*closed*Chopping out the rear cats.

So from what research I have done, I am still getting mixed results as to whether cutting out the rear cats is a good or bad thing.

I want to keep the muffler and I don’t have the patience or know how to mess around with the primary cats.

from what I have read, the engine either needs that back flow or it doesn’t.

can anybody point me in the right direction?

 

For what purpose do you want to remove them?

 

There's not really any benefit to removing them unless you are doing a serious performance build in which case you would likely be doing headers and a full exhaust system anyway.

 

Tbh if you have to ask that question it is safe to assume that a cat delete really won't benefit you much.

If you were to run equal length headers, a matched exhaust, cam gears and a tune it may help a bit to delete the cats. Same goes for any forced induction application

Other than it being very loud, drone-y and very much stinky, the gains will more than likely will not meet your expectations

 

A full exhaust system built from the headers back specifically designed for your vehicle is a reason to remove them.

The engineering that goes into perfecting the length, diameter, placement of changes in size and combination of pipes, etc. in relation to combustion chamber size and number, in order to optimize exhaust scavenging timing is pretty advanced.

You’re not looking for the right “back pressure” but the correctly placed and designed restrictions and openings of the exhaust.

No full system specifically engineered for your vehicle (or the trial and error spirit to dial it in yourself), no point. May even mess the OEM engineering up and end up with worse exhaust scavenging. But don’t tell the butt dyno based on decibels types that.

 

Thanks. That is the information I needed. I honestly didn’t think it would make a difference unless I was able to mess with the compression and air intake.
What I’ve read is that the stock engine is tuned to need that resistance from the exhaust to properly burn the fuel…. Or something like that.

 

Actually, the backpressure extends the life of your exhaust valves, helps them from slamming shut and cracking. As anyone who has ran straight pipes can attest.(unless the motor was designed for it)

 

Long tube headers, no cats, URD Y pipe and URD sims. Noticeable increase in mpg on the Scangage with CC set. Between 2 to 4 mpg depending upon speed.

 

Exhaust “back pressure” as people put it is more about timing that “pressure” so to speak.

When your exhaust pipe has changes along its path (cat-restriction, pipes crossing-opening wider, etc) it sends a negative wave back up the pipe. That ripple is like a ripple in water, or sound (or gas ha fluid dynamics).

The timing of that ripple will eventually bounce off the exhaust valve and come back out the other way.

Timing that to his just as the valve is closing will pull extra (dirty, spent) gasses out of your piston at TDC ish and help make room for more clean oxygen to be compressed and cleanly combusted the next go around.
Timing it incorrectly can actually push those dirty gasses back into the piston just before the exhaust valve closes, robbing you of power and dirtying your engine over time.

It’s not a huge effect. The engine combustion is still doing 99% of the work. But if you think of it as working with your kid… If everyone time you have to push something your little kid is on the other side pulling, it’s not going to make you twice as efficient. But why not let them, it’ll help a little. If every time you push something heavy they’re pushing back the other way, it’s not going to break you, but that slight annoyance could make the days work a hair slower by the end ha. May as well let them work right! Exhaust can be the difference in high performance applications. With our trucks it’s more of an after thought but worth knowing nonetheless.

It’s not easy getting the exact right diameter and length before the correct expansion after deleting a restriction and before the merge all before the muffler, just to get the timing of a ripple right haha. But it’s fun!

(I build exhausts for motorcycles for fun, hence the research, fiddling, application, etc) peace!


EDIT: even though backpressure is not technically an incorrect word it does make people think that an engine exhaust needs to basically be a little “plugged” to work right, but it’s more about the correct math for optimal timing of exhaust scavenging than building up some sort of constant clog to work best. Okay shutting up, bye!

 

Wut