sc400 X-pipe and stock mufflers

GreenChevelleSS

New Member
So i want to make my 92 SC400 a tad louder and get some more flow. I was thinking about running an X pipe in place of the Y pipe and run new pipes all the way to the stock mufflers getting rid of the center resonator and the 2 rears in front of the axles. Anyone think this is a good way to go? Planing on leaving the Cats and the stock pipe size. Has anyone ran it this way?
 

spf_lexus

New Member
X pipe makes good power but the bad news is that x pipes quiet the car down versus increasing its dB level. thats why NASCAR uses them. I would advise against replacing the stock front Y section as its proven to be the most efficient design for anything up to 300whp. I have built a few exhausts for the 1UZ, and the best power gains w/ regard to quick throttle response would include the following:

2.25" mandrel or std. crush bends
stock front Y section + cats retained
delete all mufflers + center resonator, replace w/ 2 straight thru mufflers
2.5" or 2.75" center section, merging into a 2nd 2.25" Y tail section

Anything bigger than 2.25" will kill low end/mid range power and response but will make the entire system louder.

Hope this helps.
 

spf_lexus

New Member
Sorry but I forgot to mention an easier way to open a bit of hp/sound w/o doing a full exhaust. Delete the center resonator and replace with a straight pipe in 2.5". I bought my sc400 with this already done and it had a nice and throaty tone w/ a slight burble at idle.. but not raspy at all. Most Lexus mufflers are pretty restrictive so you can expect about 10bhp or so.
 

JBrady

Moderator
SPF is right on with his advice.

In addition the middle mufflers are worth removing.
The stock catalysts and stock Y pipe should be kept.
The center single resonator should be replaced with a piece of 2.50" pipe or a 2.5" straight through resonator like a Magnaflow.
DO NOT cut the stock Y pipe before it merges. KEEP the stock Y merge. Cut just after it merges into the single 2.36" center and slide the 2.5" over this part.
There are two designs for the SC400 middle section after it splits back into duals.
One uses straight through type round mufflers with S looking pipes in and out.
The other uses conventional oval type mufflers with center inlets and side CASE outlets. The second style is more restrictive but both can be replaced with straight 2" mandrel pipe or slightly larger but NO larger than 2.25". You will also need a splitting Y pipe.
If you have the oval middle mufflers I would start there before doing any center resonator changes. Have them removed and have 2.0" pipe installed from the stock center splitting Y pipe back to the stock mufflers. This would be your least expensive way to go as the shop can easily cut after the Y split. They could actually re-use the stock flanges between the middle and back mufflers.

Below is the style with the round middle mufflers. It also shows the third center catalyst found on California cars.
 

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JBrady

Moderator
Here is a picture of the 1st gen LS400 which is very similar to the SC400 with oval middle mufflers. You would cut AFTER the second Y section splits it back into dual and replace back to the flanges with 2" pipe. I would have the exhaust shop re-use the flanges by welding them to the 2" pipe.
 

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spf_lexus

New Member
1 thing i'd like to add. I love stripping weight out of my car (im a bit obsessive w/ this project) and after deleting all mufflers, both cats, and replaced the heavy stock log headers with stainless long tubes, I saved a good 45lb overall. Thats considerable.
 

GreenChevelleSS

New Member
Since your saying to remove the mufflers would be the best way to increase performance without increasing sound too much? I guess I could remove the mufflers first and see how it sounds before modding the exhaust.
Ok whats the best performance mods on the exhaust for the sc400? what brand of headers are the best?
 

spf_lexus

New Member
The BEST headers available have to be RUSH imports headers. www.rushimports.com.au. They are the only tri-Y long tube design which will pretty much outflow any competition. The downside is that you will have to relocate an o2 sensor bung or 2 and relocate your cats further down the exhaust. IMF and S&S headers will flow very well as well and retain the stock cat locations but wont make as broad of hp/tq gains versus the rush headers.

If you deleted the 4 main mufflers and replaced with 2 high flow mufflers you could pick up about 15bhp with the stock headers. 2 magnaflows will sound great w/o being obnoxious but this is the only brand of muffler i use. I have ran flow masters once and they can sound raspy from my experience.
 

GreenChevelleSS

New Member
Ok I removed the mufflers at the rear. Pipe is still there after the axle. I like the way it sounds alot.
Will leaving the resonators hinder exhaust flow? I thought they were straight through? Should I go ahead and remove the center one and add the 2.5" pipe? Or remove all three? I dont want this car to be loud, pretty much I like the way it sounds now without the mufflers.
 

spf_lexus

New Member
Deleting the center resonator with a 2.5" pipe will open up a few hp and a few dB. Its going to be louder for sure since you already removed 2 of the 4 mufflers. If all your looking for is a louder tone, then leave the center resonator and put straight pipes in place of the 2 mufflers you took off. I have heard stock sc400's w/ all mufflers deleted and it sounds BAD... very raspy. A muffler shop can fabricate a full exhaust (cats-back) for about $500 if you shop prices. it wont matter if you use mandrel or crushed bends and you'll end up with a much cleaner sounding setup w/ higher gains.

