Have an 87 bII, do I need a cat installed on my truck? We don't have to pass emission tests here.

Just didn't know if it would affect the engine any with back pressure or something along those lines .

Don't have a problem replacing it just wasn't sure if it was needed for anything other than emmisions.

Less the old beast looks like a diesel without.

Thanks .

 

Lake and Porter counties test:

BMV: Indiana's Vehicle Emissions Testing Program

You may not have to test, but it may limit your resale if that is a consideration at all.

Is your cat bad, is that what you are saying? Or is it good and you just want to get rid of it?

If it's bad, well, toss it and be up front when you sell it.

If you just want to pull it, I would unbolt it, up to and including the whole darn system if it's all welded. Then get another down pipe/y-pipe etc from a wreck. Keep it and reinstall for sale, pass it on with sale or sell it after you dump this one.

As far as the way your BII runs, for your year, you should not have a sensor after the cat. Double check that. You do have one before the cat, so make sure that one is in place, connected etc.

It should still run ok without the cat. You don't need backpressure. More exhaust flow may change things a bit, but you are EFI, right? That system should be able to compensate for easier flow on the exhaust side methinks.

 

Nope, no engine actually needs a cat converter to run.

Backpressure is BAD. You don't want backpressure at all, you just want good velocity thru the system to scavenge the upstream exhaust gas. The reason people think you need backpressure is because they put 3" exhaust on a little motor and lose performance. This is not because it needs backpressure, it's because the engine can't produce enough exhaust volume to completely fill the 3" pipe and therefore the velocity goes down.

 

Dixie, Immediately after removing the cat on my '94 Ranger 2.3L there's been an occasional backfire that I've always associated with the change in back pressure caused by removing the cat. It occurs when lifting my foot off the fuel petal after sustained highway driving. If not due to the change in back pressure what do you believe is the real cause? You challenged something I've believed for a long time and I'm genuinely interested.

 

I don't have sensors past the cat so there is no issue there. As far as what I call back pressure is more along the lines of vaccum and volume. I don't think the converter is of much use after this long, I was just more concerned about upsetting the "pulse" of the exhaust. would I need a resonator instead of straight pipe.

I understand I don't need a cat, other than for controlling emissions I'm just not sure what kind of volume restrictions the thing may have. I don't want it to run like spit at low rpm

I suppose it's going to be a trial and error thing. I may play around with another resonator because another concern is noise.

Thanks.

 

An actual backfire is just like it sounds, when instead of combustion and related gases leaving the cylinders thru the exhaust it goes out the intake instead. With carbureted engines you'd see this as a flame out the top of the carb combined with a loud bang. It can happen with EFI too but the flame is usually hidden by the air intake tube.

I think what you're hearing instead is just a bit of unburned fuel exiting the cylinders into the exhaust, due to suddenly letting off the throttle and severely limiting the air to the engine when running under load. This happens even with stock exhaust but you don't normally hear it because the factory cat muffles a lot of that sound along with the actual factory muffler. The cat also operates at something like 3 times the temperature of the exhaust exiting the engine (because it's job is to burn everything that comes out of the cylinders) and because of that it can cook off unburnt fuel as well, before it hits the tailpipe where you can hear it.

 

If you leave the stock pipes alone except for removing the cat then you probably won't lose anything. If you shorten them so that they dump under the cab then you'll need to play with pipe size to get the right velocity going. Mine dump just after the cab so I run 2" exhaust pipe which actually has an inside diameter of 1 7/8". Works fine for my 351, didn't lose any low end torque.

 

Thanks Dixie, rep added