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February 9, 2009 9:53 PM   Subscribe

Autofilter: Is there any other part of a car that I can replace and give a decent boost of performance like K&N Air Filter? Also my trunk door does not stay up.

A recent check-up has told me that the air filter and cabin air filter of my 05' Mazda 6 (2.3L) need to be replaced. Knowing that air filter is relatively easy to replace, I did not do it at dealer's place. (same place that inspected my car)

I then proceed to Autozone/Advanced Parts to get a quote on air filters of my car and was told by a clerk that, since my car is still pretty new, it's worth looking into a K&N air filter. "It's prolly the only air filter that you will feel a difference on performance, and you only need to clean it instead of replace it," according to him. Although I do know the importance of maintaining my car, I don't know too much about DIY tuning-up. My first question : Is there any other parts on a car that I can replace with almost-zero mechanic skill that gives performance improvement (or is considered a good investment)? Second question, I have the hatchback model and the trunk door does not stay up. The mechanics said something about replacing "shocks" and will cost $100+. Does this sound reasonable? Is it possible for me to replace them myself? If not would it make any difference if I get it replaced at the dealership or a cheaper place that I have had decent experience with?

My car is a 05' Mazda 6 2.3L hatchback with about 70k on it. Got the car last year and it's been very nice. Please pardon the long questions (trying to get my weekly question count) and thank you very much in advance!!
posted by jstarlee to Travel & Transportation (17 answers total)
You may want to look into better spark plugs and/or spark plug wires, depending on what the car already has. Those are pretty easy to install. I got an easy 1 MPG by putting Bosh platinum plugs in my Elantra.

The K&N filter may make a noticeable difference. I'd suggest not cleaning and re-oiling it; that can foul an air sensor if you do it wrong. Fortunately, you don't have to replace it very often, so it works out to about the same price as conventional filters over time.
posted by kindall at 10:05 PM on February 9, 2009

for the trunk, you're looking for a "Gas Strut". I'm not sure how hard they are too replace, it's not a spring, so it shouldn't be too hazardous or anything..
posted by defcom1 at 10:08 PM on February 9, 2009

the drop-in k&n filters won't really give you much of a power boost anyway. most always, gains that come from replacing your air intake typically involve removing the filter box and replacing it with a whole intake system like these, though to be honest most of the time these things are way overhyped too. it depends on your car, and on where the flow restrictions are, and so on. there's a good list for your car here, they claim 5-7 hp for a cold air intake, but the numbers on these boards are often inflated.

most of the time your best bang-for-the-buck performance upgrade on a stock car is the tires, frankly.
posted by sergeant sandwich at 10:14 PM on February 9, 2009

The gas spring that you are looking for is a very easy install. To get an idea of how easy it is, just lift up your trunk now and take a peek at the thing that looks like a shock attaching the trunk to the rest of the car. See how it is attached, that is all you will have to mess with to swap it out.

As for a filter, it is more than just a filter really, it is an intake. Yes, this is a very easy install, and if you get the right kind it can actually help power, sound, and gas mileage.

There are very few other tweaks that are so easy. If it is time to replace your tires, you can go with something grippy. You can feed it good gas. You can swap out the plugs (as mentioned above). You might look into an underdrive pulley (it lessens the load that your air conditioner and alternator put on your engine, at the cost of crappier A/C and power system). Anything else that will make a meaningful difference is going to cost money or labor.

Good luck!
posted by milqman at 10:17 PM on February 9, 2009 [1 favorite]

I have the hatchback model and the trunk door does not stay up. The mechanics said something about replacing "shocks" and will cost $100+. Does this sound reasonable?

Yes, and I don't know your specific car, but generally this is an easy replacement job.

Go fast:
-low restriction air filter, like K&N - dead easy, mild improvement
-relocate air filter with really low restriction - harder, a few hp to almost 10 hp depending upon vehicle.
-fancy plugs and wires - perhaps a few hp or so
-low restriction exhaust mods - expensive, not diy for you, another 10 hp perhaps, but likely a bit less
-if you have a turbo, drill out the boost lines - dead easy lots of hp gains, can I say voids the warranty
-mod chips, can make a real difference depending upon the vehicle, let someone else install it
-do you want really big gains? - add a turbo, add nitro, get really into it and blueprint
would you just like to look like you are going fast? add a wing.
posted by caddis at 10:18 PM on February 9, 2009

Stay way away from Bosh platinum plugs, pure junk. Use the plug that is made for your car, OEM.
posted by raildr at 10:27 PM on February 9, 2009

From the Mazda3 forums I've haunted (I have a 2005 2.3L '3):
  • A K&N filter will get about 2~3 BHP improvement - not noticeable. If you want to see more improvement without spending any money, get it dyno tested on a hot afternoon, wait, then put it back on the dyno on a cool morning.
  • The air intake on a 3 isn't too bad, all things considered - a new airbox / CAI will net about 5~6 BHP improvement on top of a K&N filter (7~10 BHP). From what I remember of the 2005 6's, the intake is actually better designed than the 3's (it's a bit cramped in the engine bay of a 3!), so I doubt you'd see that much difference.
Locally, K&N (& other foam filters) are colloquially known as "wombat filters" ('cos that's about all they'll stop from getting sucked into your engine). They don't work by filtering particulates through a paper screen like normal filters, but by sticking them to oil held on the foam mesh. If you don't clean and oil them regularly, more dirt / dust / other shit in = more wear.

