I recall someone on here said they tried it once!

I'm thinking of unbolting the exahust from the two rear cats, removing the resenator and muffler before I get to the track in a few weeks, should improve my times by abit? I've ordered the C3 pully and the exhaust shop is fabricating me a CAI that's all I'm planning on doing so far & possibly the exahust if you guys think it's a winner

 

It's worth a try. A few have tried exhaust cutouts and it's possible you might have a gain. Not sure whether its on this forum or on mbworld but one of those threads are on the necessary back pressure needed for our motors to perform. Hence the need for the cats. Most have gone to high flow cats, but very small gains have been proved. Also the lack of monitoring DA and just dyno's are unpredicatable results that may not translate over to the track in lower et's.

 

You could be right! may have been on MB forum, It's a easy mod as nothin is permenant I can simply bolt it back on when I get home!

I'm thinking the 4 stock cats should be enough back pressure for the engine, the only real back pressure is the muffler anyway as the resenator is straight through! I'm just worried about doing damage to the engine, people have said they have had warped pistons from not enough back pressure!!

 

Like a turbocharged car, a twin-screw supercharged car doesn't need back pressure. Removing the exhaust back is probably a good idea. For the OP, to point you in a direction, Woody once removed his and ran straight pipes to the back. There's a thread on ehre somewhere and a sound clip of him driving on youtube. If there is any restriction, removing the exhaust will lower the intake manifold pressure. This is however a good thing because the engine is becoming more efficient.




To quote a buddy of mine:

A) NO engine wants backpressure. They want exhaust velocity and scavenging. Backpressure is an unwanted by-product of the first two.
B) The best turbo exhaust is no exhaust. a 6" open pipe the same size as the exhaust on the turbo with no muffler or anything would work best, and thats just there to keep things from hitting the turbine.
C) Centrifugal superchargers(paxton, vortech, novi, etc) like similar exhaust to N/A - but they throw much more exhaust than a N/A motor, so you want bigger pipe all around.
Roots type, which make boost at all RPMs, want no exhaust as well. With a roots, the intake pressure is always greater than the exhaust pressure. It provides its own scavenging effect in that the intake charge blows the exhaust out of the chamber during cam overlap. This is why on blown drag cars they have an individual open pipe for each cylinder(you cant have scavenging with individual pipes). Best flow, least restriction, and built in best scavenging via the blower.

The NA dispute:

i have to disagree with you here...if you're going to be running lower than like 6000 rpms at any point while driving your car, you're going to want back pressure. backpressure is just liek water pressure and air pressure, and not enough of it can slow down your exhaust velocity. think of it like a hose: when you put your finger over it, the water sprays out fast, but not much is getting out, right? this is an example of high back pressure. however, when you let your thumb off, it doesn't come out very fast--and think if you were to increase the size of the tube-it would just trickle out. you need the pressure created by the exhaust to keep a high velocity--but the more exhaust you have coming out (the more power you have) the bigger your exhaust needs to be. All cars need back pressure--even stock cars don't run open headers because they run better with an X-pipe.

The response:

Thats exactly what I said, but backpressure is the by product of exhaust velocity and scavenging, it in itself isn't beneficial in any way. If there was a way to get rid of backpressure and still have scavenging and velocity(like a roots blower for example), that would be ideal. Of course, every car on the road isn't going to be running a roots blower...
Sure you get more velocity with your thumb over the hose, and the water pressure is higher in the hose, but the pump at the other end has to work harder to push it! In an engine, the "pump" is the piston... you don't want to make your pistons work harder, do you? The only reason you make more power with smaller pipes converging into a collector is because the collector provides scavenging, and exhaust velocity contributes to this effect. There is a fine balance between exhaust tubing size and backpressure, too small is too much of a restriction and negates the scavenging gains, too big kills velocity and therefore scavenging. In a perfect world, the piston would push all the exhaust out of the chamber on its own(basically require a 0cc chamber, piston basically hits the chamber...), but we all know that aint possible. In that case, no exhaust would be the best exhaust.

 

when I was installing my exhaust I drove around with everything from the second cats back off and I had VERY little low end torque, so i'd keep that in mind

 

The fact is that some have tried (in some cases elaborate) systems that have sounded great but lost HP. This have been done with at least one set of cats removed and again, lost HP.

So far, I have not seen a thread that has proved to be worth spending the money to change your exhaust in the name of HP. Now for those who want a better sounding exhaust note.....

 

I can tell you that the real gains are realized when you get rid of the cats if you can get away with it. Better performance, better sound, less weight, need I say more. Hehe One thing though, your fuel mileage will drop like a rock because you'll be on it a LOT more. LOL

 

Something else to note, if you remove the muffler, resonator, and two cats, you're dropping more than 75lbs from the car. This in itself will make the car perform better all around(accel, braking, handling). I think the stock muffler weights about 45lbs.

 

Thanks for all the comments guys!

The only thing that worries me a little is what Voyager said the last thing I want to do is loose bottom end torque, I was planning on removing it from the last two cats, so I'd still have 4 cats (which we all know are very restrictive).

I think I might take them off a few days before I go to the track and drive around & see if I notice any gains, (I'll probably think I am due to it being so loud lol)

 

sounds like your looking for something like this to swap on for the track day

 

Correct me if I'm wrong but is that a manifold attached to a straight pipe ?

I'd have no tourqe at all if I did that ahah!

 

yes that is a straight dump tube off the manifold, torque is not a problem with them, i was runnign a very similar setup when we went 11.9's @ 119.8mph. actually we ran that with exhaust cutouts in the downpipe but these will flow a little better and also give the ability to drop the entire catback and both downpipes off the car, im guessing around a 100 pounds of weight savings

For a forced induction car the best exhaust is NO exhaust, this is as close as we could get while not burning the car down

 

that has to be earsplitting loud!!!

 

its not as bad as i expected, idle is loud but not obnoxios, WOT sounds phenominal, its the midrange throttle that drones like no other, hence its not something you would want to run daily

 

Hrmm interesting!!!

And you definatly noticed some gains from removing the exhaust system? or was it gains from the vehicle being lighter?

 

By the way have you guys got a Video? I'd absoutly LOVE to hear the sound of it

 

I just had my car srt6 dyno by eurocharged/ Jerry 354 rwhp/ 351 torgue no muffler replaced with y pipe and installed a header silencer in 1 exhaust tip, no drone at any speed, at wot sounds great. Normal driving u would not know muffler is gone!!!! When on dyno it got everyone"s attention at wot, it was loud but in a good way. Sounds very nice when you get on it. I do have a video/audio of car on dyno just got it edited will try and post tomorrow.Danny

 

Wow that sounds cool Danny!

whats a header silencer?

 

ITS a round pipe that insert into exhaust has holes in it . Here it is, i can buy these for about 35$ each u could cut in half and try one on each side. Collector Header Insert Muffler Silencer Baffle:eBay Motors (item 330245499557 end time Nov-10-09 12:43:06 PST) These are used on racing MC and drag race cars to meet noise requirements . Danny

 

There is a cutout pipe I used on my modified turbo Miata for drag days. Just past the headers. Nice once in awhile to use on the street to. Attached to the cutout pipe was an electric flap that opened with the press of a switch. The switch was attached to my console. Just push the switch and the butterfly flap would open or close when needed. See link attached for info. It was a great product and well made. Also very reasonable and easy to install. when it was closed it was a good seal with no exhaust leaks. I am thinking about getting one now for my Limited. It's alot of fun. http://www.quicktimeperformance.com/QTEC/index.php