2.5 swap soon, what’s wrong with header plus sport 2 muffler

[RodrigoP002]

Hey (Brian, hopefully)

My roadster sport 2 arrived the same week my 2.0 died. I’m doing a 2.5 swap and contemplating some performance upgrades to it.

Couple of questions:

1. Am I right that a header is a better upgrade than stage 1 cams for a naturally aspirated 2.5?

2. How come all of gwr full exhaust package come with the super q and not roadster sport? Would it just be way too loud? Even the header descriptions on GWR seem to contemplate a super q and not sport 2...

3. Is there a particular header you’d recommend for 2.5 and roadster sport 2 muffler?

[Brian]

Indeed our feedback from customers over many years is that changing the header will result in preference for the SuperQ. That's why the RoadsterSport II product description, and all the header and combo product descriptions, direct you to the SuperQ if considering a header change. And once in the SuperQ product description there is a long discussion of the reasons but in brief that's the choice we designed from the ground up to control everything that happens when you install a less restrictive header.

Nonetheless, sound preference is very subjective and there are many customers using the RSII with header (and all our other mufflers too). We have younger customers using our Race muffler with headers, and our Street Single and every other choice we offer. But again our experience year after year is that most customers end up wanting the SuperQ with header change and going with less muffler tends to get a result that is too loud, or too much rasp, or too much drone, or some combo thereof, etc. Best header for 2.5 for best power is our big 1.8 inch, which explained in more detail in the product description for that item, but obviously bigger pipe will also send the most sound down the pipes to that RSII muffler.

Cams really do not make power, they shift power. The stock cams for 2.5 were designed to get a heavier car off the line and moving (as installed in the Mazda3, Mazda6, CX5, etc). Thus, the focus of the stock cams in the 2.5 is not peak power but low and midrange torque. What you are doing with adding cams to 2.5 is changing the shape of that power curve, moving the peak power further up the rpms. You get a higher peak power, but you really have not added power, you have moved the peaks from low and mid range to top end. Thus, indeed if the question is how to make more power, the answer is Header for that 2.5 install because stock header was pathetic for even the 2.0 motor.

This does not mean you won't want cams with your 2.5, I really like Mike's 1.5 cams with any 2.5 install (see Mike at Xero Limit for those), because it gives a power curve that is more what most want in a sports car. The counter argument is that there is nothing wrong with making an NC feel like an old school torque hot rod using stock 2.5 cams that focus on low and mid range torque and we have plenty of customers with automatic in particular that keep stock 2.5 cams because the resulting power curve compliments the shift program of the automatic that tends to keep the car in that low/mid rpms anyway. An automatic owner in particular will often intentionally stay with stock 2.5 cams because they want peak torque right in the middle of the range their transmission is programmed to operate (when not using the paddles and/or heavy right foot to pin the rpms higher).

[RodrigoP002]

Any guesses/thoughts on whether loudness would be better controlled if I went: 1.6 catted Street header with RS2 and maybe try out the glass baffles?

Or maybe the catted Street header is not going to improve performance in a 2.5 engine car?

I want to add some power while engine is out but I also JUST got this rs2...

[Brian]

More flow equals more power with more sound...it's really as simple as you would expect. Thus, our Magnaflow CARB header is same primary pipe size as factory but primaries not pinched in half, so it will make a few more horsepower and pass a little more noise...and that is true for 2.0 and even more true for 2.5 liter. And our RoadsterSport Street header with even bigger primaries and bigger cat cells will make more power than the Magnaflow and pass more noise too. And then our catless RoadsterSport 1.6 inch primary header will make more power than any catted header and also make more noise than any catted header. And then our biggest 1.8 inch catless header will make even more power on the 2.5 liter and also pass even more noise than catless 1.6 inch primary header. So again, it's just as simple as you should expect, more flow equals more power and more sound.

If I was to use RSII with header, which again we don't recommend but let's pretend that I already own it, my choice would be our Helmholtz midpipe with that to cut drone before it reaches the muffler. This choice would certainly not make everyone happy because it would RAISE RASP since the Helmholtz midpipe lacks a traditional fiber resonator to catch rasp and cut volume. And the Helmholtz midpipe would mean more total volume for the same reason, but for me the drone potential of a highflow header is the part that bugs me the most so I like to cut that drone with the Helmholtz midpipe despite knowing I would get more rasp and more total volume than using our traditional fiber packed midpipie.

[RodrigoP002]

And what header would you choose in that 2.5 hypothetical if you want to use your rs2, Helmholtz, and want to be as close to not obnoxious loud and droney?

[Brian]

And what header would you choose in that 2.5 hypothetical if you want to use your rs2, Helmholtz, and want to be as close to not obnoxious loud and droney?

Subjective sound preference is going to be different for everyone with this answer, as is the planned purpose of the build. If I am building a 2.5 that will be a track car then my answer is certainly our big 1.8 inch primary header shown here for best power and best torque everywhere and RS2 is enough muffler to get me under the sound limits of most any track sound limits, and the Helmholtz midpipe with that combo will mean enough control of drone that the entire combo doesn't drone me crazy.

On the other hand, if this is pure street toy build that will never go to compete in SCCA track or autocross then my choice could easily be our catted street headers, and here in California where CARB is required for street cars the choice would be our Magnaflow CARB header with our Magnaflow CARB midpipe.

[RodrigoP002]

Hey Brian,

Leaning towards doing things in the right way and getting a header and exchanging rs2 for super q.

Is there a video with what such combo sounds like with the 2.5L engine?

[Brian]

I consider most videos useless for learning anything relevant about the exhaust because it depends on so many variables like where the camera is located, bias of the mic style used, the speakers you are listening to the recording on, and such basics as how loud you turn up those speakers. Regardless, our 2.5 Project Blue at Laguna years ago was the first car with the big 1.8 header and 2.5 liter. It was standard Roadstersport midpipe at the time, and SuperQ. So if you changed out for Helmholtz midpipe it would nip out the bit of drone you hear and give more upper frequency balance and more overall volume and burble/pop. Hundreds of customers have posted videos over the years you can find at youtube, facebook, etc.