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I've improved my MPG from 53 to 65+

6315 Views 21 Replies 9 Participants Last post by  cakley
For the last 37000 miles I've have only been able to get an average of 53MPG. So I have tried to improve the engines ability to breath and exhale or intake and exhaust flow.

I was going to replace the factory muffler after inspecting the inside to find out how restrictive it is with a free flowing muffler. Problem is there are no lightweight small mufflers on the markets. Stock muffler is 8lbs. So I decided to keep the stock muffler and just modify it. On the backside of the muffler and above the outlet pipe I drilled a large hole. One more hole was drilled into the outlet pipe. I shaped and welded a 1 7/8" 90 degree elbow from the muffler to the outlet pipe. This allows the exhaust flow to bypass the most restrictive part of the muffler. Sound was hardly increased. Can't tell anything from inside the car. Total cost was 1.99 plus my time welding. Only one test drive showed little improvement in MPG. However the RPM's raised quicker and a slight power increase was felt. An alternative to the elbow and easy to do is just remove the muffler and run a straight pipe.

Next mod was on the intake side. If you look at the air intake you'll notice that its right behind the radiator and after the engine warms up the intake pipe warms up a lot. There is a resonator located in the drivers side fender with a pipe running from it to the intake pipe. I placed tape over the inlet and just disconnected the pipe from the resonator. It’s held in place with a squeeze clamp and requires no tools to remove. I just let the hose hang. Perhaps the better set up would be to extend the length of hose to get cooler air. I wanted to keep it so I can return to factory setup in minutes. Basicly a cheap CAI cold air intake!

After I performed this mod I drove 8 miles across town and got 70.5mpg!!!. I took a longer way home to look at some houses total miles was 21 and final MPG was 65.5 The car felt like didn't loose power up hills. MPG was increased on flat roads. The car increased speed quicker and with less pedal. I'm real impressed and pissed at the same time. I wish I had done this 37,000 miles ago :!: :idea:

I'm going to DYNO test the car before I get my Volk rims installed then once more after the rims so that I can have solid proof that I have improved the car.
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For the last 37000 miles I've have only been able to get an average of 53MPG. So I have tried to improve the engines ability to breath and exhale or intake and exhaust flow.

From your description you have de-tuned the Insight to much a more aggressive driving style.

Better: as long as your style doesn't begin to take additional advantage of the increased performance.

Worse: if and when you decide to try and achieve the ultimate MPG performance the Insight is capable of.

The intake resonator is more than just a noise reducer. You can achieve mid single digit performance improvements if the intake is tuned to a specific resonant frequency. To peak engine torque and HP at streetable RPM's a correctly restricted exhaust systems has similar benefits.

Colder intake air temps (IAT sensor reading) below a rather warm 120ish appears to narrow the lean burn window.

With the Insight the peak MPG performance point is rather narrow. Consistently drive outside the envelope and you'll see correspondingly poor performance. Make the envelope bigger (as you apparently have) and you reduce the upper MPG potential.

Not a criticism. Just an FYI for others looking to get ultimate MPG.

John K. Bullock
aka. Insightful Trekker

03 5spd
78.8 best tank avg.
94+ best one way commute
87+ best round trip commute
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