I have an SA with a 13b turbo and I’m thinking of air filters. I’m trying to keep the air cool as possible so I want to avoid sucking heated air from under the hood. I’m looking at drawing air in from under the bumper/headlight. There is space, I just need to drill the 3.5” hole to facilitate a 45* tube.

my original thought was to buy K&N’s Orion universal in-line enclosed cone filter. 4”in 3” out. There is consideration of a 3.5” velocity stack at the mouth of the intake tube.

So it would go:
3.5” velocity stack, 3.5” 45* pipe, silicon reducer 3.5” to 4”, enclosed air filter, silicone reducer 3” to 3.5” another 3.5” 45* pipe to the 3.5” compressor inlet.

bpv vent between the air filter and the compressor inlet.

or

i stick a air filter at the mouth of the tube and have a clear shot to the turbo. Air filter service would require wheel removal and wheel splash hard removal. I’m not talking about a daily driver so this would be an inconvenience but no hardship,

pros and cons? Would the both flow the same? One louder than the other?

any thing I missed?

 

i might do like the example pic, and put the filter thing on the turbo (or turbo adjacent, depending on the easiest place), and then just run a duct to the front of the car somewhere, you can run flexible hose, doesn't need to be round the whole time either

 

If you have enough room for a decent size (big) air filter straight off the compressor housing, my vote would be do that, and then just duct cold air on to it.
Turbos hate long and convoluted intake feeds.

 

If you shift the radiator around 140mm to the left (drivers' side for LHD car), this creates a nice opening for a cold air fed airbox that will shoot directly into the compressor inlet. Or if you want to use a pod style filter, you can enclose within the airbox.

This is how the factory Mazda Competition Manual prescribes the intake setup for 1st gen race cars. That was for a NA 13B application but the design will still work for a turbo. I'm adopting this design on my turbo car.

See pages 11 to 12 of the Competition Manual here: http://foxed.ca/rx7manual/manuals/comp.manual.pdf

 

I routed the turbo air inlet to the right of the radiator and put a dual cone filter in front of the intercooler. I'm blocking some airflow to the intercooler and radiator, but the system seems to work well -- good IAT and coolant temps. Hoses and tubing are 4".

Also, the filter has remained fairly clean over 12 years / 30K miles.