The definitive "What Air Filter?" discussion thread

[CazzaVR 0]

Great post, Kev + thanks for stickying :)

 

I wouldn't pay full whack for any of the expensive filters- got my BMC for £35 on Ebay. Cleaned it and it's as good as new 8)

 

You've got me thinking about those cams now... :roll: ;)

[mariojoshi 1]

Here's my 4 pence...

 

Yes, I'm a bit of a chav at heart (aren't we all?) So I did want a bit of induction noise to compliment the sound of that beautiful V6.

The only way to get this without actually decreasing performance due to the dreaded heatsoak (other than drilling the air box) was to pay a bit more for something with a carbon surround. Que the BMC.

 

Added to this that stealth have dyno'd them to show an actual (small) increase in power.... I didn't think it was worth looking at anything else.

 

I've been really happy with it to be honest. Silent unless you're giving the loud pedal a bit of abuse!

 

Having said this, I'd agree that cams are a far more worthwhile mod, but then since I'll be pulling my engine apart anyway, It's easy for me to say that. If I wasn't... I'd still probably buy the BMC.

[g60karmann 0]

K&N panel with snorkel removed and cold air feed from below fog light, definetly the best bet for a g60

[ProdigalSon 1]

^^^^ Ditto above. Cold air feed taken up through hole left by deleted carbon canister, currently into 'slightly modded' stock airbox (if that's not a contradiction in terms!).

 

K&N panel filter inside the stock airbox was a PITA to fit - slightly too large, so had to squeeze the top and bottom of the airbox to get it in! :roll:

 

Didn't notice much of anything performance-wise with the K&N alone, but when I added the cold air feed wow! At motorway speeds the engine just seems to breathe more freely, especially on WOT and/or at high revs. Feels more powerful, but I don't have any empirical data to prove that :lol:

 

That's my tuppence worth. :wink:

[boost monkey 0]

Ditto all the above, an awesome technically-minded post there from Mr. Cheesewire :notworthy:

 

Viper intake / Ram-Air will do nothing on a road car except sound bad and empty your wallet :salute:

[ProdigalSon 1]

Only useful thing to do on the air intake (upstream of the inlet manifold) would be to remove restrictions as much as possible/viable, to minimise the engine equivalent of 'breathing through a straw' (try it, you can pass out really quickly, it's fun :) ).

 

The snorkel in the stock airbox on a G60 seems to be a decent compromise between flow and killing the 'wob-wob' sound of the charger, which when it's not being damped resonates like a badly worn wheel bearing :eek: Removal of the snorkel seems to improve flow into the airbox, as does careful drilling or a second (eg. cold air) feed, but it's always a tradeoff with the increased noise! :lol: My intake is louder than my exhaust right now... :roll:

 

I read an interesting article by an Audi turbo owner somewhere, where he used a homemade manometer to measure the difference in atmospheric pressure and the pressure in his intake at various points (pre- and post-filter, mass flow sensor, etc.), the idea being that in a truly unrestrictive intake system, the pressure will barely drop below atmospheric so the engine won't be working to draw breath. He found that there were a few points that really restricted the air flow - guess what, they were the filter and the grille over the flow sensor, neither of which you really want to ditch :sad:

 

Most decently designed intake systems won't have ridiculous tight bends or changes in pipe diameter to cause turbulence and restrictions in the airflow, but having said that, I'm thinking about the stock boost pipes on my G60 :cuckoo: Guess they were building it with cost in mind. :shrug:

[boost monkey 0]

You can't really increase the size of any air piping (air intake ducts, boost pipes, exhaust system, inlet manifold runners) without hurting air speed. The wider a pipe is the lower the velocity of the fluid (in this case, air) running through it.

 

Manometers are good devices, I recommend playing with them. I wrote a report on the drop in 'head' or pressure loss throughout a liquid system last term, and it's interesting to see which types of bends and fittings flow better than other ones. Haven't got the time atm to go into it, but will try to elaborate at a later point.

[g60karmann 0]

seeing as your the boost monkey and into the engineering side of motor sports, ever thought about having a go yourself at designing a complete boost pipe replacement kit for FMIC and SMIC g60 corrado's? I know a good place for pipe / intercooler fabrication

[boost monkey 0]

:oops: cheers dude. I guess I am ok on the theory.

 

Ideally, yeah. It's nice having a bro with a G60, and i'm sure he appreciates having a brother constantly trying to make it more efficient!

