Staight pipe exhaust, running lean?

[hondajt]

I took a piece of straight steel pipe and replaced my muffler with it.

Does this increase combustion temp's?

I had a friend of mine tell me I could burn up my valves because I would be running lean. Imean, the cat's and o2 sensors were still in place. I just unclamped the muffler and clamped on a straight pipe.

any thoughts?

[bladrnr]

Why would it run lean? How would you know if it was? I was thinking about doing this myself. I also like the hotbodies megaphone exhaust for GSXR1000. I want to try modifing it for a 6th gen bike if i ever get one. It just looks like a short piece of pipe to redirect exhaust heat. It doesn't seem like a big deal to do this but hotbodies does recommend a new fuel map for their exhaust.http://www.exoticsportbike.com/images/gsxr05_utxs.jpg
http://www.exoticsportbike.com/image...gapohone_3.jpg

[SLOVFR]

Well first you would be right up there with the annoying Harley guys. Then you will also loose horsepower due to lack of back pressure. And to finish you will run too lean and can cause internal engine damage to to excessive heat....

[Action]

IMHO you should be all right. The cat will provide enough restriction to keep you from running lean enough to burn valves. If you want to know for sure run it for an hour then pull the plugs and see how they look. The best thing would be to get a Power Commander (or a programmable ECU) and fine tune it with an exhaust gas analyzer on a dyno. The cheaper route would be to down load different maps off the internet and keep reading the plugs.

That being said, I’d like to put in a quick plug for NOT running straight pipes. Unless you really spend some time and money to have a custom map built for your bike, you are going to lose power. Your loud ass bike is also going to annoy everyone around you and contribute to the passing of BS laws that say NO Modified exhaust on bikes. I’ll put up some serious bucks if you show me an otherwise stock bike that makes more HP, and has a better torque curve, with a straight pipe.

Action

[Molsan]

Originally Posted by SLOVFR

Well first you would be right up there with the annoying Harley guys. Then you will also loose horsepower due to lack of back pressure. And to finish you will run too lean and can cause internal engine damage to to excessive heat....

I thought most of the back pressure came from the cat.
you could remove the miffler entirly with no real impact on the motor as long as the cat is in place. Is this incorrect?

[Ghost 1]

Gentlemen, There is a black art to exhaust design. A pipe is designed to use its sound waves (the positive and negative ones) to either help create negative presure in the cylinder at certain RPM to help extract burned fuel charge or to facilitate drawing a fresh charge into the cylinder. Length, shape, and where the pipe begins to expand into the collector or muffler all determing when these particular sound waves hit the cylinder. This stuff is even beyond me, and I'm factory Honda trained!
I HIGHLY recommend reading Kevin Cammron book on motorcycle performance. You would be floored reading about what all your exhaust can actually do for your bike.
Also note that exhaust pipe makers don't make straight pipes for sport bikes. Maybe there on to something there. Naturally, they make straight pipes for Hogs, but thats for noise not performance.
While on the subject of Hogs. They have a problem discovered by HD R&D that a Hog with straight pipes would shatter their exhaust valves with time. The wrong wave at the wrong time over long periods of time.
And really, lawmaker don't need any assistance from you in deciding motorcycles should be choked down, supressed, repressed.

[hondajt]

interesting. It's really not that loud, and I had significantly more power on the highway. And around town, i thought it rode great. I'm also 250lbs, i don't know if that makes a difference.

I'm just worried about damage. So how does the muffler change make it run leaner? If I removed the cat I would understand, but just the muffler?

I appreciate the repsonse, I am just looking for clarification. Not an arguement.

[CUL8TER]

Seems to me it would be no different than running gutted stock cans and theres plenty people running these with no problem..

[hondajt]

^^thats what I thought too. But there are many people on here who are much more educated than I am. I am interested in hearing there explainations.

Just because everyone's doing it, doesn't make it safe.

[SLOav8r]

Originally Posted by CUL8TER

Seems to me it would be no different than running gutted stock cans and theres plenty people running these with no problem..

Gutted cans still provide back pressure and a sound chamber. While not perfect, they're still safe and open things up a bit.

Straight pipe may be ok in the short term, but the long term effects could be anything from developing a love for nascar to blowing your top end apart.

There are far less risky things to do for a little extra scoot. (power commander, sprockets, etc)

[hondajt]

Thanks for the input.

Anyne have any more technical information please? Just curious.

[Molsan]

Aye, I would love to hear more...
bad pun?

The view of harmonics and such is intresting but with the cat in place i would assume it would insulate the engine from reverbirations (or the lack of) in the muffler. I also don't see the back pressure being out of sinc with the removal of the muffler as the muffler has little to no effect onback pressure.

[derstuka]

Besides annoying those around you with the noise, I don't think that putting a straight pipe on your bike will hurt it really, since it still has a cat and all.

Usually what would happen is if you reduce the backpressure drastically enough, you create a greater scavenging effect on your motor. That is, since your motor can exhale (spew exhaust out) more easily....your then motor starts pulling more air into each fuel/air mixture, which makes for an overly lean combustion. If this mixture is excessive enough (as in, the ratio of air to fuel is increased too such extent) this will cause your motor to run very lean....and this will cause the combustion to be become very hot, and it can burn a hole right into your piston, and/or melt your valves as well. Seen it happen.

IMO...since you still have a cat on, and your motor fueling might compensate for the lean condition slightly, you should not really have a problem.

I am a noise NAZI, so I would put an exhaust can back on it personally.

[Action]

Big D beat me to the post so I hacked my responce somewhat. Molsan, since all the header pipes dump into an open chamber in the front of the cat, I think you’re right; it will cancel out any pulses. I don’t know if catless headers flow better than gutted headers because of the gas flow in the area where the cat used to be. I’m also not 100% sure exactly how lean the factory setting is and the difference in flow rate of say the TBR exhaust vs. the factory exhaust. If the VFR had a mass air sensor and 02 sensors that were constantly in the loop the ECM would compensate, within limits. As for the bike feeling stronger; I would suspect that’s because it’s louder. I would LOVE to be proven wrong, but the only way I’ve seen meaningful gains on a VFR are by using a PCIII w/custom map, aftermarket filter, catless headers, and pipes. Even with all that you’re talking about a 10hp gain for about 1700.00. A sprocket change will probably make the bike feel just as strong for just a little cash.

[hondajt]

So, i've done some reading.

I cannot seem to find anywhere that helps me explain this.

Does replacing the slip-on muffler with a slip-on straight pipe increase exhaust flow?

If it did, I could understand how in theory the engine combustion temps would rise. Thus the possibility that damage could be done.

But i haven't seen any information that states that it will increase flow.

Anyone care to help a nerd?

[Action]

Deleted because I wasn't paying attention to what year Hondajt is riding!

[hondawolf]

I've ran the gutted cans and now have straight through pipes on my 04. Runs fine, have done thousands of miles this way with no loss in mpg or engine running hotter. Still have the cat. If I get rid of the cat, then I will look into a PC3. But you also have your o2 sensor to know if it's a little lean and make some adjustment.

They are some crome tips with a glass pack insert. Surprisingly a little quieter than my gutted stock exhaust. I like them since they are smaller and work fine with the saddle bags or two up riding.

[hondajt]

thanks, but the 5th gen doesn't have that. My micron exaust is straight through.