Although mods like that have always been first on the boy hot-rodder's list, unless the engine is being grossly choked either by poor intake design (which most modern cars aren't) or because other engine mods (e.g forced air induction, longer cams, etc) necessitate better breathing, they're generally not worth the money.

If you're not the boy-racer type, stick with standard parts, keep your tyres pumped to specs & in good condition, and find a mechanic that does good tune-ups. Note that Mazdas have always had poorer low-down grunt than their opposition - it just seems to be their engine design philosophy. Though my current 3 has better low-down power than my mother's '75 808 (back when it was new!), my old 1.3L Toyota Corolla still had more...
posted by Pinback at 10:58 PM on February 9, 2009 [1 favorite]

It's fun to tweak cars, but if you want to make a real improvement in your cars performance, you'll have to take approach your car as a system. Aside from maybe playing with the car computer, there are few areas on a modern car where you can change one element and expect an improvement.

The single-item changes I can think of that make a real difference are:

- tires (grippier on corners, fun!)
- struts/shocks

I'd also look into whether there's data logging software for your car. There are some laptop packages that let you look at many aspects of your engine's performance. It's possible to spend a lot of time geeking out on graphs and stats - you may love it!

Other performance improvements (new cam, new valve springs, new air intake and exhaust, turbo/supercharger) are best undertaken after you are comfortable doing major work on your engine.
posted by zippy at 12:48 AM on February 10, 2009

I'd suggest as others have above, decent tyres, lighter wheels, better suspension components and higher octane fuel.
Modern engines are very efficient, and you will need to spend large amounts of money to get noticeable horsepower gains.
If you do the hatch struts yourself, make sure you remove and replace them one at a time.
Have fun, and drive safe!
posted by Duke999R at 2:24 AM on February 10, 2009

higher octane fuel


The amount of energy available in all fuels is roughly equivalent. The octane number refers to the fuel's resistance to detonation ("knocking"). In fact, you may notice that some gas stations don't call it octane rating, but rather AKI--"Anti Knock Index".

Now, it is true that if you have a high performance car, and you put lower octane fuel in it than the manual suggests, the engine management computer will retard the spark timing in order to prevent knocking. This will decrease performance.

However, giving a car higher octane than the manual suggests just wastes your money. The engine is going to run just like it always did.

It is true that if you install aftermarket engine management, or increase your compression through a turbo-/supercharger or piston mods, you may need higher octane to keep your engine from knocking. But, it isn't the fuel that's giving you higher power, it's the aggressive timing or higher compression.

Here's the wikipedia article on octane rating.
posted by Netzapper at 2:35 AM on February 10, 2009

higher octane fuel


That was once sound advice. These days it is not so easy. Modern cars have knock sensors and computers and some of them will advance the timing beyond spec if no knock is detected. I don't know if the Mazda 6 is one of these. A check of the racer boy forums for this vehicle would likely answer that question. If it is, using higher octane fuel would buy a few hp gains. I know for certain six cylinder Honda Accords from a few years back one of the design engineers publicly estimated a five to six hp gain from premium fuel on this vehicle rated for standard fuel.

posted by caddis at 4:19 AM on February 10, 2009

There is a downside to the K&N. Once you clean it, there is slight tendency to get a messed up mass airflow (MAF) sensor. Basically, what happens is the cotton gauze and the oil from the K&N are sucked inward and collect on the MAF's delicate probes, ruining them. This problem is widely known and something you should consider.

Honestly, one thing that's free and can improve performance is adjusting your tire pressures. You can adjust for under-steer and over-steer and really improve how the car feels -- corners, tracks. Try running 40 lbs in the front, 38 lbs in the back, for example. It make take a few attempts, but you can find the "zone" where your car feels perfect by making tiny adjustments front and back.

For the trunk strut: 1) go used. There are tons of salvage yards that part out wrecked cars. You can easily pick a strut up on the cheap. Ebay is another option. Then I would install it myself. Check your local library for a repair manuel for your car, or find a forum; it probably only requires basic tools and half an hour.
posted by luckypozzo at 5:10 AM on February 10, 2009

Nice car! I really like those.

Caddis is right, higher octane *may* perform better. I had a Ford Contour, which is on the same family tree as the Mazda 6, and it benefitted from higher octane fuel. There were sensors that changed timing and whatnot to take advantage of the higher octane. I think that engine has some variety of variable valve timing, and I wouldn't be surprised if moving up to a higher grade made the car feel a little faster.

