I want to fabricate my own intake pipe

[Gen1GT]

Don't waste your money with that custom intake stuff. Your intake tubing flows more than enough air for the power your car is making. You could have 9" piping, and it won't make a whack of diffrence since the stock AFM is a bottleneck. I've dynoed the stock intake with a K&N, Fram, and with no filter, and they all made the same power. Which means the restriction is at or after the AFM.

You have a SOHC or DOHC? If you have the SOHC, don't waste your money on any kind of intake system. If anything, just get an adaptor and pod filter. If you have DOHC, get the RX7 AFM with the adaptor and pod filter. I got 3.5hp over the ENTIRE rev range and 5hp at 7000rpm. It's a myth that it only gets power above 6000rpm. That was just one guy's experience. The key is dyno tuning it. Adjust the spring tension while on the dyno. One click made a 4hp difference on my car.

[LazerDKA]

I had a friend weld a plate to a 90° 2.5" pipe piece, cut a hole in the plate first, and I bought a 2.5" to 3" adapter for the cone filter. The rest of the pipe, from the MAS to the intake manifold, will require 2 smaller pipe ports for the valve cover and that other small pipe, so a custom collar with 2 small branches should work, and the rest can just be a 2.5" pipe with the necessary bends to get a nice fit. People on here have said not to remove the H-box, due to torque loss, but you'd have to do more research to find out exactly what you want to gain from your setup. As for costs, my plate and pipe just from the MAS to the filter cost me a grand total of $30, with a friend doing the welding as I don't have a welder. He told me I could get the rest of the pipe, and have a custom collar made,for around $25, so don't waste money buying from someone else looking to make a couple bucks, make it yourself with help from friends. I was offered the same piece I had made for $75. Saved myself $45 by buying the pieces and having it made.