3A92 1.2L Mirage exhaust header by SuperCircuit

[gone.a]

The above charts make me wonder if its really the second cat that is the restriction point? I know cats are supposed to flow very very well but its weird you picked up such a significant gain by simply removing the second cat with no tune. Speedlab was able to eek out about 5 hp more after tuning (on top of their header). I bet with a tune and some higher octane gas you would be in the upper 80's for PS/HP which according to your dyno would be about a 25% increases over stock.

A 25 percent increase in HP with basically headers, a tune, and a second cat delete, would be impressive in this day.

[cyclopathic]

Hi, the vehicle dynoed by supercircuit was my mirage. There are 3 runs, the second is only removing 1 cat which have very minimal gains and supercircuit asked me if I would like to try to Remove the second one which leads to the 3rd result.. The gain for me was very significantly felt. The quality of the extractor is very good, this company in Malaysia is well known for their custom and higher end extractors. For me, this is one of the best mod so far.

So basically 2nd cat is restrictive? I wonder how much difference high flow converter would make.

[Daox]

I agree. This is odd. The dyno from Supercircuit completely contradicts what Speedlab found when they did their exhaust testing.

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

I just find it incredibly hard to believe that Mitsu could have left a nearly 10% increase in power on the table just due to a CAT that doesn't flow good enough. Perhaps the CAT was beginning to clog on the Supercircuit test vehicle? I also find this highly unlikely though...

[jjjoooyyy]

I agree. This is odd. The dyno from Supercircuit completely contradicts what Speedlab found when they did their exhaust testing.

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

I just find it incredibly hard to believe that Mitsu could have left a nearly 10% increase in power on the table just due to a CAT that doesn't flow good enough. Perhaps the CAT was beginning to clog on the Supercircuit test vehicle? I also find this highly unlikely though...

There are many possibilities though but it is my vehicle being tested, before/after is greatly felt, well I don't believe being given a free tune up by changing an extractor right? I have also compared the dyno chart to speedlab and was amazed as well but yea. I'm not selling any extractor for anyone, just saying that the before and after feeling is really alot of difference, base on drive feel alone and am sharing the good stuff..

[cyclopathic]

I agree. This is odd. The dyno from Supercircuit completely contradicts what Speedlab found when they did their exhaust testing.

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

I just find it incredibly hard to believe that Mitsu could have left a nearly 10% increase in power on the table just due to a CAT that doesn't flow good enough. Perhaps the CAT was beginning to clog on the Supercircuit test vehicle? I also find this highly unlikely though...

I wonder if second converter has enough time to get to right temperature. Car is running rich at idle, so if it is used for short trips only, that would explain converter clogging.

Other possibility oil consumption?

[91cavgt]

I don't believe the cats are a restriction at all, regardless of what the dyno shows. A logical explanation for a large increase in power when the second cat was removed is due to exhaust scavenging. The header, being a long tube design, needs a certain amount of room after the header for the exhaust pulses to suck the next pulse (i.e. scavenging) and this ends up with more power due to less exhaust being left in the cylinder when the exhaust valve closes.

You see, the cam shaft and cam timing in factory engines that do not have an EGR setup are designed to leave some exhaust gases in the combustion chamber when the exhaust valve closes. If you install a long tube header with the proper exhaust after the header then you effectively change the cam profile to, essentially, leave less exhaust gasses in the cylinder. When you have fewer exhaust gasses in the cylinder, you leave more room for more air and fuel to get in there. This adds more power.

But when you put a cat right at the end of a long tube header, it negates the scavenging effect and thus, you loose power. I am willing to bet money that if you had 1 to 2 feet of straight exhaust after the header, and then the cat, you would still see some power increases and not as much of a loss that was seen when the cat was right at the end of the header.


A well designed exhaust system has to have ALL of the components designed around each other. One part in the wrong place or not ideal in the particular setup can drastically decrease power.

[HitShane]

I don't believe the cats are a restriction at all, regardless of what the dyno shows. A logical explanation for a large increase in power when the second cat was removed is due to exhaust scavenging. The header, being a long tube design, needs a certain amount of room after the header for the exhaust pulses to suck the next pulse (i.e. scavenging) and this ends up with more power due to less exhaust being left in the cylinder when the exhaust valve closes.

You see, the cam shaft and cam timing in factory engines that do not have an EGR setup are designed to leave some exhaust gases in the combustion chamber when the exhaust valve closes. If you install a long tube header with the proper exhaust after the header then you effectively change the cam profile to, essentially, leave less exhaust gasses in the cylinder. When you have fewer exhaust gasses in the cylinder, you leave more room for more air and fuel to get in there. This adds more power.

But when you put a cat right at the end of a long tube header, it negates the scavenging effect and thus, you loose power. I am willing to bet money that if you had 1 to 2 feet of straight exhaust after the header, and then the cat, you would still see some power increases and not as much of a loss that was seen when the cat was right at the end of the header.


A well designed exhaust system has to have ALL of the components designed around each other. One part in the wrong place or not ideal in the particular setup can drastically decrease power.

So, maybe remove the resonator and install a high flow cat there instead, then a exhaust before the tail pipe?

[gunlak]

can anyone just open up their secondary cat so we can see how it is restrictive or not. and if possible the resonator too.

someone opened up the muffler already somewhere in the forum.

[jjjoooyyy]

I don't believe the cats are a restriction at all, regardless of what the dyno shows. A logical explanation for a large increase in power when the second cat was removed is due to exhaust scavenging. The header, being a long tube design, needs a certain amount of room after the header for the exhaust pulses to suck the next pulse (i.e. scavenging) and this ends up with more power due to less exhaust being left in the cylinder when the exhaust valve closes.

You see, the cam shaft and cam timing in factory engines that do not have an EGR setup are designed to leave some exhaust gases in the combustion chamber when the exhaust valve closes. If you install a long tube header with the proper exhaust after the header then you effectively change the cam profile to, essentially, leave less exhaust gasses in the cylinder. When you have fewer exhaust gasses in the cylinder, you leave more room for more air and fuel to get in there. This adds more power.

But when you put a cat right at the end of a long tube header, it negates the scavenging effect and thus, you loose power. I am willing to bet money that if you had 1 to 2 feet of straight exhaust after the header, and then the cat, you would still see some power increases and not as much of a loss that was seen when the cat was right at the end of the header.


A well designed exhaust system has to have ALL of the components designed around each other. One part in the wrong place or not ideal in the particular setup can drastically decrease power.

Quite technical there.. And quite explained nicely.. I wanted a full conversion from after header then with a mid box and muffler by supercircuit but according to them it won't give any gains so it is still stock today.

[gone.a]

Someone should just disconnect everything after the header. It would obviously be too loud but for a dyno pull or two it would answer a lot of questions.