School me on exhaust..

[dieselfan1]

1 hour ago, Grumpy Bear said:

Three years worth of records show my truck has increased fuel efficiency right at 5% per year and now sits at 100K miles. My last 36 tank moving average is over 30 mpg. As you now an average is the middle and as it is still rising my current tank over tank numbers are closer to 31 mpg. (I rarely drive in town). 

 

She still has the complete factory exhaust. One thing I've noticed over decades of driving stock is that the factory systems take quite some time to get mellow. 

 

Are we saying I can expect another 1-1.5 mpg if I change exhaust? 

Why not?

[KARNUT]

Let’s see GM completely redesigned the Chevy small block with cylinder deactivation, external vacuum pumps, start stop technology, you know stuff that can potentially prematurely wear your engine out. But some how they forgot to address the intake and exhaust? Me don’t think so. If you live at max RPM I’ll bit. Normal driving nope.


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[timber74wolf]

Yes, interesting.

     Let's see who responds besides me. So, no. The best answer is that there is no guarantee that your MPG will increase 1-1.5 if you change your exhaust.

So, in my experience over the years and miles driven I have ran the stock exhaust system, stock program for 20k plus miles on my 14 5.3. Then I ran a Gibson dual exhaust, then added the Super chips programmer (87 tune), air ducting; not a CAI, and a K&N filter. Then after another 20K plus miles I changed the intermediate pipe back to the sock intermediate pipe, plus I added the flapper valve. The only gain I made was more torque by adding the stock intermediate pipe and flapper valve. Then after another 20K plus miles I removed the Gibson dual exhaust and returned a stock exhaust system and did the muffler delete. After all this experimenting my MPG averaged stayed roughly the same. Now at 101K the mileage is still roughly the same. I even ran 93, 89 and 87 octane fuel over the years. MPG are still basically the same. back and forth to the gym, work and home, plus my military weekend travels. I am always watching my MPG trying to get the best, but regardless; driving habits, traffic, weather, hills, acceleration, deceleration, etc... plays a factor in MPG.

My 18 only has 10K miles on it. Only thing I have done is did the muffler delete. I have a Superchips programmer, because I have had good luck over the years with all my trucks using this brand. Yes, I have tried other tuners. Just my 2 cents.   

[Grumpy Bear]

On 9/14/2019 at 10:29 AM, dieselfan1 said:

Why not?

An internal combustion engine is a demand device. It makes EXACTLY the power it needs to overcome the load against it. Nothing more, nothing less. That a given there are two ways to get more work (miles) from a fixed volume of fuel. 

 

1.) Reduce the load against the motor. 

2.) Get more work from the same amount of fuel. Make it more thermally efficient. 

 

Claims of increased mileage fall into the first camp. Reducing pumping losses by lowering back pressure. 

 

Here's the problem. A manufacture makes the claim. Is it true? Yes it is. It's physics. Question is, can you measure it? I'll give you two reasons why you can't. 

 

First, when the manufacture shows the backpressure reduction probes the exhaust and does a dyno pull at WOT which may show a several pound reduction. Running down the road at part throttle and at low rpm that impressive reduction becomes next to nothing and sometimes, depending on the tuning of the exhaust as a unit by even raise the pressure! What were are talking about isn't several pounds of pressure anymore. We are talking about a few inches of water pressure in difference. It takes 27 inches of water to make a pound, roughly. This equated under cruse conditions a fraction of a percentage point in pumping loss reduction. So yes and it doesn't really matter UNLESS your running WOT at peak torque rpm. 

 

My wife was told once that having a child when over 40 would DOUBLE the risk of having a child with a serious birth defect. It's true! What they did not tell her that it increased the odds from 1% to 2%. REALLY.

 

Exhaust systems are like that. It might be the truth but it certainly isn't the story. 

 

Second reason: This is my trucks every tank over three years. Picking the increase out of this noise can be done. It can't be done over a few tanks.