Si Vs Non Si oem airbox

[Hondanickx]

I've been toying around with the Si airbox and found several interesting differences.

The Si Airbox has a smoother air path towards the MAF Housing .The MAF sensor hole size on the SI is 31mm and 26mm on the non Si .The mounting holes center distance is also different between the two.49mm for the Non Si airbox and 52mm for the Si airbox.

A better air guidance towards the maf Housing on the SI airbox .Also seen is the big difference of the air intake .The Si has a Oval air intake of 60x80mm ,the Non Si has a air intake of 60mm round.
The Si Air intake is 33% bigger in surface area !

The Si Airbox has more clearance inside the airbox for better airflow .There're no air guides in the Si airbox and it has a better flow of air.

Big difference between the two air intakes.The Si has a large and short intake path.
Longer and smaller air intake path for the Non Si.

I've also added the dimensions of the Si and Non Si oem MAF housings.
The intake side of the Si is bigger then non si.
60mm Vs 57mm which equals to aprox. +10% in surface area!

Overal the Si Airbox would be a great upgrade for any non Si owners .
The airflow towards the filter is impoved everywhere ,and the intake side from the MAF housing is also slightly bigger.
Only thing that needs to be done is modify the MAF sensor hole and mounting holes.
MAF sensor hole needs a bushing to make the hole smaller.The mounting holes need to be drilled out and receive new smaller threaded bushing.
I'm 90% done with that just waiting for some parts to finish it.

 

[Hondanickx]

So i started to modify the SI airbox to fit my Non Si .I decided to remove the back portion that is used for the lower resonance box .It's only there to reduce the induction noise and plugging the hole will increase flow a little too and add some intake noise.

I started by heating up the lower portion with a paint stripper .There's a line around where you can cut into with a sharp knife .After heating it and prying with a flathead screwdriver it easly gets lose.
I then made a plastic patch out of the plastic i just removed to seal the hole.I decided to weld/melt the plastic used a big soldering iron to melt and fuse the patch with the rest of the airbox.
After that i used a stainless steel mesh and some plastic (PP) welding rods to melt the mesh into the plastic .This will reinforce the whole back .

Now i only needed to go in there and smooth out the inside with a flexible grinder / hanging motor (dremel sort of like).

The Si MAF sensor hole , and mounting holes are different then the Non Si .
The MAF sensor hole can be reduced with a piece of PP plastic pipe which will be glued into place .
The brass inserts for the mounting holes need to be pulled out or Drilled out so i can glue some smaller brass plastic inserts in there.

I first tried to heat up the plastic and pull the brass insert out ,but this wasn't moving and it was getting dangerous because the whole MAF sensor housing was getting heat up.
I do not want it to deform or even get ripped out so i decided to go and start drilling the brass out.

Step by step using a larger drill i got it drilled out but it was very tricky!
The brass will pull on the drill and you need to drill very very gently and apply almost no pressure .
The last piece of brass got stuck in there and needed to be pulled out .
I also had a small crack in the plastic mounting holes from the drill bit twisting and pulling.
But it only was on the top and it gets glued anyway.
The top of the brass bushing has some kind of shim on top which makes it look like the bushing is bigger.
The last picture i put the new smaller (m4) brass bushings in so you can see how they need to sit.
I will use the MAF sensor to mount and glue them in place so they have the correct spacing.

All i need to do now is put the plastic tube on a Lathe and turn it down a bit for it to fit in the MAF sensor hole.
Because of the Corona virus here i can't go anywhere so this will follow on a later time.

View attachment 207973

 

[360glitch]

Interesting findings. Thanks for sharing!

 

[Chaucer]

I've been wondering what my Si intake looked like as far as airflow goes, so thanks for the really good pictures.

 

[Myx]

This is a great write up. Your attention to detail is outstanding and you are very good at putting together a visual of your findings. Big thanks for doing this. It's a fascinating read and I am learning a lot. You are a great service to this Honda community (As corny as all this may sound). Much appreciated!

 

[Hondanickx]

Thanks guys! I'm always interested in technical stuff and i also do this with things i do or make.
Unfortunately i discovered a fault of mine on the MAF sensor location.It seems like the sensor mounting studs on the SI are also shifted into another direction.
Which makes 1 mounting hole shift beyond the stud. I Will need to add material to the stud to install a threaded bushing or drill and tap .
The bushing i made to reduce the MAF sensor hole Fits great,only need to trim it on the inside with the Dremel and grind it flush.

 

[jayy_swish]

Why not just go aftermarket intake ? ...unless you are going for an OEM parts only/look

 

[Hondanickx]

To be honest all aftermarket intakes that are out are great but none pleases me 100%.This toying around with the oem intake is to try stuff out and make some gains with spending little money .
I allready have my own aftermarket intake "in development" .I'm also still working on the intake air duct ,to guide air from the grill directly to the airbox and seal it off from the engine bay heat.(like the stock Type-r intake duct).
That intake airduct can also be used with my "aftermarket intake". (Or any other one).The mold making is not easy and takes a lot of trail and errors.First test pieces going to be made out of fiberglass and maybe carbon afterwords.

 

[Hollywoo0220]

Do understand that the airbox model differences cater to the differences in each of the turbos 11blade/9blade exhaust exducer. The 9blade would create an approx +\-18% increase in breathing over the 11blade. Thus the requirement for Increased capability for MAF voltage registry for the Si design.

 

[Hondanickx]

Finished the conversion on the Si airbox.
It did take some plastic welding and special glueing to get it done. Pp plastic is the worst and needs special glue.
But it all Fits now.
Will test it out this weekend.

 

[The Vyzitor]

could you use the non-SI top half of the box, and the SI lower?

 

[Hollywoo0220]

could you use the non-SI top half of the box, and the SI lower?

No.
Each of the Boxes match their own diagram.

 

[Hondanickx]

As Hollywoo0220 already said no,Because the si has a oval entrance and non si round.

 

[Hondanickx]

Installed the si airbox today .
All runs great and smooth .
LTFT went from -7 ~ -8 up to -3 ~ -2.
STFT went from -8 ~ -9 up to 0 ~ +3
So overal significant gaines are made.
Will be driving some more tomorrow ,Because LTFT kept going down.

 

[Hollywoo0220]

Installed the si airbox today .
All runs great and smooth .
LTFT went from -7 ~ -8 up to -3 ~ -2.
STFT went from -8 ~ -9 up to 0 ~ +3
So overal significant gaines are made.
Will be driving some more tomorrow ,Because LTFT kept going down.

If I am not mistaken:
If you are adjusting your air “volume”, then you may not wish to run the CAN tunes. You would in essence run a little richer than within the set AFR perameters For your particular model/make.