Hi Clif,

You seem to be the resident expert on this stuff -- I appreciate the empirical data you have posted -- and so I have a question for you. As I was perusing the web and seeing that Midas and Meineke does custom exhaust modifications, I also noticed that the Car Talk guys had something to say about performance modifications such as this.

They claim that, because this modification changes the amount of back pressure (or whatever), you may end up voiding the warranty. And they said that there may be some potential for damage as a result of the modification, because of those changes.

I was wondering what your thoughts and/or experience is with this issue. I don't really have an opinion myself, I'm just curious what the viewpoint is from you and other performance enthusiasts you may know. Thanks!

 

That isn NO way was directed at this site, I have only met nice folks here; it was pointed at the linked site that was provided by CGameProgrammer I apoligize if there was any confusion.
There is a Dyno close to me but I did not do a before so the data would be useless, doesn't mean I don't want to head over there though
Clif

 

I read all your posts, Duc, but I couldn't really see why modifying the muffler but not the catalytic converter (the main source of exhaust obstruction) would improve efficiency. So I sought a second opinion on a site that has alot of people that build, repair, or modify cars, and none of them saw replacing the muffler as beneficial.

If I were to do something like this, I'd want a thumbs-up from people who modify cars very often and really know what they're doing.

 

Oh, whoops - it read as you were talking about the good people of the GH community.

I do remember you mentioning that earlier. It still would be nice to know what HP you're running and if it did have a HP increase over stock #'s.

 

Having to have dealt with Honda on several occasions I can tell you they do not give up the blame very easy but they have to prove it is your fault in order to void the warranty. I did/do not worry about it because millions of people go straight to the muffler shop the day they buy there car and I have never heard of anyone having a problem. That said it does not mean Honda won't stick it to you, it is a coin toss but one I have never seen anyone lose.
Clif

 

I can definitely see your side and respect the fact you are a fact man, I myself am a see it for myself guy to.
Clif

 

I plan on taking it in, thing I worry about is on the VTX (Honda moto) HP/TQ can vary by as much as 10 on two identical stock bikes. I may appear to have gained a lot or none at all without a pre-run I will never know.
Clif

 

Looks like no Dyno for me.
Cheapest around (I can find) is $85, mod only cost me $90 so it does not compute in my book.
Clif

 

Can't we all just get along?

Well, seeing is believing eh? I was kind of skeptic as well when I first read this thread and everything Duc had to say. However, when I thought about it, Duc's mod made a lot of sense as far as decreasing backpressure, but I think that has been discussed to death in this thread.

Well, I really came on to post about a trip I just came back from. I took a trip the day before yesterday going from south cali to el paso, texas, that's about a 620 mile trip one way, and then comming back yesterday taking the same route. I thought this would be an excellent opportunity for me to test my 05 hch. Weather conditions for thursday were pretty nice, I just had some winds in some stretches of the road coming towards the side of my car. Because I was pressed on time on Thursday, I put cruise conrol on at 80 mph for the whole trip. I never once lowered my speed, not even when climbing mountains. I had a passanger with me who weighs around 150 lbs. I had to refuel twice on Thursday, filling the tank up in my hometown and again after I had travelled about 373 miles. On Friday I filled up after 400 miles traveled, and then again after 425 miles traveled. Here are my results for Thursday: The first tank (traveling at 80mph) averaged 36mpg. For this, i used real time computations dividing the actual miles traveled by the amount of gallons put at the gas station (not using the car computer). For the second part of the trip on Thursday, I avereged 39.3mpg's. Now, for the second part of the trip, half of the tank was used to get to texas and the other half leaving texas. There was a small amount of city driving, I would probably say about 50 miles overall, where I couldn't drive 80mph of course. For this 50 miles of city I drove the car around 60 to 70mph without cruise control.

Comming back from texas I was not in such a hurry, but I didn't want to "up" my mpg's by driving the car like a hybrid, afterall this was a test, so I decided that I would only lower the speed by 5mph. That being said, on the way back I set cruise control for 75mph for the whole trip. There were some winds coming straight towards the car for some stretches of the trip. like I said, at the end of the second tank I avereged 39.3mpg. The third and last full tank avereged 44.8mpg. I had to refuel about 50 miles from my town but I have not computed the mpg's for those last 50 miles, although the car's computer reads 40mpg.

So what does this all mean? Well, adding up my mpgs (36+39.3+44.8=120.1) and then dividing them to get my average results in 40mpg. If I am not mistaken, I don't think anyone in this forum has averaged 40mpg at speeds between 75-80mph. Now, because I was using cruise control throughout the whole trip, you can take out all the "hybrid driving techniques" leaving only the exhaust mod and the air intake mod to blame for the (I think) excellent performance of the car. Had I driven without cruise control, I am sure that I could have increased my mpg's in a significant way. Next month I'll be making another short trip (about 430 miles round trip) and will again use cruise control at lower speeds to see how the car performs.

Some things I noticed about the car on this trip were:
*At 80mph, the car runs at about 3.2-3.5 rpm's
*At 75mph, the car runs at about 3 rpm's
*When I decreased from 80 to 75 mph, the IG would increase between 5 to 10mph.
*On a very short and flat stretch of road (about 5 miles), I set cruise at 70mph and the IG jumped to 60mpg.
*Whenever I would catch up to a big rig, or for that matter, any other truck that was bigger then the HCH (that's pretty much any truck), and travel behind them for a short while before having to pass them, the IG would increase by 5 to 10mph.

 

Not in the 2005, but in my 2006 I get 36-43 mpg at 75-80 mph, without using cruise control though. 36 is what I got going from LA to San Diego with temperatures around 55. The opposite route, taken the same day, gave me 40 mpg, so 38 round-trip. But when it's warmer I've done 41-43 mpg round-trip, at times. Basically it varies pretty wildly.