So my exhaust is Swiss cheese. Pretty much from the cats back, at every flange it's rusted through. Some of the hangers are shot etc, it's in bad shape (sounds good though, haha). I already kicked off the resonator because it was removing itself. I'm up for inspection in July and I have a guy that'll pass me but my question is this. What am i incurring by running this essentially wide open exhaust system. Can I be messing up my mileage because there's not enough back pressure? Do I lose power as well if it's too wide open?

 

I have heard/read that too open an exhaust system will have a negative effect on power/mileage.

But I think as long as the cats are there that would supply enough back pressure.

 

Backpressure is a myth, exhaust systems do not create horsepower except in respect to the header. Headers direct the flow of high pressure gases smoother, to create less friction, which may increase some power. However; the exhaust system is merely a system designed to create a seemingly quieter and cleaner environment only. "The best muffler is no muffler at all".

 

I have to agree and disagree. Mufflers are just that. Mufflers. They muffle the sound so the vehicle runs quieter. Backpressure(also known as exhaust flow/restrictions), however, is not a myth. If you don't believe it, try running with a 1" pipe coming out the back end of your Disco. Or, try removing your exhaust after the manifold/headers and see what problems then surface. The engines are designed to run within a range of backpressure values. If you leave that range, you will experience problems and failure unless you mess with the valve train. Yes, they can run with open headers, but like said earlier, the valve train is not designed for such operation.

And yes, I did look at the article you linked to and it seemed to be written by a shade-tree mechanic that thinks he's an engineer.

 

Donut Dude - I take offense at your blatant attack on my peer trained brethren...and also reluctantly agree that it is no myth. 20+ years ago, prior to the computerization of the vehicles, straight pipes would have been the way to go. However, as it is "assumed" that ordinances are being followed, as it relates to emissions at least, the engines are DESIGNED to run at peak efficiency and performance with these devices attached and working properly.

My suggestion is that if you are having issues with your exhaust - and the cost to replace it, brush up your welding skills and get to work. You can do it yourself - including purchasing the welder for under $800!!

But CB - WHY do you have to say "Shade Tree" like it is a bad thing?

 

To clarify; todays engines utilize sensors to optimally achieve the effective oxygen to fuel ratio of 14.7:1. Whether you go small, large or no pipe, the engine will ultimatley seek out this ratio by adjusting perameters. Turf63 perfect opportunity to decide what exhaust configuration you want. Good luck.

 

LRDII -
Agreed - it IS a great opportunity to decide a great exhaust configuration - but, in my opinion, that does not included "none" or straight pipes as was proposed.

I have seen degraded performance/mileage that were caused by exhaust leaks - much less NO exhaust at all - and no amount of sensor tuning (with CURRENT sensors) would correct.

The amount of correction the sensors are designed to do is drastically less than what would be required to get a properly running engine with straight pipes.

 

To say that is to oversimplify; you cannot assume that the parameters available to the engine management system are infinitely variable and can therefore compensate properly when the system is forced into a state that is very far from its preferred equilibrium condition.

Also, when a wave of pressure exits a tube the pulse of lower pressure is "reflected" back up the tube. This reflected pulse can be "tuned" by properly engineering the exhaust system to hit the exhaust valve at the exact time necessary to help scavenge combustion products from the cylinder, which then in turn helps pull fresh mixture into the cylinder, increasing the compression ratio of the cylinder charge, leading to a bigger boom. (Well, technically there is no "pulling" gong on, as a vacuum is nothing, and nothing can't do anything, it is really a matter of net pressure differentials but for the sake of simplicity I said "pull".)

Just because you quote Tom Waits in your signature doesn't necessarily mean you can ignore the laws of thermodynamics. Oh, and by the way, I used the spell check on your quoted post because I couldn't bear to see it all up there twice.

 

So what was my grade?

 

You still forget one very important part. The valve train is engineered for a certain amount of "back pressure". If you take that away, you have to upgrade the valve train or you will have failure. This has nothing to do with emissions or noise levels.

As for 'shade tree' mechanics. I don't consider then bad. I am actually grateful for them. I find it reassuring to know that they keep me in a high paying job.