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

[namco]

my only thought is, what is the oem pipe diameter? ive yet to get my car on a lift, mainly because im lazy and there is no point to waste time doing so just to measure the pipe. depending on the stock pipe size, there is a ratio that you can go up depending on power gains. keeping the car n/a, you really aren't gonna go much bigger. like my old honda, 3" wasn't required because I wasn't turbo so there was no need, I kept the exhaust at 2.5 inches and it gave me a better power band than other buying the 3" kits. now if I was turbo on that same honda, the 2.5" would have been a mild restriction where as the 3" would have been a better choice. Obviously a 4 cylinder at 1.6l to 2.2l will have different exhaust needs than a 1.2l 3 cylinder engine.

[deleted user]

My 94 Civic VX had a SMALLER diameter exhaust and a SMALLER diameter intake tube.

regards
mech

[Daox]

I've only seen a VX engine once, but I do remember it being much smaller as well...

[gunlak]

it's 1.5"

[silverstreak]

That's right 1.5, I went 1.75 on the recommendation of the mechanic and it's perfect.

[namco]

That's right 1.5, I went 1.75 on the recommendation of the mechanic and it's perfect.

In my days of honda tuning, stock 1.75" we'd go to 2.25" or 2.50" if we stay N/A, and 2.75" or 3" if we boost. The rule back then before we started gaining knowledge was add .50" to .75" diameter n/a and 1.00" to 1.25" for turbo (which as you can see, fits what I first stated). Granted, those are also usually bigger motors to begin with, you can still kinda of hold the same ideology to a point.....

Now, going off rpm multiplied by engine displacement divided by 2, 1.50" pipe is good for about 80hp which is about where the mirage IS stock for stock. Any kind of power gain will REQUIRE bigger pipe, otherwise you are causing a breathing issue (all motors are "basically" air pumps). More air in, plus more fuel, = more mass exiting the exhaust, meaning more pipe diameter. too big and the air slows down from the cooling causing the next exhaust pulse to essentially travel backwards towards the motor hitting against the exhaust valve (and possibly causing damage, this one of the reasons I hate the term backpressure, because what it means in technical terms isn't what the word actually means in english).

I would say, the 1.75 is a good starting jump, especially if you don't plan to do much in the long run. A more free flowing intake, mixed with a bit more fuel, and your larger exhaust, shall give gains. At this point its a matter of slight tuning to get said more fuel mixed with said more air to utilize the bigger exhaust.

On that note, I'm thinking of doing mine at 2" I don't want to go too big, but then again I plan to turbo so a part of me wants to do 2.25"...... decisions decisions lol

[Daox]

If 1.5" is good for 80hp (and I agree it is), then 1.75" is good for around 110hp. That is a 36 hp gain over stock power, or 49% increase in stock power. Unless you're running nitrous or forced induction you aren't going to hit that, and that just means you loose more low end which is where you want it for a daily driver. Going even further, 2" is then good for 145hp, and you're definitely not going to hit that without major power adders.

For mildly modified systems I'd stay stock, or possibly go 1 5/8" if you're pushing it. This is good for 93 hp which is a 25% increase over stock. With intake headers and some other goodies I'd say you'll have a hard time exceeding this. Personally, I'd stay stock as it'll give you a bit more low end for daily driving. 80hp is still almost a 10% increase in power for this engine.

[namco]

If 1.5" is good for 80hp (and I agree it is), then 1.75" is good for around 110hp. That is a 36 hp gain over stock power, or 49% increase in stock power. Unless you're running nitrous or forced induction you aren't going to hit that, and that just means you loose more low end which is where you want it for a daily driver. Going even further, 2" is then good for 145hp, and you're definitely not going to hit that without major power adders.

For mildly modified systems I'd stay stock, or possibly go 1 5/8" if you're pushing it. This is good for 93 hp which is a 25% increase over stock. With intake headers and some other goodies I'd say you'll have a hard time exceeding this. Personally, I'd stay stock as it'll give you a bit more low end for daily driving. 80hp is still almost a 10% increase in power for this engine.

I have big plans for this car rofl. After my exhaust and then getting together my turbo components, that will be done. And then much further into the future engine build. So yeah.

I agree though, 1.75 would be perfect for a full n/a setup, or even mild supercharge/turbocharge.

[Teasmade]

....Now, going off rpm multiplied by engine displacement divided by 2, 1.50"..........

What formula is this, and why is it a good one to follow, please?

[cyclopathic]

What formula is this, and why is it a good one to follow, please?

RPM * Displacement / 2 = amount of air consumed at 100% efficiency. Normally naturally aspired engines have ~85%, and turbo'ed ~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.