Resource

Alot of the single turbo guys including myself often put mesh screen over their turbos thinking that it will give them optimum flow.

If you take the time to measure each and every wire on the screen mesh and do the calculation you will see that the screen mesh is much more restrictive than the popular K&N type filter.

Just something to think about.

CTHIS RX7

I dont think so!

680RWHP12A

i agree

Silver7

How do you know this? did you measure every hole in the K&N filter and compare it to the screen?

RICE RACING

I think it's time I ran a test to see the pressure drop over a 5" pipe.....One covered in mesh, and the other with a 12" long K&N (like on my car)

I think the K&N would win, sure as hell will protect the engine more that a coffee strainer ! LOL

Silver7

Of course I am being sarcastic but do you have any info to back this up or is this just a theory of yours?

RICE RACING

I tend to look to F1 when I could not be bothered thinking !

early 80's (550 to 700bhp) cars had coffee strainers, or no air filters !

mid 80's (1200+bhp) had pleated K&N style filters, even when running 65psi boost ! ........ hmmmm I think I will follow F1.

I think a good size K&N cannot be beat, + the fact that you have filtered air and no chance of inhailing debris should make it a forgone conclusion. Unless you have a gay engine bay of **** exhaust manifold that stick the turbo in a place where you cannot fit a good size air filter, then you have to go with the coffee strainer !

Evil Aviator

One of your fellow Aussies, Grahm Bell, performed some similar tests:

With an 850cfm carb @ 1.5" Hg, the measured airflow was...

554cfm - Carb with Enclosed Element and Single-Snorkel Air Intake
780cfm - Carb with Performance Foam Air Cleaner
823cfm - Carb without Air Filter
839cfm - Carb with Air Horn
853cfm - Carb with K&N Air Filter & Stub Stack

RICE RACING

Thanks Evil Aviator ! Saves me doing a test now

Evil Aviator

No, you still need to test the screen! LOL

Well, either that or just use your F1 logic and call it a day.

CTHIS RX7

Just because they use filters in F1 doesn't mean they are less restrictive then no filter at all! Just use common logic with that one.

RICE RACING

We are comparing coffee strainers to K&N filters, unless I missed something ?

I agree with you that no filter is better than any type of filter, unless I am mistaken you sort of cannot measure a pressure drop over nothing ?????

But in practice, filters are required, especially on a rotary wankel as they tend to fuckout pretty fast when running no air filter at all.

Also CTHIS you can do some pretty special things with clever designs incorporating venturi inlets + pleated filter elements that can offset the pressure drop (flow restriction) casued by the filter.

I think that is what the data presented by Evil Aviator eludes to, and these are solid tested figures against a known pressure drop, no filter v's filter flowed less ? I know it goes against logic but unless you are an aerodynamisist then it becomes just a bit to complex even for a mechanical engineer to explain.

The fact is a properly sized filter is the best solution, I got 472rwhp with an air filter and road exhaust on my 13B @ 20psi ...... the few extra BHP I lost from running the air filter is not worth worying about, just as F1 engineers realize that an engine that lasts a race distance is worth more than an engine which makes a little more power but only lasts 2 laps after injesting a piece of debrise or looses power over a race distance due to abnormal loss in compression due to excessive wear cause by running on unfiltered air.

Your choise bro, I choose reliability anyday over no filter or a coffee strainer !

maxcooper

I looked at the screens that race supply shops sell for protecting radiators, oil coolers, etc. the % blockage was way higher than my intuition led me to believe. Here are some examples from a Pegasus catalog:

#10 mesh, 0.025" wire diameter, 0.075" opening size, 56% open (44% blockage!)
#6 mesh, 0.035" wire diameter, 0.132" opening size, 63% open (37% blockage!)
#4 mesh, 0.047" wire diameter, 0.203" opening size, 66% open (34% blockage!)

Now, I don't necessarily think this means you get 44, 37, or 34% less flow, but does seem like it would have some negative impact. Note that the blockage tends to go up with a tighter mesh, and all the ones I listed here are probably a good bit bigger than you would put over a turbo (they look way bigger than window-screen size).

-Max

CTHIS RX7

I also choose reliabilty with the filter, but like you said it is a restriction on airflow and I think the coffee strainer will also flow better then the filter without the help of any areodynamic aids on the front of your turbo.

