Mazdarian

iTrader: (1)

Hi all,

The following started out as a pretty simple idea; I recently installed a different front bumper that has some pretty nice - potential - air intake openings smack-bang in the high pressure zone. Thinking about getting the most out of this, I figured all I'd need is a completely air-tight path from the opening in the bumper, through a filter, all the way to the throttlebody. Simple enough so far.

A quick rundown of the current situation;

- MAF replaced with a MAP-sensor (stand-alone ECU warranted ditching the old L-Jetronic)
- Stock S4 TB, Plenum, UIM and LIM
- Stock S4 intake duct and elbow
- Aftermarket air filter (size and shape to be decided)

Wants;

- Fab up a new airbox in the stock location to hold an aftermarket air filter (not partial to cones or whatever, function over form)
- Feed said airbox from the sweet hole in the bumper
- Have the whole thing seal air-tight bumper to TB

Now for the tricky bits;
A proper airbox needs to have a certain volume, so the engine doesn't drain the static air inside in a few revolutions. I read up and the rule of thumb seems to be roughly 10 times the enine displacement - on a piston engine.. Now, I know this is a topic of many debates, but does the same hold true for a 13B ie. ~13 litres for a ~1300cc engine?

Then there's something known as an airbox' resonant frequency, and here's where I'm running aground; There's enough info to be found on piston engine resonance and calculating airbox volume, inlet surface area and duct size accordingly, but translated to rotary engines there's precious little to be had. There's a whole lot of math involved, but it comes down to this; properly balancing airbox volume, inlet size and duct length will see the airbox bring air from the outside in at the same frequency as the engine is sucking it out.

What I'm after is the intake frequency of a 13B rotary engine so I can start doing the math.

That, or I'm a n00b and the location of the inlet in the bumper combined with the whole system being sealed increases the stored potential energy enough to cover for the engine's consumption, rendering this entire thing moot

Let me know!

j9fd3s

iTrader: (3)

plan B is to look at what Mazda has done, and follow their lead:

Air filters; the obvious one is the Rx8, its HUGE. in fact the whole air-box works really well at 232hp.

the other air filter thats nice is the AP1 S2000, its a huge cone filter, but its paper, 80mm opening (ap2 is different). it is proven at 240hp.

for ducting, the competition catalog specs 110-120mm duct with a 90x150 opening in the bumper. this is for 265hp. they don't really use a box as such, its just a rectangle opening into the round duct.

chuyler1

iTrader: (1)

How much benefit are you really going to get when still using the stock S4 UIM/LIM. Aren't those going to squash any attempts at tuning the rest of the intake system?

Mazdarian

iTrader: (1)

I think i can get away with that size ducting from the bumper to the box, the opening's pretty close too but I'll whip out the old tape measure when I get home in a few minutes. Might as well have a look at that RX8 filter as well, NoT ReAlLy PaRTial On RuNnInG HoNdA sTuFf Tho

Thanks for the input man

Mazdarian

iTrader: (1)

This too is a topic for many discussions as I've seen.. I'm just trying to max out this setup and actually drive the damn thing XD

Mazdarian

iTrader: (1)

Yeah, I can get away with the dimensions specified in the competition manual. Thing is though, I already tried that style of airbox (EFI Hardware sells them, I made one) but it wont clear the secondary fuel rail w/o the box becoming either too small or too intricately shaped to be practical. Looking at the front of the S4 elbow the mounting flange dips down between de rail and the TB. Another reason why that plan failed was a lack of space for a proper sized filter, so no group B rally style intake for me

Thus I settled with the stock elbow, rubber duct and a filter at the end, hence the need for a airbox..

Edit: RX7's didn't compete in group B, but group C I believe?

peejay

You could always run only two injectors and plug off the secondaries.

RX-7s ddid compete in Group B, but their engine setup was the same generic MFR arrangement used in GTU and other places. Fun fact: The GSL-SE was the car that homologated the 13B for use in the GpB cars.

Mazdarian

iTrader: (1)

Thx Peejay, didn't know that

About the secondaries; I already have 4 650cc injectors, fittings, bungs, lines, and a design for running two rails parallel so ditching the secondaries would be a bit of a waste

I Just wanna build a big box in the stock location, with a adequate feed and have it be either tuned to the engine, or pressurized enough by the feed to overrule the need for tuning.

The more I think about it the more I'm leaning toward the latter..

j9fd3s

iTrader: (3)

look at the honda filter, its perfect. its a big paper cone, velocity stack, 80mm opening. plus a little peg to locate it.