Repco Air Filter - terrible?

marty085 · Postby **marty085** » Mon Jul 07, 2014 5:03 pm

Bought a Repco branded air filter yesterday, thought I'd give them the benefit of the doubt after the Repco guy told me the Ryco's quality are questionable lol. I put it in today and seriously, it's a different car... for the worse. It is struggling for air when you give it a bit of throttle, particularly in the lower rev range... it's just massively retarded now, and I use that term literally. I am thinking of taking it back tomorrow and telling them i'm just not happy with it. Anybody else had experience with repco filters? I noticed it has a HEAP more filter "folds" than the no-name one i pulled out.. there's so many of them that there's no gap between them.... Might take a photo this arvo and post it.

Edit: Might add that I bought this one after ordering and paying for a genuine Mazda air filter at the new Mazda Kirrawee store, only to be told when I went to pick it up that Mazda don't make/sell them anymore... WTF?

Mr Morlock · Postby **Mr Morlock** » Mon Jul 07, 2014 9:00 pm

Mazda sometimes stop selling certain items because these are readily available in the market place. Buy known brands if you can and Ryco does have a reputation.

bruce · Postby **bruce** » Mon Jul 07, 2014 9:02 pm

Just take it back and exchange it for a Ryco.

Ben MX5 · Postby **Ben MX5** » Mon Jul 07, 2014 9:20 pm

I just replaced a filter with a geniune Mazda item from MX5 Mania. Can't quiet remember what the old filter was - Repco or Ryco I think, it was pink and had many more folds than the standard Mazda item. I also noticed that it was a lot floppier and the rubber overmoulding had a few messy bits. I'm yet to give the new filter a proper run, but cruising it certainly sounded better.

Before picking a filter I asked a few older heads and got consistent feedback that OEM filters regularly replaced are the value performance option. I take it from the earlier posts that Ryco have a good rep too?

ED_MX5 · Postby **ED_MX5** » Mon Jul 07, 2014 9:57 pm

Just to clarify here, not mentioning any particular brand at all.
Unfortunately there has been a lot of misinformation regarding air filters and oil filters.

It is very difficult to comment on how an air filter acts by it's 'feel' because it filters differently.
Some filters are very good at keeping your engine clean because they filter a lot more of the fine particles out of the air. Some filters give good performance because of flow.

It is physically impossible to have both. If it flows, the hole is bigger allowing more sh*t to get into your engine. If it filters very well, it cannot flow because more is blocking the passage of air.

Think of it this way, if going by feel and response, the best air filter is...NONE.

People need to be aware of this. If you want to really protect your engine, use a ryco or equivelant. They have more folds/mesh to filter more crap out. A K&N filter by comparison will flow very well, but does not filter as well. Don't get me wrong, it's not as if a performance filter will blow up your engine, its just comparatively not as good at filtering.

Hope that makes your choice easier and more informed.
Same thing goes with oil filters and fuel filters btw, more flow, less filtering sh*t out.

marty085 · Postby **marty085** » Mon Jul 07, 2014 10:29 pm

Okay thanks for the feedback / comments. Some good points raised. I might take it back and swap it for a RYCO if they let me, I've always been happy with RYCO in the past. Drove it home and noticed same thing.. just really feels like it's struggling for air when you put your foot down. But I note the comments by ED about "feel".

Ben MX5 · Postby **Ben MX5** » Tue Jul 08, 2014 9:45 pm

Hi there,

I just wanted to respond to:

ED_MX5 wrote:It is physically impossible to have both. If it flows, the hole is bigger allowing more sh*t to get into your engine. If it filters very well, it cannot flow because more is blocking the passage of air.

This might be true in the practical sense of what's available for our cars...I don't know I'm a newbie...but at least in theory some filters can have better overall performance (e.g. a good filter might offer better flow but the same filtration as a bad one) because the restriction to flow is highly dependent on air velocity.

Extra folds provide more effective surface area so the air travels slower and so faces less resistance. But this only works up to a point - once the folds get too close together the narrow gaps between the folds impose a significant restriction of their own. It's a bit like selecting the number of fins on a heat sink.

It's not just the size of the holes that matter but also the number of holes. Imagine a 1m x 1m piece of steel mesh formed of 0.3mm thick wire spaced to define with 10mm x 10mm holes. Now imagine a 1m x 1m piece of steel mesh formed of 3mm thick wire spaced to define 10mm x 10mm holes. Both pieces will filter out the same size debris, but the second piece of mesh is going to be much more restrictive...no doubt filter manufacturers have spent a lot of money on this idea at a microscopic level.