RICE RACING

I think this is dead on. You just need to look at the area of a 12" long K&N like I use on my road car v's a mesh screen that is flat over a 5" diameter hole, not to mention the turbulence it will cause to the air try to rush past it @ 150km/h air velocity speed (assuming a 5" inlet dia) @ WOT for 560bhp......K&N's have been proven to smooth the flow out due to their design and if you mount one of a small extension of pipe say 4 to 5" before the mouth of the turbo you give the air a chance to stabilize before it makes it's path to the compressor, all of this would be a flow improvement over a "coffee strainer" attached to the mouth of the turbo. You better hope nothing flies up against your coffee strainer cause of it's small surface area even the smallest item over it will cause a large impedment to air flow, not to mention it will not stop anything smaller than a peble or fastener from entering the engine, let alone small particles of road grit, sand, dirt etc etc.

Yes coffee strainers are good at filtering coffee beans, K&N's are good at filtering air, large volumes of it, efficiently with minimal losses in power when sized correctly for the application.

RICE RACING

did a few calculations of air speed across filtered area.

5" dia coffee strainer air speed across element area = 150km/h !!!!

12" long K&N air speed across element area = less than 16km/h !!!!

Both of the above have very different filtration area's coffee strainer = 0.0126 m^2
K&N filter area = 0.1260 m^2

The K&N has over 10 times the area of a coffee strainer.

If you have a close look @ a K&N pleat it would indicate that it would be far more free flowing at that air speed compared to the coffee stariner @ over 150kph not to mention the disruption to the air flow (not vary laminat at all !) just before the compressor v's an air speed of under 20km/h then having a free shot and laminar flow to the mouth of the compressor wheel.

Again I know which I would choose ! And this goes part of the way to explaining why later turbo F1 cars were not to worried about running K&N style air filters on thier compressor inlets, or why they run similar K&N style pannel filters on modern F1 atmospheric engines !

They plain and simple do not cause such a restriction as you think, air flow across it's area at a speed of under 20km/h is not exactly restrictive now is it ?

CTHIS RX7

Thanks for that explaination!

nocab72

you guys convinced me, bye-bye screen door filter.



K

fdracer

would any style cone-type filter be similarly as effective as the k&n brand? i'm saying would the generic filters that have the same design as the k&n, have similar pressure drop? or is there something exclusive to the k&n design that allows it to flow so well?

Astro

how do metal filters rank in all this?
like the HKS MF filters or the blitz ones?
I think im gonna go with a simple K&N but the metal ones sure do look purdy!
haha

Resource

Wow,I leave out of town and see this got blown up.Good to see this is being debated.

Even if you were to use a screen over your turbo you will need to use something thicker and stronger than the regular metal screen door material.I used the regular metal mesh and it started to fall apart under boost,the edges started to fall apart and were sucked in.Whoops....


And yes I measured how thick the wire was,counted how many rows by how many rows and did the math.That was enough to convince me to throw on the K&N.

RICE RACING

That goes to show you just how much force is acting over such a little area @ WOT and full power air is around 1.204kg per m^2 (density) and at around 560bhp you are sucking in around 26kg/min worth over a small area.

I will do some more calculations ! I would say the small gauge wire is failing under the force of air speed acting on it causing it to collapse under the load.....this is fun

SPOautos

Just to throw in just a little more info, names being with held I know of a turbo dragster that was on the dyno and looking for about 40rwhp more. They found it by cutting off the bell/pipe inlet on the turbo. Seems as though that is a restriction. Has something to do with the way air flow when it is sucked, I believe it was something like it comes from the sides not the front. Then when you throw that inlet bell on there is acts like a wall that your turbo has to suck the air over.

Anyone want to comment on that?

Oh yea, when the cut if off they got something to the affect of 50ish rwhp but this was on a dragster making somewhere over 1000rwhp and running like 40psi of boost. I dont think any of us would gain that kind of power from cutting it off.

Just though I'd throw that out there since it seems to go inline with this discussion.

STEPHEN

JBC

Air would turbulate to much when passing through a screen/mesh type covering. It wouldn't have the same problem w/ passing through a filter, plus the design of some filters can aid in air velocity which is why K+N and that "Tornado" thing can be so effective.

RICE RACING

C'mon man how dumb are you ! Thats not gonna stop the coffee beans from gettin into my engine now is it !

Seriously though, that is interesting, Hmmm open channel flow ? I know when I was studying fluid dynamics that most types of squared off flow entries had greater loss coefficients compared to bell mouthed ones, having said that there are "many" profiles and styles of bell mouths....may be in his case the bell mouth was not optimum ? As you know there are lots of variables, specially when you are talking BHP instead of pure air flow measurement, but either way that is interesting data .......... The plot thickens

right size K&N = 1
Coffee strainer = 0
Free air = Most Power + most risk ?