Mirage exhaust mods summed up. (Factory setup is best)

[Eggman]

RPM * Displacement / 2 = amount of air consumed at 100% efficiency. Normally naturally aspired engines have ~85%, and girl's ~124% give or take.

What OP means that if for 2L this was the best, then for engine of 60% size cross-section should be also 60% smaller. This is not 100% accurate, just a rough estimate.

I don't understand what you mean by 'girl's'? Could you explain that too?

[cyclopathic]

I don't understand what you mean by 'girl's'? Could you explain that too?

Damn tablet. Spellchecker turned turbo'ed into girl's. My eyes going bad... I corrected original. Good catch.

[Eggman]

That's hilarious.

[namco]

I don't understand what you mean by 'girl's'? Could you explain that too?

as he said, I was rough estimating, but its a good starting point. i already have my 2" exhaust planned out. i plan to turbo so ill need it. others will be better off with 1-5/8ths or 1.75 going n/a.

my other issue is most "high flowing" exhaust mufflers are 2.25 or larger, most mufflers in the 1.75 range are either really bad sounding and flow good (standard glasspacks), or flow little and are really quiet.

$250 for everything i need, 5 feet of 2 inch pipe, an expand piece to go from 2" to 2.25 for the muffler, the muffler, 3 mandrel bent 180 degree's so I don't have to worry about bending my own, 3 hangers (to hit the 3 stock spots on the catback), a gold tip because my car's theme is black and gold, the flange with gasket (2" with oblong holes which is good for mating to stock size cat), and new spring bolts.

Only cost after that is painting the exhaust with some kind of heat resistant paint, in either black or gold so it doesn't rust during winters. Winter is almost over so I got time before I would need to paint. And the exhaust should be done in about a month when I have full funds to play around with. hate when money is tight.....

[namco]

So, Update, I got my car on a lift. With a micrometer, the exhaust pipe outer diameter measure around 1.42 to 1.46 depending on the few times i measured and remeasured, which is slightly smaller than 1.5.

On that note, I cut the rear resonator off, and the exhaust got throatier but no real volume added (which, its a resonator not a muffler) but still funny after I did it....

I then measured the pipe thickness itself at about .2, which makes this exhaust about 1.25 inner diameter stock. This is insanely small. I dunno what exhaust speed lab created with what pipe size, but there is no way in hell 1.25 is enough for any kind of "real" power gains. I also don't know what designs they went with, did they put the resonator center and muffler rear, did they keep it like stock, did they do straight pipe to muffler? We just don't know!!!

Now, most aftermarket honda exhausts are 60mm outer diameter, making them about 2.36 outer diameter, so about 2.25. On economy based honda's, the pipe mimics what we have (my ex coworker had a baseline civic with same pipe size) and they jump to 60mm even 70mm (2.25, 2.5) for N/A and 3" for turbo. Now if we assume fire cycles, as in our 3 vs a honda 4, yes, they do technically flow more exhaust, but if we go based strictly on each cylinder on its own, the question is then how much does our little motor flow per cylinder vs a honda? I get we have 1.2l of motory goodness, and most low end honda's are around 1.5l to 1.8l these days (assuming 2000's to current as "newer"), but how much FLOW is there?

Now, ill use 1.6l for example, lets divide that by 4 cylinders, is .4 per cylinder. This isn't exact maths here, but its a good way of looking at it. Now our 1.2, divided by 3, is also .4 per cylinder!!!! Our bore and stroke is very similar to those 1.6l honda motors as well. Now we make about 80hp-ish right (on the 1.2l) and the honda 1.6's made about 120. if we play the division game again (once again, not good maths, but good for visualization) 120hp divided by 4 is 30hp per cylinder, and 80 divided by 3 is 26hp per cylinder. Now, I know, its not perfect, and its probably a fair bit "wrong". But as I said twice now (and now a third time) its just for visualization and thinking.

So, the motors are fairly similar, so why is it okay for the honda to have a big exhaust vs the mirage? and by big I simply mean 2.25 to 3" depending on build application. I'm sure someone will spew "1.2l" as the reason or "3 cylinders" but that doesn't mean ****. Exhaust pipe doesn't care if you have pushing X amount of cylinders because they are all released in timed bursts.

Now, from that fact of timed bursts..... our 3 cylinder fires all 3 cylinders once per cycle from what I understand, and that cycle is divided into 3's. So, fire, fire, fire. Honda's 4 cylinders, fire two at once, so fire fire (with pairs). Now I will agree that two cylinders firing at once will push more exhaust gas than 1, but once again it comes down to individual cylinder flow...... how much flow is really needed. This brings me back to my original statement, that 1.75 would be great for N/A and up to 2.25 for turbo setups which is indeed smaller than honda's with 2.25/2.5 being great for n/a and 3" for turbo. If we based our info on these ideals, its just works.

