This stuff is exhausting...

JohnW8

JohnW8

New member
I'm driving a former spec miata in ITA and am looking to make improvements to the exhaust. I've added a racing beat header, which isn't ideal but it was sitting on the shelf in the garage. The car has the Springfield Dyno exhaust which is very popular in the Spec Miata class but it's dang loud and lacking in low end torque. What would be a good source for info regarding a better exhaust system for a Miata that helps low end torque, still breathes up top and quiets things down a bit to eliminate sound violation worry at some tracks?

Keep in mind, I'm not made of money.
 
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JohnW8 said:
I'm driving a former spec miata in ITA and am looking to make improvements to the exhaust. I've added a racing beat header, which isn't ideal but it was sitting on the shelf in the garage. The car has the Springfield Dyno exhaust which is very popular in the Spec Miata class but it's dang loud and lacking in low end torque. What would be a good source for info regarding a better exhaust system for a Miata that helps low end torque, still breathes up top and quiets things down a bit to eliminate sound violation worry at some tracks?

Keep in mind, I'm not made of money.
Click to expand...

You are describing what we have done over the 4 or so versions of my system. I get to pay for the development, our customers benefit!
 
Muffler ...

There is no hard & fast rule about the perfect performance muffler for every engine or exhaust system. However, years ago, I became a Borla convert.

#1 ... Many moons ago, we did a dyno test on a customer's ITS 240SX KA24DE engine w/open exhaust (cuz that's how he planned on running it). After the final test, we installed a Borla exhaust (sans pre-muffler). No HP loss, but an immediate 12 ft/lb torque increase.

#2 ... My own street Mustang GT came w/a Magnaflow exhaust system that was straining to push 6500 RPM. With nothing more than Borla system, the engine immediately pulled to 7000 RPM.

#3 ... And my newly built ITS car has 2 of the Borla XR-1 mufflers tho no before/after test was made. I chose them only cuz I never felt cheated buying Borlas.

And I have never seen Borla not finish well (if not 1st OA) in any muffler test article.

With all that said, it does surprise me a bit that due to probably more dyno testing than any other sports car engine out there, that THE muffler has not been determined for the Miata.

Andy, you sound like a person who has spent a fair amount of time under the hood of the Miata ... is there not THE perfect muffler for the Miata?
 
The issue isn't the muffler. It's the size of the primaries, the bends, the length, The collector. 2 into 2 into 1? 4 into 1? Shape of the collector, and length. Size of the pipe after that...length of the pipe.
Then there's reversion stuff, and crossover balances, etc etc etc.
Oh, and the muffler.

This stuff depends on other factors as well. The porting and gasket work. The intake. Etc etc. And, of course, the tuning via the ECu.
It's all interrelated, which is why you usually find the guys who have done it, and done it again, are pretty quiet about "the answer". One, because they spent $$$ (I did three complete systems on my car searching for better answers, and one header is unlike any I've ever heard of, a complete custom unit), and two, because there IS no ONE answer....it's all dependent on many other factors.
 
No perfect solution. It's the solution you have in mind for your program. I am a Borla guy too, and I run one currently. But as Jake said, header sizing, step down, collector design and placement, then exhaust routing and muffler placement are all factors.

I'll say I sacrificed about 3 peak whp for the addition of 6 ft/lbs right in the middle of the power band. Depends on what everyone is looking for in their results on what they design.

Then you go and run the same process with your intake...

Then you develop the 2 systems that work best together...
 
Exhaust work is one of the big payoff areas for IT. I've spent thousands on header/primary/merge/pipe diameter/lengths and so on. The guys I know that take the time and do it right benefit greatly from the development.

You'd be remiss if you didn't contact some of the exhaust tuning companies that specialize is race header design. There are a few of them in the country and that is where I'd start. You've got to have all your ducks in a row though as they'll need detailed data about your engine such as port volumes and cross sectional area as well as all the standard stuff like cam profiles, valve sizes, stem diameters, and so on.

R
 
One of the big problems with the Miata head is that the ports are crazy small. In most Honduhs, you can bolt on horsepower by taking advantage of flow that is ready to be freed up. The Miata manifold is effectively a decent header attached to those crappy heads.

It's the reason most don't spend the money on these cars in this area. Want to be 95% of the way there? Bolt on the ISC intake and exhaust and do a ton of tuning with a programmable ECU. That last 5% will cost ya.
 
Even on platforms with decades of development behind them, and good "off the shelf" options, exhaust design can (as Andy described) allow you to change the shape of the curve and characteristics of the car to suit a given track, driving style or strategy. For example if a car has strong torque, one might design the exhaust to maximize this strength. If it has otherworldly torque, one might use it to open up the top end more.

Some common approaches are to calculate the harmonic "trough" on the intake side, and then design the exhaust side to peak there as an offset. In my case I did the math, and made changes to primary diameters and lengths on the new header design, but now am setting up dyno time to validate what works best on the real thing - basically testing multiple primary lengths, and then tailpipe diameters and lengths. I know what I expect, but will do what the dyno says works best in the end.
 
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