Donaldson/Tempest Filters

[Brian2034]

Time to dump the Brackett and upgrade? To a different filter 

Donaldson or Tempest

The Donaldson has good reviews and seems to offer an increase in manifold pressure. (On back order in Canada)

I can’t find much information on the Tempest filter but some forums say Tempest are the same type filter as the Donaldson, some have suggested the Tempest is a relabeled Donaldson. (available in Canada).

Any experience here with either, especially the Tempest 

[jetdriven]

We put a Tempest filter on a Piper Arrow and it seems equivalent to a Donaldson, its synthetic paper media.  They flow more air than a Brackett.

[Marc_B]

@Brian2034 I've used Donaldson filters since I purchased the Mooney.  Easy to care for.  Works well.  No experience with Tempest, but sounds like they're equivalent.  If you can't find one, go with the other.  They're both synthetic media.

[Brian2034]

8 hours ago, jetdriven said:

We put a Tempest filter on a Piper Arrow and it seems equivalent to a Donaldson, its synthetic paper media.  They flow more air than a Brackett.

That’s what I was thinking, Donaldson and Tempest are the same type filter. It looks like Spruce.ca carries Tempest but has to special order Donaldson.

[testwest]

I'll have a Challenger filter for an M20J for sale in the classifieds as soon as my supporter status gets updated.  P/N CP-1174. Hope this is not too much of a thread drift....

[McMooney]

Is there a replacement for the brackett that's on my E?

[N201MKTurbo]

What’s wrong with the Brackett? A good Arizona product. My intake ducts always seem clean.

[Paul Thomas]

7 hours ago, testwest said:

I'll have a Challenger filter for an M20J for sale in the classifieds as soon as my supporter status gets updated.  P/N CP-1174. Hope this is not too much of a thread drift....

When ram air has no effect on performance, do those actually make a difference over the stock foam filter?

I get the other benefits, I'm speaking purely about performance.

[testwest]

The idea is a bit less loss in the induction path, so a *small* amount of better efficiency. Lots of little things can eventually add up. That is why Jetdriven's Mooney is so fast. Our Mooney became a 162 KTAS cruiser instead of 155 KTAS on the same gas, with lots of small efficiency improvements such as the filter, antenna removal and relocation, tail fairings, Lopresti cowl and so on. 

 

[Vance Harral]

Chiming in with the "no free lunch" reminder.  Nothing wrong with chasing a few extra horsepower, but any filter that allows more air to flow will by definition allow more foreign material into the engine as well.  There is no magic filter material that overcomes this universal truth.

That said, my understanding is that essentially any filter is "adequate", and there's of course no simple calculation for how many more days/weeks/months you can run your engine with better filtering/less airflow, vs. an alternative.

The best reason to use something other than a Brackett filter is probably just to avoid the oily goo that comes with it, performance and longevity questions aside.  I think about this every time I change our filter and wipe the goo off my hands and the airframe.  But I've yet to try an alternative.

Most recent thread I can find on this recurring topic: 

 

[neilpilot]

On 6/24/2025 at 11:27 AM, Vance Harral said:

Nothing wrong with chasing a few extra horsepower, but any filter that allows more air to flow will by definition allow more foreign material into the engine as well.  There is no magic filter material that overcomes this universal truth.

Actually, this is not true.  It is indeed possible for a filter's design to be altered to allow lower pressure drop and/or more air flow while providing equal or even superior solids removal.  Not saying this applies to Donaldson filters or any Mooney air filters, but in general terms regarding air (and liquid) filtration.  Filter media geometry can make a significant difference.  It's no magic, but engineering.

[Vance Harral]

20 minutes ago, neilpilot said:

It is indeed possible for a filter's design to be altered to allow lower pressure drop and/or more air flow while providing equal or even superior solids removal.

Sounds like the claims of gasoline additives that improve mileage.  Maybe a grain of theoretical truth, but never seems to hold up when put to a practical test.  I'm only interested in practical data, and I'll believe it when I see it.  If you've actually got some, I'm all ears.

The most recent serious, scientific look I've seen on this stuff is from a Kitplanes article: https://www.kitplanes.com/oil-filter-testing/.  The topic is oil filtration rather than air, but the principles are the same:  The report can be summarized as: "more flow = more dirt".  Again, though, one can't necessarily jump to the conclusion that "more dirt = less engine life".  For any given airplane in any given environment and working life, there is some level of filtration that's adequate, and anything better than that isn't meaningful.

