Possible engine issues

[Mgajohnson]

Would like to hear from some experienced riders or mechanics about possible engine wear from a more free flowing exhaust system. Just curious on other peoples opinions. Thanks in advance for your time.

 

[wozza]

I would be interested to know why a free flowing exhaust would cause more engine wear?
I know most engine wear is caused by initial start up of the engine - this is where using a good quality oil comes in.
Personally I can't see fitting a more free flowing exhaust making any difference to engine wear, but there are far more knowledgeable people on here than myself, so hopefully they'll soon enlighten us.

 

[Mgajohnson]

I was told less back pressure can possibly cause problems

 

[Lou Wambsganss]

My take on this is an emphatic False. For a few reasons:

1. A more free-flowing exhaust system will, if anything, permit the easy exiting of hot exhaust gasses, so the exhaust side of the head and the exhaust system should run slightly cooler if anything. Because of this, many race cars and bikes that run headers with a straight-thru exhaust system will wrap the headers with fiberglass insulation tape. This keeps the exhaust gas hot, which keeps it from condensing as it cools, which keeps it flowing faster, which helps with scavenging. It's Bernoulli's Principal. As the velocity of a gas increases, it's density decreases. Conversely, as density increases, velocity decreases. It's how a venturi in a carburetor pulls gasoline out of the bowl, and the basics of how a wing provides lift.

2. Even if you were to restrict an exhaust system, on a liquid cooled engine like this, it would take a lot of restriction to build up enough heat to overcome the cooling system's capacity and cause damage such as exhaust valve burning. Before things got hot enough to cause mechanical damage inside the engine, you would get very bad knock (detonation), and poor performance to the point of non-rideability. Due to the detonation, and the inability of the cylinder to fill the combustion chamber with clean air/fuel mix.

FYI, on the NC, just changing the muffler makes very little difference to the exhaust backpressure experienced by the engine. This is because the catalytic converter is the bottleneck and it is built into the exhaust pipe at the front. It's the maybe 4" diameter tube section of the pipe. You can delete the cat by installing a straight pipe exhaust, but it might actually decrease low end torque without also using a fuel tuner like Bazzaz or Power Commander to compensate the fuel map to suit the new exhaust system characteristics.

 

[Lou Wambsganss]

I will add this note, though. In EXTREME cases, running EXTREMELY short headers can cause exhaust valve or seat breakage by allowing cold outside air to contact the hot metal in between exhaust strokes. However, we are talking basically running a hot, high output engine with no exhaust system at all. Some old WW1 era air cooled radial engines ran a stub 4" header on each cylinder, and that was enough to prevent cracking. Any later radials run a collector ring exhaust, so this was not even an issue.

 

[silverhound]

I was told less back pressure can possibly cause problems

There is some truth to "no back pressure" can possibly cause problems such as if you ran your bike for an extended period with the exhaust system completely removed but who in their right mind would really do that? There's also a chance that in extreme cases you could create a lean condition that would eventually cause damage but it's highly unlikely without possibly running short/straight pipes and opening up the airbox way beyond a what any sane person would do.

Lou Wambsganss gave you a pretty thorough answer but the bottom line is that this way of thinking is held-over back from the days of carburetors and 2-cycle engines. Frankly I wish that open pipes or some less restrictive mufflers caused engine damage but they don't. It would reduce the number of riders who think it is cool to ride ridiculously loud bikes.

Even with the Cat removed there is still enough back-pressure for engines to keep running fine for years. The ECU on your bike will compensate for most changes in exhaust or air intake. Since you're not really contemplating anything out of the ordinary you have nothing to worry about. Get the exhaust you want and tell your friend to read up on engine technology at least from the last decade.

