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Anyone have any experience with the air filter and cat back exhaust mods that clif described over at greenhybrid forums? He insists that these changes improve acceleration as well as mileage. Here's the link to his thread:
http://www.greenhybrid.com/discuss/f12/new-exhaust-2-1-4-a-4093/

Hi Shumai:

___Given the HCH-II has one of the most efficient emissions system in any car in existence let alone the FE is so far over the top, attempting to beat the Honda Engineers at their own game would be an almost insurmountable endeavor indeed.

___Feel free but to lose Tier II/Bin 2 and for a FE increase which is highly doubtful, it would be a waste of some of the best ICE and emissions system engineering on the planet :ccry:

___Taken from a non-modification type, the FE numbers achieved in the HCH-II review (http://www.cleanmpg.com/forums/showthread.php?t=15422) should make many think twice about losing what they already have. Honda has surely incorporated a given amount of back pressure from the SULEV-II CAT as well as a given Lamda with the O2 sensors intact into the ECU MAP for maximum FE and minimum emissions in the HCH-II’s iDSI. Without a reprogram of that map from some very expensive analyzers, I can just imagine what that engine is doing with the possible screwed up feedback it is receiving???

___On a similar note, we have seen any number of mods for Insight’s that claim 20% increases in FE and the only one that has been shown to work is the < $5.00 Cal-Pod IMA switch on 00-03’s which removes IMA assist and regen from the Insight’s normal operation. It does not really increase FE, it just gives the driver the ability to remove assist during an Acceleration and the harsh kWh payback once up to speed.

___Good Luck

___Wayne

Intake mods can't improve part throttle FE on a modern FI spark ignition vehicle.Any decrease in resistance before the throttle plate is compensated for by closing the throttle plate more so that the total mixture"inhaled" pre cycle will be the same. If you have drive by wire, then it will literally be automatic, if you control the plate, you will just adj the throttle opening with your foot to maintain a certain RPM.

In respect to exhaust-there just isn't much back pressure at part throttle, so the headers are already plenty big enough, and low resistance enough-any mods will interfere with tuning.

Save your money, or go for weight loss-wheels/tires/spare if you want to do mods.Aero stuff works-basjoos-but it is lots of work.

Leave the intake/exhaust alone.Like Xcel said-Honda engineers are somewhat competent-unlikely that they can be easily outdone .

Luck,
Charlie

Hi shumai;

I'll resoundingly second what Wayne and Charlie said.

Cold intake kits, High flow filters, exhaust mods, and other "performance tuner" retrofits of ANY kind literally amount to proverbial snake oil and produce no measurable improvements of any kind on the HCH-II. :(

In fact, the sad part about many of these mods is that they will hit your FE and depending on which country you live in, they will definitely interfere with your warranty.

Cheers;

MSantos

Like Msantos says-they usually don't improve ANYTHING! In fact, they don't even make the vehicle accelerate more quickly. The aftermarket manufacturers that even post "numbers" always post peak HP numbers-they never post actual acceleration numbers. A tiny change in peak hp probably won't make you faster, since you usually are giving something up at lower RPMS-and are always giving something up in FE.

Now this isn't to say that the poster in GH is deliberately lying-he isn't. However, it is impossible for an individual to separate out changes in FE that could be from driving style from changes in FE due to a mod. How many people want to think that a mod that cost them $250 and many hours of work is pure snake oil?? No one!
It is really hard to beat the OEM engineers in respect to FE and performance-especially Honda. Most of the HOTROD tuner cars aren't getting their stunning performance from simple intake/exhaust mods. They all use preformance adders like superchargers and N20, and with heavy duty cranks, pistons, cams so they can rev waaaaay high with 2X atm pressure. Yeah, they need intake and exhaust track mods since they might be moving 30X the air (450 hp vs 15 hp) that you are tooling along at 60 mph.
Save your money. If you like to tinker think in terms of weight/aero/RR. Some folks do gearing changes(on other vehicles) to get lower RPMS, but I certainly wouldn't do that on a hybrid-too complicated/expensive.
Luck,
Charlie
PS It is hard to beat pilot modifications for COST EFFECTIVE FE

^ What they said. Also, welcome to CleanMPG! If you're interested in improving fuel economy, look around. Driving style has a big impact on your fuel economy. Beating the EPA - The Why’s and How to Hypermile (http://www.cleanmpg.com/forums/showthread.php?t=1510) is an excellent place to start.

This thread is old, but relevant to my question so I'm posting here.

I'm taking to heart the lesson from posters above ("can't beat Honda's engineers"), but now my HCH1 has 162k miles and is showing rust on most of the exhaust system. A dealer that I consider reputable quoted $2500 to replace the whole thing. Ouch!

If I have to replace the exhaust anyway, are there other improvements to be had from aftermarket systems? Leaving aside FE and potential power increases, what about corrosion resistance for the next 162k miles, or even reduced weight via lighter materials (alum instead of stainless??) or shorter route (side exhaust??)?

P.S. - I don't want to raise noise level, and especially don't want a rattling coffee can-like exhaust.

162k is longer than mine lasted here in Texas where we don't have road salt. I needed a couple joints rewelded at ~100k and 120k respectively. I'd stick with OEM - it lasted a long time for you.

You might get better prices here (and they're oem parts), and pay for installation only.
http://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=CIVIC+HYBRID&catcgry2=2003&catcgry3=4DR+MX+%28HYBRID%29&catcgry4=KA5MT&catcgry5=EXHAUST+PIPE+-+MUFFLER