exhaust resonator

[joeb]

my friends 08 infiniti G35 has a dual resonator design. its somewhat odd in that the motor is laid out nicely for a true dual exhaust. it has tubular headers with close mounted cats like the newer rwd sts models but than both pipes meet in a Y. it is not a "X" crossover or anything nice. just a simple Y. than it spits into separate resonators and dual mufflers. i know the FWD cars like the 96-03 sevilles have a single exhaust pipe and it has a J bend in it to go around the gas tank. i am not sure where the gas tank is on the infiniti? i am also not sure if the newer infinitis have a true dual exhaust. i just put a new exhaust on my grand prix and it basically has the same layout as the seville. new muff is quiet. almost caddy quiet.

[Cadillac Jim]

All these things have a reason. As an engineer, I can say that good practice demands that the engine response, torque curve, and power are tested for every reasonable configuration before the production configuration is frozen. In any case I can see some sense in the configuration that you describe, which is similar to my FWD Eldorado.

The X-pipe and a Y-pipe with a common pipe to the rear have a similar effect on back pressure, equalizing the pulsed pressure from the uneven firing from the two banks. If the cats precede the Y-pipe that will reduce the effect but only slightly at high RPM where the lower restriction of dual cats is more important anyway.

The difference between an X-pipe and two Y-pipes, other than cosmetic, is that the common pipe to the rear gives you an opportunity for a volume resonance that can enhance torque off-idle, which is particularly important with smaller high-output engines.

An X-pipe exhaust is not a true dual exhaust, it is a single exhaust with two outlets, whether the X-pipe connection is six inches or six feet. There are very good reasons to do this.

[joeb]

I have seen a nice pic of the Sts-v borla system. I think it has dual resonators or no resonators depending on your tastes. They refer to the muffs as silencers. I assume the system would work on a rwd Sts since I think the exhaust manifolds are similar? Or maybe not? I know it has supercharger but am not sure on exhaust side.

[Cadillac Jim]

I wouldn't assume that exhaust parts for an STS-V are really right for an STS or SLS because the exhaust system helps define the torque curve, particularly for the very low end and the very top end of the RPM range. The needs of the STS-V are very different from those of the STS and SLS. I would assume that the bottom-end volume resonance(s) of the STS-V exhaust are more pronounced than those for parts for the STS or SLS because of the lower displacement and differences in the camshaft, but I could be wrong because the supercharger may make low-end resonances unnecessary or even unhelpful. The high-end free-flow probably won't hurt anything, though, although it will certainly cost more for capability that the STS/SLS will never use.

[joeb]

SLS is transverse and fwd which requires a 2 into 1 pipe. For packaging issues. I don't think the rwd Sts needs high exhaust flow compared to the Sts-v car. More air in, more exhaust out.

[Cadillac Jim]

I disagree that a transverse engine must have a front Y-pipe for packaging reasons. The 1990's Northstars have it behind and under the car, where there is a clear option to have a twin cat and cat-back system, or to combine and use the cat as a front resonator, a configuration that enables a lot of off-idle and low-end torque enhancement. A twin cat and cat-back system without any interaction would give better flow and higher top-end horsepower but these engines are highly tuned and use resonances to hold up the bottom end for use with an automatic transmission.

Of course you are right about the STS-V needing more exhaust flow than the STS/SLS. 465 horespower vesus 300 horsepower tells that tale pretty clearly. The rate of fuel/air in, times energy per weight of fuel, times efficiency, is the horsepower output.

[joeb]

new cars have cats mounted very close to exhaust manifolds to heat fast. i know there are quite a few higher output transverse V6 motors in cars now. my friend has 2012 accord v6 which is 270hp? am heading over to his house today. might take a peek. i assume it has typical single cat after front Y pipe. like my 96 sts. or a 04 sls. make it clear though that i keep referring to a RWD 05-09 sts for dual cats/resonators and comments keep going back to the older FWD sts/sls cars. 2 different layouts to discuss.

[Cadillac Jim]

The DI versions of the VVT DOHC 3.6 liter V6 that GM uses as the standard engine in the CTS and as an option in other cars started out at 305 hp and is 318 hp this year. I assume that it has a shorty manifold with close Y-pipe and single cat, because that works so well for this horsepower range. I think of this configuration as the successor to the Northstar.