 

[gregsfc]

Fantastic thread. I'm glad I joined this forum in addition to the CTX700 forum. Alot more members over here, so more folks with more experiences and knowledge. I want to remove my muffler and run a straight pipe from that location back; hopefully running the straight pipe roughly the same route as the current muffler. I was worried about harming the engine, mpg loss, and/or longevity issues, so have not decided to try it until now. I've been searching all over the internet trying to get a consensus on whether or not running this bike w/o a muffler would be a risky maneuver. There are a couple of members over on CTX forum that removed their mufflers immediately after purchasing their bikes, but really no one over there gave any kind of convincing argument for or against doing this other than the same ole political stuff about noise.

I'm not a fan of loud pipes, but recently I had my muffler off and painted it matte black with plasticote to get rid of that big, ugly chrome can. I think it looks much better black, but I really liked the way it looked w/o that big honking can on the back, right side. Additionally, when it was off, I was able to get my right hand up underneath to clean the bike much better and easier, and I cleaned it up underneath really well. It would be nice to have it this way all the time. I can't do this with that big 4" muffler on there. And thirdly, when I had the muffler off, I cranked it up, and to my surprise, it sounded great to me; a little louder than I'd like, but not obnoxiously loud, so I took it for a test ride. I could tell no difference in performance, but it was much easier to accelerate smoothly, because now I could hear the engine above 30 mph and had a better idea when to shift in this quickly-revving, engine, but it was not overly loud. When engine braking and downshifting, I couldn't even hear the engine with the muffler off. In fact, when downshifting, engine braking, and cruising, I could still hear the drive line noise over the engine and wind noise, so I don't know how one could say this is a loud bike, even with the muffler off. I did not exceed 3500 RPM when I did this test, and I normally don't ever exceed about 4K. It may be louder at higher RPM, so maybe that's why folks say it's loud, because to me, it ain't loud w/o the muffler. Above the legal limit...yes, but loud...no!

At this point, as long as I can maintain my great fuel economy, and I can find someone who has this size diameter pipe to work with, I can find no negative to going muffler delete with this bike. But something that is a deal breaker would be if I can't find a slip on solution. I'm not going to weld to the current pipe.

Ideally, I'd like to curve up and out and back like the stock muffler and go to 1 1/2" diameter to possibly slightly deepen the sound, but so far I can find nothing for this size pipe. I guess I'll ask a muffler shop and go from there. If I just run a pipe straight back so that it's behind my head, it'll be in the way for cleaning, so I hope to find a way to curve it along the outside of the swing arm. But if I do have to run it straight back, I'll still have the appearance and sound benefits, so I think I'll do it anyway, but it has to be slip on. I can't find any information about how to do this work. Looks like 1" o.d. to me. Can't find anything on the internet except 1" o.d. from Napa, and I'd have to get 1" i.d. to slip over, if I'm right about the diameter, but I don't see a single product that's 1" i.d.

 

[Lou Wambsganss]

Be careful with any exhaust pipe you can buy at an auto store. The vast majority of it is alumnized steel. Between external moisture (Rain, etc), internal moisture (condensation, combustion gasses), and abrasion from road dirt, it will rust badly within maybe 2 years.

If you really want to custom make your own straight pipe, most exhaust shops could probably mandrel bend and weld a stainless pipe up for less than $100. However, by that point, you could basically buy a Danmoto XG-1 (https://www.dan-moto.com/DM_US/nc-700-750-x-s-2012-2014-xg-1-product-1060.html?zenid=s9dbus7rd4j6bh112kvi1k5m12), which is a stainless straight pipe with a dual tip. It's a complete kit with everything you need in the box. I have the Danmoto Jisu and am very happy with the price, build quality, and (so far) the durability.

 

[Smallville]

If you plasticote that muffler, i bet it will make a stink and melt all over. If you want a black muffler you should use high temp paint.