 

I have chats on PM with a few people patient enough to read my brain dirge :nuts: and there are plenty of things that can be done to the boost pipes on a G60. I'm pretty sure a few on here have already done so (Yan and possibly Aqua?) Mass-manufacture of something like an engine and it's associated parts is always going to lead to a trade-off between cost and product quality. DOn't get me wrong, the pipes aren't a bad design but a thick black plastic pipe running across the back of the radiator is just asking for trouble imho :cuckoo:

 

I will have a think my good Kar-man.

[MagicIan 0]

Are there any companies that make a heat shield for a cone filter? Like a box without a top so that when then bonnet is shut it makes an enclosure.... :shrug:

 

You could have the best od both worlds then, an angry roar with minimal hot air being sucked in?

[CazzaVR 0]

The Jabba G60 kit comes with a heatshield. Also ITG filters from the US have heatshields. Think several people on here have made their own too...

[ProdigalSon 1]

Why not place the cone filter inside the driver's side wing, and run hose through the hole for the carbon canister - that way you get nice cool air from just above the road, you keep the roar, and you get a lovely amplified resonance inside the wing :nuts: :norty: :clap: :lol:

 

Not everyone's cup of tea (and I am thinking of backing down the throb of mine a bit :oops: ), but good for a laugh...

[CazzaVR 0]

A cold air intake or a BMC CDA is the best way forward, although I'm sure a heatshield would do a decent job. The carbon canister is easily relocated or deleted. Have a look on US Ebay for the kits, they're usually really cheap, but always buy a good filter e.g. Green or K&N to go with it.

[lj-maguire 0]

hey guys i used to have a k&n panel filter on mine with the front of the box cut off and it sounded like a v8 was in my tsr engined mk 2. got a corrado now woth a race engine waitin to go in:D

[Kevin Bacon 5]

the idea being that in a truly unrestrictive intake system, the pressure will barely drop below atmospheric so the engine won't be working to draw breath.

 

But a petrol engine will always be in vacuum when the throttle is closed or partially open, so what's the point? Only throttle-less diesels see atmospheric pressure off boost.

Engines don't work to draw breath. They're not a dog panting after a sprint.

It's basic physics. The cylinders suck in what they need, simple.

 

He found that there were a few points that really restricted the air flow - guess what, they were the filter and the grille over the flow sensor, neither of which you really want to ditch :sad:

 

The MAF gauze is there to straighten the air, which is critical with turbo engines as they can suck air "around" the MAF element and miss it completely.

 

Audi man has too much time on his hands and is trying to fix things that aren't broken.

[boost monkey 0]

Interesting.... I can't run a cone filter on mine as the mech K-jet requires all that vacuum piping and the airbox :shrug:

 

What does the MAF look like on your cars? Is it a single hot wire element like this | or is it a grid of hot wires like this #?

[ProdigalSon 1]

the idea being that in a truly unrestrictive intake system, the pressure will barely drop below atmospheric so the engine won't be working to draw breath.

 

But a petrol engine will always be in vacuum when the throttle is closed or partially open, so what's the point?

I think the point is that we're interested in the other end of the rev range, not idle or slightly open throttle - unrestrictive intakes will always have more benefit at high revs as the air is sucked into the cylinder over a very short period of time, so the 'breathing through a straw analogy' becomes highly relevant to the maximum amount of air that can be drawn in at the top end. I admit, it is probably tenths of a percent in a real engine, but in pure engineering terms, we're interested in the ideal system, no?

 

Engines don't work to draw breath. They're not a dog panting after a sprint.

It's basic physics. The cylinders suck in what they need, simple.

To go to the other extreme, if you blocked off your inlet, your engine would stall because it couldn't suck in what it needs. We may have to agree to disagree on this one :wink: but I do think that the action of the piston moving away from the valves causes a 'sucking' effect that tries to suck in what's needed, but may achieve less than 100% fill depending on the ability of the air to flow in unhindered. Limited air fill might only mean that the air/fuel ratio is a little rich at high revs, so no great damage (and may protect the valves from getting too hot), but not ideal performance either...

 

He found that there were a few points that really restricted the air flow - guess what, they were the filter and the grille over the flow sensor, neither of which you really want to ditch :sad:

The MAF gauze is there to straighten the air, which is critical with turbo engines as they can suck air "around" the MAF element and miss it completely.

 

Audi man has too much time on his hands and is trying to fix things that aren't broken.

