Mpg

I know we all heard this before but I'm doing it again. I recently put on a dual exhaust with a super 40 flowmaster. I was looking for more HP and a better MPG for my 03 silverado. I was getting 400 miles to the whole tank and now after having the exhaust, its dropped to 380 miles to the whole tank.
WHATS UP WITH THAT !?

Any inputs on tuners would be nice

Dont mess with mother general! If the dual exhaust was such a good thing (other than making the truck sound powerful) Dont you think GM would put it on and advertize it? OR better yet sell it as an option?
They have been building vehicles for 90 years, In general they know what there doing. Enjoy the sound and drive like theres an egg under your foot.

Well, they do put duals on the SS model

Why don't they? Cost, cost and cost. On most engines the gain in power is not worth the cost. If the duals are set up properly they can help facilitate great horsepower and in some cases mpg. You have to know the size of the pipe needed by the engine and amount of backpressure the engine requires to stay in the curve. Each engine has a sweet spot for power, horsepower, and mpg. Gains in one sweet spot does not mean gains in the other, sometimes they do but not always.

Did you leave the cat. converters on? The new trucks require a certain amount of back pressure in the exhaust sysem. So if you make the exhaust too free flowing, it could rob your power and mpg. I think most people get better results getting air into the engine than improving exhaust.

Did you leave the cat. converters on? I think most people get better results getting air into the engine than improving exhaust.

You got that one right, you can stuff a lot more air in before you require a larger exhaust. Read this post about half way down by Hit Man X and you will see the size requirements for the different engines and horsepowers. Those guys over there are doing serious engine mods, they know their sh!t.

http://forum.ls1truck.com/index.php?showtopic=1053&hl=exhaust+size

You got that one right, you can stuff a lot more air in before you require a larger exhaust. Read this post about half way down by Hit Man X and you will see the size requirements for the different engines and horsepowers. Those guys over there are doing serious engine mods, they know their sh!t.

http://forum.ls1truck.com/index.php?showtopic=1053&hl=exhaust+size

Well, that makes me feel better about having my single in/dual out flowmaster

The most restrictive part, your single in, is the point that dictates the size of the pipe. Dual out always sounds better but gains you closer to nothing when it comes to performance or mpg. Don't be discouraged, you did make it sound better and releive yourself of some cash ..... :eek7:

The most restrictive part, your single in, is the point that dictates the size of the pipe. Dual out always sounds better but gains you closer to nothing when it comes to performance or mpg. Don't be discouraged, you did make it sound better and releive yourself of some cash ..... :eek7:

Nope, I left that part up to the original owner; the exhaust setup was in place when I bought it.

I myself believe that any decrease in mpg with the install of an exhaust can be linked directly to increased weight in the right foot. Meaning that the louder your truck is the more your gonna romp on it to hear it rumble. I never really have been one to give a rats ass about mpg but i ususally get around 320-340 miles out of a full tank.

Now please do an experiment for us. Drive like hell and don't get out of the gas for a tank and tell us the mpg and performance. Next take the exhaust off at the manifold and then drive like hell agian and tell us the results.........

A few motorheads have done dyno tests and shown us that engines require backpressure dependent on the build of the engine.

I myself believe that any decrease in mpg with the install of an exhaust can be linked directly to increased weight in the right foot. Meaning that the louder your truck is the more your gonna romp on it to hear it rumble. I never really have been one to give a rats ass about mpg but i ususally get around 320-340 miles out of a full tank.


I agree.

BUT, in certain situations it does help though correct? Like my cats for example. they're stopped up, and if I cut them will I loose too much backpressure and it hurt instead of help? What about using a factory muffler with no cats.??

BUT, in certain situations it does help though correct? Like my cats for example. they're stopped up, and if I cut them will I loose too much backpressure and it hurt instead of help? What about using a factory muffler with no cats.??
Removing cats is completely unecessary. It doesn't add any hp so why do it? Get a performance cat if anything. Trucks just sound terrible with them off. Whenever i think of a truck with no cats, i think of hillbilly redneck country bumpkin with big super swampers in the rear and stock tires in the front with a rake of like 45 degree. Not to mention its absolutely annoying.

They're stopped up, I just want them gone to rid me of the smell, and shitty mileage.

I know several people that have tried to remove the cats and they say they lose all low end power. The truck can barely make it from first to second, it bogs down it second, but when the truck gets up to speed, it is fine. I personally would just replace the cats with new ones.

They're kind of pricey last time I checked.....maybe I'll just buy a new truck :D

They're kind of pricey last time I checked.....maybe I'll just buy a new truck :D

Buy a truck if you want, but can you and I work out some kinda deal for your grille?

Of course. I really am in the process of getting an 04... If I do I'll let you know and we can work something out.

I put duals on my '02 about three months after buying it (new). I talked with the truck shop quite a bit. One thing he asked me was if I wanted a louder (2 chamber) or quiter (3 chamber) system. I told him I was doing it more for performance than noise so I'd took the quiter one (yeah, right!!!). My exhaust is is like this: The two ex. manifolds come into a single 3" pipe, into the muffler ant then split to a dual with 2 1/2" pipes and out the rear. The power improved while miledge stayed about the same and if anything, maybe a bit better. The bottom line is the Superado just plain runs better. Because of the system that I also know the back pressure is the same on both sides of the engine.
When I first saw it I didn't quite understand the setup, but now thatI've had it awhile, I really like it.

So what did they do with your O2 sensors before and after the cat? Did they program them out or does it throw an SES not having them as you described?

well thanks for the imput Im not much of a motorhead so anything helps. I guess I'll put a aftermarket intake on. Im not bad on the pedal so It will just be a trial and error thing.

Removing cats is completely unecessary. It doesn't add any hp so why do it? Get a performance cat if anything. Trucks just sound terrible with them off. Whenever i think of a truck with no cats, i think of hillbilly redneck country bumpkin with big super swampers in the rear and stock tires in the front with a rake of like 45 degree. Not to mention its absolutely annoying.

I think the technical term is "Billy-Bobbing" your vehicle. :lol2:

I have my so called "billy bob" truck also...its the link in my signature at the bottom.

I just want this thing to run like its supposed to and catalytic converters are not cheap at all. My finances wont let me buy new ones.

I have my so called "billy bob" truck also...its the link in my signature at the bottom.

I just want this thing to run like its supposed to and catalytic converters are not cheap at all. My finances wont let me buy new ones.

I REALLY like that Ford! That is my idea of a perfect four wheeler. I work my HD and sometimes am far from the road, but really, I'd shy away from anything off road that would leave a good scar.

As far as not having the dough to get convertors, I can really understand that. I would have to think real hard about it myself in the same situation. I feel the same way about a Nelson tune, but I guess everyone has their priorities... :iceslolan

I understand the financial problem; I am still in school and can not afford things like new cats either. So here is what I do. There is a conversion shop about a mile from my old house, and they are constantly customizing vans and trucks. They always put duals on the trucks. Whenever I need exhaust parts, I just go there and they will sell me some stuff out of the trash pile. One time I got an muffler off of a new chevy and the stainless pipes off of a dodge, put on an 89 chevy for $75. Maybe you can find a place like that close to you, its worth a look

I think I know of a few places I can check like that. I wish I could get some factory ones with about 10K on them.

As for the Ford, there is NOTHING I've thrown at it that it hasn't handled. Since this is a MPG thread, guess what the Ford gets with a 400 big block. Yeah, 6 mpg.