 

[spark82]

Hi people, my 2 cents:
four stroke engines mostly don't really care about the exhaust system, save for extreme conditions mentioned above. This 'legend' of a modified exhaust causing engine problems is mostly an old thing, when a lot of bikes and even cars were two-stroke, where the exhaust is a very important part of the aspiration of the engine. In that case if the exhaust modification is not correctly calculated then it causes power loss and even lubrication problems as oil is in the fuel for those engines and if there is no backpressure, unburnt fuel can escape the crankcase and the cylinder, leaving some parts of the engine without cooling and/or lubrication (mostly higher cylinder head temp being the problem) Or the mixture can become lean because of the higher airspeed in the carburetor etc. So all in all, if you have a two-stroke engine, then the exhaust is more important, with four-strokes not that much. And even less with fuel injection where the ECU modifies things according to several parameters including engine temp, lambda value (fuel- air ratio) and much more. Of course some things can change, for example fuel consumption if the modification is extreme, but it is unlikely that there'll be irrevesible changes or any permanent damage to the engine.

 

[BerndM]

If you plasticote that muffler, i bet it will make a stink and melt all over. If you want a black muffler you should use high temp paint.

Rustoleum BBQ spray paint from Walmart has a nice finish and dries in minutes.

 

[gregsfc]

If you plasticote that muffler, i bet it will make a stink and melt all over. If you want a black muffler you should use high temp paint.

I didn't use the high-temp paint, because I didn't want it to be permanent for resale value reasons.

I would have thought what you did about the platicote as well, but didn't happen. No stink; no melt; still just as black; muffler covering must not get that hot. However, it's a little tacky and attracts dirt a little more than the other components of the bike. I agree that it's not a permanent solution, but I don't think it's going to hurt anything, and it looks much better than a chrome can on an otherwise, blacked-out bike.

Went to one muffler shop; they didn't have pipe that small. Can't find anything about 1" ish pipe on the internet. I've got a couple of other folks to talk to around town.

 

[Ruggybuggy]

The ECU on your bike will compensate for most changes in exhaust or air intake.

So are you saying that the fuel injection system on the NC's is a closed loop system? Almost all fuel injected bikes use a predetermined fuel map.

 

[NCfanboy]

"The ECU on your bike will compensate for most changes in exhaust or air intake."

X2 as long as the modifications are reasonable. The fuel injection system makes use of narrow band sensors, so if you were to go into the engine and make major mods (not even available) you would need the Bazzaz fuel injection controller. An exhaust system upgrade or high flow filter are within the flexibility of the sensors so no fuel controller is necessary. The bike will adjust all on its own or you can reset the system which has been posted before.

 

[Smallville]

The fuel injection systems on most bikes (nc included) is fairly crude. The ECM will not adjust to changes other than at idle. Idle and just off idle is where the ECM reads O2 sensors. After that the predetermined map takes over. Even the changes that the ECM can make are small due to emissions requirements. Now changing a muffler will not be outside the acceptable parameters of the FI system. However it will not be running at peak performance. Adding a high flow filter will make the problem worse.

 

[silverhound]

So are you saying that the fuel injection system on the NC's is a closed loop system? Almost all fuel injected bikes use a predetermined fuel map.

No, I am just stating what Smallville and NCfanboy are also commenting on more thoroughly which is that there is some ability to compensate "electronically" with a FI bike verses no ability with a carbureted bike where you have to make physical adjustments or jet changes. I did not mean to imply that the ECU will be able to adjust and compensate for optimum performance. Ideally to get the best performance after making exhaust or air intake changes you could install an aftermarket FI modulator like a Power Commander from DynoJet and have a custom map made on a dyno but I don't think they make one for the NCX models and frankly I think the results would be negligible since the NCX engines are relatively low HP/Torque to begin with. Most likely any changes one makes to the exhaust or intake of the NCX will result in the bike running richer meaning worse fuel mileage or carbon buildup on the plugs as opposed to leaner which could in fact lead to burned valves or worse. So no real irreparable damage just crappy performance perhaps until the problem is remedied but not as crappy if there was no compensatory adjustment at all.

 

[Ruggybuggy]

I fully understand this but clarification was needed.