What I do think is meaningful is that if you're really going to go chase this idea of better intake flow, the first thing you should do is fly a short flight with no air filter at all and gather data.  You're not going to destroy your engine doing so, and it will show you the limit of what's possible.  In those vintages of Mooney that have a ram air door, you can perform the experiment simply by opening the ram air door, perhaps shortly after takeoff when you're away from most of the dirt.

[EricJ]

Just now, Vance Harral said:

Sounds like the claims of gasoline additives that improve mileage.  Maybe a grain of theoretical truth, but never seems to hold up when put to a practical test.  I'm only interested in practical data, and I'll believe it when I see it.  If you've actually got some, I'm all ears.

It's pretty trivial.    Increasing the area of the filter media makes it flow better while maintaining the filtering ability.   That's pretty intuitive.   Paper pleats easily and allows a LOT more media area in the same filter volume than most other media, and it filters way better than cotton or oiled foam, for example, neither of which pleat well.

Science! 

[Vance Harral]

50 minutes ago, EricJ said:

That's pretty intuitive.

Intuition is not data, and is frequently wrong.

If it were a simple matter of "more area = more flow", then the best solution would be to speed tape 2 or 3 or 4 filters in front of each other at the airbox.  That's even more media area, so it must mean more flow, right?  Also, if I remove the air filter altogether, the filter media area is zero, so does that mean the flow rate is worse with no filter than with a filter?

Obviously this doesn't pass the smell test.  Probably because the flow equation in a real world installation is more complicated than you're making out.  If we want to go full nerd, the relevant equation is Darcy's Law, which models the flow of fluid through a filter as a function not only of filter area, but also of pressure differential across the filter.  I'm not smart enough to describe the relationship between pressure drop and number of pleats in an aviation air filter, but I'm willing to bet there's a dependency.

Anyway... I promise I'm not just trying to be a contrarian about it.  But saying "it's intuitive", or "Science" isn't going to sway me.  Data or nothing, and the only data I'm aware of says that for products actually on the market, "more flow = more dirt".  Again, and I can't emphasize this enough, that doesn't mean "more flow = less engine life".  There is some quantity of dirt below which there is no meaningful impact on engine life, and high flow filters may well be above that threshold for most operators.

 

[Slick Nick]

Your oversimplification is incorrect. You can increase flow without decreasing filtration. 

To use round numbers, let’s say an engine gets all the air it needs with a 10cm x 10cm square filter. So 100 square centimetres satisfies the needs of the engine at full throttle, at all Rpm’s. Suppose the filter area provided was 12x12cm now. You can afford to run a finer filter media, filtering MORE dirt, while still giving the engine all of the air it can physically deal with. If the stock size filter is more than adequate for the needs of the engine, then there are improvements to be made in filtration without sacrificing the amount of air available to the engine. 

[EricJ]

1 hour ago, Vance Harral said:

Intuition is not data, and is frequently wrong.

What I said is correct.   Apparently my error was assuming something that is intuitive to many/most would also be intuitive to you.    My bad.

1 hour ago, Vance Harral said:

If it were a simple matter of "more area = more flow", then the best solution would be to speed tape 2 or 3 or 4 filters in front of each other at the airbox.  That's even more media area, so it must mean more flow, right?  Also, if I remove the air filter altogether, the filter media area is zero, so does that mean the flow rate is worse with no filter than with a filter?

Serializing filters doesn't increase the area.   That should be intuitive, too, but I know now to give you a pass on that.   Most media filter pressure drop behaviors are characterized, at least on a first order, per unit area.   So you can decrease the pressure drop by increasing the area of the filter, or increase the flow rate by keeping the pressure drop constant.   It's similar to a pressure drop across anything, including a hose or pipe, and increasing the area of the hose/pipe allows more flow with the same pressure.    Intuitive to many, mathematically demonstrable to the skeptical, but I leave that as an exercise for the interested.

1 hour ago, Vance Harral said:

Obviously this doesn't pass the smell test.  Probably because the flow equation in a real world installation is more complicated than you're making out.  If we want to go full nerd, the relevant equation is Darcy's Law, which models the flow of fluid through a filter as a function not only of filter area, but also of pressure differential across the filter.  I'm not smart enough to describe the relationship between pressure drop and number of pleats in an aviation air filter, but I'm willing to bet there's a dependency.

