Diameter is not chosen arbitrarily, it's a matter of flow and resonance frequency tuning.

As i can see here the diameter is almost the same till the end when becomes narrow.

That cone inside the Felicia's air filter box among others has to do something with the air noise?

The snapshot is from this video:

 

 

The guy prefers the factory system.

 I have just found something relative althought i don't agree with the holes in the bottom of the air filter box.

 

 

https://www.rs2000-16v.co.uk/newsitefiles/filters.htm

 

On the other hand i have seen this trick with the tube and the bell mouth in racing cars.

 

Update: before i show what i have done to my "engine cover" i want to show you the inside of the air filter box.

 

 

I other car air filter box that plastic tube is a cone facing opposite or a cylinder and then there is a tube with almost same diameter which drives the air into the throttle.

In Felicia it's opposite and maybe is has been done from the engineers for the regulations (noise) but personally i don't like it.

 

 

That cone has some notches to fit with the air filter box upper part

 

 

 

but the connection isn't 100% tight and some air was passing from the side plus due to clamp overtighten one side is a little bit pressed but i will fix it.

I decide to remove that cone  tube permanently and make some adjustments.

 

 

I start searching for "Bell Mouth" and "Velocity Stacks", i have found these:

 

 

 

 

 

 

My thought was to install a tube like this to make more air come inside the tube to the throttle like this

https://www.briskoda.net/forums/uploads/monthly_2024_05/ScreenShot_20240507205715.thumb.png.421728bb6f43890beaaeca5a7e30a265.png

 

but first of all i had to work inside that cylinder, to remove any notches and make it smoother.

Why don't you fit the sprint filter 

Those notches would be present no matter the filter brand, are restrictions to the air flow and i have removed them via Dremel bit and sandpaper (photos tomorrow).

After the refinishing work, cleaning, painting, install to the car and 100km test in variable conditions to measure the results.

 

 

Except all these notches (B) i will make smoother the left side (A), thus i believe more air will come inside smoother without turbulence.

 

 

 

The same with the left side.

I have finished the Dremel work and almsot finished with the sandpapers, then painting, cleaning and what's next?

The cover, i will cut a part of it.

3 hours ago, D.FYLAKTOS said:

Except all these notches (B) i will make smoother the left side (A), thus i believe more air will come inside smoother without turbulence.

Hahaha, they are going to make as much difference as the swimming of a lonely sardine on the waves of the Atlantic 

I had the cone removed for about 15 years, thus i could reach the 6100 rpm (5500 is the red zone) very easy with 2rd-3rd gear in Mountain Roads.

You couldn't and still you can't.

 

Sandpapaer work is finished, no notches at all.

 

 

 

 

 

 

 

 

 

 

Time for cleaning and painting.

I never liked the engine cover, always causing me troubles so now it's time to modify it.

 

 

 

 

 

I also made a repair on a crack.

 

 

 

Next step is put back the two parts on engine and a 100Km road test in different conditions.

 

 

You just destroyed a perfectly good intake....

On 15/05/2024 at 16:10, D.FYLAKTOS said:

I had the cone removed for about 15 years, thus i could reach the 6100 rpm

It doesnt make any power above 5000

Count the rpm drop in gear change, make the change in 5000 rpm and make the same change again in 6000 rpm, then see where you are in the 1st change and where at the 2nd.

The top performane for my car is above 5100 rpm.

Just before installation.

 

 

 

Finally i have access to the throttle cable any time.

 

 

 

I have already done 30 Km in City Traffic, the rest of the test will be in Highway to see the Fuel Consumption difference.

As Scotty Kilmer would say, it's just a beauty cover.  It might have some very minor effect as a sound and heat insulator.  If you wanted you could possibly refit it with a hinge arrangement to give the access you have gained without it on.

 

Give your tyre size, final drive/axle ratio and gear ratios and I've a formula given to me by someone else that could work out the rev drop in the gears from whatever revs, I'm sure Thefeliciahacker could also look at some formulas or tables or calculate it too.

 

Edited 23 May, 20242 yr by nta16

I have done a 108 km distance test for this modified air filter box, results and photos (proof) soon.

 

I removed that part to have space to work better and let some hot air from the manifold to go upward to "escape" easily.

If i could i would remove the rest but i can not duplicate that Γ shape, i can not calculate the capacity of that plastic "tube" and i have not so much time for experiments with different size tubes etc to find "the best" for my driving style.

3 hours ago, D.FYLAKTOS said:

let some hot air from the manifold to go upward to "escape" easily.

You might not want that on your winter cold starts, it's all compromises.

 

Unfortunately the 3.40' is a ''rule'' for VW no matter the season but if there is one positive thing is that now with the modified air box filter in the first few hundered meters the car is one click smoother.

Does not wan't to go forward as use to, it's not abrupt as before, i can't describe exactly that but for sure you have felt it in the carburettor days when the chock was pulled out and the engine was in a ''hurry'' mode.

