The airbox mod

[paulie0735]

Had a few hours spare today so decided to have a go at making a spacer for the airbox in the XR5. For those of you who don’t know the ECU actually sits in the airbox and all but covers the inlet horn. Why they put it where they did is anybody’s guess but it really does mess with the airflow and reports from some manufacturers of these spacers is that this modification is good for around 12 -14 hp in the upper rev range.

So, with a few hours to kill here is what happened;

First up removed all the bits,


It’s a bit hard to describe but the cooling fins on the back of the ECU actually penetrate into the airbox about 10ml, which puts them almost right on top of the air horn!! Not good for smooth air flow.


This is inside the CAI tube, again not a good design for efficient air flow.


First step was to make a template, first one made of cardboard to get the basic shape, than a more accurate one made from 4ml MDF


Final fitting and some trimming had it close enough to use as a final template


The spacer material I used was just an old nylon chopping board, cheap and easy to work with and more than suitable as a trial spacer. I glued 2 pieces together to finish up with a 14ml spacer.


Installed and ready to go


So what’s it like with the spacer fitted?
Well it’s no different to drive around normally and 90% of the time you would not know it was there, but! There is a definite improvement in the upper rev range, not sure how much more power it makes (I’ll run it up on the dyno in the next few days) but it is much more willing to rev infact its now has a noticeable ‘kick’ from about 4800 and will spin through to 6500 quite willingly now, where as before it felt labored if you pushed it much past 5000. Having seen the original setup first hand I’m not surprised its made a difference, the factory setup really was very restrictive.

I’ll get my son to draw it in autocad and I’ll have a few made out of 12ml alloy plate so if anybody is interested let me know.

PS, some people suggest that its put there (in the inlet airflow) to keep it cool, well I gave mine a ‘pretty good’ work out with everything that I could think of ‘switched’ on and after some adrenalin charged driving I pulled up and popped the bonnet and the ecu was hardly warm so I don’t subscribe to that theory. Only down side is the ECU cover won’t go back on (just) so I’m hoping that using a 12ml spacer rather than 14ml may actually give me enough room to get it back on.

Cheers.