So I just got a 1.8 into my 91, between the donor chassis and my car I was able to cobble together a continuous piece of pipe, but that's about all I can say for it. The cat's internals were fractured and fell out all when I took it off, the stock muffler is full of it's own rusted out guts and the rest is a patch work of pipe, but the bastard runs again!

I'm working on piecing together a DIY turbo, but in the meantime I need an exhaust so i don't sound like I a civic with a test pipe.

Can I go ahead an build a 3" exhaust so that I'm set when I turbo it and run a 2.25" restrictor at the header/cat coupler? I've seen it used to fix boost creep, but this is stock and I need to maintain back pressure. Will a single plate be enough or a couple waste of time? I don't want to buy resonator/mufflers twice.

 

Back pressure is the enemy always. Velocity is what most mistake for backpressure. In other words. The 3 inch without the restrictor will make more power and torque everywhere than the restrictored exhaust.

 

I think he means for pre-turbo. To keep sound and riceness to a minimum.

 

This. I was reading about spec miata exhausts and they said that 2.25 was a good spot for hp/tq naturally aspirated.

I only want to do this once though, that's why I'm hoping I can do a 3" and make due while I collect parts. I just had to run to walmart and the sound makes me cringe so I have to do something about it soon.

 

Leafy is right. Smaller pipe is good for N/A because it keeps exhaust velocity high for the full length of the exhaust and helps cylinder scavenging. Putting a restrictor in won't create the same effect, since exhaust velocity is still going to drop immediately after the restrictor. Just build your 3" exhaust and run it without a restrictor.

 

ok I see what leafy is saying. Im just going to use some stuff I have laying around and make it work until I can utilize a full 3" system.