I've always noticed that there's a tonal difference between the two pipes, but I just assumed it was the difference in length. However I noticed something else interesting about my exhaust behavior. It creates a vacuum at times during the engine cycle. I can take a shop rag and hang it over the exhaust pipe of either bank, and there's not a constant positive flow of exhaust out the tailpipe at idle. It actually sucks the rag into the tail pipe as well as blowing it out. Obviously more has to be coming out of the tailpipe than going in so the rag doesn't get very far up the pipe (maybe 2-3") before it's blown out. But it is most definitely got a funky positive/negative pressure pattern at idle. And if you hold rags over both pipes at the same time, I can see that the vacuum pulses are not happening at the same time. It alternates between the banks. I assume this phenomenon happens because the cam holds the exhaust valve open even after the piston is headed down for the intake stroke thus sucking some exhaust back into the combustion chamber and creating a vacuum. But having that reverbing up and down the entire exhaust track can't be good for efficiency.
So what I'm considering doing is getting an X-pipe installed just after the two pipes join each other on the passenger side of the truck (before the CATS). Then the positive flow from one bank can satisfy the vacuum created by the other. And when they are both flowing positively, they can get the benefit of both exit tracks thus reducing the back-pressure that the CATS and mufflers create. Does that sound like a good thing to do or is there a compelling reason to NOT install an X-pipe?
I also considered installing the X-pipe just after the CATs so that the exhaust that's getting sucked back up the line flows through more than one CAT theoretically giving the exhaust more CAT-time to cleanup. But from an efficiency standpoint, not a civic-minded standpoint, the CATs put up a fair amount of back-pressure (even being high flow CATs) and installing the X-pipe before them would allow either exhaust bank to flow exhaust through both CATs and mufflers simultaneously thus reducing the instantaneous flow through both exiting tracks which reduces friction and thus reduces back-pressure. Lower back-pressure USUALLY means better performance. And the shape of X-pipes usually promotes a venturi-effect to help with scavenging. That's all theory and advertisement hype. So I thought I'd pose the same scenario to others and see what you guys thought. But most of all, I want to get opinions on whether installing an X-pipe would improve efficiency enough to improve gas mileage vs running straight dual pipes?
Keep in mind, this is a stock engine with only 2" exhaust pipes coming down off the headers. The X-pipe would be a 2.5" just because that's all I can find for an affordable price. Here's what I'm looking at getting, Vision Motorworks T304 stainless 2.5" X:
T304 stainless (that's not chrome). $40 inc shipping
Magnaflow's X has a better flow design with more subtle transitions entering and leaving the X. And the casing looks like it is formed with a bit more precision than the above. But it's made of a slightly lower quality 409 stainless:
$90 shipped...over twice as much as the above. I don't live where it snows a lot so corrosion resistance isn't nearly as big of a deal to me. Either will outlast the aluminized steel tubing the exhaust is made from. Magnaflow does sell this X in a 2.25" version which would fit the existing pipes. But do the benefits of the Magnaflow make up the difference of costing over twice as much? If this were a true performance application, it would be a no-brainer. But on a stock motor, would it really make a difference? Also keep in mind, my MAIN focus for adding this is not for performance. It's to see if I can get any better fuel economy by reducing the length of the negative-pressure reverberations that I see travelling up and down the exhaust line and reduce back-pressure by giving both banks two separate exit paths to travel.