No disagreement there! :lol:

 

Engineering types - set us straight please! Willing to be proved wrong :salute:

[cardboard 0]

i have the carboni running on mine at the moment. does sound amazing and with the pick up not being in the engine bay i presume the air is still cold. not run it through a dyno tho but planning on it

[Kevin Bacon 5]

Interesting.... I can't run a cone filter on mine as the mech K-jet requires all that vacuum piping and the airbox :shrug:

 

What does the MAF look like on your cars? Is it a single hot wire element like this | or is it a grid of hot wires like this #?

 

You can replace the whole lower half of the K-Jet air box with an open element. I think JD Engineering used to sell them.

 

Early Bosch MAFs were a platinum wire but later and current ones are a thin film and are a lot more stable, reliable and cheaper to produce.

 

I think the point is that we're interested in the other end of the rev range, not idle or slightly open throttle - unrestrictive intakes will always have more benefit at high revs as the air is sucked into the cylinder over a very short period of time, so the 'breathing through a straw analogy' becomes highly relevant to the maximum amount of air that can be drawn in at the top end. I admit, it is probably tenths of a percent in a real engine, but in pure engineering terms, we're interested in the ideal system, no?

 

OK, fair enough, it wasn't clear where in the rev range we were talking :wink:

Besides which, Audi man has a turbo, therefore intake pressure will be way above atmospheric at full throttle, so I'm not sure what he was trying to demonstrate / argue there!

Most normally aspirated engines hit 98KPA at wide open throttle, which is near as damn it atmospheric. Could even be 101KPA on a thick day, there are slight variances. Fiddling about with MAF guazes and filters won't produce any discernible differences there.

If you were to junk the whole intake system and replace with throttle bodies, that's when you start seeing differences. Usually because the torque is shifted way up the rev range. Instead of long, torquey pulses from the stock intake, you get short little blips of air, but the actual amount of air the cylinder can draw in does not change.

There is a misconceptiopn that altering the intake allows *more* air in, which isn't true. The *timing* of the air pulses entering the cylinders can change, but you can't fill a 1 litre cylinder with 1.2 litres of air. Unless you force it in with a turbo of course.

Dunno, maybe I'm wandering off track here and not grasping what's been discussed, it wouldn't be the first time :D

 

To go to the other extreme, if you blocked off your inlet, your engine would stall because it couldn't suck in what it needs. We may have to agree to disagree on this one :wink: but I do think that the action of the piston moving away from the valves causes a 'sucking' effect that tries to suck in what's needed, but may achieve less than 100% fill depending on the ability of the air to flow in unhindered. Limited air fill might only mean that the air/fuel ratio is a little rich at high revs, so no great damage (and may protect the valves from getting too hot), but not ideal performance either...

 

True. Although a diesel would pull your arm into the intake before it even thought about stalling :wink: Very nearly saw that happen once :D

I hear what you're saying, but I'm more into cams, capacity, throttle sizes etc, which make big differences as they directly govern the amount of air drawn in. I don't really get too involved with intake dynamics as my experimenting over the years has shown it doesn't make much difference, or the differences it does and can make aren't particularly desirable.

 

Take the M3 CSL for instance. They spent 100s of 1000s completely redesigning the intake system, new cam profiles, more aggressive mapping, raised rev limit etc etc and the net result was 360hp, up 17 from it's stable mate and the torque's the same. When you've got 343hp to begin with, another 17 is not a lot for the investment....and most of that comes from the extended rev limit, not cylinder filling.

[boost monkey 0]

Broseph,

 

if the AFR is running too rich then the valves are more likely to run hot I think :scratch: The whole engine will run hot if it's overfuelling because of bore wash. When the excessive petrol is lit, it gives off a lot more heat obviously, and not as much power as there is not the ideal stoich. ratio of air to fuel.

 

Think that makes sense.

[Kevin Bacon 5]

Quite a few OE turbo engines blast fuel into the cylinders if the EGT gets too hot.

 

If you're running max revs and wide open throttle, the exhaust valves are barely seating at all, so have virtually no time to transfer heat to the cylinder head (hence why they are usually sodium filled), and therefore glow red hot. Blasting extra fuel into the air stream absorbs some of the heat and most of it goes straight through unburned (clouds of black smoke!).

 

Now, on part throttle or a cruise, then yeah, excessive fuel will ramp up EGTs significantly as the burn temperature is higher.

