Chigga

it doesn't help much, however it does let the exhaust run a lot cooler than with cat.

for s/c cars, your exhaust acts different than turbo'd car, how fast your s/c spins may be related to the way the engine is set-up, tuning, cam , headers, you wont' get as much effect by changing after-header piping as you would on a turbo car. Someone can probally explain somwhat more simpler than me, I'm using my fluidynamic terms to explain it, so it may sound somewhat vague.

think of this way, a turbo car's exhaust gas shoots out from the hot side and goes as a stream, so the larger the better.

s/c car exhaust doesn't, because it is not compressed (or rather expand), it still has turbulance characteristic in the exhaust flow much like N/A engine, except the velocity of exhaust gas would be faster, in order to increase your engine's rev speed you must work on the header first, then after the pipes. Don't get me wrong, cat-back or like exhaust DOES HELP, but it won't help as much as a proper header.

Guru

I've removed my cats and the loudness level increases dramatically especially at low RPM's so be careful and make sure what you do is reversible. I simply cut mine off and just rewelded them back in afterwards since I was not happy with the noise level.

morris

iTrader: (2)

Thanks everyone, firs problem is unless a miracle occured last night they dont make headers for GS400's.

Next I am not trying to get a peformacne increase through freeing up hte exhaust like most. I am simply trying to get my SC to turn freely when under boost.

And yes Iwill definitely make what ever we do reverisible, heck I migh just unbolt the cats and see if that frees up the blower.

SCV8

Sounds like you need to just do a test to find out if that's your problem before you get yourself into a fabrication project.
You could use a pair of domestic water neck attachments(where the radiator hose attaches on american cars), and clamp some tubing over them just to get a little convergence in the system.
I've heard of cool air going back in after shutdown and warping exhaust valves on short manifolds, never experienced it, however.

RRocket

Just wondering....at some point in the exhaust stream, do the pipes cross over each other? Like an H-pipe or something? If not, the un-equal pressure can cause problems. The solution would be to fab up an H-pipe, or better, an X-pipe. Just tossing out ideas...

morris

iTrader: (2)

In the GS400 exhaust it comes down from the enigne on both sides and joins together, then it splits off into two separate sides going throught the cats, resonatorss and then mufflers.


We wound up not doing it yesterday so we are sort of at a stand still right now and regrouping. I'm beginning to think it isnt my specific setup and is more a factor of some common design element of the car ie exhaust. It seems everyone is okay for lets say 7 pounds of boost once we go over that it sounds like the majority of folks have the slippage.

herragge

If you want less restriction while still meeting emmisions there are always universal high flow catalytic converters instead of tossing your stock cat in favor of a test pipe. You can find them here . They're made by magnaflow so very well build quality and highly respected.

morris

iTrader: (2)

Thanks Herrage butr at this point I could care less about emissions or actual flows, the whole point was to see if the backpressure was prevetning my blower from spinning at higher boost levels.

I think I am gonna scrap the whole thing, I've grown weary of this.

jtanoyo1

Freeing up exhaust pressure in turbo'ed cars will give you more boost naturally so most decatted cars are also fitted with boost controller to prevent boost spikes.

I gained over 20rwhp when I removed my stock downpipe and fitted a 3.5" straight through RSR downpipe & exhaust.

By the way, I don't think freeing up exhaust back pressure is going to do anything in your situation since you are s/c.

pchuon

ebay sells universal cats and test pipes for cheap. check them out!

RRocket

Try finding an "exhaust dump" or exhaust bypass. They're cheap. You cut the exhaust and weld them BEFORE the cats. Before racing, you open the bypass, which will basically give you an exhaust which bypasses cats and mufflers. Backpressure should be nil. They even make electric ones that bypass at the push of a button. The manual ones are under $50.

morris

iTrader: (2)

Thanks its no longer an issue for me.

RRocket

What was your solution??

morris

iTrader: (2)

I scrapped the whole thing, I'm selling the super charger. The design just isnt up to delivering more than they made it for. Imagine that