A bypass pipe buried inside the OEM muffler

[joecvt]

After reading Cakley's muffler modification and the modified version,
I did one mod a while back by cutting a door and drilling some holes
as explained in this old thread:
http://www.insightcentral.net/forum/...657&highlight=
I drove with this mod for awhile but I began wondering if I could have
directed the air flow better. After studying images of the whole exposed
muffler, I thought that I could squeeze a bypass pipe in the last chamber
to direct the airflow right out the exhaust (with no back pressure) so I
decided to do it. I bought a new exhaust (since the old one had holes
drilled into it I thought I would use it as a backup). Here is the link
explaining the internal bypass pipe OEM muffler modification.

Here are a few pictures if you want a quick reference:

The internal area of modification
The internal pipes cut and ready for the bypass pipe
The bypass pipe installed and sealed with JB Weld
The muffler painted black and ready for installation

I can not detect any increased noise level but I can feel the engine
pulses. It is too early for me to comment on performance or mileage
but it has to be better than the standard restrictive muffler.

JoeCVT - Just your average CVT owner

[joecvt]

After driving with the modified muffler for 350 miles over 5 days, I'm
still at 62.7 MPG in a CVT (thats about 1.5 MPG better than my average
in the warmer weather). Still too early for any final conclusions, but so
far, it seems like it works as designed. If I put a MIMA controller in
(later on - after the 36,000 mile warranty), I may get closer to the EPA
rating of a Manual Transmission Insight

I mention the EPA rating because I know that I can't beat you guys
that typically get way beyond what the EPA achieved.

JoeCVT - Just your average CVT owner

[Insightful Trekker]

FYI,

Joe the IMA warranty is 8/80K. Not trying to discourage anyone in here but its best to be fully informed before making any warranty voiding modification.

HTH!

[joecvt]

Thanks Mr. Trekker,

I guess I should have explained why I mentioned the 36,000 instead of
the 80,000 IMA warranty. The wires cut would be under the "Gear
selection" console for MIMA. If there was anything wrong in that
area (warranty related) I wouldn't want them to see any cut wires.

I don't think Honda would have to uncover that area to replace any
IMA component under the IMA warranty but thanks for mentionng it.

I say "Gear selection" loosely because it is a CVT. There still are
some gears in there!

JoeCVT - Just your average CVT owner

[Insightful Trekker]

If that's the logic you choose to apply, then why wait

[joecvt]

Any shift linkage problems before 36,000 miles or anything that would
involve taking the shift cover off to expose cut / tapped wires. It may
be a stretch but it is only a little longer to wait...By that time, hopefully
MIMA_C will be available for purchase.

Update of the bypass pipe mod: I'm at 440 miles on this tank with
62.7 MPG....So far, so good...

JoeCVT - Just your average CVT owner

[joecvt]

I'm supprised that there are no replies within a week related to the
bypass pipe modification. I think that this is the best air flow mod
that can be made to the OEM muffler while still having an OEM look.

I'm now up to 550 miles on this tank at 63.4 MPG

JoeCVT - Just your average CVT owner

[originalbadbob]

OK, Here's a reply. I'm interested, but don't know if I want to go to the trouble for about a 1.5mpg increase. It might be more with the 5 speed, but I'll probably wait for some more info before I go to the trouble to do it.
I just wish I could get one of those really big exaust pipes out the back like the kids have, but don't want to cut up the back panel for the look.
Robert

[Insightful Trekker]

Well its been "done" in here in the past with mixed results. Search some of Cakley's old posts.

Glad your results are so positive.

Remember that the exhaust and intake system are "tuned" in a compromise of power / torque / RPM.

In an internal combustion engine increasing power through reducing exhaust restriction reduces low end torque. Its simply the physics of the equation.

In your specific set of circumstances and driving conditions the trade-off has apparently increased MPG. Not trying to discredit your claims but as you know there are many variables that effect MPG. It will take long term monitoring and compairson of other non modified Insights driven under similar conditions to confirm your results.

Change the pattern and the result will change.

But I think what has really caused this topic to be overlooked is that MIMA has most everbody's attention right now.

You've simply been overshadowed. Sorry

[b1shmu63]

I have been following this topic but have not commented.

I do intend to do a muffler mod at some point. Jack MPG has a complete muffler kit that he claims got him much better mileage on his trip to Tour de Sol. I have also considered a bypass valve but I'm sure that it would tend to stick with time. If I did modify the exhaust I would braze it closed again in the interest of toxic gas emission prevention. I have considered changing the muffler for some kind of free flow design. I think I would prefer to take the original muffler off completely and save it as stock, replacing it with a custom free flow design.

Mima has been a buzz lately but if you are really interested in the full capability that it has to offer then the Insight has to be optimised as much as possible. Hot air intake and exhaust mods will help as well as anything that will increase battery life, increase efficiency, modify the characteristics of the nut behind the wheel, or reduce drag.