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CAI , Exhaust, or Programmer

3356 Views 9 Replies 6 Participants Last post by  06MonteSS
I have a 2003 Silverado 1500 with the 5.3L. It has 125,000 miles and I'm trying to decide what to upgrade first. I want to improve my mpg mostly. How much of an increase can CAI's really give you. I was looking at getting a K&N because most people seem to get those and they seem happy with them. I saw on a review where a guy improved his miles per tank from 320 to 400 after the CAI, is that possible seems a little too much for just a CAI. Also is a throttle body spacer worth it? What exactly does it change?

Also how much does exhaust improve your mpg if you drive normal. I know driving habits can change after exhaust is installed and more than likely I would fall in that category so I'm thinking this is going to have to wait. I've also read getting headers can help. Can someone explain how this can help, I'm not very knowledgeable with this stuff but trying to learn.

For the programmers I was looking at the Diablosport Predator. Everyone on here seems to like that, but how much does it really improve your performance and mpg.

For right now I want to just do one of these because I don't want to blow all my money on my truck. What do you guys suggest?

Thanks in advance!
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My experience with KN filters is that I love them. I do prefer the drop in replacement filters as opposed to the "CAI" version being they really aren't cold air intake systems. The "CAI" just absorbs the surrounding motor heat with their "Heat Shield" to protect them. The only benefit the CAI will have is moving air in the tube over the stock tube. As far for the lower temp it takes approximately 10 degrees lower intake temp to produce 1HP. So unless you have a well ventilated hood where you need a rain catch to prevent your filter from getting soaked or a ram air system, I would just go with a drop in replacement filter. Just be careful when using KN filters when you clean and re-oil them. Too much oil on it will can foul up your MAF sensor negating that extra horse power and gas mileage you were getting. My opinion this you will see most improvement on in gas mileage and throttle response for the money for what you are looking at.

As far as aftermarket exhaust goes if you get too big a diamater in pipe you will loose horsepower. You sould only have to go bigger if you have a boosted engine where the gasses have a reason to need to exit quicker with the added heat. My experience with exhaust systems is they hurt my gas mileage due to I like the deeper sound so much I have a tendency to get on the gas more. As far of improving the gas mileage they say it does but I cant prove or disprove it without a dyno. I grabbed an exert from to help you with your size delima.
To reduce additional backpressure, the OEM exhaust tubing can be replaced with madrel-bent tubing of the same size or one size up from the OEM. As a general rule, you can enlarge the pipe diameter of your OEM exhaust system by 1/4- to 1/2-inch to increase your horsepower. However, any additional increase in pipe diameter is likely to decrease your performance; specifically, low end torque.

Bigger is not always better.

Muffler Inlet / Outlet Size
Engine SizeHorsepowerSingle ExhaustDual Exhaust
150-200 CID​
100 to 150​
2" to 2-1/4"​
200-250 CID​
100 to 200​
2-1/4" to 2-1/2"​
2" to 2-1/4"​
250-300 CID​
150 to 250​
2-1/2" to 3"​
2" to 2-1/2"​
300-350 CID​
200 to 350​
2-1/2" to 3"​
2-1/4" to 2-1/2"​
350-400 CID​
250 to 550​
3" to 4"​
2-1/2" to 3"​

Use as a general guide for engine size and performance.​

My opinion is reprogramming your ECU should be done only after you've done all the upgrading on parts for awhile. I prefer paying someone for a custom tune to your car. If you do get one I suggest one that will let you change your shift points as well. When I had my accord tuned it wasn't for fuel efficiency. So no experience on that I can throw my 2 cents on.
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If you have questions about Tuning the member JennaBear is a vendor on this forum that deals a lot with Tuning. She will give you some good advice if you plan on doing the tuning route.
is her company.
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