Finally replacing entire exhaust. Advice?

[jbbchinook]

So, I have owned my 87 4Runner Sr5 since September of 2013 and love it. The exhaust has seen better days. The manifold has a crack above the O2 sensor, front pipe to catalytic converter is warped and leaks badly. Also leaks from cat to the pipe before the muffler, which is also all rotted out and leaks in 10+ areas.

I thought about getting headers and all custom, but read about many people having problems with theirs.

So this is what im doing:

I bought an OEM exhaust manifold, and OE replacement front pipe. The Outer Diameter of the front pipe is 1 7/8 (1.875). Should I run 1.875 pipe all the way to the muffler? I am not putting a catalytic converter on it. I am having trouble finding a muffler with an Inlet pipe with 1.875 diameter, should I just use an adapter piece that goes from 1.875 to 2.00 inlet on the muffler? Then would I want 2.00 tail pipe or 2.25?

Replacing the catalytic converter with straight pipe is ok right? I see vehicles all the time where the cat has been removed and they use a larger diameter pipe with rounded ends, do I need to do something like that?

Thanks for any answers to my many questions in advance. This is my first time replacing an entire exhaust system. I have been doing research and ordering everything, I have a friend who is going to weld and help install everything.

 

[KidVermicious]

For a stock motor it would be better to stay 1 7/8th into and out of the muffler, but if that's tricky it won't hurt much to convert to 2" right at the muffler. I'd leave it 2" the rest of the way though.

Replacing your cat with a straight pipe will not give you any more power at the wheel, and it won't hurt anything mechanically either. The reason you see guys put the larger diameter pipe in it's place is because they're trying to fool anybody who glances under the truck into thinking that the cat is still there, and they do that because it's quite illegal to run without it. If you don't have emissions inspections in your state then you probably won't get caught, but it's not unheard of to have a zealous or grumpy officer do a walkaround of your truck looking for violations, and if they want to they can impound a truck that isn't street legal, and if you don't have a cat you aren't street legal. I'd run a cat for that reason alone, even if I didn't give two shits about my trucks' emissions.

 

[Rokynutz]

Washington state

Yeah here in Washington state, only certain counties have emissions. Kinda weird in my opinion. But down here in cowlitz county at least, we have a huge off-roading scene. Most of the law enforcement around here are also part of off-roading, this includes the staters. Only thing they really give a s@&$ about is oversized tires on the roadways. But they have to be WAY OUT OUTSIDE THE LEAGAL BOUNDS.

In correspondence with the exhaust size, I agree with Kid.

 

[jbbchinook]

Thank you for your response. I have decided to just do 1 7/8 to the muffler, and past it if possible. Answered exactly my questions.

Yes I live in Washington and my truck is registered in Mason County (no emission tests). I believe even in King County a truck this age (27 years old) does not require testing either. Been pulled over many times amd cant imagine having an officer look at my exhaust for violations.

 

[Rokynutz]

Glad we were of help. I forget what my buddy did to make sure the o2 sensor didn't trip when he deleted the cat.

 

[KidVermicious]

OP has an '87, there's only one O2 sensor.

 

[giro]

Replacing the catalytic converter with straight pipe is ok right? I see vehicles all the time where the cat has been removed

If you're not getting any more power by not having the cat (from Kid, though I thought you got a tiny bit due to less back pressure), and the cats aren't that expensive (mine was $80), why delete it.

The cat helps convert over most of the nasty stuff coming out of your engine from non-perfect combustion into stuff that isn't nearly as bad. Just put in a cat, and worry a little less about carbon monoxide poisoning or having your rig impounded.

 

[Rokynutz]

OP has an '87, there's only one O2 sensor.

That was more or less a open ended thought on my end. Thinking while typing...you know how it goes.

 

[KidVermicious]

If you're not getting any more power by not having the cat (from Kid, though I thought you got a tiny bit due to less back pressure), and the cats aren't that expensive (mine was $80), why delete it.

The cat helps convert over most of the nasty stuff coming out of your engine from non-perfect combustion into stuff that isn't nearly as bad. Just put in a cat, and worry a little less about carbon monoxide poisoning or having your rig impounded.

x2, although I'm not going to preach. I will always run a cat, even on a trail-only rig. There's really no reason not to.

