It is time for new Cats and exhaust. I am thinking Magnaflow for both, but am wondering what your experiences have been. Is there an actual performance increase with the high flow cats?

Also, for the muffler, I am wanting to go with Stainless Steel, but considering the originals have gone 12 years, not sure it's worth the extra money. We are have a kid this fall so I also don't want a really loud muffler.

Any advice?

 

Straight-through glass-pack mufflers like Magnaflow are stupid loud for an anemic Rover V8, and they're very likely to have an annoying drone. Plenty of enthusiasts do install them, but they typically have less than a year experience with their Rover, and they typically keep it for no more than a year afterward.

I tested six different aftermarket mufflers on my Rover, and not just different brands of the same design. I tested glass-packs, "turbo" style, chambered, "vortex" (glasspack with a venturi), "VT" (glasspack with flapper valve), and laminar core type mufflers.

They're all louder than the stock turbo style. A performance gain from the muffler on a Rover is an absurd proposition. The muffler is only going to limit flow at the high-end of flow, and if you need more flow at redline, you're driving like an idiot. If you install a loud muffler, you'll sound like an idiot too. Trust me that I'm not just an old fart. I have multiple citations for loud exhaust, just not on a bloody Land Rover that wouldn't be quick if you dropped it off a cliff.

The muffler in the rear position is great and shouldn't be eliminated. Mufflers farther back on the tailpipe have a two big advantages. First, exhaust gases are cooled off and more dense at that distance from the combustion chamber. Therefore, you can flow more with a smaller muffler. Performance-wise, it is the most advantageous position for a muffler, but the vehicle leaves little room for it, hence the center muffler. The center muffler has to be much larger to flow the same as a smaller rear muffler. Second, the rear position muffler is much better at cutting drone.

I'm using two mufflers, a three-chamber, and a laminar core in series (in place of the stock resonator), and it's still louder than stock. I do not get any drone. I have more than enough flow. I don't necessarily recommend what I have. I just recommend the largest muffler you can fit in both the center and rear positions. That will keep it as quiet as possible while flowing plenty. Remember even two aftermarket mufflers is louder than stock, so you cannot go too big (until it doesn't fit).

Pipe size is based on the oem y-pipe and s-pipe. It's easy to adapt to a 2.5 or 2.25 center muffler. The rear muffler is 2.25 and harder to adapt to a different size. So I recommend 2.5 center (because they're easier to find), and 2.25 rear.

I live in a practically rust-free area, so mild steel lasts more than 10 years, and aluminized steel 20 years or more. The only call for stainless would be for appearance, which makes sense on a late model Range Rover or something, but probably not a Discovery 1. Offroad damage is more likely to damage exhaust parts before rust will.

 

I believe mufflers can be designed to reflect a sound wave back at the exhaust port and scavenge. This is really the only thing an exhaust system can do for you performance wise other than simply flow "enough." A chambered muffler will do this, a straight-through will not, as it acts just like a piece of straight pipe. The problem with the Land Rover (Discovery and all classic Land Rovers), is the center muffler position is a bit too far back, resulting in an effective collector length that puts any bump in the torque curve well below the stall speed of the torque converter. So it's meaningless, and the only practical parameters to consider become ground-clearance, protection from damage, and the sound qualities and volume.

 

I will pass on the high flow stuff. I am really not interested in having a loud car.

Has anyone had experience with the Davico Cats?

I will look around and see what I can find that is direct fit.

 

I wasted an entire weekend on Davico. Unbolted the Y-pipe and cats, bolted up the Davico pipes and had a major leak at the flange at the header. After several trips to the parts store for this and that, I realized the specs were off. It would not fit. Took the whole dang thing off and the old pipes BACK on.

Bought two new Magnaflow 94105 cats from Auto Zone for $75 each. Paid the welder $200 to install them. Drove off with my old cats and recycled them for $120. Guess it cost me $230 in the end.

Muffler was good so it stayed on.

 

I pulled the trigger on Walker Ultra Direct fit cats. I will update after they are installed. I'm going to do the throttle body cleaning with some seafoam prior to install.

 

I got the Walker cats yesterday, have not had a good test drive yet. They did not simply bolt on, and the passenger side had to be but and welded back on with a little bending. It did not meet up with the muffler either so they had to cut and weld in a piece of pipe to connect the Y pipe to the resonator.

If I could do it again I may do the magnaflow, but they got it in there, and they gave me a good price on install. I would rather do thing myself, but this wwas not a one man job, and did require welding and a torch to bend pipe.

 

I know Jamie had trouble with Davico (as did I) and now you have had problems with Walker. I guess there is no good, cheap alternative.

 

I don't know, the magnaflow comes in two pieces so maybe that compensates for variance in the location of the engine. I can't see any way there is a bolt on replacement that would not require some bending. The length being an inch or two too short is hard to fathom, but this is also not the original engine. Theoretically I suppose it should be in the exact same position as the original, but I doubt it is.

The owner of the shop and I had a beer and a chuckle watching the young guy try to get it in. The head guy came over and got it done.

 

I had the Magnaflow cats with stock muffler for a while and hated it. With stock cats and no rear resonator it sounded good, about like a Silverado, but when I replaced the cats with Magnaflow the sound got.... Tinny, kinda. I dunno how to explain it. If someone were to use Magnaflow cats or do a cat delete as I have now, I would absolutely recommend aftermarket mufflers.

I will say, having had in the ballpark of 10 different exhaust setups with quite a few different muffler styles, power gain is possible. That said, it's pretty minimal and you also have to swap your intake for a high flow like the one I did a write up on. The real point of restriction is the exhaust diameter and the cast non-equal length manifolds. Switching to equal length headers and going from the 2-1/8" pipe in the y-pipe as well as the stock 2.5" single out up to 2.5" y-pipe and 3" single out made a large noticeable difference. The headers were the biggest part because the equal length primaries gave it a nice scavenging effect at the collector. Going full Magnaflow would gain you very little in the way of power, so little that I doubt you would notice the difference without an intake and you'd notice very little and only at the top of the RPM range with exhaust and intake.

If you really want to gain power, a cam with a port and polish on the heads and equal length headers is the way to go. Short of a cam any gains are going to be negligible.