Get a corsa pro series muffler (2.5") and spray paint it black with high temperature exhaust paint. It's hands down the best muffler for this car and V8s in general. I tried so many different mufflers for this car including the AMG one and the corsa is the only muffler that eliminates all drone when driving and sounds the best when you step on it. It also has a really iconic V8 rumble sound at idle the other mufflers did not have. Then you can buy brabus tips separately and put them on the corsa.

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For wheels the gold standard for a wider stance is the staggered 8.5" fronts 9.5/10" rears on 245s in front and 265/275s in rear that came with the sport option for the car. Anything more is pushing it in terms of performance and gas mileage but you could probably fit up to 295s in the rear if you can find an 11" wheel.

If you're talking about spacers on the narrower wheels then you don't want to be putting huge spacers when instead you could just get wider wheels with smaller spacers to achieve the same flush look.

 

Ok I’ll check out corsa. For the wheels I already have 245 in front and 275 in rear with the silver arrow rims and I plan on keeping the orbital wheels to the car. I just want to make these ones have a wider stance.

 

I like the looks of dual tips on the R129, and angled dual tips might look good, but you'll have to cut your bumper if you want to them to fit cleanly.

 

You don't want to install a 2.5" inlet muffler on a 2.75" exhaust. Doesn't matter how free flowing the muffler is. The bottleneck will be at the inlet. If you're going to go custom fab dual tips, you'll want to get a shorter muffler so you'll have space behind the bumper to route piping for the tips. Even the stock tips have bends in them due to the spacing/position/size of the stock rear muffler.

 

You don't want to install a 2.5" inlet muffler on a 2.75" exhaust.

Source? I discussed with 2 local custom exhaust shops when choosing between 3 and 2.5 and both of them said 2.5 is better and will improve flow velocity since the 5L v8 doesn't need more than 2.5". I think there were posts where people opened up the resonator and muffler on the R129 and the inner pipes were smaller than the pipe that entered the system but I might be wrong.

I think there are a lot of parameters at play with the exhaust flow velocity versus volume but from what was explained to me getting rid of the secondary cats and resonator and muffler already reduces a lot of back pressure so a 2.5" "bottlenecked" system without all of those is similar to a 2.75" system with all of those included in terms of flow. But if you go from the dual 2.25" to 3" from the secondary cats the 3" is too big for the system and you will lose low end torque.

 

Nobody said to go to 3" from the secondary cats. You made that up to give yourself something to talk about. You yourself talked about choosing between a muffler with a 3" vs 2.5" inlet. No mention of dual 3" pipes from the secondaries. Pathetic. I've wasted more than enough time and effort on you. I've explained things to you before when you asked why you're wrong and all you do is come back with stupid butt hurt snide comments unless you've gotten yourself in a pickle because you thought you knew/are more capable than you are. I was and am addressing the OP. You can do whatever you want with your car, but yet again you're advising people on things for which you have no idea what you're talking about.

I opened up the muffler myself. The single inlet splits in two inside and snakes around. The two pipes are perforated, enter a chamber in the rear where there is nothing but matting, no pipes at all, exits the chamber through pipes and out the back. Yes the split pipes are smaller than 2.75", but the volume of air traveling through them is not reduced and backpressure is not increased because there are two tubes. It is not a single tube snaking around in there reduced from 2.75". You have no clue. Your source is custom exhaust shops? Did they do flow analysis?

You can open things up before a bottleneck as much as you want, it will still be limited by the bottleneck. Increased velocity at the reduction to 2.5" at the end of the exhaust system would only occur because of increased pressure in front of the reduction. Is there the equivalent of a reduction to 2.5" in the exhaust from factory at the rear muffler? No. What happens if you increase backpressure from stock? Pressure and heat build up more than stock. Is that a good thing? No. A reduction to 2.5" at the very end of the exhaust system would not increase velocity or scavenging through the exhaust system.

If you try to blow through a long straw of uniform tube diameter, the pressure through the straw will not change much if the very end of the straw is a bit wider. Reduce the very end of the straw a bit, and you can bet you will notice the increase in backpressure.

 

The exhaust gases cool down as they travel through the system so switching to 2.5 at the end instead of 2.75 won't affect the performance for a NA 5.0L v8 making just over 300hp. There are guidelines for how large exhaust piping should be and 2.5" is still within the range for the M119/M113 engine's displacement and horsepower. The pipes start out as a dual system in the SL500 with two 2.25" pipes which merge into a 2.75" pipe at the resonator.