The backpressure thing is a misunderstanding of how your exhaust works. At the risk of presenting myself as an expert (I'm not, just to be clear ), no motor needs backpressure to run, and if you think a bit about how a motor works you'll wonder why you ever though that. What a motor does want in it's exhaust pipe is velocity. There's a given volume of exhaust to evacuate from the chambers, and if the pipe is too restrictive (due to size or a clogged cat or what have you) then obviously not all that volume can be moved, and it stacks up in the cylinders and the next fuel/air charge burns poorly. On the flip side, if the pipe is not restrictive enough, that also impairs the motors ability to rid it's cylinders of exhaust. As each pulse of exhaust is shoved through the exhaust pipe by a piston on an exhaust stroke, it creates a vacuum behind it, and that vacuum serves to pull the next pulse of exhaust from the next cylinder to hit it's exhaust stroke. Too big a pipe/not enough restriction leads to inefficient exhaust scavenging from the cylinders and the same end effect as too restrictive a pipe. So it's not backpressure that's desired or created, it's just a given amount of restriction. Our motors would run very poorly with a 3/4" exhaust pipe, and they'd also run fairly crappy on open headers. Between those two extremes is a sweet spot, and Toyota engineers set up the stock exhaust to hit that sweet spot and be as efficient as it can be working with a stock motor. The restriction provided by the stock cat and muffler is factored into the system.

Obviously once you start tuning a motor and introducing more air and more fuel, a different exhaust is needed. And if you know what you're doing, you can fine tune that exhaust setup to have beneficial effects on your horsepower/torque curve. But when you take an otherwise stock motor and just hack off the cat and straight pipe it, you do nothing for nothing, and in fact you probably impair the exhaust systems' efficiency ever so slightly. You definitely do not get any magical HP gains just from opening up your exhaust on an otherwise relatively modern and efficient motor. This ain't the 50s.

 

[KidVermicious]

That was more or less a open ended thought on my end. Thinking while typing...you know how it goes.

Nope. I never think while I type. That's why half my posts have that little "edited by" line at the bottom. :thumb:

 

[junkyardbiker]

Im not running a cat on mine, since when I aquired my 1st gen 22re the exhaust was rotted off just after the O2 sensor and the cat and muufler were just random pieces of metal leftover hanging on the hangers. I got a Walker muffler and just had it put in and some pipe to get the exhaust out from under the truck due to the headaches I was getting everytime I drove it. It does run rich but I think that due to the O2 sensor probably being shot and I cant get it out to clean/replace it. eventually I'll just replace all of it, but for now Ive not noticed any gains or losses.

 

[wallytoo]

i'd just run a cat, that way the "stock" exhaust parts will fit/line up correctly, no adapters needed.

fwiw, i replaced the entire exhaust (but not the manifold), including the cat, for a total of less than $500 with shipping, and removed the old system and installed the new one in less than 2 hours. this included getting the somewhat hard to find hanger that attaches to the back of the cat from toyota, as well as all new rubber insulators. everything lined up perfectly, and the installation was a breeze. no cutting.

 

[jbbchinook]

Thanks again everyone for all of the advice. I will consider putting in a CAT only to destroy the earth slightly slower (even though it is already so f***ed up it wont matter, but thats another topic).

As my exhaust sits now the CAT has actually been punched out. Discovered this when I replaced the gaskets on it to put a bandaid on the exhaust leak there. Didnt last long.

Somebody mentioned my truck is an '87 with only one O2 sensor, which is correct, and its on the manifold. Lately my truck has been running rich, and will even backfire given the right circumstances.

With the exhaust replacement I am also going to put in a new O2 sensor, spark plugs, wires, cap and rotor, as well as a fuel filter to hopefully address the running rich problem.

@walltoo your truck looks a lot like mine! maybe slightly better paint even. I uploaded pictures but now how do I get it to show up next to my username on the forums??

 

[wallytoo]

if you search for my non-build thread (repair/maintenance instead), you'll find a breakdown of the parts i purchased for the exhaust sytem, along with other things i've done to mine to enable it to serve as my DD. to date, since i put it on the road last June 28, i've driven it over 22 thousand miles (nearly 14K since January 1). i just replaced the distributor O-ring to reduce the leak there, but even with that, i was only "using" about a 1/2 quart of oil per 3500 miles. not bad at all in my book.

my non-build thread may point you in the direction of some causes for running rich, too.

 

[jbbchinook]

Awesome, Im definitely going to check those threads out. My truck has 237k miles on it, but I think the motor may have been rebuilt or replaced. It runs really good, and doesnt "use" a single drop of oil over 3-4k miles.