Rock-a-Lex

iTrader: (4)

Hello,

I don't know much about exhaust systems; maybe someone can clear things up for me.

If I want to buy headers...say from S&S don't they just have "one size" header to bolt up to a stock GS400? If so, how do people here change their piping to a 2.5" or greater? How will it match up to the S&S headers? Do they have to have their headers custom made? Isn't the stock GS400/430 2.25" piping?

Correct me if I'm wrong but is this correct...

Stock - All 2.25" piping?

Engine---->Manifold---->(3) catalytic converters---->Mid-pipe---->"Y" pipe---->Mufflers


What I want to do...

Engine---->S&S Headers---->Universal hi-flow cats---->2.5" Mid-pipe---->"X" pipe---->Mufflers (I have Borla SS')

Thanks!
Nick

Caoboy

iTrader: (2)

um, shouldn't it be

engine > headers>cats>x pipe> piping to mufflers?

Rock-a-Lex

iTrader: (4)

OK...so the mid-pipe is after the "x" or "y" pipe. Sorry, I haven't been under the car in a long time. So now that things are straightened out what about my question?

PureDrifter

iTrader: (10)

most shops weld on adapters that go from stock size-whatever the customer orders.

ex. on my exhaust, i had them cut right after the factory cats and start building the new exhaust. so it goes from the factory (~2in iirc) to my new 2.25in. (recco'd for non FI 1uz engines, at least it is for the 2LS, anything bigger causes a loss in low-end tq.)

JBrady

The stock system is mostly 1.97" (50mm) with a 2.36" (60mm) center section. The stock GS system is much better than the LS and SC systems and is IMO the reason for the 10hp/10tq higher rating on the GS vs the LS and SC.

The first S&S header car ever actually dyno tested the stock Y pipe against a custom 2.25" Y pipe with no peak power increase and a loss of mid range response. I do believe it is possible to improve on the stock system but from an overall drivability and cost standpoint I would not recommend it. I would simply suggest installing the headers with the stock exhaust for best response at the least cost.

The S&S headers are designed as a direct replacement for the stock exhaust manifolds. To install you remove the stock catalysts and the stock exhaust manifolds and heatshields. Install the headers. Install the oxygen sensors into the headers. Install the catalysts to the headers. Bolt the stock exhaust to the catalysts.

Some people will want to change the stock exhaust after the catalysts. This will change the sound of the car and may or may not improve performance. It is not required.

If you want to change to say 2.25" pipes off of the catalysts you will either cut the stock flanges off the stock exhaust or obtain matching flanges. Any custom system can be added after the cats in this manner but again performance may be helped but it may be hurt depending on design.

It sounds like Puredrifter had the stock pipes cut a short distance after the cats on his LS400. The LS has a very strange design after the cats that has a very short and funky 60mm section that then narrows to a 50mm where the second oxygen sensor is located (one in each side). The GS has mandrel 50mm from the catalyst outlet flange. I have said elsewhere that the GS Y pipe works very well and improving on it will not be simple. The LS is not as good and the resonator in the center section is smaller inside than the GS restonator. After the resonator the GS splits decently into twin resonators. The LS has a less efficient split and more restrictive mufflers.

Rock-a-Lex

iTrader: (4)

Great write-up Jbrady and thanks to all! I'll probably just grab those S&S headers and install them alone as you suggested.

PureDrifter

iTrader: (10)

yea, LS exhaust is pretty nasty

for the record i had mine cut RIGHT after the 02 sensor/cat flange. theres MAYBE 1.25-1.50in. of stock pipe, TOPS.

GS FONZy

iTrader: (6)

I remember reading that post, but you guys thought the car was having mechanical issues because it dyno low numbers stock, right?

Low end and mid range didn't gain with the 2.25 Y pipe, but what about top end? How much power was lost in mid range?
Sorry, but I do not remember where I read that post. All I remember is it was a green GS, right?
Wait, I think is the header sticky, I am going to search

JBrady

Peak gain was ONE horsepower. Overall drivability was worse. Midrange is not easily measured as most dyno runs on these cars are 4000rpm to redline. The car was silver but there is a green car shown in the header thread that was present at the dyno testing and was tested but did not have headers.

Again, while I believe a cat back system can be designed to outperform the stock GS system it is more likely that attempts will create a system that is less pleasing to drive. In fact a 1993 SC400 owner installed the S&S headers and initially used 2.5" duals to a 3.0" single center with a single center mount catalyst. He hated the combination. I advised he drop down to 2.25" into a 2.5" center pipe. He decided to go dual 2.0" into a 2.5" center and single center mount high flow metal substrate catalyst. He was THRILLED with the 2" system and felt it performed GREAT at all RPMs. This actually was one of the reasons I now suggest the stock system to most people.

Here is a picture of his 2.5" to 3" system. Notice he used a high quality racing style merge collector from Dr. Gas

GS FONZy

iTrader: (6)

I can't see pic

PureDrifter

iTrader: (10)

i can

https://www.clublexus.com/forums/sho...d.php?t=329306
thats what the 1uz sounds like with 2.25piping, x-pipe, and 2 mufflers. (no resonators)