I have had K&N filters on a couple of cars, and had no problem with them. Maybe it was the placebo effect, but both cars felt a little peppier. Maybe not more powerful in HP ratings, but definitely in letting the motor rev a little easier. In both cars, the engine felt torquier. Sounded better too. Was it worth the $50? Yeah, to me it was.

One of the cars, I purchased brand new and installed the K&N right away. I had zero issues with dirt or wear. Three years and 40,000 miles later, the engine was as clean as factory. No deposits, no performance issues, no dirt in the intake passages. Cleaner, IMHO, than cars with regular filters.

I'd stay away from the cold-air types of intakes. They can wreck havoc with the engine management sensors. I've never seen a car with one that didn't develop some kind of idle issue.

I'm sure there are enthusiast forums out there, start reading those and get a feel for what they are doing. Sometimes there is really good info out there.

Best advice short of bolting stuff on, is make sure the engine is in top tune.

If you have platinum spark plugs, they probably will last the 100,000 miles they are supposed to. When/if you decide to replace them, go with whatever is the factory replacement. In the Contour, which came with Autolite double platinums, I decided to replace them with the fancy Bosch 4+ plugs at 70,000 miles, just because I figured it was about time. The plugs I pulled out were pristine- perfectly within specification and no deposits. With the new plugs, the car ran like crap. A few thousand miles later, I put a new set of the Autolites in and the car was back to normal. And the Bosch plugs looked pretty bad. If the car specifies double platinum, make sure that's what you use.

Can't speak to the Mazda, but I can tell you that in that Contour, all the factory components were top notch. The spark plug wires were much sturdier than even the "premium" wires at the stores. I replaced them with another set of the Motorcraft ones at 100,000+ miles and it made no difference- the existing ones were working just fine.

Another thing to consider is the oxygen sensor- as they age, they start to get imprecise. They won't trigger an error, but gas mileage will start to go down and the idle will get rougher. Same advice as above- unless there is a known issue with the factory sensor and the fanboys are unanimous about a preferred replacement, use the same brand that was installed in the car from the factory.

Keep an ear out for rumbly noises from the wheels. The Contours were known to have wheel bearing issues. When I replaced mine, I noted a return to better MPG and performance. The bearing was bad enough that it was adding friction.
posted by gjc at 5:11 AM on February 10, 2009

luckypozzo makes a good point. The MAF is susceptible to that problem in some cars. They make a MAF clearer in a spray can- that should probably be part of regular maintenance. 2-4 times a year, give the thing a little bath and it should be fine. They work by putting a tiny heated wire in the path of the incoming air. The computer calculates the difference between the power it puts into the sensor and the power it gets out (speaking roughly) versus the temperature of the air, and uses this to calculate the mass of the air coming into the engine. It uses this to determine the correct amount of fuel to inject to match the mass of the air going into the engine. If it's not cleaned regularly, gunk can build up and eventually wreck the tiny wire.

Oh, and when you are changing the struts on the hatch, don't do what I what this guy I know did and climb into the trunk with the hatch unsupported, disconnect the strut and let the hatch slam down on your back nearly severing your spine. It hurts...
posted by gjc at 5:20 AM on February 10, 2009

Lots of good advice in here so far. One word about replacing your air filter though.

Although I just purchased a K&N air filter myself, for my '02 trans am, I now regret it. After doing some reading, it turns out that replacing the air filter with a "better" one is pretty much useless. The reason is that to your engine, there is no difference between the air restriction from your air filter and the air restriction from the throttle plate. So unless you're driving around at full throttle all the time, you won't notice any difference. And for my car at least, the stock air filters are good for 450hp+.

gjc makes another good point and is dead on with his description of oil fouling the MAF sensor.

Replacing your hatch struts is pretty easy; I just helped my roommate do his a few weeks ago. They may cost a hundred bucks or so though.

For cheap performance, there really isn't a whole lot you can do. An aftermarket intake will give you a few hp and better throttle response. An aftermarket exhaust would probably be your next move, that will give you a few additional hp and improve the sound of your car (hopefully). Do not mess with your ignition (wires/plugs/blah), useless waste of time. Modern cars come with perfectly fine ignition wires, coils, plugs etc. It's in the OEM's best interest to get good gas mileage and performance, they don't skimp on simple things like that.

Beyond that, you're looking at an aftermarket chip or a tune, a new cam, headers, or forced induction. Good luck and have fun!
posted by lohmannn at 6:15 AM on February 10, 2009

Thank you everyone for the answers!

So basically
-- K&N air filter : be careful with cleaning (or just not clean it to avoid messing up MAF sensor)
-- Spark plugs : Not hard to replace, stay with factory part
-- Trunk Strut : Get used and be careful replacing it.
-- High Octace Gas : Check owner's manual first for recommendation.

Again thank you all for all the detailed answers and your time!
posted by jstarlee at 9:20 AM on February 10, 2009

To add speed, add lightness.

Look into weight reduction. You'll get a performance gain simply by driving with a quarter tank vs. a full tank.
posted by mullingitover at 11:19 AM on February 10, 2009

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