One thing that also will affect "PERFORMANCE" is the FACT that these motors, with MIVEC, are tuned for economy, only until someone can go in and not only tune the motor for air/fuel but also the MIVEC system will we see proper gains. I guarantee there is at least 20hp hidden because of the MIVEC eco tune. Any engine with variable valve timing can have gains, especially if that system was originally tuned for eco style driving vs a variable valve timing based on pure performance (or even those in between). Even on my older del sol, changing the v-tec engagement point 1200 rpms lower (sooner) provided much improvement for the overall power range especially when WOT.

[silverstreak]

Well written Namco, you hit on a lot of good points. So here are you going to go with your exhaust from here?

[gunlak]

Here's a short video showcasing the sound of the Cherrybomb Glasspack on our Mirage. pretty much the same with the hatch.

https://www.youtube.com/watch?v=5_zA9wh2yxk&

[namco]

Well written Namco, you hit on a lot of good points. So here are you going to go with your exhaust from here?

I have been doing a lot of thinking. Too many mods to count. I still want to order the Tein coilovers but they are special order so I get iffy about that and it will probably be a later than sooner type thing. I also want to do rims and tires because personally 165/65/14 isn't enough for my style of driving, and I don't care about mpg's at all, I wanted a cheap hot hatch, I got one . I also plan to do a custom turbo, using a Haltech (mainly because they have great tech support, and for extra $$$ make you the harness you need to bolt right up to factory wiring!!!) which also means newer injectors, fuel pump, and every other supporting mod. I plan to use a subaru top mount (or any top mount inter-cooler for that matter) and some brand scoop (probably subaru because used is readily available, doesn't have to be the sti model, the wrx will work just fine).

The EXHAUST will probably come when I go to do the turbo before next winter (months, its barely spring). I am satisfied with cutting off the rear resonator, I notice no change in power or acceleration, but I get a nice little quiet growl instead of just all quiet. I'd rather have all the supporting mods to mate a turbo up instead of having a turbo with a car that can't turn, can't handle the speed, and can't stop correctly. But my plans for this care a large and grandiose but that's how I roll. The exhaust will be 2.25 though, because of the turbo. If I would stay n/a (fat change, love my STI, can't stay out of boost) I would probably rock 1.75.

[Gnarles2]

I have been doing a lot of thinking. Too many mods to count. I still want to order the Tein coilovers but they are special order so I get iffy about that and it will probably be a later than sooner type thing. I also want to do rims and tires because personally 165/65/14 isn't enough for my style of driving, and I don't care about mpg's at all, I wanted a cheap hot hatch, I got one . I also plan to do a custom turbo, using a Haltech (mainly because they have great tech support, and for extra $$$ make you the harness you need to bolt right up to factory wiring!!!) which also means newer injectors, fuel pump, and every other supporting mod. I plan to use a subaru top mount (or any top mount inter-cooler for that matter) and some brand scoop (probably subaru because used is readily available, doesn't have to be the sti model, the wrx will work just fine).

The EXHAUST will probably come when I go to do the turbo before next winter (months, its barely spring). I am satisfied with cutting off the rear resonator, I notice no change in power or acceleration, but I get a nice little quiet growl instead of just all quiet. I'd rather have all the supporting mods to mate a turbo up instead of having a turbo with a car that can't turn, can't handle the speed, and can't stop correctly. But my plans for this care a large and grandiose but that's how I roll. The exhaust will be 2.25 though, because of the turbo. If I would stay n/a (fat change, love my STI, can't stay out of boost) I would probably rock 1.75.

I am trying to do the same thing. I am just going to wait a while for the turbo. At least until the car is paid for. By then, we should have some options for aftermarket turbo's. I am doing my suspension and wheels and tires right now as well. Even after some money is put into this car, it is still pretty cheap. Most importantly, it is unique. Just changing the wheels and tires have changed the way the car feels. So much better handling and responsiveness. The steering is still too over-boosted but at least it now has some feel. Once I get my springs and sway bar on this weekend, we will see how much better it will get.

[namco]

I am trying to do the same thing. I am just going to wait a while for the turbo. At least until the car is paid for. By then, we should have some options for aftermarket turbo's. I am doing my suspension and wheels and tires right now as well. Even after some money is put into this car, it is still pretty cheap. Most importantly, it is unique. Just changing the wheels and tires have changed the way the car feels. So much better handling and responsiveness. The steering is still too over-boosted but at least it now has some feel. Once I get my springs and sway bar on this weekend, we will see how much better it will get.

I think the fact that the car is so small, mixed with a rather quick rack for its size, makes for that finnicky feel. You will get used to it. Compared to my subaru, the turning radius of the mirage is a god send. On a 2 lane road (2 on each side) i can be in the left lane and u-turn into the slow lane of opposing traffics in one swoop, my subaru would require a 3 point turn..... i rather like this mirage and its fun as hell to drive. I cant wait to see the capability when both suspention and engine are tuned for performance!