Unfiltered air intake: How harmful??

[givory]

I've heard in my two short years of vintage racing wildly conflicting advice about the use [or not] of an air filter regarding engine wear. I have a 2L 914/6 with Webers. The car is race only, run on very low dust tracks. I've been told by some that even small quantities of dust cause huge cylinder wear. But the many who run naked intakes don't seem to complain. And how much power loss should I expect with the standard hooded K&N's vs no filter? I can't tell with a seat of the pants test.
Thanks for any advice,
Gavin
VARAC #58

[neilca]

Gavin,
I seriously doubt you will loose any HP with the use of filters. I would suggest running some kind of filter if for no other reason, to keep water out of the engine. These pancake motors are like buckets ... left uncovered they will fill up.

[J P Stein]

Here's an option to the hood type w/K&N. Filtered air is good, me thinks. ........

[carnut169]

run on very low dust tracks

Until the guy ahead of you lets his car go off the track slightly and you run through a cloud of crap. I would never run a car w/o a air filter of some type.

[Grady Clay]

Gavin,

My sentiments also, always use filters. The current generation of filters don’t degrade performance. The top of the filter is actually a “reflection” plate and useful with a C6, 910, … RSR cam.

One little piece of “foreign object” like a small piece of sand can get alongside the piston, score your nice Nikasil cylinder, damage the perfect Mahle piston, and cause the ring to disintegrate. It’s amazing how a small grain of sand can be a $10K+ problem.

Any damage to the ring’s sealing surfaces severely degrades the performance.

All the high performance (high compression) engines have a piston-to-head clearance of 0.025” to 0.038” in the squish area. Any little piece of debris causes damage to the surfaces and potentially increased susceptibility to detonation and worse.

When the valve closes it needs to completely sit on the seat. Even small dust particles will quickly cause the valves to start not seating and sealing perfectly. Good buy horsepower.

Sean is right on. If you competitor, or you (never happens) go off track and kick up debris there is the chance that some of it will end up in the engine with unpleasant results.

I am not familiar with all the current flavors of filters, but I would expect the filters like the ones JP has have the filter element extend below the base plate so water can’t drain from the filter element to the base plate and then into the vents and air jet openings. The 911s and 914-6s with stock air filter assemblies will tolerate being out in the rain and snow. Not so with aftermarket filter assemblies, IMHO.

Best,
Grady

[givory]

Thanks Grady - that makes it VERY clear what I should do! ... I was starting to get nauseous by the time I finished your comments on the risk of naked intakes. I will never again say a disparaging word about my hooded K&N's [though those ITG's do look sharp].
Gavin

[Grady Clay]

Gavin,

I hope I scared everyone.

Well, in the late ‘60s and early ‘70s I got a hard time because I ran Carrera 2 GT air cleaners on the 587/3 engine in my 718-055 rather than the cool open 904 intakes. I used the same filters on the 904. Gee, I never had a problem with debris in the engines. Many others suffered the consequences.
Of course I was also verbally abused for using an umbrella on the pre-grid to keep me cool. I was accused of being a sissy. Guess who won.

Some tests I never did were to vary the distance between the top of the intake stacks and the underside of the “reflection plate” - top part of the air filter assembly.
Who has ever done these dyno tests?

Who makes air filter assemblies that the base plate perimeter goes an inch or more below the top of the carb?
The drip covers are also a good idea because they keep water away from the filter element when sitting. If you race in the rain, the element will get very wet. When running, the engine can ingest lots of water (up to a point) but it should never see water and then just sit. That is death to wonderful engines.

What cams, carbs, and intake are you using? What class?

Best,
Grady

[304065]

Grady,

I see what you mean by "reversion plate," I had thought this was a primitive watershield, but now I see it's designed to reflect the intake pulse! Cool!

[Grady Clay]

John,

Right on.

The photo looks like 46 IDA, C6 manifolds and the tall intake stacks. Obviously twin plug. Do the carbs have the tall tubes? What cam, displacement, other? What is the distance from the underside of the deflector to the lip of the stack on 2-3-5-6? 1-4 are compromised because it is a 911R sorta.

Best,
Grady

[304065]

Grady,

Man, I wish I knew! That photo is from Ernie Wilberg's excellent collection of 911R photographs and is an acutal photograph of 11899011R, viewable here. http://www.pbase.com/911r

[Grady Clay]

John,

Well, you got me. I’ll retract the “sorta.”

My memory of 911Rs is from the late 60’ and early ‘70s. I tried to buy three of them but the price was too close to 904s. All about $5-6K. Guess what I bought; 904-017.
Best,
Grady

[J P Stein]

IMO, the ITGs are strictly a dry weather filter...at least in a 914. The bases are flat, the tops are foam.

I did 4 AXs in the rain last season....never again

[jluetjen]

Even F1 cars use filters nowadays. It was only in the relatively "ignorant" days prior to the '70's when people ran open air horns.