mg drop off with exhaust???

[TxTruckMan]

Comparable mileage is not impossible. I'm just saying that to expect BETTER mileage with any mod is likely impossible. And 1-2 mpg loss is probably worst case. In many cases people probably experience <.5mpg loss. Most loss is probably from heavy feet after the mod.

[Jon A]

What's cheaper for OEMs to add to a vehicle? CAI and "Long tube headers" or AFM, DOD, FlexFuel, Hybrid systems, turbos, Aluminum components, active grill shutters, start/stop, etc? If there was anything left to be gained from a $50 intake and $200 exhaist, they'd surely take that first over these other MUCH more costly systems.

 

You're just very wrong. While mileage is very important, it is only one of many important factors. EVERYTHING is a compromise. Cost, durability, NVH, etc... another 1/10 MPG does nothing if nobody wants to buy the vehicle.. Have you read any reviews of these vehicles? Do they mention how quiet, "car-like" they are, how luxurious they feel?

 

Have you ever had a set of longtube headers on a vehicle? The chances are if you're over 20 years old and not a "hot-rodder" they are not for you. All the downsides would be a major turn-off to most buyers. First, you aren't going to make a set for $200 that you would put a 100,000 mile warranty on--such a set would cost many times that. Cast iron manifolds cost pennies, relatively speaking. And they add weight.... All the burned plug wires and various other underhood items due to the heat, the blown header gaskets, the loosening header bolts, etc, would be much fun for the warranty departments....

 

That's just one example. Why not lower the vehicle 3 inches? Extend that airdam to the ground. Why not put a 4 cylinder in it and eliminate the V8's? Skinnier tires. Much lighter/weaker frame and body. The list goes on forever.....

 

Nothing in this world is perfect. You can't have your cake and eat it too to the fullest extent. Every product is a compromise of many different design goals. Some are more important than others, but you can't knock one completely out of the park and still have an acceptable level of the others. The real world isn't so kind.

 

Your belief that absolutely everything else on this vehicle has been sacrificed in order to obtain the maximum possible mileage has no basis in reality. For people willing to accept some trade-offs, the mileage can certainly be improved upon. Just like every other aspect of the vehicle.

[mzodarg]

You're just very wrong. While mileage is very important, it is only one of many important factors. EVERYTHING is a compromise. Cost, durability, NVH, etc... another 1/10 MPG does nothing if nobody wants to buy the vehicle.. Have you read any reviews of these vehicles? Do they mention how quiet, "car-like" they are, how luxurious they feel?

 

Have you ever had a set of longtube headers on a vehicle? The chances are if you're over 20 years old and not a "hot-rodder" they are not for you. All the downsides would be a major turn-off to most buyers. First, you aren't going to make a set for $200 that you would put a 100,000 mile warranty on--such a set would cost many times that. Cast iron manifolds cost pennies, relatively speaking. And they add weight.... All the burned plug wires and various other underhood items due to the heat, the blown header gaskets, the loosening header bolts, etc, would be much fun for the warranty departments....

 

That's just one example. Why not lower the vehicle 3 inches? Extend that airdam to the ground. Why not put a 4 cylinder in it and eliminate the V8's? Skinnier tires. Much lighter/weaker frame and body. The list goes on forever.....

 

Nothing in this world is perfect. You can't have your cake and eat it too to the fullest extent. Every product is a compromise of many different design goals. Some are more important than others, but you can't knock one completely out of the park and still have an acceptable level of the others. The real world isn't so kind.

 

Your belief that absolutely everything else on this vehicle has been sacrificed in order to obtain the maximum possible mileage has no basis in reality. For people willing to accept some trade-offs, the mileage can certainly be improved upon. Just like every other aspect of the vehicle.

Well said! To add to your example: all aluminum body

[TxTruckMan]

You're just very wrong. While mileage is very important, it is only one of many important factors. EVERYTHING is a compromise. Cost, durability, NVH, etc... another 1/10 MPG does nothing if nobody wants to buy the vehicle.. Have you read any reviews of these vehicles? Do they mention how quiet, "car-like" they are, how luxurious they feel?

 

Have you ever had a set of longtube headers on a vehicle? The chances are if you're over 20 years old and not a "hot-rodder" they are not for you. All the downsides would be a major turn-off to most buyers. First, you aren't going to make a set for $200 that you would put a 100,000 mile warranty on--such a set would cost many times that. Cast iron manifolds cost pennies, relatively speaking. And they add weight.... All the burned plug wires and various other underhood items due to the heat, the blown header gaskets, the loosening header bolts, etc, would be much fun for the warranty departments....

 

That's just one example. Why not lower the vehicle 3 inches? Extend that airdam to the ground. Why not put a 4 cylinder in it and eliminate the V8's? Skinnier tires. Much lighter/weaker frame and body. The list goes on forever.....

 

Nothing in this world is perfect. You can't have your cake and eat it too to the fullest extent. Every product is a compromise of many different design goals. Some are more important than others, but you can't knock one completely out of the park and still have an acceptable level of the others. The real world isn't so kind.

