having been a supra enthusiast for a while (must admit, still am), i saw a lot of owners adding a performance downpipe, which i believe is the section of exaust pipe from the engine to the catalitic converter. this provided nice increases in hp of 60+. does anyone know anything about this for a gs4?

 

60+ HP???? maybe for turbo....

i dont think you would get too much from a GS4 but you'd get a bit... no one has it cause its not a priority yet

 

How soon before it becomes a priority?

 

It doesnt exist because there is a catalytic converter on each of the two pipes preceeding the silencer. Many people think that the large silencer under the middle of the car is a cat, but it is just a silencer....The cats are immediately following the headers on the GS4/430. From what I have been told, removing these would confuse the ecu and possibly hamper performance...........
For those with Greddy, or other 'full' exhausts, the pipe immediately preceeding the flange where the Greddy conects could be replaced. The diameter could be enlarged to exactly match that of the Greddy pipe, and it would also eliminate the silencer....This would result in a MUCH louder and free'er flowing exhaust.(too loud IMO) Or, you could let the shop who does the work put a new silencer in line on the larger pipe.....This would also work, and would still flow better.....
The last time I had my car on a lift, I was plotting a way to run dual pipes all the way to the flange where the Greddy connects, because the Greddy immediately splits into two from where it bolts on. This would create a design VERY similar to a traditional X-pipe, which should help the GS ALOT.............Only drawback to that is the noise level would be insane....

 

Yes, I concur with Tiny's comments:

When I was as SRT having my work done, I got to see both, up close and personal. They are tucked high up in the engine bay, just after the exhaust manifolds / headers.

 

what your saying makes sense....but it still is pretty amazing noone has done a custom job yet. thanks for the comments.

 

If the cats are not extremely close to the exhaust outlet, they take much longer to get up to operating temp. And since cold start emission is normally the most stringent (and the most difficult to pass on hiperf motors), getting the converters up to temp asap is very important now days. There is even talk of electriclly preheated converts. But, when do you start heating it? Kind of difficult to know when someone will be getting into the car to start the preheat process.

 

man o' man....are you guys lexus mechanics or what? your level of expertise is pretty amazing.

 

Actually, the 400 cubic inch motor with 500+ hp thats in my 89 camaro did not jump in there by itself, ( I wish it had).

But, I don't do it for a living (thank god).

It don't sound too bad
http://cis.tamu.edu/~jcb9392/car/idle.MPG

Its kind of difficult to drive, hold the camc and shift

http://cis.tamu.edu/~jcb9392/car/1st-2nd&3rd.MPG

 

that only works on turbo cars. I had one on my supra and they do ad clost to 60 hp.

All a down pipes is is like a header for a v6- v8 car, so to change the same parts on your GS4 you would need a header and Y pipe.

 

To fabricate the exhaust set-up that I outlined above shouldnt cost more than about $300-400......I hope someone tries it soon...heehee