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Discussion Starter · #1 ·
Just snapped some pictures of my recent RR L322 BMW M62 4.4 litre exhaust modifications. Pix clearly show where we cut the pipes and welded on extra flanges behind the back axle so that the original factory muffler could be replaced, ready for extreme bush work.

Total cost of the modifications, including the twin Stainless Steel Resonators was around US$350-400. Note that the custom 'handed' Resonator pair are supported by the RR's original factory exhaust hangar rubbers so removal and re-fit of the factory muffler is a quick and painless operation.

The final result is a noticeable increase in low end torque and of course, an engine I can finally 'hear'!

Outboard Soundtrack Video: https://www.youtube.com/watch?v=nbdJjZSw8A4

Inboard Soundtrack Video: https://www.youtube.com/watch?v=S0eynF_2I7c&t=9s

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Looks like a clean job, you much have ditched some weight also and it sounds great.

Why did you use Resonators to replaces a Muffler ? Now you have 2 sets of Resonators and no Muffler right ?

Thanks
 

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Discussion Starter · #3 ·
Now you have 2 sets of Resonators and no Muffler right ?
The Shop had quoted on straight pipes which (they said) would be fine but once their Tech had made the cut, removed the muffler and started the engine, the Foreman called me in for a consultation. We all (mostly!) agreed the sound was too loud and a bit ugly too if I'm honest so we sat a couple of stock Resonators on the open pipes till we found the ideal compromise in these small 'hot dog' shaped units. They are still 'mufflers' in that they reduce dB but they don't have the restrictive cross baffles found in most OEM mufflers - hence my 'perceived' low end torque increase.

Resonators are designed to restrict only certain frequencies in the exhaust sound spectrum so are usually fitted to attenuate annoying pitch resonance in a system. In this setup, where we are using the factory resonator followed by an aftermarket resonator, I think we have just been lucky to hit the right combination.

PS: The Resonators I used were likely to be US imports so I can probably find out the brand and model if anybody is particularly interested.

Here's what one sounds like with straight pipes: https://www.youtube.com/watch?v=VN6IWumzPXE
 

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Discussion Starter · #5 ·

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droning, common phrase. Often with exhaust changes you end up ruining the exhaust tune the factory developed for quiet in the cabin at all speeds. Changing the note of an exhaust often produces droning, loud cyclical notes, in the cabin at highway speed. If droning is bad you feel like driving the rig off a cliff after a few miles. If it's not too bad you invest in migraine tablets for road trips.
 

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Discussion Starter · #7 ·
Then that is what exhaust Resonators are used for - to delete the drone or exhaust 'resonation' at certain frequencies. My rebuilt RR Classic 4.6 engine's 2.5" exhaust resonates at exactly 1800 RPM (gone by 2000 RPM) and a Tuned Resonator would fix it. In the case on the 4.4 M62, I've yet to experience any undue resonation at local highway speeds (up to 80Km/h) but I have my transmission flush booked in for Monday so will be doing a long trip at the end of this month where we will be able to reach the legal Freeway speed limit. (110Km/h in AU)

We'll see what happens there but given that most highway cruising is in 5th gear at say, 2500 RPM, I don't think droning will be an issue. (If it is, it's only a 10 minute job to replace the factory muffler before a high speed journey.)
 

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One more question: did you remove the center muffler as well (the one after the catalysts) or did you just remove the rear muffler? I might try to replicate this, it does seem nice. Thanks for sharing.
 

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Discussion Starter · #9 ·
No, probably best to leave the centre pair alone as they have the cross pipe integrated and appear to be Resonators so they may be Factory tuned to remove any potential 'drone' at highway speeds. I think the system I came up with was a good compromise as some of the 'Cat Back' pipe setups I've heard on Youtube seem too noisy and too expensive.
 

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Very interesting. What material are the pipes? They almost look powder coated. Hopefully, it's rust resistant.

As far as the sound, it's great for short trips around town, but it drives me crazy on long trips. I had 1970 Boss 302 Mustang with headers and reasonators. I took it on a 3 hour trip once and then bought a Toyota to do it again.

It sounds fun to drive. Good look with it. Sharp looking truck.
 

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Discussion Starter · #12 ·
Very interesting. What material are the pipes? They almost look powder coated. Hopefully, it's rust resistant
I'll be taking a long road trip at the end of the month so I'll let you know. I'm pretty sure they used stainless 45 degree bends to mate with the stainless Resonators (a generic SS Chinese manufactured unit ca 12" long x 2.5" pipe dia.) then after tacking in place, they removed the whole show, Mig welded it up, then carefully wire brushed the job before applying a couple of coats of high temp (400 degree) mat black spray engine enamel.
 

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Discussion Starter · #14 ·
Hate to admit it but the 2.5" stainless tips we originally fitted just didn't look right so after a week or so of consideration, I imported a pair of polished flared and double walled SS tips from Worley in Hong Kong. They are 62mm ID and 3.5" OD and this design keeps the rain out! They can be pushed further on (which we might do) or removed entirely for the bush but as I wrote previously, I have retained the original muffler for 'bush work' as the Factory pipe outlets are 100% protected inside the chassis. To fit the new parts, I simply lubricated the welded tips with Vaseline and hammered the new ones over with a rubber mallet and wood block to form very tight seal.

IMO, the larger pipe outlet now compliments the sheer scale of the L322 and yes, the exhaust note has changed a bit but in a very appealing way...

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