Modified LS400 exhaust drone

[JBrady]

member richonenz posted the following question and I am moving it to its own thread.

"Hi Mr J Brady ,
I have an early LS400[ Celsior ] and have a worsening drone problem , the cats have had the guts removed and a through pipe welded in at the top but not welded at the bottom so it can float , I also have no rear mufflers just straight up to a 3" exit pipe from the last join , it never used to have a drone and was not very loud , I can only figure that the two side in centre mufflers are stuffed inside ?
At low speed and rev's its most noticible...about 40 to 60 KPH or also under a lot of load .
It's not down to the cats having a through pipe inside them as when I first did the cats I had no drone , this has developed over the last 60,000 K's or so , I presume I will have to replace those two mufflers but I'm not sure exactly what to put in there and I certainly don't want to play the try it and see game !!
Do you have any suggestions ?
Not necessarily the exact brand of muffler although that would be great if we can get them here in Aus , but more the type of muffler .
All help will be greatly appreciated !!"

 

[JBrady]

spf lexus posted the following response;

"I just scolded my friend for gutting his cats on a mustang GT and what happened? He came back crying because it sounded like garbage and eventually swapped oem back on. As JBrady has supported on several threads, lexus catalytic convertors are very high flow, and only use a couple hp, while enhancing low end torque. $100 says your low end tq will come back and your drone will magically dissappear. I only have a 2.50" dual with center 3" "Y" section with OEM front "Y" and cats with 2 rear magnaflows it's not that loud. this is also on a boosted engine. When you say 3" is this a single ehxaust or a dual 3"? If you have a dual 3", you better have some high hp mods done to the engine. Frankly all N/A 1uz's VVT-I or not should run 2.25" duals w/ 2.5" center unless you have higher hp goals than 350ish hp.


Any details on the build?"

 

[JBrady]

richonenz responds;

"Try reading the post again , I had NO drone when I piped up the cats for at least 2 years after and the drone developed over a 12 month period , also where in my post does it even mention a bottom end loss of HP ????
I mention a bottom end DRONE not a bottom end loss of power .
The reason I don't mention a bottom end loss of power is cos I don't have a bottom end loss of power !!
Maybe I didn't make it very clear , my system is standard apart from the piped up cats and only the very rear part of the system is 3" , when I imported the car the rear mufflers where missing so only from the joint after the back axles where the rear mufflers go on is it 3" .
I have had this same set up for 3 1/2 years and about 140,000 Kilometers , only in the last 12 months has the drone appeared and it came in gradually.
So just to make it clear the cats are just not gutted and left open , there is a through pipe in there the same diameter as the rest of the system [ that is way I had no extra noise and no loss of HP ] I have a standard Y pipe , a standard centre muffler and then the standard side entry mufflers and after the join in those mufflers I have coned it up to 3" to go out the back with no rear mufflers and I actually have 4" dumps at the end .
As a note I have a set of gutted cats on the shelf and a good set of " normal" cats as well , after the first set that where just gutted the cats reverberated quite badly , so I replaced those with the cats with pipes welded in inside , then I changed back to totally normal cats just to see if there was much difference , no difference in how the car goes , but you can just hear slightly more noise with the piped cats fitted , totally not offensive , quite nice actually and barely detectable in normal driving , get up it and you can hear it a little bit , especially at 7000 RPM in second gear !!
I have a MiNes ECU fitted that extends the redline by 1000 RPM .
3/4's of the system is 19 years old !!
So I figure the 3 standard mufflers might just be totally fuked inside ?? "

 

[JBrady]

spf lexus responds (with slight edit);

"Dual 3" exhaust w/ no cats, and only a raised redline spelled DRONE when I read ur post. Figured your welded cats broke a weld internally or your muffler packing is blowing out. btw, 1uz maxes out power at 6000rpm, add some cam and that 7k will actually do something. "

 

[JBrady]

Ok, to the above posts and questions posed:

If a system changes sound after a period of time something must have changed (obviously) so what is it?

The engine performance itself can change but that does not seem to be indicated.

