New airbox modifications, no more of this drilled malarkey

[Khare]

Honestly, the variation on the day in terms of ambient temperature, humidity, atmospheric pressure etc.
Will provide noise enough to cover any effect from the airbox work.
This is why you have to do this sort of thing in the same session.

If concerned about heat soak, look at trying to shield the metal intake manifold from the exhaust heat below & that coming from the rocker cover.

All the graphs I have come with the ambient temp, intake temp and humidity logged on them, and I always go around the same dates when the weather is roughly around the same. Believe me I'll know if it's an improvement or not, I wouldn't even need a rolling road to tell you if it's better or not. The 16v engine is crossflow, so the intake manifold is away from the exhaust manifold, however you're right, heat does rise from the camshaft cover. However unless I wrap the runners in reflective gold foil then there's not much I can really do, some heat soak is something inevitable.

I'm going to evaluate this setup then I'll play around with adding a second bigger cold air feed, to create positive pressure inside of the box.

[Metallix]

I know the 16v engine & the backend of the 16v intake manifold (the plenum) sits above the exhaust manifold.

The stock setup has a heatshield attached to the cast manifold, but this is often binned.

Heat reflective tape on the underside of the plenum could help, or if the rocker cover was coated (a bit extreme though)

Look forward to seeing the comparison between the two dyno graphs for the different air box mods

[Ess_Three]

Why do people seem to think they want/need turbulent air PRE filter?
Or even POST filter?

You want laminar flow into the manifold, with as little restriction as possible...turbulence is engineered into the design of the head, valve location etc. to give good mixing of the air/fuel mix.
The injectors point at the back of the hot inlet valves for better atomisation...
So why do you want turbulent air in the airbox again?

Anyone looked at a MAF of a 20vT engine?
Or a TFSI?
Or a TSI?
Thet have straighteneing vanes pre-MAF to give laminar flow across the MAF.
So laminar flow must be good, then?
As in non-turbulent, free from obstruction, path of least resistance laminar flow?

So why would losing turbulence in an airbox be a problem? 

[Ess_Three]

I know the 16v engine & the backend of the 16v intake manifold (the plenum) sits above the exhaust manifold.

The stock setup has a heatshield attached to the cast manifold, but this is often binned.

Heat reflective tape on the underside of the plenum could help, or if the rocker cover was coated (a bit extreme though)

Look forward to seeing the comparison between the two dyno graphs for the different air box mods

If heat is that much of a concern...run a heat insulating (phenolic) gasket between the inlet manifold and the head, and ensure the heatshield above the exhaust is fitted.
You can put your hands on the inlet manifold after a good thrash that way - from experience!

As long as you have good flow through the engine, you'll not be adding much to the inlet air flow temperature with those two basic steps...it's not like the air is in the plenum long 

[Agreeable Slick]

Why do people seem to think they want/need turbulent air PRE filter?
Or even POST filter?

You want laminar flow into the manifold, with as little restriction as possible...turbulence is engineered into the design of the head, valve location etc. to give good mixing of the air/fuel mix.
The injectors point at the back of the hot inlet valves for better atomisation...
So why do you want turbulent air in the airbox again?

Anyone looked at a MAF of a 20vT engine?
Or a TFSI?
Or a TSI?
Thet have straighteneing vanes pre-MAF to give laminar flow across the MAF.
So laminar flow must be good, then?
As in non-turbulent, free from obstruction, path of least resistance laminar flow?

So why would losing turbulence in an airbox be a problem? 

Pre filter, not bothered. Post filter turbulence on a N/A engine helps especially of these age and no doubt not very well taken care of (despite being owned by enthusiast) engines. On a forced induction engine turbulent flow doesn't matter for obvious reasons and laminar flow is king. Flow is also tuned to the back pressure of the engine depending on inlet/exhaust valve stroke and opening times, so smoothing the airbox can lead to minor performance drops. 

Injector positioning is generally into the bowl of the piston crown which creates an extra turbulent charge mixture, but then we start getting in to much more developed engine than a humble 8V 1.8 digi.

It would be interesting to see a back to back test, but I would be surprised if there is anything more than a few fractions of difference.

[Screech16v]

 I did this to my airbox when it was an abf ,totally smooth top and bottom,  "3 cold air feed from lower grill, panel filter and all that, couldnt tell any difference 

[Ess_Three]

Pre filter, not bothered. Post filter turbulence on a N/A engine helps especially of these age and no doubt not very well taken care of (despite being owned by enthusiast) engines. On a forced induction engine turbulent flow doesn't matter for obvious reasons and laminar flow is king. Flow is also tuned to the back pressure of the engine depending on inlet/exhaust valve stroke and opening times, so smoothing the airbox can lead to minor performance drops. 

So please explain how porting and polishing doesn't make things worse?
Surely removing any steps/miss-matches etc will reduce turbulence and hence spoil things.

Funny...when I studied it, smooth, laminar flow = the most air in...and on an NA engine when you have only atmospheric pressure to get it into the cylinders, it's MORE important than on an FI engine.

The plenum has the affect on pulse tuning, with certain cam combinations. Never ever have I come across pulsing issues on a factory airbox set up.

It would be interesting to see a back to back test, but I would be surprised if there is anything more than a few fractions of difference.

I have tested two modified airboxes, and gained 1-2 BHP on an ABF.
That's is std airbox removed with the car strapped on the dyno, modified airbox fitted and th car re-run...same K&N filter each time.
1-2 BHP repeatable...sure, it's well within the tolerance of dyno accuracy...but repeatable...as in put the standard airbox back on and lose 1-2 BHP?
Odd, no?

The second test was on a Corrado VR6...similar results: 2-3 BHP, repeatable...car again not removed from the dyno, just the airbox swapped and re-tested.

Add these minor gains to small gains from ported TBs, K&N filter (or new OEM filter), re-chips etc...and you can pick up a few BHP.

[VW BUSH]

Ribs in the box are there to get the part out of the mould without distortion.
It is a key design principle of injection moulding

I suggest reading something about Bernoulli's theorem and Osbourne Reynolds (Reynolds number), this might persuade some folks from the error of their ways but alas there will always be buyers for magic beans

[tweed]

Sweet as should be a good test then.

I don't know if its worth smoothing out or not. Doubt there's any difference.


Might do mine then line it with silver tape 

Not silver tape, but I did as Ess_three about lining it with heat reflective gold foil, to give it an extra layer of heat protection, but he said the plastic is a good enough insulator so there's no need for the foil. Reason I got rid of fins is to create smoother airflow upwards into the filter + more room inside (only by a bit, but the amount of plastic I removed was surprising!) 

I use silver tape for work so always have it about, gold sounds expensive lol
I thought that using the silver tape will really smooth for better airflow that's all.

[Khare]

So this is the final setup. A bit different from the sealed airbox I had planned. I think this will be a better setup overall. I did what tweed had also done to his, duct tape on the inside to smooth it off even more!







We'll see what improvements there are