Custom air box

[Evil One]

I have dealt with many different kinds of cars over the years.
One constant is that cars make more power with a larger charge of cooler, denser air.
My car came with a green cone filter sitting open in the engine compartment.
Great for sound but not so good for performance.
I had been looking at making a custom enclosure drawing air from where the stock airbox intake was and a couple of other places.
I am now on the list for the ToMyx intake, and plan to follow thru with the construction of my box.
It is not going to be a fully enclosed box, actually more of an elaborate shield forcing the engine to draw cooler air than what is available underhood.
I have dynoed cars with outside of the engine compartment filters and underhood filter enclosures, there have been 1-2 hp variance in the runs..
For me, this is chalked up to standard variance in dyno runs.
Many people worry about hydrolocking the engine with a remote mounted filter, using an enclosure pretty much quells that worry.

I was just wondering if anyone on SVXWN has built one of these and what their experience with it was.


Jim

[ensteele]

I have seen several. You might use the search and see if you can find the threads about them. Good luck.

[nextse7en]

Subaru designed the intake to be provided with pressurized air from the "wake effect" essentially, air splits when it meets the radiator, and crams into the hollow where the intake resonator lives. I don't think you are going to find colder air, or a much more effective way to create pressure in the upper intake.

If you wanted - you may find it possible to chill the exterior of the stock airbox by scooping pressurized air into some sort of heat sheild surrounding the box.

That being said, I think you would be looking at miniscule power gains, if any. The airbox is already kept cooler than the amient temps in the engine bay, because it constantly has air flowing thru it from the outside.


I would instead focus on smoothing out the intake flow from a stock box to the throttle body. Or, barring that, design a ram air duct. Ram air has been shown to add a few ponies at high speeds.

In closing, I would say that a stock airbox, with a mild ram effect, a tomynx intake - properly shielded, and phenolic spacers from outlaw would provide an optimal intake for a stock engine.
-Patrick

[Evil One]

I got my car without the stock airbox


Jim

[Trevor]

Thanks Patrick,

A breath of fresh air (pun intended!), after all the BS that has been on offer of late regarding intake systems.

Good on you, Trevor.

[SVXRide]

Originally Posted by FOMOGO

I got my car without the stock airbox


Jim

Jim,
Check my locker....I've been running a true ram air set up for over 2 years...calculations based on the pressure readings I took when I first installed it indicate ~5-10 hp improvement once you get over ~30mph.
-Bill

[Trevor]

Something which appears to be missed in discussions regarding intakes, is that the OEM system incorporates a plenum immediately before the throttle bodies and this fixes the start of a carefully designed variable system. Eliminating this plenum is surely not desirable.

[crazyhorse]

The variable part of the intake is primarily behind the throttle blades. The plenum actually slows down the incoming air @WOT. Though at part throttle it gives a reserve of air for the engine to draw from. It helps throttle response, but after tip in, it's a hinderance.
The Tomyx intake is designed to speed up airflow, and smooth out the transition going into the throttles. From the supplied data, it does just that, very well.

[Evil One]

Bill, many thanks.
This is very similar to ram air setups I have built and/or run on other cars.
The tube from the airbox down you are using... is that the snorkle from the stock airbox?
I now have to decide on making a box and keeping my cone filter, or sourcing a stock airbox to replace the cone with.
As to the plenum. at WOT I can see it as being a spot of turbulence. I can, as crazyhorse mentioned, see it holding extra volume for tip in.
One thing I have wondered since looking under the hood, and this is a WHOLE new topic/can of worms, has anyone tried increasing intake manifold plenum volume?


Jim

[Myxalplyx]

Originally Posted by FOMOGO

One thing I have wondered since looking under the hood, and this is a WHOLE new topic/can of worms, has anyone tried increasing intake manifold plenum volume?


Jim

I thought of this but that was as far as I went with it. The thought was to increase the dual piping going to the the two throttle bodies to be slightly larger than the stock throttle body size. This would help in initial tip in with increase air available but would slightly slow down intake air velocity at wide open throttle. It is a compromise. I think this setup may be best with a larger Maf sensor. Perhaps the throttle bodies themselves would be the point of discussion after this point though (larger throttle bodies). Even still, a larger throttle body in and of itself will improve throttle response. That's for another discussion though. (Just for giggles, I am looking into this now. Haven't read anything around it here yet but I'll keep searching).

[crazyhorse]

Like this?

That's a BBK throttle body for an F-150 truck

[Evil One]

My thoughts, and you have to keep in mind I come from a turbocharging background, was to eliminate the divider in the intake... bubble the top... and go with a single blade TB such as the accufab unit used on the 03-04 cobras.


Jim

[nextse7en]

To suggest that you could increase power levels by further modifying the intake beyond a slight smoothing of the intake to the plenum, and a ram air setup is dubious at best.

Please rember, these cars are not mid 60's american V8s, there is no identifiable restriction area that can yeild large gains when rectified. What you do to the intake, you must to to the injectors, what you do to the injectors, you must to with the ports, what you do with the ports, you must do with the valves, what you do with the valves, you must to with the cams, what you do with the cams, you must do with the exhaust, and when you are done with all of it, you must consider the MAF and ECU.

In the end, it must be said that Subaru made this particular engine to produce a particular amount of HP/Torque. To increase the amount of HP/Tourqe, you must do one of the following.

Update the entire engine with cams, intake, heads, exaust, maf and ecu. This will create more HP - albeit in the higher RPM band (then you'll want to get a 5 speed, or at the very least, 4.44s)

-OR-

Update the entire engine with cams, intake, heads, exaust, maf and ecu. pistons, bearings, etc.
and then supercharge, or turbo the damn thing.

-Patrick

[Evil One]

You are 100% correct.
Subaru made these engines to function as a perfect unit.
At stock power levels with no mods.

From looking at dyno charts and making comparisons, when you make 1 modification you run the gamut of related mods to get maximum power out of it.
Looking at the dyno chart Myxalplyx posted of his TMyx intake, even tho his car has cams it followed the stock power curve closely with the better flowing STi filter in the stock airbox.
It made more power than stock with the airbox... but still had the same power characteristics.
With the more free breathing allowed with the ToMyx intake it still followed the same power characteristics... but at the top end seriously pulled away.
This says, to me at least, that the stock airbox is perfect for a stock car... but with a few mods it starts being a bottleneck.

I am interested in maximizing the airflow of the engine.
The engine is designed to have good midrange tq and an acceptable top end.
In my opinion it lays down at least a thousand RPM too early.
I want to see what it does with optimized flow.
Subaru had to follow emissions and low sound requirements, in general this will slow down flow.
I want to dyno the car as stock as I can get it, then after my battery of mods. I fully believe that increasing plenum size will move the powerband up slightly... while sacrificing some midrange for an improved top end pull.
I know the MAF is going to be another power bottleneck.
So I will either be getting an eprom burned or purchasing a chip from LAN.

I know there have been many knowledgeable people do many things with these cars, but there shouldnt be any harm in trying some new things.
My ideas may work... they may be dismal failures.
But I will have fun trying things.


Jim

[immortal_suby]

This had to be the ugliest - but it worked
Underhood of the immortal suby (my little red wagon)




Good luck with your idea!