soundslike maybe a loose heat shield maybe, or loose bolt on flange... metal on metal resonating? Did you get rid of the factory x-pipe section?

Thank you, sir!

 

 

The factory xpipe is garbage. It is pinched and restrictive. The exhaust shop did tell me that the factory exhaust up front is actually a pipe inside a pipe. I guess to lower cabin sound. Its only like that up to the secondary cats. He said that moisture will rot out the inner pipe and sometimes plug the exhaust or cause noise in the pipe. I guess you could always put the car on a rack with it running and have someone underneath listen while you raise the rpms, to chase down the location of the noise. May even be something under the car that is loose but totally unrelated to exhaust.

 

 

I ended up installing an invidia midpipe with magnaflow exhaust, sounds good! Wasn't as deep as I thought it will be, but definitely better sounding overall than just axle back and not just louder. Wasn't as loud as I thought it will be, this is quite a good volume to me. I will make some sound clip if anyone is interested

edit: the car also feel like it accelerates much better on normal mode and a lil less better on sports mode.

Overall: could only be happier if the exhaust sounds deeper. Other than that, absolutely love it

 

Exhaust sounds great! Been Youtube-scouting and wondered whose it was. Refined and vocal when put down but reserved otherwise.

How big is the "inside" factory pipe, and why did you go with 2.25" instead of 2.5"? Seems most/all the aftermarket ones have gone to 2.5" and I don't know if diameter is a direct correlation with displacement, but when I replaced the factory 2.25" on my 3.8L Mustang V6 with the 2.5" from a 4.6L it was a noticeable difference.

How'd it turn out? Did you get the new resonators put on?

Last thing I want on my Lexus is a raspy boy-racer exhaust. Aside from full headers, from all the ones I've heard it's the removal of resonators which has been the primary culprit.

 

 

If I did it all over again, I would have ordered everything in 2.5, but the factory rear axle back, goes back down to 2.25. The bends after the axle are quite sharp, and going to 2.5, bent by a non-mandrel bending machine would end up the same as 2.25. I've considered ordering stainless bend sections, and some pieces of straight pipe and re-doing everything, but for now, its ok. I just listened to several combinations of what other people had, and most were just too obnoxious (no offense to anyone). I just wanted something more mellow, that only made noise in the throttle. As for the factory pipe piece, I should have taken a pic, just didnt think about it at the time.

 

Gotcha. Thanks for all the spade work in this, much appreciated. Sounds very reserved considering no secondary cats, but it's still rather loud inside?

I've contacted a custom exhaust place here that has a mandrel machine. Would think that with the existing template it should be easier to form the custom one. Also, the factory system appears to be straight duals from the collector, so the X-pipe was just another enhancement? Any reason why X not H?

 

Not loud inside the car at all unless your in the throttle, and its really still not that loud. The factory exhaust has what looks like a poor attempt at an x-pipe, but squished and angled. X-pipe design has better flow than an H style. It allows each exhaust tube to help the other. There are some vids on youtube that explain it a lot better, but it makes the engine make power easier, and also sounds better than the h-style. A longer resonator would also tone down the exhaust a little more, if you think mine may be borderline. I've been on the car scene for a long time. I've had 11 Camaros, then went to the Acura TL (regret lol), and now the IS. I messed with the exhaust on the Acura until I found a good setup, and based the IS setup off of that since they are both V6 cars with very close displacement. Plus, I wasnt about to spend $1k on a setup that wasnt going to be exactly what I wanted.
But, yeah, If you have a shop that does good mandrel, you can order multiple stainless pieces, or have them do the whole thing in stainless if they have it. As far as the secondary cats, you dont have to ditch them. They wont disrupt flow much at all as long as they are still good, and they may quiet the exhaust sound slightly. The big thing is moving the x-pipe forward from where the factory one is. It needs to be as close to the secondary cats as possible. Keep in mind, that if you go 2.5" all the way, you will lose a little torque down low but you will gain HP on the top. In real world, if you are doing performance mods, then torque off the line is irrelevant considering once you shift, you never see that low end again. Good luck on your install. Would definitely love to see what you end up going with and hear it as well.

 

Have to say, that's about the ideal sound I'd want -- low rumble so you know it's there, but not loud till you want it to be, then smooth through the revs and no open-pipe or fart-can rice-roar rasp. In fact, it sounds much like the better available axle-backs, but with the added benefit of freeing up the midpipe. After all those cars you've had, no surprise you've figured out what works! The most I modded were my Civic and Mustang, but never went for volume and certainly won't now with a Lexus. Loud and raunchy is easy and takes little thought or planning.

As for pipe diameter, it seems the manufacturers are all over the place, from 2.25 to 2.5 to even 2.7. RR Racing uses Ark which is 2.5 but they also supercharge. If for some reason I can't get the mandrel place to do 2.5, having that size would compensate somewhat for any crimping in the tighter turns. The change from 2.25 to 2.5 in my Mustang was also to true duals so that was undoubtedly part of the improvement. Acknowledging that there are many variables at play, do you figure 2.5 is over what our (NA) displacement should require?

 

Looking back at this, you did not replace any pipe, just did the X, resonators, and mufflers, leaving all the rest? Do the Walkers not come in 2.25" or is there an equivalent? And is the axleback pipe just 2"?
So the stock setup is basically:

header => primary cat => collector => 2" to X => 2" to secondary cats => 2.25" to resonators => 2" to mufflers

I got a quote from the mandrel place for replacing everything from the collectors back with 2.25", and it wasn't pretty, haha. But if there's no pipes being replaced that would certainly reduce the cost significantly. I forwarded your recos and he came back with Vibrant resonators and mufflers, saying he prefers their quality although they were significantly more.

 

Basically the entire midsection is new because of removing the secondary cats and the factory x-pipe section. And dynomax does make the resonator in 2.25. Thats what I was saying, that if I did it again, it would be a constant 2.25 all the way back to the axle. If you ever see a pic of the factory exhaust, you will see what I am talking about. Looks "pieced" together from leftovers. Also, YES madrel piping is expensive... lol. You always have the option of ordering the pieces separate online and then have the shop weld them up. I think before, I found 45 degree mandrel bends for like $20 each.

 

1. Okay, so for the pipe you did replace, you used 2.25"? The entire midpipe is essentially new?
2. From the collectors you had new 2.25 pipe to an immediate X, then new pipe straight down to the resonators, then new to the axleback junction, so you adapted the resonators to the larger pipes?
3. Sounds like you left the stock axleback pipe, which is 2.0", and just replaced the mufflers? If so, then to replace it, considering the turns if not mandrel would maybe be best to use 2.5".
4. Would there be a specific 2.25 Dynomax resonator you'd recommend, as I imagine they all tailor sound differently, which is what you auditioned and determined according to your goals.

There's a reputedly good muffler shop nearby that I'll visit tomorrow and see what they say. Going with the parts you listed and not mandrel, I'd hope to get a quote at least 50% less than the mandrel guy. Like you I think, performance isn't the #1 consideration for me.

 

1. yes
2. yes
3. yes. the turn on the axle back is pretty sharp and a regular pipe bender is gonna crimp the hell out of it.
4. for the resonator DO NOT go shorter than the one I used. Length is key on toning down the exhaust note. You can go 2 or 3 inches longer (as long as it fits in the same area). If I re-do mine, Im gonna use the walker 24431 part number.