gas and let it idle and it would 'walk' up that incline. I had passengers 'bail out' because they got scared of the steepness of the climb and put a hand on the Jeep and it pulled them up a climb that they couldn't have done on foot without help.
I swear that Jeep would go places that a goat couldn't. 

I was standing around the campfire one night, a bunch of guys talking about the days hunt. Somebody asked me where I went, "Oh, I went past the dry pond, took the fork to the right and went on top of that big hill to scope."
He looked at me incredulously and said, "You hiked up there."
"No. I drove that Jeep" pointing at it "up there."
"You can't get a Jeep up there."
"Yes I did. There's a trail going up there."
"That's a quad trail. Nobody's gotten a vehicle up there."
"Well, nobody told my Jeep that; follow me out there tomorrow and I'll show you."
And I did.

It did cause a butt pucker ... but it did it and never spun a wheel.
That lil V6 just chugged and moved about 6 inches with every revolution, which was prolly about 60 rpm.

Was told that was mostly because of that heavy fly-wheel.


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## tohunt4me (Nov 23, 2015)

TomTheAnt said:


> While you're in the modding mode, don't forget the Tornado.
> 
> 
> 
> ...


" vortex"


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## tohunt4me (Nov 23, 2015)

Atavar said:


> Opening up the intake without opening the exhaust and valves is going to cause issues.
> Besides, K&N’s aren’t really filters. They increase airflow precisely because they filter less.


The Reusable oil bath filters filter More . . .but . . .
You gain top end mist lube . . . You will probably Lose a catalytic converter after a few years.

I had a 65 GM V-6 with a steel air filter. Strictly oil bath.
300,000 mile truck. 20 mpg. Heavy iron.


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## Stevie The magic Unicorn (Apr 3, 2018)

If you want to spend money to pretend that your car will go zoom zoom zoom a little faster my recommendation is a racing stripe. It will have absolutely no impact on your cars performance but it will make it look more like a race car.

And unlike any of these other suggestions you won't blow your engine failing to do it right or putting the wrong part in.

If you are feeling really frisky you can glue on a spoiler.











PS I 100% believe that my advice will not result in blowing out your engine.


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## elelegido (Sep 24, 2014)

TomTheAnt said:


> While you're in the modding mode, don't forget the Tornado.
> 
> 
> 
> ...


I will add it to the gasoline magnetizer fuel-saving filter. Between the two of them, the car will end up giving me fuel back instead of using it.


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## Atavar (Aug 11, 2018)

tohunt4me said:


> The Reusable oil bath filters filter More . . .but . . .
> You gain top end mist lube . . . You will probably Lose a catalytic converter after a few years.
> 
> I had a 65 GM V-6 with a steel air filter. Strictly oil bath.
> ...


Try this experiment. Pour some dirty water through a paper air filter in to a jar. Then pour some dirty water through your oily K&N filter in to another jar. See which water is dirtier.
Also, they quit using oil bath filters because they don’t work very well.


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## Null (Oct 6, 2015)

When a clutch is fully out your rotating mass becomes the combination of the engine, transmission, diffs, axles, wheels/tires, rotors, etc. 

A lightened flywheel as a percentage of this total is negligible, for clutch engaged acceleration.

Engine RPMs when slipping (partial clutch engagement), or freewheeling are easier to change up and down. For experts this can mean better/faster rev match with a lighter flywheel. However, a lighter flywheel can also cause RPMs to fall below the next gear for a rev match, so after a shift you may be using system inertia to accelerate the engine to match road speed (losing energy and time). 

Straight line acceleration under a clutch out scenario, the difference will be almost nil. You'd be better off with lighter wheels, an underdrive pulley or similar methods. With the wheels you also get an increase in suspension performance.

As an aside, I'm a trials motorcyclist. The flywheels on these 250cc-320cc 2 strokes can approach 10 pounds - they are MASSIVE relative to the displacement. They are extremely slow to increase revs freewheeling (clutch in) and take forever for revs to decline. 

However, what trials motorcyclists do is rev up the motor to store energy over time into these flywheels, and unleash it all in short bursts. This allows us punch to power up/over obstacles. It allows us to have much more torque than the gas engine can actually apply on demand from throttle alone. Another consequence is that the vibrations of the single cylinder configuration are massively reduced since the piston/crank velocity doesn't vary as much between strokes.

