I've decided on a 430 and one of the first few mods i'll do (aside from TC and valvebody upgrade) is a custom exhaust. I'm not partial to dual pipes and am wondering if anyone has gone single outlet. I'm thinking straighter 2.75 piping to a three inch Y pipe out to an HKS universal muffler (maybe slanted up and out) with some hi flow cats.

Think i'll get some decent power under the curve with that? Is 2.75 too much pipe until the Y or is it not enough? I want to add a few horses and let the engine breathe better w/o sacrificing low end grunt or hp but i can't stand duals.

I think it's a solid plan, but if any exhaust pros can help me out i'm all ears.

I like to plan out mods before i get the car so i can get an idea whether or not i'll be happy. ;P

 

Except for the headers, the GS exhaust system is relatively efficient from everything I've read. Those that have dynoed cat and axle-back exhaust systems only see a 1 - 2 hp increase. You may get a little more with what you're talking about, but you also risk check engine light issues with the high flow cats.

I personally wouldn't recommend doing all that custom exhaust work unless I had FI on the car to take advantage of it.

Oh, and we have sub-forums for questions on exhaust, engine, etc Moving your post there

 

(Thanks for moving it, once i realized i wasn't in the engine section i cringed. I gotta say though, you're the nicest mod i've seen on any forum. Never a sour reply or anything and always willing to help, kudos!)

Yeah i read up a bit more on the hi flow cats and saw the cel light risk, which i'd rather not set off. I'd also read that opening up the cats would help out the torque curve and add a lil more power (once the headers are available that should help even more)

I haven't decided on the future of the car yet, it MAY be SC'd at one point but if that does happen it'll be some time away. Think i'll start with basic tranny upgrades and

Do you think that my piping is too big for NA applciation as of now? I'd be satisfied with 2-3 hp peak if it broadened out the curves more (espicially with the SRT intake). I'ven never tried makin an exhaust for a v8 so i'm not sure if what size is too big or just right, espically with going from duals to single.

I really like the look of the HKS hiper turbo single exhaust and will probably end up doing the exahust mod anyways, i just want to do it right.

 

CB,

The largest pipe I would recommend from the cats (before the Y pipe) is 2.25". The stock GS400 is 50mm (1.96"). I haven't measured on the GS430s (if you get the chance you can post the size) my guess is the same at 50mm. The Y section can be improved upon and again, the GS400 has a 60mm single middle section with a 60mm resonator (2.36"). That pipe section may benefit from a 2.5", 2.75" or 3.0" section but without actual R&D it is difficult to make a recommendation. Low end torque is usually best with smaller diameter high velocity pipe.

After that the rest of the system is good and probably not worth custom modding. There are many aftermarket muffler choices. The stock cats are very high flow (and expensive) metal core cats. Again, not worth changing. I looked at a buddies LS430 and Lexus has changed the manifold design. All the GS400s, LS400s (1998-2000) and SC400s (1998-2000) have the same exhaust manifold and those are what I am attempting to build headers to replace. I say attempting as the fabricator has a major backlog and the project is waiting on him. As I said the 430 manifolds are different and it would be interesting to at least see a set off the car without heat shields.

Anyway, their may be as much as 10hp in a PROPERLY designed and sized Y pipe section but without testing we just do not have good data.

Dave... if you know of any testing with a CAT back system along with dimensions and preferably pictures I would like to see those results.

 

ill definitely follow up with everythin i do to the car with pics and stuff including measurements and prices

Also i too, feel 10 hp is there for the takin, i made 9 hp to the wheels on my s2k with a single exhaust with no tuning, so the 3UZ is ripe for the picking, and even more so with an SRT. I believe a large single outlet pipe will show gains (as well as look damn nice) i just have to experiment with it a few times, figure out the best flow for a v8 exhaust, espicially with the pipes merging into a Y and then into a single exhaust.