There you have it.    Darcy's law:  Q=-K*A*(dh/dl), where Q is the volumetric flow rate, K is a measure of conductivity of the media (porosity, sort of), A is the area of the filter, and (dh/dl) is essentially the pressure drop across the filter.   It's pretty trivial to see that all other things being equal, increasing the area A linearly increases the flow rate of the filter, with a constant pressure drop (dh/dl).  Pleating a paper filter increases the available surface area of the media in a constant volume of filter space.    Stacking one on top of the other does not increase the area, it just doubles the drop (dh/dl). 

1 hour ago, Vance Harral said:

Anyway... I promise I'm not just trying to be a contrarian about it.  But saying "it's intuitive", or "Science" isn't going to sway me.

That's okay.    It's true whether or not you're swayed.

[Vance Harral]

43 minutes ago, Slick Nick said:

If the stock size filter is more than adequate for the needs of the engine, then there are improvements to be made in filtration without sacrificing the amount of air available to the engine. 

Sure.  But the stock size filter is not necessarily "more than adequate for the needs of the engine", for practical reasons.

To give one example, the original M20 design used a Continental C-145 engine, whose intake path nicely matched the position of the "chin" airframe intake on the cowl, and the size of that intake presumably provided plenty of air to the engine.  When the design was retrofitted with a Lycoming O-360, the airfame intake was no longer aligned with the engine intake, and this was resolved with an air box that makes the air effectively traverse an S-turn, reducing induction efficiency.  The Lycoming also needed slightly more air to make rated power.  But the cowl was not redesigned at the time for whatever reason.  I don't know if it was the total air volume or the S-turn that had the most impact, but the combination of those things produced a sub-optimal induction system, which was mitigated with the ram air system, which does produce a small power increase when opened.  This small but observable power increase means that with ram air closed, the induction system is definitely not "more than adequate for the needs of the engine".  Ergo, those airplanes can get a small performance benefit from a more free-flowing filter, at the expense of allowing more foreign material entering the engine.

Mooney dropped the ram air in later models with better cowls and induction designs because it provided no benefit, and I speculate that in those designs, the airflow provided by the stock filter is indeed more than adequate for the needs of the engine as you say.  If that's true, there would also be no benefit to a more free-flowing filter (and the dirt it allows) in those airplanes, because the extra air volume such a filter would allow wouldn't actually benefit the engine.  That doesn't stop 201 and Ovation owners from considering "better" filters in search of a few extra horsepower, and I'm not smart enough to say they're wrong to do so.

[Vance Harral]

23 minutes ago, EricJ said:

 It's pretty trivial to see that all other things being equal, increasing the area A linearly increases the flow rate of the filter, with a constant pressure drop (dh/dl).

"All other things being equal"... This is the part I'm not getting.  Are you saying the pressure drop dh/dl is independent of the filter media area?  As in, there is the same pressure drop from the front to the back side of the filter regardless of whether the filter media has zero surface area (i.e. there is no filter), or it's an infinitely folded pleat?  If that's actually the case, then yeah, it's just linear math.  But I don't think that's how it works.  I'm open to enlightenment.

 

26 minutes ago, EricJ said:

Stacking one on top of the other does not increase the area, it just doubles the drop (dh/dl).

That's my point.  You can't change the design of the filter - including its total surface area - without changing the drop dh/dl.

Stacking two filters on top of each other most certainly does change the total surface area of filter material that the air passes through, but you're arguing that doesn't count because of the pressure drop it causes.  I'm still trying to understand why the design of a single sheet (of however many pleats) doesn't also cause a variation in pressure drop.

[philiplane]

On 6/23/2025 at 10:59 PM, N201MKTurbo said:

What’s wrong with the Brackett? A good Arizona product. My intake ducts always seem clean.

Bracket filters are oiled foam. They are restrictive, and don't filter as well as a cellulose media filter. (What some refer to as a "paper filter", but cellulose media replaced paper decades ago.) 

There are plenty of studies on filter airflow comparisons. Cellulose media is best, oiled gauze is second, and oiled foam is last. As a bonus, cellulose media not only flows best, but filters best too.

[Slick Nick]

1 hour ago, Vance Harral said:

Sure.  But the stock size filter is not necessarily "more than adequate for the needs of the engine", for practical reasons.