Lightened flywheels as a straight line acceleration tool is the wrong mindset. From a dig where you have time to preset a launch RPM a heavier flywheel will get the vehicle moving faster than a lighter flywheel.

Personally, I don't like light flywheels in almost any application. They tend to increase noise, increase vibrations, REQUIRES non-lazy shifting all the time, etc.


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## elelegido (Sep 24, 2014)

Null said:


> When a clutch is fully out your rotating mass becomes the combination of the engine, transmission, diffs, axles, wheels/tires, rotors, etc.
> 
> A lightened flywheel as a percentage of this total is negligible, for clutch engaged acceleration.


Yes, the rotational inertia of all those rotating parts is one consideration and, in an accelerating vehicle, the parts are also being accelerated linearly as the vehicle, and all its parts, are moved down the road from point A to point B. A lighter engine mass will mean faster vehicle acceleration because both rotational and linear inertia are reduced. The question is how much faster.

The effect on linear acceleration of a heavy flywheel is easy to see - all you have to do is put a spare flywheel in the trunk of the car and see what difference it makes. It's also easy to calculate. My car weighs 900kg and the standard flywheel weighs 6kg. Lightened 3kg flywheels are available, which would be a mass reduction of 3/900 = 0.333%. Stock 0-60 time is 11.9 seconds and since acceleration = force / mass, a 0.333% decrease in mass would mean a 0.333% increase in acceleration, bringing 0-60 down by 0.13 seconds to 11.86 seconds. Not much of a difference.

The effect on angular acceleration of lightening the flywheel can't be worked out the same way because the rotational inertia of all the drivetrain components is not known and it's further complicated by the fact that some of the components in the transmission and all of the components downstream of it are subject to the effects of gearing.

In order to work it out precisely, the torque curve of the engine would be needed, as well as a data dump from the ECU during a 0-60 run to see the acceleration of the engine at each engine rpm as it goes through the rev range.

I've done a guesstimate based on the rotational inertia of the flywheel and the estimated time it takes to accelerate from 4,000 - 5,000 rpm in first gear, and come up with the answer that a 3kg lighter flywheel is equivalent to adding 3bhp in first gear in that rev range. So, again, not much of a difference.


> Engine RPMs when slipping (partial clutch engagement), or freewheeling are easier to change up and down. For experts this can mean better/faster rev match with a lighter flywheel. However, a lighter flywheel can also cause RPMs to fall below the next gear for a rev match, so after a shift you may be using system inertia to accelerate the engine to match road speed (losing energy and time).


True, but most competent drivers can probably change up fast enough for that not to happen


> Straight line acceleration under a clutch out scenario, the difference will be almost nil. You'd be better off with lighter wheels, an underdrive pulley or similar methods. With the wheels you also get an increase in suspension performance.


Yes, the alloys on my car weigh around 30kg. With 15" alloys, 60mph is 860 wheel rpm - it takes a lot of torque to accelerate 30kg of wheels from 0 - 860rpm and linearly to 60mph in 11.9 seconds. Lighter wheels would help, but the expense would be high. Other than spending megabucks on magnesium or carbon wheels, I don't see how to reduce wheel mass.


> Lightened flywheels as a straight line acceleration tool is the wrong mindset.


It does seem to be. But it would be interesting to see if anyone has done a real world before/after comparison to be able to lay it to rest.


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## Null (Oct 6, 2015)

I can guarantee you several people on drag racing centric forums have beat this topic to death. 

The likely answer to whether or not lightened flywheels make material difference is "it depends." Drag racing v track, dirt v tarmac, turbo vs NA (lag), driver skill, car that rev matches vs not, etc.

Also what you driving that has THAT poor a 0-60. Even my Camry hybrid can do 0-60 in the high 7s.


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## tohunt4me (Nov 23, 2015)

Null said:


> When a clutch is fully out your rotating mass becomes the combination of the engine, transmission, diffs, axles, wheels/tires, rotors, etc.
> 
> A lightened flywheel as a percentage of this total is negligible, for clutch engaged acceleration.
> 
> ...


You skip the clutch ?


