Montero Sport Exhaust

[rabyroy]

I know you must install a catalytic converter when doing an exhaust system to stay legal but how about the pre-cats that are on the 97-99 Sports? To me this seems like overkill and is causing serious restrictions. I want to replace the pre-cats from the manifolds with a y-pipe that will run into a high flow catalytic converter and then into a Flowmaster. Has anyone out there done this? Will a muffler shop do this or is it illegal? The OEM pre-cats are over $400 a piece and the main cat converter is $680. Thats insane!!! Why can't you just replace it with a universal type $100 converter?

[cwic]

The prob is that the O2 sensors are before and after the pre-cats and moving or relocating then will mess with the ecu to the point that the vehicle may run much worse afterward. There is prob a place that u could relocate them to get the readings close enough to specs to not mess with the ecu but there is no way of tapping into the ecu to reprogram it to accept new info it will be getting from the relocated O2's. It would take alot of dyno runs with a top of the line machine to find out where to put the O2's that would keep the readings within the ecu's specs.
Clay

[byrdman]

Okay, I have just joined the masses of aftermarket frustrated MS owners... So in desparation I fabbed my own stainless 2.25" exhaust from the Y pipes back (4 days of slow going). I did go with a high flow cat (stainless Magnaflow <$100) and relocated the O2 sensors appoximately in the stock location (one forward and one aft of the cat). No problems with the O2 sensor. I went with the biggest borla muffler (had one before and liked it, quiet) in the stock location and a second 4" round magnaflow tucked up aft of the rear wheel (very tight) to keep it quiet. Still too loud - will swap borla out for a Magnaflow, seems to be a heavier gauge shell. Will post results.

Having just done all this on my 3.0 98 LS, I know I've only got a flex pipe after the Y and one big cat. Where are the pre-cats you guys are talking about?? Do you have a smog pump too? In the old days you needed 3 cats (2 pre cats + 1 main) to get a 3-way catalyst. You usually get a 3-way cat now in just one can and it doesn't require a pipe (no smog pump).

FYI I called almost every aftermarket exhaust maker and nobody wants to do a Montero system. Sounds like a cottage industry begging to be born... anyone?? How many did Mitsu build anyway??

[Joel_CA]

For the 97 and 98 3.0L models- the precats were standard on California emissioned vehicles ONLY. Other federal emission standard vehicles did NOT have precats but DID add an EGR valve to reduce NOx emissions (to which the CA version did not). In 99, all 3.0L had precats AND EGR valves as a means of keeping up with the ever climbing emission standards.

Joel, CA

[byrdman]

Back to rabyroy's Q about removal of the precats... I had an old RX7 with 2 precats and 1 maincat setup. Going to a single big 3 way cat made a very noticeable improvement >4000rpm, but it only had one O2 sensor prior to the first cat.
If the non-CA vehicles only have one cat with a sensor before and after... I am betting that they would also have the same ECU and similar engine mapping (most likely differences would only be during cold-start and warm-up).
You could test out your O2 relocation by tapping a hole after your main cat on your stock system (pick a place you can deal with splicing out or patching if it goes horribly wrong) and see how it runs. Worst case you have a hole to patch and it doesn't work. Hardest part might be getting your O2 sensor lead long enought. If it does work after a couple days... I think you'd be okay to go with a single high-flow cat... but it's your a$$, either way!-- good luck if you do it... Anybody else try something like this??

[rabyroy]

So, you think that if I get a y-pipe for a 97-98 MS, non-Cali emissions, I can replace my y-pipe with 2 pre-cats and bolt up to one high flow cat, and then into a performance muffler? Also, because of the elimination of the pre-cats, could I just replace my stock computer with a non-cali ECU and cut off the now useless two O2 sensors?

[CerOf]

the pre-cats are pretty high flowing to begin with. removing them make net you 2-3hp on paper, but at the rear wheels or even in combination with other modifications will net you zero.

I looked into this about two years ago and came to the conclusion they are not very restrictive.

If anything, with out them, you would lose too much low end torque.

