Thanks. If anyone else wants to know, I was about to ask for a link, but a yahoo search brought the site up first on the list (and it's the most obvious url possible)

http://www.randomtechnology.com/

They list a 2.0 one for the Eclipse and the Galant, would that fit a Lancer? Also, if it does fit, they also list a 2.5" version, which would be great for you turbo guys who keep asking how to free up their exhaust.

 

I'd be interested in the group buy. This would go well with the Kamikazi headers,downpipe, mil eliminator group buy. Who do I need to contact.
-Brett

 

Yikes... way too much to reply to in this thread...

But before I reply to all the stuff... great place for exhaust components:

http://shop.store.yahoo.com/exhaustpros/

Their high flow cats are all around 70-90 bucks, some around 67... and they have ones with O2 taps in them... why does that matter you ask? Because if you relocate one of your O2 sensors to AFTER the main cat under the body of the car, no more CEL if you are getting it currently with your headers.

Alrighty.. uh... engineering.. yeah I finally have my degree in that in 2 weeks... so anywho..

First of all understand a couple fun things.

Pipe flow doesn't behave like normal air flow... so there is more to be concerned with.

Turbulent flow actually results in a greater volumetric throughput than laminar flow even though it's coefficient of resistance from friction with the walls is higher. It has a greater "average" velocity profile. So... in theory you can actually make an argument that mandrel bent is bad. How so?? Because mandrel bent piping is smooth enough that laminar flow can result. This will theoretically reduce your overall flow rate compared to the exhaust shop "crinkle" bend approach. So why do all companies make everything mandrel bent. Can we say marketing?!? Also, there are some cases when the unit is properly tuned with the right diameter and so forth that yes indeed mandrel bent is better.

The key to power with engines is allowing for high rates of exhaust transfer while maintaining backpressures that work with the original tune of the engine. Therefore the "funnel" idea helps this in some ways. It makes it possible to have a high flow rate of exhaust while maintaining enough backpressure to keep the engine running well. A high torque engine is one with some seriously bottled exhaust, a high horsepower engine is a very high flowing exhaust. What we need is in between. Our engine's are pretty torquey for their size, so we can afford to dump torque in favor of hp, and still come out with more torque than most uh.. civic engines.

If you want to understand the funnel effect look up the concept of a C-D Nozzle (converging diverging nozzle). Essentially what happens is that the gases are compressed by the geometry of the "funnel" making for a greater density of air. The same amount of mass has to flow through the nozzle regardless, so velocities increase. Now when the nozzle expands again the speeds go right back to where they were before. Except in one special case, when mach 1 is achieved at the throat. then the gases actually accelerate further and exit the nozzle at very high speeds until the pressures collapse back to atmospheric creating a sonic boom. (But the boom isn't really a factor... as your air compressor nozzle does this every single time you use it to blow dust off the car... no broken windows though )

So although you can increase your immediate tip exit velocity of your exhaust gases, you still have not increased your mass flow. So that is where back pressure comes in. If you have no back pressure you achieve your highest mass flow possible. The air "falls" right out of the engine pretty much with nothing to stop it. This result in lower torque... not sure why at this point.. I'll poke around and see if I can figure it out.

So although "funnelling" your exhaust is all great and dandy for higher exit velocities, you've done nothing to improve your mass flow rate, the mass flow rate is going to be determined by the engine and the restrictions present. You have to always take things back to mass flow as volumetric flow is misleading. But also in this case if you take your higher exit velocity and multiply it by the exit area, you aren't going to be any better off than at your slower but larger area'd flow.

Make sense? Shoot with questions as need be.

 

Looked at that random technology link. All those dynos are very very misleading. The only one that may be at all ok is the 300ZX dyno. Everything else they changed exhaust components other than the high flow cats. So therefore all those dynos are junk for evaluation of the use of high flow cats.

Which then brings the 300ZX dyno to be somewhat suspect as well, and the fact that the if you consider the 300ZX against the Maxima. Both showed about 14 hp increase approximately, yet the maxima had a change of cats and a cat back exhaust system versus stock and yet the 300ZX got that much of a gain with only a catalytic change???? the ZX is turboed though as well, so that may explain it. But all that data is pretty questionable.

 

this is the best I've found so far as far as why you need backpressure to not cut too much low end torque:

"Increasing the exhaust pipe diameter allows the engine to push more exhaust out. In theory you could make the pipes as big in diameter as you want, but in reality, you can't make it too big or else you begin to lose low end torque. Why is this so? Exhaust backpressure (pressure caused by exhaust waves bouncing into obstacles forcing them to head back up the exhaust system) actually helps the engine run by pushing pistons down while the exhaust valve is open. You want to make your pipe diameter just the right size so that there is no lack of backpressure, but also not too much backpressure. This can be sensed in the performance of the engine while driving."

 

Found some more information about backpressure. Since it's an important topic for people, I started a new thread on it. See the additional info at :



https://www.evolutionm.net/forums/sh...threadid=52600

 

i know no too much about cats from carb. moving your quick light cat would be bad only for the environment and not for smog tests.

That first cat is only for the first 1 minute of your car starting up and your second is fully heated by minute 2.

Now a high flow cat may take a tad more to warm up but it is presumable that you could pass emissions (not visual but still pass the actual test) with a header and high flow cat if you drove your car for about 30 minutes then went straight to the test center and rolled into the test. yes 5-10 minutes would be sufficient but 30 allows for some cool down as very few test centers let you roll in straight from the street (stupid paper work and such).

needless to say the law is against tampering with any emissions device so visual inspection could be a problem still.