To give one example, the original M20 design used a Continental C-145 engine, whose intake path nicely matched the position of the "chin" airframe intake on the cowl, and the size of that intake presumably provided plenty of air to the engine.  When the design was retrofitted with a Lycoming O-360, the airfame intake was no longer aligned with the engine intake, and this was resolved with an air box that makes the air effectively traverse an S-turn, reducing induction efficiency.  The Lycoming also needed slightly more air to make rated power.  But the cowl was not redesigned at the time for whatever reason.  I don't know if it was the total air volume or the S-turn that had the most impact, but the combination of those things produced a sub-optimal induction system, which was mitigated with the ram air system, which does produce a small power increase when opened.  This small but observable power increase means that with ram air closed, the induction system is definitely not "more than adequate for the needs of the engine".  Ergo, those airplanes can get a small performance benefit from a more free-flowing filter, at the expense of allowing more foreign material entering the engine.

Mooney dropped the ram air in later models with better cowls and induction designs because it provided no benefit, and I speculate that in those designs, the airflow provided by the stock filter is indeed more than adequate for the needs of the engine as you say.  If that's true, there would also be no benefit to a more free-flowing filter (and the dirt it allows) in those airplanes, because the extra air volume such a filter would allow wouldn't actually benefit the engine.  That doesn't stop 201 and Ovation owners from considering "better" filters in search of a few extra horsepower, and I'm not smart enough to say they're wrong to do so.

I was speaking in reference to the later J model which had a redesigned induction system that did away with the ram air system entirely, since it no longer provided a benefit. For the record, I run a Donaldson on my MSE since I believe them to be a better quality filter. 

[N201MKTurbo]

1 hour ago, philiplane said:

Bracket filters are oiled foam. They are restrictive, and don't filter as well as a cellulose media filter. (What some refer to as a "paper filter", but cellulose media replaced paper decades ago.) 

There are plenty of studies on filter airflow comparisons. Cellulose media is best, oiled gauze is second, and oiled foam is last. As a bonus, cellulose media not only flows best, but filters best too.

That’s what the other filter guys say anyway.

Do you have any references?

[Pinecone]

There was a test on car air filters a number of years ago.

The testing found that a brand new factory paper filter flowed as much air as a cleaned and freshly oiled K&N.  And the paper one filtered better.

As the filters got dirty, the paper air filter showed greater and greater restriction with the same level of filtering.  The K&N showed little change in flow rate, but it actually filtered better as it got dirty.

[philiplane]

https://aviationconsumer.com/maintenance/engine-air-filters-dry-pleats-or-oiled/

Donaldson also published their study on filter media, it is in their product support library. And they can make any type filtration a customer wants. Cellulose media, foam, inertial, and even oil bath.

Unlike K&N, who only makes oiled cotton gauze filters, and Brackett, who only makes oiled foam filters.

Edited June 26 by philiplane

[EricJ]

15 hours ago, Vance Harral said:

"All other things being equal"... This is the part I'm not getting.  Are you saying the pressure drop dh/dl is independent of the filter media area?  As in, there is the same pressure drop from the front to the back side of the filter regardless of whether the filter media has zero surface area (i.e. there is no filter), or it's an infinitely folded pleat?  If that's actually the case, then yeah, it's just linear math.  But I don't think that's how it works.  I'm open to enlightenment.

dh/dl is hydraulic drop per length that the fluid travels through the media.   If the input pressure is the same and the depth of the media is the same, the drop will be the same.   That's why stacking filters doubles the drop, because it doubles dl.

15 hours ago, Vance Harral said:

That's my point.  You can't change the design of the filter - including its total surface area - without changing the drop dh/dl.

And the point of pleating is that it increases the area of the filter media within a particular volume without increasing dl.   

15 hours ago, Vance Harral said:

Stacking two filters on top of each other most certainly does change the total surface area of filter material that the air passes through,

No, it doubles dl.   The air gap between them is just an air gap.

[N201MKTurbo]

4 hours ago, philiplane said:

https://aviationconsumer.com/maintenance/engine-air-filters-dry-pleats-or-oiled/

Donaldson also published their study on filter media, it is in their product support library. And they can make any type filtration a customer wants. Cellulose media, foam, inertial, and even oil bath.

Unlike K&N, who only makes oiled cotton gauze filters, and Brackett, who only makes oiled foam filters.

All the data from the article is on page 22 which isn’t in the web version of the article.