Lose the cats and no fault codes
 

My wife has a Mazda MPV, we had emissions fault codes telling us that the van needed a new cat. $500.00 WOW, no thanks. I found something called a "spark plug de fowler" and mounted it to the 02 sensor behind the cat. It's essentially a spacer for the sensor that screws into the tailpipe mount and then the sensor screws into it. End result is a sensor that is mounted about 2" back from the pipe.
Code went away, passed aircare emissions test and it's been good for the last 6 months.

So....should I try this with my D2?

In 2014 BC Canada will be getting rid of the emissions testing anyway, i'm more concerned with fault codes popping up.

Looking to give it some better flow, less heat near the u-joints of front drive shaft, better sound, maybe a bit more power, maybe a bit better milage...who knows? All I hear around this forum is theories but very little hard evidence.

Also adding heders to this set up when and if I do it.

I would greatly appreciate any feeback on this. Maybe i'll just end up being the ginny pig.

I looked into the headers, but they're too big with 1.5" primaries. That would be good for a motor making a torque peak above 4000rpm like many LS motors do, but anything close to a stock Rover V8 peaks below 3000rpm. Those big (for a 4.0 V8) headers could improve flow at 5500rpm for additional horsepower, but I don't drive my Rover like that. For the best torque, the primaries need to be about 1". Because of that, I'm convinced the stock manifolds are actually better. If you want steel tubes instead of cast iron, you could use the manifolds off a P38. I'm pretty sure they are basically like shorties but don't know if they fit the Discovery body. Since they don't hold the heat in, Rover wrapped them with heat sheilds.

As for the cat-delete, I'm skeptical there's any gains in it. If they do restrict the flow more than straight pipe then it only really matters when the flow demand is highest, at high-rpm. This just isn't where I would try to tune any gains on a Land Rover. That's also why I won't use a straight-through muffler. They might flow more on the bench, but that only matters on the car at something close to redline. A chambered muffler has a better chance of improving torque, and it's not because of "backpressure." Although they don't flow as well as other designs, the advantage is the open chamber effectively terminates the collector length and can reflect sound/pressure waves back at the exhaust valve for a bump in scavenging at certain rpm (determined by the collector volume which is a function of cross sectional area and length). The straight-through, in contrast, effectively extends the collector length all the way back to the resonator or tailpipe exit (way too long). So the chambered muffler is useful not because of backpressure, but because of allowing you to tune the collector pipe length.

Unfortunately there's little room on the car to change the exhaust pipe routing while still maintaining ground clearance so fine-tuning pipe lengths proves impractical unless you are willing to run the pipes below the frame or fabricate something rather exotic.

In essence, my conclusion is the stock system is very close to ideal. Nearly any aftermarket muffler will flow better than stock but the benefits of additional flow are very minimal and only at high rpm. A chambered muffler could improve torque, but rather doubtfully since the exact position of the muffler can't be changed. It may be that it needs to be 15 inches farther forward to gain anything and you can't put it there because the transmission pan is there.

Perhaps the best modification you can do is install a larger rear muffler to make the car a little quieter. The temperature and pressure of the exhaust gas that far back is much lower and therefore the requirements for flow are reduced and you can probably add case volume without lowering performance.

The spark plug anti-foulers on the downstream O2S trick will work on any vehicle, although you may have to bore the anti-fouler out with a 1/2" drill bit first.

On additional power, the exhaust system on these trucks isn't super restrictive, so I wouldn't expect any monumental power gains from exhaust mods. You can expect the exhaust note, however, to change in tonality.

Yes, i've used the non fouler before in my wife's mini van. I think I'm gonna try to out. Really all I'm paying for is the 2.5 pipe. and a few bucks in "non foulers". If it doesn't work I'll put the new cats on that I was gonna get anyway. Sometimes you gotta just do stuff, just for the fun of it.

I apreciate the inof on headers. I'd been saving up for the hedman 98300 for a while and that was gonna bew my plan.

It's just hard accepting the fact that there are no easy, cheap power mods for these babies. Oh well, i still love the thing.

so did this work?

Unfortunatly I did'nt end up trying. I found a great deal on hi-flow cats so just went that route instead.

Awesome write up. Question, does this mean high flow cats don't help anything at our normal operating rpms?

running with not cats update
 

Ok, I wanted to update this thread. I did order new cats but before installing them I ran my truck for one month with straight pipe. Below is my write up.

Install:
This was very easy. I just bought a bunch of angled pieces from the auto parts place and then returned the ones I didn't need. The pipe size where the cats is is actually 2". I read a lot of differing sizes but they are 2"...they were on mine anyway.

Sound:
Way more aggressive sound. I liked it...a lot. But if your not into a raw V8 sound then you would not dig this. Also I think it would have probably sounded better and maybe a bit quieter if I had welded the pipe. I just used clamps so I had a few little leaks.
It was not too bad in the truck. On the HWY at 65 it was pleasant, nothing obnoxious.

Power:
I did not notice anything. But to be honest, would you really notice anything under 10HP unless you put it on a dyno tester.

MPG:
Mine went down. After the straight pipe install I lost roughly 30miles on a tank. It was hard to tell because the pipes were not welded so maybe the leaks caused a bit of fuel drop. also it got a lot colder out right after I did this and my truck get worse milage in the cold and also the O2 sensors were constantly throwing me codes so I'm not sure if they sent signal to pump more fuel into the engine or not. So MPG was kind of inconclusive but It definetly did not get any better milage. I'm just not sure it if was worse.

Smell:
Didn't notice anything inside the truck or out.

Codes:
I did install the spark plug non fouler spacers but I'm not sure of they really worked. My rear driverside sensor threw a "not working" code P0137. Then I dropped one of the spacers and that went away.
My passenger side ddi the same thing. P0157. I'm not sure if this was due to a bad O2 after screwing it out and back in or if it was not working from the straight pipe.
Seemed that every time the CEL went on I had a new code.

In conclusion:
Well I would for sure swap your cats out. New high flow cats are cheap and Mine were under $100 for both. I sold my factory cats on ebay for just over $250.00 for both. to be honest though if you are thinking about doing straight pipe for any type of gain in HP, milage etc...don't bother. It's not worth it.
Also another thing that I noticed was my engine knocking on start up every morning. It never did that before.

Mine has been this way since the hg job, definitly louder I also run a flow master type muffler and no rear resonator, not sure of MPG gain or loss, there is a smell just like any old engine with no cats

Made up some adapters to get the downstreams out of the pipes no o2 codes

Where did you find the O2 spacers, or how did you modify the stock bungs?