The middle side entry mufflers may have rusted out internally changing their function and tone.

The center resonator may also be rusted out internally.

Eliminating the cats will change the chemical make up of the exhaust gas. Water vapor is present in exhaust gas especially when the engine is cold. Revving to 7000rpm will cause more internal load on the exhaust since there is a larger amount of physical flow at higher RPMS.

Most of the stock system is low grade stainless that will rust a bit over time. I am unsure of the packing material in the center resonator or the material in the middle mufflers.

Exhaust systems are like a trumphet or slide trombone. Each change will change the tone. First place I would look is the center resonator. Change it out with a good perforated core (not the stamped louvers that stick into the flow) 2.5" straight through resonator. How this interacts with your tubed cats is unknown but I would go with the longest one that I could find and fit.

I would then replace the side inlet center mufflers with 2.0" resonators again as long as I could find. This would require a 2.5" into 2.0" Y pipe. I would suggest buying or making a proper merge collector type Y pipe although you could get by with the stock one.

If you still are not satisfied with the sound I would go with 2.25" turbo style mufflers like Walker turbos.

Keep us posted on what you decide and how it turns out.

 

[JBrady]

By the way, if and when you replace the center mufflers please cut one open and take pictures. I haven't done that yet and am interested in the flow path.

Thanks

 

[richonenz]

OK it's kind of like I figured , using good quality resonators I will have to work it out for myself , unfortunately there is just not enough people with Celsior/Ls400,s to have a few that play .
I will use a good quality centre resonator as long a unit as I can source and then see what that does .
Mostly I'm looking to reduce noise [ drone ] in the cabin , the car is fairly quiet , sometimes [ when I actually have the car !! ]at night I wind all the windows down so I can actually hear it .
I have my own Tig and plenty of experience at building exhausts , I used to build under seat exhaust's for V4 Honda bikes !!
Unfortunately I don't have a hoist and that makes it difficult IE: lying on one's back with the exhaust 4" away from your face !!
So I will change the centre unit first and see what that does and yes I will slice it down the centre to see what's what .
As a note I think in 3 1/2 years of having the MiNes in I have taken it to 7000 RPM 5 times , generally my wife has the car and even with myself driving it , it rarely goes above 3000 RPM .
Thank you all for the input , I'll repost when I have an update.

 

[JBrady]

OK it's kind of like I figured , using good quality resonators I will have to work it out for myself , unfortunately there is just not enough people with Celsior/Ls400,s to have a few that play .
I will use a good quality centre resonator as long a unit as I can source and then see what that does .
Mostly I'm looking to reduce noise [ drone ] in the cabin , the car is fairly quiet , sometimes [ when I actually have the car !! ]at night I wind all the windows down so I can actually hear it .
I have my own Tig and plenty of experience at building exhausts , I used to build under seat exhaust's for V4 Honda bikes !!
Unfortunately I don't have a hoist and that makes it difficult IE: lying on one's back with the exhaust 4" away from your face !!
So I will change the centre unit first and see what that does and yes I will slice it down the centre to see what's what .
As a note I think in 3 1/2 years of having the MiNes in I have taken it to 7000 RPM 5 times , generally my wife has the car and even with myself driving it , it rarely goes above 3000 RPM .
Thank you all for the input , I'll repost when I have an update.

Excellent. I look forward to your results and pics of the stock center mufflers opened up. Having another experienced exhaust builder working on these cars increases the data available and good data is hard to find.

Regarding the 7000rpm runs member RMS did a stock engine with a new intake manifold and headers. Running stock cams and stock untouched or even cleaned heads, cams, valves, ports made peak power of 307hp at 6500rpm and was smooth to 7000rpm. So, while YOUR engine probably falls off fast above 6000rpm due primarily to manifolding it is not the cams that are holding it back.

You may want to check out my new Y pipe thread.

 

[JBrady]

Here is Erol's (RMS) test of a pure stock untouched longblock Tokyo taxi cab 1uzfe with his 50mm ITB and racing header setup.

Stock the engine is rated 250hp/260tq