 

Your belief that absolutely everything else on this vehicle has been sacrificed in order to obtain the maximum possible mileage has no basis in reality. For people willing to accept some trade-offs, the mileage can certainly be improved upon. Just like every other aspect of the vehicle.

Of course they first have to be able to sell the vehicle, and it has to be able to perform its intended purpose, but that doesn't make me wrong. You're right that every decision is a compromise between design and performance parameters (FE, HP, weight, etc.).

 

And you don't think that the OEMs (with their BILLIONS in R&D) can't design a set of headers that work to OEM requirements? Please show us any evidence of any powertrain mod that improves normal fuel economy. Then you can prove me and the OEM engineers that made the comments "very wrong".

 

I stand by my comments. Look at what Ford just did - they invested millions of dollars in R&D and added probably several hundreds of dollars to their manufacturing costs just to convert the F150 to mostly Aluminum. And you think they left mileage on the table with the exhaust. Okay.

[Bbowen826]

You have to remember when ever you change something that was factory it will take the vehicle computer time to adjust to it. Originally the computer isn't adjusted for the difference in back pressure so you will get worse gas mileage. Over time the computer will be able to adjust some for the different exhaust. However in a lot of cases the factory computer will never adjust fully to the changes you made. If you want the best performance and gas mileage out of a different exhaust you will need a custom tune. I always recommend when ever you decrease back pressure with the exhaust you should increase air intake. Same thing will apply with an air intake. It will throw off the factory readings at first. A custom tune is the way to go. You do not want to buy a performance chip such as superchip because they are programmed to give you more power and mpg on a factory set up. If you put one on a vehicle with an exhaust and intake it will more then likely throw the parameters of the motor to far out. I have seen countless vehicles that have done this and they have a tapping in the motor because between the chip trying to increase air flow and the bolt on accessories the factory knock sensor can not compensate enough. Ask anyone who has a custom tune and they will tell you that's the way to go. It will tune your vehicle specifically for what you have changed on it.

[Jon A]

And you don't think that the OEMs (with their BILLIONS in R&D) can't design a set of headers that work to OEM requirements? Please show us any evidence of any powertrain mod that improves normal fuel economy. Then you can prove me and the OEM engineers that made the comments "very wrong".

 

 

 

Of course they “can” – as with any other Engineering choice based upon compromises, they “can” do any of them depending on where they want to fall in the spectrum of the compromises.

 

Your belief that “OEM requirements” means best mileage possible, that nothing else matters, is untrue and the reason for your mistaken belief. And no, OEM Engineers aren't agreeing with you on that point--you must be misunderstanding what they said. Many other things matter enough that mileage is compromised for many reasons.

 

 

Engineering texts are full of graphs like this:

 

 

As you can see, when backpressure goes up, BSFC typically goes up as well (which is bad). Simply running a set of open headers would be an improvement for most engines. If mileage was all that mattered, that’s what they’d do. But it’s not. Not by a long shot. There was paper after paper written in the old days on the increase to BSFC by simply adding a cat, but that’s old news.

 

 

Do you know any Diesel owners? Over the past few years they’ve been slammed with newer EPA mandated crap that has really hurt them making a dramatic example. Tell your diesel owning friends that after cutting off their DPF and getting a tune, the dramatic increase in mileage they’re observing can’t really be true. They must be imagining it.

 

 

Ah, we hadn’t even mentioned the tune yet. While the gains for most gasoline engines is a bit more subtle, there is still some to be had. For example, most are tuned to run at stoichiometric at cruise--around 14.7:1 AFR. This gives the best overall emissions compromise. Yes, even with emissions there is a compromise as no single operating condition provides the absolute lowest of all.

Anyway, 14.7:1 does not give the best mileage:

 

 

As you can see, leaning it out will give better mileage—but NOx emissions will increase.

 

 

Often adding a bit of timing from factory settings will improve mileage. But here again, as you add timing the NOx emissions begin to increase quite dramatically.

 

 

 

 

That’s just scratching the surface of some of limits placed on OEM calibrators that an aftermarket tuner does not need to worry about. There are many other things such as running overly rich under heavy acceleration to provide an added safety margin against detonation if somebody does that with bad gas and a hot engine, running overly rich by switching to PE mode at moderate throttle when it’s really not needed (for the same reasons), limiting the timing and being overly aggressive with the knock sensors, etc. The list goes on and on forever. One could write a book—in fact, many have. You might want to pick one up.

 

 

No offense intended, but if you don’t know a whole lot about engines you might want to refrain from making such broad, sweeping declarations about them. As with any other machine Engineered to strike the best compromise among a plethora of design goals, if one decides one aspect of performance is more important than all the rest, of course it can be improved upon—but naturally the others are likely to suffer to some extent. That really ought to be common sense to anybody interested in such subjects.

[rudapa]

So with all this said, anyone's MPG improve with the new exhaust? No one in this thread so far.