 

From what I read on sdhotwn, I'm just as good with the stock exhaust or just a cool sounding muffler as I am with a catback, unless I have a turbo, in which case I would need a larger throttle body, header, high flow cats, and catback to really see a difference. Either that or some major $$$ in engineering and testing an exhaust system to create the perfect amount of backpressure, flow, and tune. So anyway, what kind of mufflers SOUND good?

 

not quite urbanknight... There ARE gains to be gotten by opening up our exhaust systems. That is because they have too much backpressure and too many restrictions to allow a decent flow of exhaust.

Really what I wrote refers mostly to a straight through exhaust system like all the performance systems. With them the trick is then sizing the piping appropriately and trying to induce the right number of restrictions appropriately to keep backpressure up (bends, converters, resonators, and mufflers). An exhaust is good for probably about 5 hp. It's hard to say though for sure. It's usually not worth the money to go out and dyno after just doing an exhaust system. I frankly don't have the money to dyno every single component I put on .

So catback exhausts are worth getting, and they help a lot of other mods.. NA or turbo otherwise. But I personally see no reason whatesoever to spring the money for extra expensive stainless steel mandrel bent exhaust systems when you can get a 2% less efficient (theoretically) exhaust for 300 ish with resonator and muffler from your local exhaust shop.

 

So what size catback would you recommend for NA setup? And will this still produce the guessed 5 hp gains if I keep the restrictive cat on?

 

I personally prefer the 2.25" exhaust... and yep you'll still get the gains with the restrictive cat in there.. I still have it..

I know that I had an intake on and that didn't do jack... after I did my exhaust though I noticed I'd be able to break the tires loose in 2nd gear... so that's my butt dyno to prove that I had an improvement with the new exhaust. . LOL.

search for low db High flow exhaust.. that's my thread about my exhaust system. So you can see my stuff there.

Later.

 

Lots'a good info sdhtown! This topic coukdn't be more confusing.
Glasspaks or no?
One resonator or muffler (basically the same anymore)? Neither? Both?
Mandrel bends? Or is crimped ok?
2.25"? 2.5"? 3"?
Nozzle design (2.5" to 2.25" to 2")? straight pipe (2.x" all the way)? Diffuser (or reverse nozzle)?

My freakin head hurts.

What we NEED is a good program to determine flow volume and velocities give the different options. Any takers?

In the mean time, here's a few sites I've found. Good info.
http://customimport.simplisticmedia....t/exhaust.html
http://www.carcraft.com/howto/0304_head/
http://www.4x4extremesports.com/inde...m/exhaust.html a page on which a Montero tuner discussed tuning the exhausts on another Mitsu product.

Basically, when I weld up my design, I'm doing 2.5" DP and then 2.25" the rest of the way. I'll butt-dyno the test pipe and cat differences (again); truth be told I didn't notice much difference when I spent two nights breaking rusty bolts free to install it.
The mid-pipe will have a resonator and then go into the exhaust (another resonator). I'll only be using mandrel bends for the 90deg bend in the DP, the rest will be crushed. Cheaper and at least as much flow.

Wish me luck

 

It's hard to say what would be the ideal given all the factors etc. But basically what I've done with my exhaust, and which I think is at least a good option, but I can't say if it is the best or not... is 2.25" piping cat back. I put in a magnaflow resonator and a magnaflow muffler. Both are straight through. I'm buying the Kamikaze headers and putting them on, and will dyno shortly thereafter to show what gain that gives me over my previous dyno with my exhaust and intake. But that I believe is 2.5" downpipe. I think 2.5" downpipe and 2.25" back is the way to go. But I don't think you'd get hurt all that much by 2.5" either. It's hard to say, as we don't know how much backpressure overlap we need for our engines.

I think if you take the cat out you definitely need to go 2.25" for DP and catback. Any obvious degredation in tone toward the "fart" sound is an indication that the gases are escaping under minimal backpressure. So at that point you have gone too far, and since that seems to be what people are getting with kamikaze headers, no cat, and 2.5" back.. that such a configuration is too open for our cars.

That's just my take, and not hugely scientific.

I'm also not a big fan of the fiberglass pack setups, fiberglass deteriorates and ends up not doing much in the end. I'm a huge fan of Magnaflow exhaust components at this point from having a lot of good luck with them on several cars now.

Crimped is fine for our cars, the difference will be extremely minute.

If you buy a prefabbed cat back, which are all pretty much 2.5" I believe, then you'll need to keep your cat if you have headers...

If you are going to go custom exhaust... 2.5" or 2.25" DP, either way, catalytic left in, 2.25" the rest of the way back with single muffler would be probably about the best configuration. I have two mufflers because I wanted it to stay pretty quiet.

Hope that helps!

 

Correct me if I am wrong tho but isnt it also true that alot of downpipes lets just say 3" are actually necked down closer to the engine? This is because at this point, the first foot, the gasses are hotter therefore moving faster and there is no need of the larger diameter at that point only after the flex section? At least for FI that is. So I do see your waterhose theory but doesnt heat also play a roll in this. Hotter gasses do travel faster than cold correct?

 

Unless thermodynamics has completely lied to me, yes. Hotter gasses do move faster than cold. I see what you're saying, but the NA engine is a different beast. The gasses only get pushed out as hard and fast as the pistons can pump them. If the exhaust is designed to help "suck" the gasses out just a little (not enough to eff your timing or compression) then the engine's that much more efficient.
I think what we're trying to design is an "exhaust syphon" ??? sounds similar, though.
But I see what you're saing for the FI setups, and I think you'd be right.