You can grab Dynomax thrush mufflers for $35/each online and will sound better than just deleting mufflers.
 

brawls43

Member
I have built a few exhausts for the 1UZ, and the best power gains w/ regard to quick throttle response would include the following:

2.25" mandrel or std. crush bends
stock front Y section + cats retained
delete all mufflers + center resonator, replace w/ 2 straight thru mufflers
2.5" or 2.75" center section, merging into a 2nd 2.25" Y tail section

Anything bigger than 2.25" will kill low end/mid range power and response but will make the entire system louder.
I have a couple questions for you spf, what would be the lightest overall system, which retaining throttle response, and getting max power gains?

I run my SC400 as a race car, but can't modify the engine. I can delete cats if I want, but with 130k miles, I'm not making tons of power. We do have sound limits, but they're not tough to make. Currently I'm running stock through the first Y merge, I cut it there, and welded a 2.5-3 expansion, and we're running a single 3" glasspack, and 3" single out the back.

I did this to minimize the number of mufflers, and the 3" gives me a slightly higher overall flow area, compared to two 2" tubes. Its actually fairly quiet, which is why I'm considering ditching my catalysts. Would I be better off running a 2 or 2.25" dual system with an x-pipe?
 

spf_lexus

New Member
A dual 2.0" system is probably the best size for stock power when no other mods will be done but at 2 inch, you really need mandrel pipes to make the most out of it. 2.25" you MAY lose a tiny bit down low but not much and this size has been sort of the sweet spot if your planning on headers or any other mods in the future. Throw a Lextreme torque convertor in there and you wont be able to tell the difference down low.

I would keep the front cats and the entire front Y section in tact. Cut 2-3" after the 2 primary pipes have merged together. Its a small Y pipe but and a few members have tried improving on and always lost power. Most of this info was discovered by forum member JBrady so I gotta give credit hehe. Since you want the most power overall, I would forget the X pipe because you already have a balance pipe installed and removing it will guarantee a power drop. What you could do is completely mimic the stock exhaust layout and replace the second Y pipe with a much more efficient design. If your looking for the best of the best, go with a Burns Stainless Y pipe with a 2.5" IN and 2.25" out. This means a straight 2.5" pipe in between the Y pipes. Or 2.35" IN or 2.0'' for the smaller ID. Using mandrel bends will ensure the most gains out of your setup and will preserve throttle response.

I run an X pipe, 2 magnaflows and with my cats deleted I managed to drop a solid 40 pounds from the system. I run cat-less and X-pipe because i have forced induction but if I did not, the stock Y section and cats would still be in there.

Since you said your already sinning a single exit exhaust, you would have to start over. On the topic of Cats, leave them! Stock Lexus cats are already high flow metal substrate so there might be like 2hp gain at redline. The real problem with taking them off is reversion, and leaving them in place preserves the low end torque and mid range throttle response. As Jbrady puts it, they act as 1-way check valves for exhaust pulses.
 

Launch

New Member
SPF if you are running a forced induction why would you keep any cats? I assume your SC'ed and not turbo?
 

Spinnetti

Member
The BEST headers available have to be RUSH imports headers. www.rushimports.com.au. They are the only tri-Y long tube design which will pretty much outflow any competition.
May be best one available for the lex, but you'd be better off having good ones made. These collectors are awful, there's no cylinder paring for scavenging, not stainless or ceramic coated etc... On my LS, I just cut off everything behind the rear axle.. Its a race car, but isn't loud; would be ok on the street I think...
 

spf_lexus

New Member
It comes down to packaging... LS400 and SC400 have next to zero room for custom equal length setups. These are the best out there that fit the car. LS is even more crampted than the SC. Thes wont even come close to fitting the ls400. Shorty headers are the only setups that make due with the room available. Not to say a custom set of equal lengths is impossible, but you have alot of room constraints to deal with. These are stainless steel btw.
 

spf_lexus

New Member
SPF if you are running a forced induction why would you keep any cats? I assume your SC'ed and not turbo?
I do not run cats on my car. Currently im supercharged and its slowly turning into a weekend track car so eventually I wont have to worry about the smog checks altogether. I was referring to a naturally aspirated setup where the cats preserve the low end and eliminate reversion. FI is a diferent story, where you have much more exhaust flowing at all rpm's and reversion isnt as much of a deal. I wasnt too worried about flow loss but with the Rush design, I would have to adapt some smaller Hilux/tacoma cats to make them fit under the car and I just decided against it.
 

brawls43

Member
I'm confused on the reversion thing with the cat, and how the cat acts as like a one way valve in that regard. It seems like the cat itself should cause the reversion wave? Not let the energy wave through, then stop the reversion wave caused later down the pipeline?
 

spf_lexus

New Member
Im not an exhaust expert by any means, (thats JBradys expertise) but I have learned a lot from him. The cats are very high flow to begin with so they do not limit flow through them. Exhaust is flowing at its fastest when it exits the head and will slow down as it cools when traveling through the system. The cats are placed very close to the heads so that the heated gasses flow at their fastest before cooling. Once the pulses pass thru the cats, they cannot flow backwards at low rpm and this is why they are useful. Hope this helps.
 

brawls43

Member
I appreciate the help, I'll see if I can ask JBrady some more questions. As an engineer, I tend to ask a lot of questions, and seeing data helps. If there's dyno charts of with and without cats, it'd be cool to see.
 

spf_lexus

New Member
No worries brawls43. JBrady is our exhaust pro on this forum. He has a wealth of knowledge on these engines and their needs exhaust wise.
 
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