[byrdman]

rabyroy- you'd still need the two O2 sensors as the non-CA have one each before and after the main cat. I replaced my single main cat with a high-flow and kept stock O2 sensor locations (exhaust failed at the flex joint just after the Y, and ya'll know the rest of the $tory). So don't cut NOTHIN' on the O2 sensors, in fact you may need to extend the O2 leads depending on how your CA O2 harness is set up, you'll need your aft O2 sensor to pick up a couple inches behind your main cat, maybe a foot before the muffler. I am sure your ECU needs the O2 info to run, but don't know what you'd get on the chip swap (scares me)-- that's why I was suggesting to test this whole thing out by relocating the sensors before going to far down this road of expensive parts... You would get the chance to see if your CA ECU will run okay with one sensor placed behind the main cat like it would be if you switch to a single, high flow cat. Non-CA O2 sensors are one before, and one after a single main cat on the 3.0. You can get the O2 sensor bungs to weld in from burnsstainless.com for about $12-- then weld it in-- the aft one sits almost horizontal on the pipe to clear vehicle, make sure you double check that the leads will reach and clear the body work. If it don't work stick the O2 back where it came from and put a 18mm bolt (make sure you get the right threading-- I think its 18mm x 1.5 or 18mm x 2.0, or try a cheap spark plug this size if you can't find a bolt) in the unused bung- I guess you'd need that 18mm bolt to plug your original hole for the test anyway. Only way I can think of to avoid totally messing up $1000 of factory cats and then spending more dough on new parts to get your answer.... and you've still got to keep the emissions demons happy- or fooled.

All this sounds like a lot of work unless you want options for bigger gains down the road... I think CerOf is right to think it will be a small gain on the pre-cats alone, but you're talking about no pre-cats and a high-flow main cat, and I disagree that it won't turn into a small gain at the wheels. Also, the whole low-end torque thing is all about keeping high velocity of the exhaust gases in the Y-pipe before they merge at the Y (and after if you can do it) so, I can't see how putting a big porous brick (pre-cat) in the way of the flow is helping with exhaust gases or torque...?? Anyway, this whole pre-cat thing may not be worth the small gains unless you've got strong motivation like other engine mods or you scrap the whole $$$ exhaust on a rock!

Anybody got nitrous? I think my next move will be the manual hubs... and can anyone tell me what's up with the blue smiley puking from its eyes?

[rabyroy]

I guess I'll just scrap the whole idea of trying to gain some HP by messing with the y-pipe and cats. Every article I read and show I watch about gaining HP always includes a larger intake and larger exhaust. Why is it different with the MS? Is it because a smaller engine relies more on air velocity than air volume?
Thanks for all your info...

[CerOf]

you lose torque when you lose back pressure.

A certain amount of back pressure is needed or you lose low end torque.

the catalytic converter, while not necessary, is, especially for the Montero Sport (IMO) very necessary, especially when you go up in pipe size and have a freer flowing muffler.

The Montero Sport is a dog as it is off the line. Losing too much back pressure (Freeer flowing) will make it even worse. Granted, your high RPMs and high speeds will be better, but at what sacrifice...you arrive at a point where more modifications will actually HURT your 0-30mph, 0-60mph, and your 1/4 mile time.

From some "looking into" that I did, a 2.5" exhaust with a magnaflow/flowmaster(insert favorite high flow muffler) along with a high flowing catalytic converter is about optimum.

This would be a Cat and Back system, not just a cat-back system.

Any more than the above, and you will end up losing *too* much low end.

This is all taking into consideration you have an air intake system as well.

Again, just my experience.

I encourage everyone to test and try different things. Who knows, it could be or net better gains.

Oh, when I say "loses torque," it doesn't lose it, it just moves it higher up in the rpm range.

For me, that is bad. I need the torque down low, for accelerating onto the freeway in the city and for off-roading.

I'd rather have quicker 0-40mph times than 60-90 times.

[byrdman]

I think the whole deal is that Mitsu did not put a big bore V8 in the Montero... SO what are we left with?? We have to get the most out of the 3.0 (or 3.5 for the fortunate!) they gave us. Most of the stuff you see aftermarket is for more HP, and you get it at high rpm... but this thing is a TRUCK! Mine barely spins 3000rpm at 70mph in top gear... so what if I can gain 10hp at 5000rpm? I can't use it most of the time.

I've got 2.25" ( up from 2" stock) pipe after the Y, a high flow cat, and two high flow mufflers... essentially 2.25" straight through over the stock 2" with kinks in it. I can tell you I want more low end power!