Fuel Consumption now is one click lower even in City traffic, i have photos to post and the TC-6 proves it.

The ''moment of truth" came, it's time for a road test to see the behaviour of the car and the Fuel Consumption with that slightly modified air filter box.

I choose to fill the tank with 98 octane gasoline from a specific gas station (more for this in a future topic), i have done about 45Km distance in hard City Traffic, about 50 Km in the Highway where i pushed at least two times the car to the red zone (5500 rpm and 140Km top speed) in purpose and return home in City Traffic.

The whole test distance was 108.8 Km , the receipt in the gas pump station shown 9.020 ltr so the FC was 8,29 ltr/100Km or 34.075 UK mpg. 😍

The TC-6 shown 8,4% Average and 9ltr Total which is almost identical to the 9.020 of the pump which means the specific gas station does not steal from the pump.

I could get lower MPG in Highway but that was not my purpose, i wanted to push the car to see the behaviour in high rpm, the torque, the behaviour in middle rpm later in an uphill etc with the modification.

 

At 13:00 i am already in City, the distance is 102.7 Km

 

 

 

The distance is 103.2 Km, normally the FC start rising due to traffic.

 

 

 

and arrived in gas station at 13:28 so i did 6.1 Km distance in about 28 minutes (actually is 2 minutes less, it's the time to stop in the station and the time for the pump to do it's job) but you get the idea.

So in the FC sector the modified air box filter worked very good, no problem with 4th gear and 100Km speed to reach the 140 Km, no hesitation to touch the 5500 rpm limit (with the previous damned-useless-crappy 15W-50 i couldn't even reach the 5000 rpm).

No problem with the 10W-40 Synthetic oil, take a look the needle in the temperature gauge.

 

 

Except the work inside the air filter box i reinstall a hose which brings air from the grill inside, so what are the results from that increased amount of air in the throttle?

 

 

 

Gold start: The sound of the motor (idle) is covered a bit from the air filter box noise, we all have heard that deep ''Moooa" of some exaggerations in air filters (extra holes or cut big pieces from the bottom of the plastic box etc), well this exists now but it's not loud and does not bother me, has one click more ''bass" than normal and it's pleasant.

1st gear and go on:  the car is one click smoother especially at night when i am on a basement of underground parking and making circles to reach the exit. In the past i though that someone was ''pushing'' me a bit and was annoying.

Drop of the needle: when i am in 2nd or even 3rd and i had to stop while pressing the brake pedal and engage neutral for the last meters the movement of the needle is smoother, it's not abrupt. The car does decelerate quieter, more softly, before the sound was different and i had the thought like someone suddenly ''brake'' the engine, the feeling that we have when the throttle is dirty or we are about to run of gas. Remind me back in the car carburettor days or still today the feeling with my small carburettor motorcycle, my throttle isn't dirty but every time (for example a sudden traffic light) that feeling and sound of that ''cut'' was unpleasant.

Acceleration middle rpm: one click better, more smooth although in 3rd gear if the rpm dropped (uphill) to 2000 i hear the sound of the engine more ''Moooing" so i downshift to 2nd or take that small uphill all the way with 2nd and not 3rd. I will pay attention to this in the future.

Acceleration high rpm: far better than before, no problem at all, i reached the 140 with 4th and i could go more but there was no reason and i don't like speed traffic tickets. Ok with the 5th too, no problem in Highway.

Fuel Consumption: Dropped even in City Traffic, soon photos as proof.

 

I am not an engineer or a scientist but in my car (ECU chip, custom exhaust, gauze air filter) that patent worked. Keep in mind that i have tested paper filters, another brand gauze filter, 2 kinds of POD filters, factory air box with or without the inner flap and so far that combination works, if i had a problem i would mention and accept it in public but as is now it's an all around Winner.

 

 

 

Well done.

 

Sounds like you have improvements from some sort of ducted air, cold air intake kits sort of thing.  It doesn't matter in the least about any whiteboard, blackboard, technical books, bench or lab testing, technical training, education, learning, theory, or intuition, if something works in real world application and use.  What works well or badly or in-between on one vehicle may vary on another, if it works on yours it works.

 

If there was something negative i would post it, i have a spare air filter box so if things could turn otherwise i would install it and everything would be as ''stock" but now i see improvement even in Fuel Consumption in hard City Traffic.

As for the cutting on that cover, i don't regret it, i didn't like it from the beginning and when @Papez show me the pictures i took my decision.

 

I am soon planning to switch to 5W-50 oil to get every benefit imaginable. 

17 minutes ago, Thefeliciahacker said:

I am soon planning to switch to 5W-50 oil to get every benefit imaginable. 

Depending on the quality of the particular oil that sounds a very reasonable or good idea to me, it's not all about particular numbers or ingredients but how well the whole package works, lasts and protects in the engine and use as a whole.  Diminishing returns of course but the better the appropriate oil the better the working, protection and longevity.