I replaced the crappy 3" eBay intake today (that came with my CRX) with an Injen one. The Injen one is only 2.5" though...I had thought it was also a 3 inch tube. How does the size of the tube affect performance? TIA

 

From what I am familiar with, car factory equipped with a B16A have an Airbox outlet diameter of 3", but the intake arm has an internal diameter of approximately 2.5". The throttle body equipped stock with a B16A is supposed to be matched with this intake arm size, or rather the intake piping is matched to the throttle body size for optimal flow characteristics.

The advantage of getting a replacement intake is:
A larger air-cleaner intake element capable of greater airflow
and/or
A replacement air intake pipe with smoother internal flow characteristics.

Major brand aftermarket accessory manufacturers, such as AEM, manufacture intakes for specific models of cars that came equipped with B-series motors. The cars that come factory equipped with the B16A have 2.5" intake pipe internal diameters while the Integra Type-R has a 3" intake internal diameter. Note that the Integra Type-R's B18C also comes with a larger throttle body from the factory.

 

So, it sounds like you're saying the 2.5" is best. Correct?

 

2 1/2" or 3", It really doesn't matter because it is not the "volume of air" that matters in gaining horsepower, It is the "velocity of air" going in. That is why we get rid of the restrictive factory airbox. The car is only going to use what it can unless you increase the velocity by forced induction. I would say that 2 1/2" will be plenty. Hope this helps!

 

That's a great explanation. Thanks! So, with the 2.5" intake, will I gain a little low-end torque, similar to how it works with the diameter of the exhaust?

 

With a factory B16A throttle body, the 2.5" diameter intake piping will have optimal airflow. The intake piping won't matter if you've got a restrictive air cleaner/filter, which is your primary bottleneck.

Basically, get intake piping that matches your throttle body size.

 

2.5 is about the same size as the throttle body, and anything larger will create turbulance.

 

The AEM and Injen intakes for the CRX are 2.5 inches because they are designed for the stock engine (why manufacturers design these performance parts for a stock engine that nobody uses to go fast is beyond me). But AEM and Injen use 2.75 inch tubing for the B16A. For this reason, I would use an intake for the 1999-2000 SI instead of one for the CRX. They require only enlarging of the hole to the fenderwell and either relocation of the battery or a smaller one (like the Odyssey).

 

Are 90-93 teg intake tubes 2.75"?

I really don't want to relocate my battery.

 

I used the crappy 3" intake, cut it in half and added about 12" of straight 3" exhaust piping (sprayed with rustproofing in and out), two new couplings and routed the filter into the wheel well. And Voila, a DIY 3" cold air intake. If you use a smooth 3" to 2.5" coupling to the throttle body, the transition will increase velocity and will not cause alot of turbulence.

BTW, (answering your question) I noticed more midrange torque by doing this on my B16a. Leave the <3" for D16's. Someone dynoed before and after 2.5 to 3" and noticed improvements across the board. Anyone remember where they're at?

Later, Overkll

 

So, 2.75" is optimal for a B16? Has anyone gotten the one designed for a 99-00 Si to fit without relocating the battery?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hash Browns &raquo;</TD></TR><TR><TD CLASS="quote">The intake piping won't matter if you've got a restrictive air cleaner/filter, which is your primary bottleneck.</TD></TR></TABLE>

This is what I'm trying to decide on, also. Instead of using the layered cotton fabric K&N style filter that comes with the Injen intake, I opted to put the Weapon R foam one (that came with the car when I bought it) back on. Which would you suggest?

 

a drop in filter will always out flow a cone filter.