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## tohunt4me (Nov 23, 2015)

Atavar said:


> Try this experiment. Pour some dirty water through a paper air filter in to a jar. Then pour some dirty water through your oily K&N filter in to another jar. See which water is dirtier.
> Also, they quit using oil bath filters because they don’t work very well.


I only pour soapy water through an oil air filter to wash the dirt out !

Try THIS EXPERIMENT.

Blow out a paper air filter & an oil air filter with compressed air.

The paper air filter RELEASES MUCH MORE DIRT !

THE OIL TRAPS IT.


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## Null (Oct 6, 2015)

tohunt4me said:


> You skip the clutch ?


On a bike with a sequential gearbox? Usually.

In a manual car, no. Even with a syncro'ed transmission it's still faster to change gears if your gear selection and engine RPM match.


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## elelegido (Sep 24, 2014)

Null said:


> The likely answer to whether or not lightened flywheels make material difference is "it depends." Drag racing v track, dirt v tarmac, turbo vs NA (lag), driver skill, car that rev matches vs not, etc.


I don't see that it depends on any of those things. If you think about it, the amount of energy wasted on accelerating a heavy flywheel is _only_ dependent on the inertia of the flywheel. It doesn't matter if the flywheel is accelerated by a turbo engine or by a N/A - the energy required to accelerate a flywheel from, say, 3,000 to 7,000 rpm is going to be x Joules, regardless of the source of that power, and regardless of what happens at the other end of the drivetrain. It's just a question of how much torque is used to accelerate the excess mass of a heavy flywheel, which would otherwise be used to accelerate the vehicle.


> Also what you driving that has THAT poor a 0-60.


Small 1.4 litre Nissan; never sold in the USA. Very tuneable, though - 0-60 in the mid sixes is achievable by adding a turbo.


> Even my Camry hybrid can do 0-60 in the high 7s.


Yes, cars have improved a lot. I grew up in the 80s, when the 8 second 0-60 of a Porsche 944 was  .


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## elelegido (Sep 24, 2014)

tohunt4me said:


> I only pour soapy water through an oil air filter to wash the dirt out !
> 
> Try THIS EXPERIMENT.
> 
> ...


Sounds like an experiment for the Project Farm guy on Youtube.

I'd forgotten about foam and oil air filters. All my 70s bikes had them.


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## tohunt4me (Nov 23, 2015)

elelegido said:


> Sounds like an experiment for the Project Farm guy on Youtube.
> 
> I'd forgotten about foam and oil air filters. All my 70s bikes had them.


You can still buy a foam " wrap around" for circular air filters for use in ultra dusty conditions. Lawnmowers & outboard motors also used to use foam & oil.

K& N is cotton Fiber saturated with oil.
Not foam. Not paper.


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## elelegido (Sep 24, 2014)

tohunt4me said:


> outboard motors also used to use foam & oil


All the outboards I've had have been air filterless from the factory. I guess they think there's no dust or airborne particles out on the water. Probably true; they've been like that for a while.


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## tohunt4me (Nov 23, 2015)

J


elelegido said:


> All the outboards I've had have been air filterless from the factory. I guess they think there's no dust or airborne particles out on the water. Probably true; they've been like that for a while.


Just water.
Water can be hard on paper.

And Lots of Bugs in the swamp.


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## Atavar (Aug 11, 2018)

tohunt4me said:


> I only pour soapy water through an oil air filter to wash the dirt out !
> 
> Try THIS EXPERIMENT.
> 
> ...


Yeah, but you can see through K&N media


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## tohunt4me (Nov 23, 2015)

Atavar said:


> Yeah, but you can see through K&N media


It's cotton. It's sturdier


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## tohunt4me (Nov 23, 2015)

Null said:


> On a bike with a sequential gearbox? Usually.
> 
> In a manual car, no. Even with a syncro'ed transmission it's still faster to change gears if your gear selection and engine RPM match.


I used to have an old H-1 Kawasaki I would ride with a broke clutch cable. No problems.

Think I paid $400.00 for it back then. Was a teenager.


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## Atavar (Aug 11, 2018)

tohunt4me said:


> It's cotton. It's sturdier


You can still see through it.


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## Atavar (Aug 11, 2018)

K&N filters are good for racing applications where you really just want to filter out nuts and bolts and bugs, and where engine life is measured in hours.


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## tohunt4me (Nov 23, 2015)

Atavar said:


> You can still see through it.


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