[TiMSmo0th]

What about the [glow=green,2,300]HKSuv[/glow] exhaust system?
Or is that system way to0 expensive?
Has it been tested by any of our members?

[byrdman]

At the risk of driving rabyroy insane... here goes.
Its not that a "smaller engine needs velocity" its that you need to preserve velocity at low RPM to allow your exhaust to help pull more intake charge during the period of valve overlap (when both intake and exhaust valves are open). True for any engine.

At higher RPM you simply have alot more air flowing to do the job, and you've already got lots of velocity. Why talk velocity? Its all about INERTIA of the air in your exhaust... and some smart dude figured out that you'd measure this as 1/2 mass (of air) times the velocity SQUARED. Any change in the mass of air has a small effect, any change in the velocity of the air has a HUGE, SQUARED effect. We need the INERTIA of the hot exhaust gases shooting down the exhaust pipe to help pull in the fresh intake charge.

So what's the deal with bigger pipe?
2" pipe = 3.14 sq inch area
2.25" = 4 sq inch area = 127% bigger than stock!!!
2.5" = 5 sq inch area = 160% bigger than stock!!!
This doesn't mean you get 160% more power from a 2.5" exhaust, but it does mean that if you actually could make 160% more power, you'd have about the same velocity as the 2" exhaust. Think about the whole setup you'd need to get that much power.

What's the downside again?
Lets say 2" pipe at 2500 rpm.
You'd pump about 2.1 cubic feet per second of flow with the 3.0 engine. You'd have 2.1 cubic feet per second of flow even with a 2.5" exhaust, which sets up the problem. Let's estimate the speed of your exhaust gases at 100 feet per second (its likely higher, but 100 is a nice round number). You can figure out how much inertia or energy 2.1 cubic feet per second of air has moving at 100 feet per second... I calculated it as HP, and I have ignored alot of details but you will get the idea... think of it as HP available to help pull intake charge.

2" @ 2.1 cubic feet per second = 100 fps velocity = 14.5 hp

2.25" @ 2.1 cubic feet per second = 76 fps velocity = 8 hp

2.5" @ 2.1 cubic feet per second = 61 fps velocity = 5 hp
...you can definitely see big pipe = less inertia = less power to help your intake charge at 2500rpm.

What's the deal with back pressure? If you put a low back pressure exhaust in (BIG PIPES), you need to richen the mixture and maybe fool with timing. You'd even have to go with changing valve timing with a new cam to take full advantage of the freer exhaust. You also have a ECU which may not be able to learn to shoot more fuel for your new exhaust. If it doesn't, you just leaned out your mixture and LOST POWER. If you can't take advantage of an exhaust by BURNING MORE FUEL, you don't get much power. Sometimes you get a little tiny bit because the engine has to push exhaust through a VERY restrictive exhaust, so you free up the HP lost to pumping.

The Montero doesn't have a VERY restrictive exhaust, so no dice there, and if you want to gain power by freer exhaust, you have to do something else also - check out the guys running the 1/4 mile in other threads. That's why they've done intake work etc... bottom line is the whole set-up has to work together. Big pipes on otherwise stock setup will probably loose you bottom end power for a small gain at high rpm.

I went with 2.25" pipe with a otherwise stock engine at can feel the loss of some power at low rpm. I did it cause I coudn't find stainless cat and mufflers I liked with 2" in/out. Now I am looking at things to help get the engine happier with the bigger pipes.

[rabyroy]

Byrdman, Strangely enough...I understood everything you said. Thanks alot for your detailed input. I hope you find the secret to getting more HP from your Sport because I've yet to find away. I've even thought about joining the "Dark" side and switching over to Toyota or something just because the aftermarket world seems to cater to them more than Mitsubishi. My two favorite shows on Spike TV is HP TV and Trucks. Everytime they look for more HP, besides changing out the intake is they go with a bigger exhaust. I know the shows are all edited for time but they never mention having problems with the fuel mixture or backpressure. You said you lost some HP when you switched to a larger exhaust???
How about reprogramming the computer with Hyperchip programmer?
Thanks again...

[cwic]

Jet performance can do a ecu reprogram for u for around $400 but u will have to ship it to them and use premium fuel.
Clay