[ProdigalSon 1]

I think the point is that we're interested in the other end of the rev range, not idle or slightly open throttle - unrestrictive intakes will always have more benefit at high revs as the air is sucked into the cylinder over a very short period of time, so the 'breathing through a straw analogy' becomes highly relevant to the maximum amount of air that can be drawn in at the top end. I admit, it is probably tenths of a percent in a real engine, but in pure engineering terms, we're interested in the ideal system, no?

OK, fair enough, it wasn't clear where in the rev range we were talking :wink:

Besides which, Audi man has a turbo, therefore intake pressure will be way above atmospheric at full throttle, so I'm not sure what he was trying to demonstrate / argue there!

Most normally aspirated engines hit 98KPA at wide open throttle, which is near as damn it atmospheric. Could even be 101KPA on a thick day, there are slight variances. Fiddling about with MAF guazes and filters won't produce any discernible differences there.

If you were to junk the whole intake system and replace with throttle bodies, that's when you start seeing differences. Usually because the torque is shifted way up the rev range. Instead of long, torquey pulses from the stock intake, you get short little blips of air, but the actual amount of air the cylinder can draw in does not change.

There is a misconceptiopn that altering the intake allows *more* air in, which isn't true. The *timing* of the air pulses entering the cylinders can change, but you can't fill a 1 litre cylinder with 1.2 litres of air. Unless you force it in with a turbo of course.

All makes sense, interested to learn that NA engines are so close to atmospheric at WOT :study: :salute:

 

It's easy to forget that the engine is a hugely dynamic system and you have to consider the effects of changes at all rpm to get a decent view of performance changes (good or bad). Yes, cams, throttles and displacement make much more difference - we just got stuck on inlet stuff due to the thread title!

 

Dunno, maybe I'm wandering off track here and not grasping what's been discussed, it wouldn't be the first time :D

:lol: Ditto here! :roll:

 

To go to the other extreme, if you blocked off your inlet, your engine would stall because it couldn't suck in what it needs. We may have to agree to disagree on this one :wink: but I do think that the action of the piston moving away from the valves causes a 'sucking' effect that tries to suck in what's needed, but may achieve less than 100% fill depending on the ability of the air to flow in unhindered. Limited air fill might only mean that the air/fuel ratio is a little rich at high revs, so no great damage (and may protect the valves from getting too hot), but not ideal performance either...

True. Although a diesel would pull your arm into the intake before it even thought about stalling :wink: Very nearly saw that happen once :D

:shock: Whoa! Sounds like one of those grisly UTube vids of nasty accidents :pale:

 

I hear what you're saying, but I'm more into cams, capacity, throttle sizes etc, which make big differences as they directly govern the amount of air drawn in. I don't really get too involved with intake dynamics as my experimenting over the years has shown it doesn't make much difference, or the differences it does and can make aren't particularly desirable.

 

Take the M3 CSL for instance. They spent 100s of 1000s completely redesigning the intake system, new cam profiles, more aggressive mapping, raised rev limit etc etc and the net result was 360hp, up 17 from it's stable mate and the torque's the same. When you've got 343hp to begin with, another 17 is not a lot for the investment....and most of that comes from the extended rev limit, not cylinder filling.

It's the law of diminishing returns, see it every day at work :wink: At some point it just becomes pointless (or more often cost prohibitive) to try to wring more power out.

[Kevin Bacon 5]

....and then you move onto turbos :wink:

 

Funny thing with those is, all 'normal' exhaust and intake dynamics go completely out the window :lol: So in some respects a turbo engine is far easier to cobble together and get good results!

 

Anyway, that's O/T, LOL!

[JMC 0]

Here's an interesting one for you guys. I was down at G-Werks at the weekend chatting with Darren and we got on to the topic of air filters. He mentioned that the standard paper air filters were better than the K&N's as the K&N panel filters actually hurt air flow. Well I decided to put this to the test (being a geeky scientist) on sunday. Went down to see Charlie at Surrey Rolling Road, and compared K&N panel filter and standard paper filter on my G60. Basically they performed the same until 5000rpm (with the K&N perhap 1bhp better) then after that the paper filter actually performed better. And not just small amounts either - there was a 6bhp difference at the most extreme point, and these were repeated over a few runs (022 is with the K&N panel liter and 024 with the standard paper air filter). As per usual Dr D was right, although this one is somewhat counterintiutive...

[CazzaVR 0]

Blimey, that's quite a difference! :shock: Would never have thought that would happen! Learn something new every day :)