[legierk]

Interesting posts. Good reading. I'm doing complete dual exhaust and CAI and don't expect significant mpg increases. In fact, I will probably see initial decreases. I'm willing to sacrifice that. I'm old school....an engine is an air pump. Sucks air in....blows air out. Yes, the computers are regulating the flow now, but I don't see the harm in at least allowing more air to pass through, even if the computer (ECM) balks at it.

[TxTruckMan]

Of course they “can” – as with any other Engineering choice based upon compromises, they “can” do any of them depending on where they want to fall in the spectrum of the compromises.

 

Your belief that “OEM requirements” means best mileage possible, that nothing else matters, is untrue and the reason for your mistaken belief. And no, OEM Engineers aren't agreeing with you on that point--you must be misunderstanding what they said. Many other things matter enough that mileage is compromised for many reasons.

 

No offense intended, but if you don’t know a whole lot about engines you might want to refrain from making such broad, sweeping declarations about them. As with any other machine Engineered to strike the best compromise among a plethora of design goals, if one decides one aspect of performance is more important than all the rest, of course it can be improved upon—but naturally the others are likely to suffer to some extent. That really ought to be common sense to anybody interested in such subjects.

Please reread my posts. I know and agreed that the entire design process is full of compromise. And I never said fuel economy was the most important. I simply said that its always considered and one would not gain any FE with an exhaust or CAI swap. And I still stand by that comment.

 

And sure there's always a lot to be gained with a custom tune. Like you said, the aftermarket isn't as concerned with emissions and such. And don't forget warranty and longevity - these too play heavily with OEMs.

 

You're right that I don't know a lot about engines, but I'm an engineer and I know how to read. I have never heard or read of anybody gaining any FE with only exhaust and CAI mods. Dyno results don't lie, and most show no to negative gains below 2000 RPMs (where 90% of daily driving occurs).

[hzhardy]

When I drive my truck right I gain about 1-2 mpg on my average. I really see my benifets towing since the extra power allows me not to push it so hard to get the same perfirmance.

[2014 Sporty Shorty]

I noticed a drop off as well after I redone my exhaust with a flowmaster 44. The mileage was only worse in V4 mode though and wasn't changed while being in V8 mode. Now that I'm tuned it doesn't go in garbage v4 mode anymore so I don't care. Plus the drone was horrible but again that's no longer an issue. I think the lack of restriction in v4 mode with having a higher flow muffler, no resinator, no secondary cat, and no valve is why the v4 mileage was suffering. I personally don't care about mileage because it's a truck and fuel consumption didn't cross my mind while I wrote the check. I have my longtubes now and will be testing a new cam in about 3 weeks so once I get those on and start tuning again I'm sure my mileage will be even worse haha. Not to mention I will be going E85 only soon, 14mpg average here I come.

[mike94silverado]

Some people will say I'm wrong, but from what I've been told, the OEMs tune the intakes and exhaust for max fuel economy (and sound of course). Any changes to the intake or exhaust will most likely result in worse fuel economy. If there were gains to be had from those two components, the OEMs would be all over it. They're looking to save tenths of MPGs any way they can.

you are exactly right. I love when people buy a truck, change the tires and or level it or like on the 900's remove that plastic lip then complain about MPG.... GM does what they do to specifically hit a target and any mod is going to affect it. that XFE model a few years ago is a good example. it has a special rear end gear but it also had a tonneau cover and low resistance tires they didn't include those features for the hell of it

[Jon A]

Sorry guys, I realize a couple charts I tried to post in my prior post didn't show up. I edited the post to fix that so they're there now.

 

 

Please reread my posts. I know and agreed that the entire design process is full of compromise. ... I simply said that its always considered and one would not gain any FE with an exhaust or CAI swap.

 

Reading it again wont change what it said. You said ANY "powertrain mods." Programming the Powertrain Control Module is considered by most a "powertrain mod." And even you specifically mentioned headers, not just a catback.

 

 

Dyno results don't lie, and most show no to negative gains below 2000 RPMs (where 90% of daily driving occurs).

 

What results are you talking about? People rarely dyno gas engines below 2000 RPM as that's really lugging them. Here's a dyno from an LT1 that demonstrates the types of gains a set of longtube headers and removal of the cats can have with these engines:

 

 

And the 6.2 in the trucks is tuned more strongly toward low RPM operation. As you can see, the 50-60 lb-ft increase in torque extends down to 2500 RPM which is as low as they tested it. Do you have some sound reason based in solid Engineering or your extensive engine building knowledge to say those same gains would not have extended down below 2000 RPM?

 

So with all this said, anyone's MPG improve with the new exhaust? No one in this thread so far.

 

The thing is, just a catback is going to make such a small difference virtually nobody measures their mileage in an accurate enough manor to show it one way or the other. When one does a bunch of little things that add up to a significant gain is when it's easier to detect if measured in a scientific manor. Unfortunately it is much easier to get a
significant difference the other way--lift kit, big tires + gears, etc....