[CalgaryTSX]

Interesting findings..

I've had a DIY cold air intake with a K & N drop in filter for many years. Similar to the Comptech.
Sorry if I missed it, what air filter are you running?


Since the 1st Gen TSX engine bay is so sealed and so hot, I would still want that air horn out of the engine bay, making sure it is not drawing in any hot air.
But to extend that larger diameter air horn, even a few inches, thru the sheetmetal requires one to cut that hole larger.
To cut that hole larger and make the cut clean looking is not be easy.

For even more cooler air into the engine, you should bypass the throttle body coolant lines, if you haven't already.
Super easy to do on the TSX with zero downsides, even in the Canada winter where I live.

But the intake manifold gets super hot. I've seen folks install the insulating gaskets between the 2 halves of the intake manifold and between the base and the cylinder head.
Minimal improvement. One really has to somehow modify the intake manifold base so coolant doesn't flow thru it.

Another easy mod, if you haven't already is an underdrive crank pulley.
I've had a RSX-S OEM underdrive crank pulley on our TSX for over 10 years, zero downsides.
You can feel the difference revving thru the gears on a manual trans.
If I were to do it again, I would find an even smaller diameter crank pulley.

 

[CalgaryTSX]

I kept my stock power steering and alternator pulleys.
While aftermarket shiny aluminum pulleys for those look nice, zero power gains.

Another low cost suggestion for OP @lnlds would be to remove both exhaust resonators.
Even with his high flow cat, the car will gain just a bit of sound.
Low cost, zero HP gain but lose some useless weight!

 

[CalgaryTSX]

Underdrive crank pulleys are worth researching.

I've had one on my 5.0L Fox Mustang for 20 years.
I think the 5.0L Fox platform is where the development for underdrive crank pulleys started...


I've been looking for one for our lame Honda HRV which has the Civic R1.8L engine, but no one makes one...

 

[CalgaryTSX]

^^ That's a classis chassis dyno operator error or cheating.

A short ram air intake will always make more power on a chassis dyno, with the hood up.
But that's not reality, especially with the super hot and sealed TSX engine bay.
For a true comparison, you need to dyno with the hood closed.

With the hood up, the short ram intake is drawing in nice cold air. With the hood down, not so much...

You can see that the hood open or closed will have minimal impact on a chassis dyno with a cold air intake drawing air from outside the engine bay.

 

[CalgaryTSX]

I do monitor intake air temps on our TSX using a Scangauge.
The original air intake temps on the TSX are incredibly high due to the OEM hot air intake and the throttle body coolant heater lines.
The engine bay in the TSX is incredibly sealed. You can see all the rubber seals at the leading edge of the hood, down the sides and the trailing edge of the hood, the sealed up rad support and the plastic lower engine cover.
Go for a drive in your TSX and then touch anything in the engine bay.

If I drive thru the rain in our TSX, the engine bay is dry. Unlike our HRV, our Dodge truck or my Mustang.

long intake is always loosing power vs short one.

It's not that simple. There are numerous things going on here...

Length of the intake pipe.
Size and flow of the air filter.
Quantity of air (restriction).
Temperature of incoming air.
Ram air affect, if any.