I didn't bring up the piping from the secondary cats just to give myself something to talk about. I know I didn't introduce context for it but the reason it's relevant is that secondary cat and resonator deletes are very common for this car and members on this forum. Obviously the best choice would be to go with 2.75" piping all the way to the end for the sake of staying within the guidelines of how the car was originally engineered, but most exhaust shops do not carry 2.75" piping and can't mandrel bend 2.75" piping if you brought your own, only 2.5" and 3", so anyone with an M119 R129 getting a resonator delete or secondary cat delete will have to chose between 3" and 2.5" and I'm saying 2.5" is the better option here as a 3" pipe will result in even more reduction in temperature and volume of the exhaust gases and it will be harder for the engine the push those gases out because gases are not the same as liquids.

The straw example is different because the straw is much shorter and the temperature difference between the inlet and outlet of the straw is minimal. Plus you're assuming blowing hard through a little straw which is way too small for the amount of air that human lungs can displace in strong exhale. But imagine this, you use a really wide straw around your mouth that's 3 inches wide, then it tapers down to 2 inches. There won't be any difference in how much back pressure you feel when blowing through the straw because the 2 inch straw is already sufficient for handling the amount of air you're pushing through. Similarly the volume of air moving through the exhaust decreases as it flows through the system as its temperature decreases so a bottle neck at the very end is not equivalent to a bottleneck higher up in the front. Your bottleneck idea would only make sense if we were talking about an incompressible liquid fluid whose volume doesn't change throughout the system.

The muffler is so close to the end of the system that the reduction in exhaust gas volume by the time it reaches the muffler means that going with 2.5" over 2.75" won't make a difference, and at that point neither will going with 3.0" so this is a pointless argument.

 

I see your model year is 2001.

Here's a video of my 99, I don't know, it might be useful for anyone wishing to discuss this issue visually.

 

Arguing about 2.75" and 2.5" or 3" mufflers and/or pipe on a 302 hp car is just plain funny.

 

Had an Cadillac with 500 cubic inches.
Gentlemen that is, 8193.532 cc.
On a 2.5 single exhaust system.
Hmmmm?

And those who may remember.
A 4-4-2 with a dual.

Regards,
aam.

PS.
Stepping hard on the gas pedal, I could see the gas gauge dropping....
Gas was cheap....

 

Had an Cadillac with 500 cubic inches.
Gentlemen that is, 8193.532 cc.
On a 2.5 single exhaust system.
Hmmmm?

And those who may remember.
A 4-4-2 with a dual.

Regards,
aam.

PS.
Stepping hard on the gas pedal, I could see the gas gauge dropping....
Gas was cheap....

I have an Eldorado 1971 with that 8.2L engine , but dual exhaust . As you said , you can watch the gas needle dropping literally as you accelerate

 

To go back to the original question: I've been looking for a replacement rear box for my -90 car and of all the options having one made locally at a specialist looks the best and its cheapest too.

 

Just be careful, if you’re thinking of deleting the resonator too, don’t let the specialist cut the tails off the centre section which is part of the catalytic converter. Those things are getting hugely expensive now.

CKS in the UK, which I don’t recommend, proposed to do just this, so I walked away.

 

Just be careful, if you’re thinking of deleting the resonator too, don’t let the specialist cut the tails off the centre section which is part of the catalytic converter. Those things are getting hugely expensive now.

CKS in the UK, which I don’t recommend, proposed to do just this, so I walked away.

What are the tails on the center section? Are you talking about the secondary cats?

 

Definitely a garage Queen of Queens.

 

Haha, Brauhaus already chewed my arse years ago over this photo because ... well that’s another story 😬

 

Haha, Brauhaus already chewed my arse years ago over this photo because ... well that’s another story 😬

That's funny, between then and now you acted like you forgot that happened.

You're also still laughably wrong. Nobody said you know or should know everything. You're the one that acted like you do.

Yeah, you're still butt hurt.

 

Well mine most definitely does NOT look like that. It would help if i didn't keep reversing into things too. But thanks for the heads up on the CAT tails, the cat set up is very large so I can see why preserving these matters. For some years I thought my '90 build car didn't have CATS but they are most definitely there.

 

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