The OEM filter element I just put in seems to flow better and has less folds than the pink one I just took out. I imagine that Mazda wouldn't cut any corners on filtration given they're responsible for warranty claims, so it seems the OEM filter is better overall.

Does anyone have industry experience with filters? Has anyone carefully tested filters?

-Ben

marty085 · Postby **marty085** » Tue Jul 08, 2014 10:10 pm

Ben MX5 wrote:Extra folds provide more effective surface area so the air travels slower and so faces less resistance. But this only works up to a point - once the folds get too close together the narrow gaps between the folds impose a significant restriction of their own. It's a bit like selecting the number of fins on a heat sink.

Yeah! That's exactly what I was thinking... there's virtually no gap between the folds in this Repco one.. still haven't taken a photo yet.. will do so ASAP.

93_Clubman · Postby **93_Clubman** » Wed Jul 09, 2014 12:10 pm

Ben MX5 wrote:Has anyone carefully tested filters?

Don't know about OEM style filter tests, but various pod filter tests follow:
http://www.australianauto.com.au/html/d ... %20Out.pdf

http://mkiv.com/techarticles/filters_test/2/index.html

http://mkiv.com/techarticles/filters_test/1/index.html

ED_MX5 · Postby **ED_MX5** » Wed Jul 09, 2014 4:03 pm

Ben_mx5,
You do have a valid point. You can still have decent flow and good filtration in one filter.
I was trying to keep it as simple as possible. But essentially I am was comparing good oem style replacement filters to high flow filters on a very broad scale. Going through all the different brands will yield many different results, some performance filters will out filter a cheap standard replacement etc etc depending on quality. The basic principal remains the same however. A designated high flow filter for performance will compromise filtration and vice versa. Same as car manufacturers with camber and tyre pressures. They set it up to be comfortable and quiet. We enthusiasts often prefer more feel and grip at the expense of some driver comfort, coil overs are best example... who in their right mind puts coil overs on a car for comfort??

ED_MX5 · Postby **ED_MX5** » Wed Jul 09, 2014 4:32 pm

http://www.bobistheoilguy.com/air-filtration-test/
http://www.bobistheoilguy.com/air-filte ... tion-test/
http://www.bobistheoilguy.com/air-filtr ... isclaimer/

As this guy says, these are not factory tests taken in a lab. Just a smart bloke in real world,
But he does this tests on his own Miata. There are more tests out there, but this is a good read too.
Some results are surprising..

Ben MX5 · Postby **Ben MX5** » Thu Jul 10, 2014 9:24 pm

Hi there Ed,

Thanks for the posts... I especially liked Bob's tests. It will be interesting to see when he publishes his pressure drop test results.

What do you use? What would you recommend for racing in the standard class? Does it really matter?

I'm new to all of this and am enjoying the engineering side of things as well as the driving, but am having trouble getting a handle on things given the amount of contradictory information and opinions out there - I spoke to one guy who is the proud owner of a Gemini that's been successfully campaigned for years without any filters at all!

ED_MX5 · Postby **ED_MX5** » Thu Jul 10, 2014 9:42 pm

HAHA.. yeah. heard that one before.
It really depends on what you mainly wish to use the car for?
Road or track?

Ben MX5 · Postby **Ben MX5** » Fri Jul 11, 2014 9:15 pm

Mostly track. The car is only a toy, so track work and club runs etc.

ED_MX5 · Postby **ED_MX5** » Fri Jul 11, 2014 10:04 pm

Ok then, a few options.
- Factory airbox, just use K&N they do work well as a PERFORMANCE filter.
-Custom intake with inlet near cold air, just use a metal gauze for trackwork. Least restriction.

I use just a gauze on my old race car.. mainly because of less restriction, and the motor gets pulled down more often than a road car anyway for inspection, so wear does not bother me quite so much. They are being used on an old set of webbers. If still being used on road, I'd suggest K&N, I have found they do have a good rep. And filter almost aswell as a standard filter. At the end of the day, you have to decide on whether you want longevity or power and just put up with a little more maintenance. Just remember will a K&N being an oiled filter, clean your intake every so often to get rid of oil residue.