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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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Pictures are not needed. I could take pictures not sure how good they come out. I try tomorrow

For the exhaust mod. Just take the car to a local exhaust shop and have them remove the muffler and weld up a straight pipe. Be sure and ask if the have the small pipe 35mm or I think 1 1/2". It should cost less than 45.00. This will also save 6lbs of weight..

For the intake mod.
1 raise the hood
2 look in the middle of the car and just between the engine and front of the car and you'll see the intake pipe
3 place tape over that pipe opening
4 follow the pipe around to the airbox the back up a few inches and look on the underside. You should see a flexible hose that goes to the drivers side fender area.
5 reach in with your right hand and trace the hose to a box. at this point feel around for a clamp.
6 Squeze the clamp and pull in back.
7 Pull the hose off the resonator.
8 Just must the hose in front of the resonator and leave it

That's it.

I'll taking a 50 mile trip tomorrow on the freeway and will post the results.
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xcel said:
___ Wouldn’t the intake mod cause a problem in colder temps when you actually want/need a bit of preheating for the intake?
Never gets that cold in Georgia. This "preheating" ideal is for the books and not real life. When you drive on the road you need X amount of power. If you had a perfect road with a 5% decline the the engine could afford to make less power and then the preheating would be useful. I live in Georgia and need power to make it up hills.

xcel said:
I guess you could simply reconnect the intake up to stock in the winter so it wouldn’t be that big of a deal
Yes. Only takes a few minutes. Once winter hits us in the south I could if needed return to stock.
xcel said:
As for bypassing the muffler, I would also guess the muffler’s back pressure has been calculated for in the engine management system. If you drop off that back pressure, I am not so sure the ECU can compensate.
I hardly think that Honda thought about exhaust back pressure. I'm not talking about a Fully Open Exhaust set up. The car still has two cats and the small pipe running the length of the car. Beside I have yet to read anything about a pressure sensor for the exhaust in any car.

xcel said:
___I will be looking forward to your Dyno test and future MPG posts ... I have to ask why you were not receiving the 70 + with your 5 Spd. in the first place? Are you a fast driver in and around town only? What was your average Hwy mpg when you do in fact get the Insight into Lean burn at a steady 60 to 65 mph?
Most owners never get the 70+ MPG. Yes I am a fast driver but I do allow the speed to drop when climbing a hill and I watch redlights so I can time them. Lean Burn also = less power. I could never climb a hill in Georgia with the lean burn. If I tried I would drop down to 40ish MPH. I have made a few trips and kept the speed lower and got around 58-60. Normally I drive 85MPH on the freeway. Faster down hill and slower up hill. In town I drive around the speedlimit.

___Good Luck and thanks for pushing the envelope.

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected][/email
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Made a longer trip today.

50.5 miles on I-75 air temp was 68 with a slight rain. Two people, two pistols, and 200 rds of .45 ammo for the range. Est weight to be 320lbs. I kept the speed around 80mph faster on the down slopes and slower on the up slopes. The car just has more power. I'm sure it's not much but any gain helps. MPG was 68.5

Drove around town and on backroads then came back. Had a slight headwind and I was driving faster. Total miles was 130 @ 63MPG.

I have notied that this surging problem others have including me is stronger with this set up.. My .02 is that the EGR system is used more to warm the air. Or because the engine makes more power I can feel the loss in power becuase of the lager drop.
Thanks for your input. The car does pick up speed with less throttle.

How do you feel about the use of Redline Water Wetter. I'm currently using it. I'm waiting for a infared laser to come in. I want to measure the surface temp on various parts on the engine. Then drain and refill without the Water Wetter and take measurements.
We'll I got 72mpg in town for 21 mile round trip with stops at three places.

megaoptimus said:
hey cakley,

So what are the pros and cons of allowing cold air to intake to the engine at all times, even during near freezing temps? Thanks for all your ideas and posts:)
Might be too cold up north for the air intake mod during the winter months.. It will be great in the summer time. So far in georgia I've noticed that it takes my car slightly longer to warm up in the morning. Thus my MPG is about the same as before just slightly higher. Vice the drive home in the afternoon I can tell and see the difference.
If you have a heated garage or take long trips then save the intake mod till summer time.

For the exhaust. My MOD was long way to go about. Any muffler shop can cut the muffler off and weld up a straight pipe for less than 40.00

If you want better MPG. Get lighter weight rims ie VOLK ce28n 14x5.5. Keep a close track on the tire air pressure.
Re: Dumb questions

ScottH said:
When I was looking at doing this mod, I realized that the entire intake could be disconnected at the airbox. Wouldn't this be more efficient at getting fresh air in than through the front heated air and the disconnected pipe that used to go down to the resonator?

Then it would basically have about 2 inches of pipe, go through the air filter (I have a K&N installed), then about 18" through the mass airflow sensor and into the intake manifold.
I had allready tried what you said. Didn't see any improvement.

Cops and mufflers.... I rode a Harley for 3 years with straight pipes. I also had a Buell S1W 105+hp 1203 cc engine with 2 1/2 headers dumping into a 3" straightpipe. It was so loud that I had to wear ear plugs. I never once got questioned by the cops.

On the Insight. Its only 1.0L engine and has to flow through 2 cats. The cats kill most all of the sound. My muffler MOD just slightly increased the sound. A straight pipe would be only slightly louder. It would still be one of the quitest cars on the road.
My tires are kept at 50psi. Checked once a week for the last three years 37000 miles. Highways speeds 80-90mph On the downhills close to 100mph.
Just pay attention to the weather. 50psi on a cold day will increase if a warm front moves in quick.
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