Speedlab intake, header, and custom tune!

[Dorifuta]

I've already ruined the exhaust to the point that starting from scratch would actually be an improvement.

[Mistah JT]

I've already ruined the exhaust to the point that starting from scratch would actually be an improvement.

Haha fair enough

[GrnBn]

I don't know where you're at with this, but for everyone else considering it a 2in. diameter might be a bit large for our cars. Consider that too large of a diameter causes flow stagnation, adversely affecting performance and economy. I think, considering our low displacement, a 1.5in. pipe would be plenty. Check out this awesome chart, it gives you a pretty reasonable approximation. See how even a 1.5-1.75in. covers the reasonable HP outputs our little Mirage is going to see without turbocharging. Once we're boosting them, 2in. will probably be much more appropriate.

http://www.exhaustvideos.com/faq/how...pipe-diameter/

[91cavgt]

I don't know where you're at with this, but for everyone else considering it a 2in. diameter might be a bit large for our cars. Consider that too large of a diameter causes flow stagnation, adversely affecting performance and economy. I think, considering our low displacement, a 1.5in. pipe would be plenty. Check out this awesome chart, it gives you a pretty reasonable approximation. See how even a 1.5-1.75in. covers the reasonable HP outputs our little Mirage is going to see without turbocharging. Once we're boosting them, 2in. will probably be much more appropriate.

http://www.exhaustvideos.com/faq/how...pipe-diameter/

I've measured the stock pipe and it is 1.5".

[Ares]

I can see how increasing diameter will lose efficiency in the low RPM range, but is bound to be more efficient in the high RPM range.

Because none of us really use the mirage at 7k rpm all the time, I think upgrading the exhaust is a mute point at this time.

I know, for a fact, that I will be turning my mirage into a weekend-track-worrior after a few years. I'll probably increase the exhaust diameter then as I'll probably always be above 5k RPM.

[Mistah JT]

I can see how increasing diameter will lose efficiency in the low RPM range, but is bound to be more efficient in the high RPM range.

Because none of us really use the mirage at 7k rpm all the time, I think upgrading the exhaust is a mute point at this time.

I know, for a fact, that I will be turning my mirage into a weekend-track-worrior after a few years. I'll probably increase the exhaust diameter then as I'll probably always be above 5k RPM.

Rev limit is at 6750ish anyway :P

[Ares]

Rev limit is at 6750ish anyway :P

For now ;p

[GrnBn]

Even at high RPM, a too large pipe causes flow irregularity. You want the skinny pipe we've got because it forces the gases to flow in a smooth and even fashion. With a turbo you want swirl and tumble in your air/exhaust stream, but with our puny NA motor, we want silky smooth flow. Really and truly, we don't make enough power to need a larger pipe. Just straight pipe it at 1.5in. from the headers back, and let all three cylinders howl!

[Ares]

There's a fine line between too large (maybe 2" or 2.25") and optimum. It's a fact that the current engine is tuned for best overall (biased towards city, I'm sure).

For people who do a lot of freeway driving, I'm sure a larger (1.75") free pipe (and a tune, of course) will result in more efficiency.

[91cavgt]

There's a fine line between too large (maybe 2" or 2.25") and optimum. It's a fact that the current engine is tuned for best overall (biased towards city, I'm sure).

For people who do a lot of freeway driving, I'm sure a larger (1.75") free pipe (and a tune, of course) will result in more efficiency.

For a 5 speed you may be right, but for the CVT equipped cars, the stock 1.5" exhaust is going to be the best at highway speeds since at 60 mph you are only running at 1800-2000 rpm.


The key with any exhaust work is you need to maintain exhaust velocity which will help to scavenge exhaust gases out of the combustion chamber. However, it also depends on how much overlap there is in the stock cam timing between the intake and exhaust valves. You want good exhaust velocity, but you also want good exhaust flow. ANY amount of back pressure is bad.

Even if you are racing, the stock diameter pipe will flow plenty at stock power levels. You would just want to replace the stock muffler with either a straight pipe or a 100% straight through muffler. However, trying to find a muffler that has a 1.5" inlet and outlet is incredibly difficult.