Exhaust Design/Advice For 5.0L Powered Miata

Hey Guys,

I am getting to the point of needing to start the gathering of parts for my exhaust. In fact, since the exhaust is going to be completely custom I'm looking for advice on design thoughts also. Here are my main questions:

1) What muffler to run? I'm still debating in my head if I want fairly loud (magnaflow, flowmaster 3 chamber, dynamax) or if I want to keep the sleeperness of the car by going with a turbo muffler that will be quiet at idle but have a nice bark at WOT. On the quieter side, I have been thinking about Summit Turbo mufflers. I ran them on my SHO and I thought they sounded great.

Summit Turbos can be had for $14.97US each from Summit Racing...they lasted more than 3 years on my SHO. This price point is important at this time because this project is making me very poor! I priced out Magnaflows and they were about $80US a piece, but stainless steel also.

So what does everyone think? Does anyone have Summit Turbos on their car? If so, what is your opinion of them. For everyone else, do Magnaflows sound good? I don't want anything as loud as Flowmaster 2 chambers. This car will be daily driven for the summer months, driven with the top down on long trips, and remember the exhaust is only a couple of feet behind my head on the Miata. In other words, buzzing, droaning, or other noises are not cool. Barking, poping, and rumbling are welcome though!

2) Exhaust design: My goal for this car in time will be about 300hp at the crank. With that said I have a few options on the exhaust side.

Option 1) Run dual 2.25" exhaust into high flow cats into a x-pipe and then back to the mufflers with 3" exhaust tips out each side of the rear

Option 2) The same as option #1 but with 2.5" pipes

Option 3) Have a Y-pip fabed up to run one high flow cat, no need for a x-pipe, and one 2.5" exhaust to the rear. Then break the exhaust off into duals again and exit each side of the rear the same as above.

Option 4) The same as option 3, but don't split the exhaust. Just run the pipe to the stock location to keep the sleeper look.

What does everyone think?

Thanks, I will keep the group posted to my progress and how it works out when done. If I go dual exhaust, I will certainly use a h or x-pipe to equal out the exhaust. I hear it sounds better that way also.

I figured that 2.25" would be to small, but my SHO had 2.25" exhaust (actually two into one into two) and made 220FWHP...so I figured I might get away with 2.25" on the 5.0L Miata with 300 NA Hp. The issue is mostly ground clearance and cost between 2.25" and 2.5".

Nvr2Fast said:

Very happy with these. They have the bark of a glasspack but are more deep and less crackly. Farthest away from a flowmaster as i could get. These are not a chambered muffler. Mine are steel, but these also come in stainless. Hope this helps some.

Click to expand...

Where did you purchase your mufflers from? What was the price?

jerry beach said:

Why would you put a cat in? Will it be smogged? I dont see how it could ever pass if you are planning to smog it. Maybe you will have to put duals on and hide one of them real good so the sniffer only gets 1/2 the exhaust.

Have you seen Michael Younts Volvo here? He is running single 3". That would prolly be a good plan. I am sure space is very limited under that thing. It could follow stock routing and keep the sleeper look. I think thats what I would look into if it were me. Good luck on your project, thats gonna be a hoot.

Click to expand...

I did pass the E-test last year with the stock engine, and yes I will have to pass an e-test every other year. I have to pass "1980" emissions standards with my "hotrod", and to do that I will need a cat or two.

I am intrigued by the idea of running a sing 2.5" or 3" exhaust. The space under the car is limited as you suggested. Something to think about.

Any other thoughts, I appreciate any feedback.

Thanks.