I have a '82 XJ6. I have checked several sites including Driven Man re: performance exhausts. Several folks recommend removing the mufflers, replacing them with tubing. It is said to up hp by 30ish. Headers are also offered, but do not have O2 sensor bungs. I need to keep my car compliant with emission standards for Albuquerque, NM. I am currently running a hollowed out first catalyst (a long story)and a stock second catalyst where the pipes Y. It currently passes emissions checks easily.
Anyone have any experience with "improving" on the stock system? Can an O2 bung be welded onto a header? If I am not using the first catalyst, do I need it?
I appreciate an help before I drop some $$$$$ into this and then find out it doesn't work and/or I can't drive it legally.
Thx!

 

I don't think there is anywhere near 30hp to be gained. On my XJS (very similar mufflers, if not identical) I think I gained maybe 10 hp from removing the front mufflers and fitting low restriction rear mufflers....just enough to feel some improvement.

Oxygen sensor bungs can be welded in, yes.

Cheers
DD

 

I am not sure what 30 hp would feel like and my info didn't tell me where in the power band it happened.
Did you replace the catalytic converters with high flow ones? And, how was the sound? Too loud? Just right?

 

You would *definately* notice 30 extra horsepower.

The sound was just about right, not really loud at all

Didn't do anything with the cats

Cheers
DD

 

If you want to best system you will want a free flowing exhaust with headers, hi flow cats, and a good set of mufflers. Now this might cost a little bit of money, but if you space out the cost, start at the engine and work your way back. The other thing you will want to look at is the size of the exhaust tubing, larger is better, as long as it will fit under the car. A free flowing exhaust is good for under hood temperature (helps to keep things a little cooler), frees up HP, and can improve gas mileage as long as you can keep your foot out of the gas (usually you want to hear the exhaust so you drive more aggressively).

 

RG, if you did the whole exhaust system (headers, new cats, less restrictive mufflers), then you may see a total of 30 hp gain. But, take out any one item and you will see a drop in power gain.

As for the "bigger is better" concept with exhaust systems, that is somewhat true. Yes, a bigger exhaust pipe is going to flow more exhaust allowing the engine to produce more power. It does this by dropping the backpressure as seen by the engine. So, the higher the engine RPMs go, the more air the motor can move, therefore generating more power. The downside to this is that backpressure is what generates your torque. So, if you like to drive your kitty up at 3,000+ RPM everywhere, then yes, go big. But, for the most part, out on the highways and even in town, most people aren't hitting RPMs like that and maintaining them.

What I would personally recommend is designing an exhaust system with a local exhaust shop. Go with the headers (long tube style, the shorty tubes don't do really anything for performance gains in a lot of cases), an X-pipe for your cross over and something along the lines of a 50 series muffler(s). Connect all this with either 2.25" or 2.5" piping (go with the 2.5" if you are really looking for power and don't mind a slight loss in off the line launch). This should keep enough back pressure on the engine to make intown driving decent yet result in some nice power gains.

Most people compensate for the loss in torque by simply using more of the gas pedal. This works, but you will see your intown mileage drop. How much, that depends on how you drive. So, understand what you are willing to loose for the gains that you are getting.

 

Thank-you all for your input. It has been helpful. I also checked with the Driven Man and AJ6 engineering. Their suggestions are about the same, of course they have products to sell. Basically I am going to leave the stock headers in place, but run a long tube extension to the cross over where the second converter lives. then drop out the front mufflers and go with just the rear mufflers. AJ6 says they will weld in a bung for the sensor for me. I may have to disguise the the fact I have removed the front converter because a visual is part of our emissions inspection here. I am not enlarging the exhaust size as almost no one feels that there is anything to gain in doing that.
I have a "new" 86 XJS coupe. When it is rolling consistently I plan to do my alterations on the 6.

 

Sounds like a plan, glad we could help.

As for the visual inspection, I have heard that taking a catalytic converter and pushing a pipe through it that is the same size as your exhaust pipe will work. So you gain power, pass your inspection and still protect the environment by using the other cat, everybody wins!

 

Hi. I am having a hard time finding front mufflers for my 1987 XJ12.
Finding rear resonators, as suggested in another thread were found easy.

Anyone have ideas on compatible and more affordable forward ones for 1987 XJ12? Hoping to be in the $40-75/ea. range. I searched the forums and anything mentioned seems to no longer be available through online searching.

 

I'm sure the local muffler shop can fix you up with something decent and appropriate.

I'm facing the same dilemma with my V12. I've not been able to find a muffler that is DIY-able (direct fit, in other words) in this case. The 2.25" inlet and 1.875" outlet is an odd combination....on top of the other physical dimensions.

Overcoming these obstacles is nothing for a muffler shop, though, as they can easily cut, bend, weld, adapt.....

Make sure to let us know what you end up with.

Cheers
DD

 

I used one of these a few years back: Dynomax 17702: Thrush Turbo Muffler In/Out: 2" | JEGS. Works great. Needed some welding of course.

 

pjprofili, What sort of modification was involved on those?

 

By the way....

80s-90s XJS with the 5.3 V12 used the same forward mufflers. This will broaden your search....if you decide to keep searching

Cheers
DD

 

Don't recall exactly now, but I do remember cutting off the rear pipe from the existing muffler and welding it onto the new one.