Stock exhaust vs aftermarket

[Guest]

I have a question regarding stock versus aftermarket: The header pipes on my GS, even though the outside are, like, 1-1/2", the inner pipe that the exhaust actually flows through (yes, there's an inner pipe on these, for those who aren't aware), is only, like, 1-1/8".
Are the header pipes on aftermarket systems single wall, or are they a double wall design, too? I'm guessing they are single wall, running out to 1-1/2", which is part of the reason why the aftermarket system are freer flowing (Well, that, and the freer mufflers.).

So far, my only experiences have been with factory systems, but I am looking to upgrade in the future, and am trying to educate myself, prior to buying.

[OldVet66]

They are single wall. The main benefit is weight. If your pipes are in good shape, you can't get anything that will make the bike run better. You might gain a little at certain speeds, but overall the stock setup is as good as it gets.

[koolaid_kid]

They are single wall. The main benefit is weight. If your pipes are in good shape, you can't get anything that will make the bike run better. You might gain a little at certain speeds, but overall the stock setup is as good as it gets.

The double wall is mainly to prevent bluing. Aftermarket will be single wall for weight savings.
Flow is a function of many things in the design; curvature and length of each header pipe, the collector (where they all join together) and the flow of the muffling device (usually called a can in an aftermarket system).
The stock exhaust system is far from the most efficient, which is why all racers remove them and install an aftermarket system. The key to any aftermarket system is to fully understand the function of an engine: it is an air pump. The more air it can pump, the more power it can produce. The intake system, i.e. the airbox, is tuned for both efficiency and noise. It is also not the most efficient method, but a compromise, just like the exhaust system.
However, and this is the key, the system must be tuned for the absolute perfect Air to Fuel Ratio, known as AFR. Without this last part, all the air mods in the world (exhaust system, porting modes, pods, etc, are for naught. When you introduce more airflow by increasing intake air and exhaust flow, you must add more fuel at the appropriate time.
Tuning is the key, and attempting to tune perfectly using the current "Plug chop" method is like cutting your lawn using a pair of tweezers. You can get there, but it takes a while.

[Road Rash]

Yeah, no offense, Old, but I don't understand the reasoning for that statement. I'm no exhaust expert, but even I know that the stock exhaust isn't ideal. Doesn't help when there is a V&H exhaust listed in your sig. So, what am I missing in reference to that statement?

Another question: Anybody know the collector exit o.d. as it his the muffler?

[OldVet66]

You won't see much of any gain with just a pipe change. If you go the rout of a 4-1 exhaust, stage three jet kit (if there is one for your bike) and quality pods, it's a different story, but that didn't seem to be your initial question. A lot of these changes are a compromise where you may be sacrificing some desirable running characteristics. It's a lot of work to get the bike's low speed behavior as smooth as the stock setup, and since you spend a lot more time in that driving range than you think you do it can really affect how you enjoy your ride. My basket case came with the 4-1 pipes, so I didn't have a lot of choice from the beginning and it's taken a long time to get it right. I rebuilt a pristine set of low mileage carburetors this winter, and I have lots of low end power I could never get out of my old set of carbs. It's been a long road and learning curve getting what I wanted out of this bike. There is still a little room for improvement, but at any rate I wouldn't recommend that it is worth the time and expense for any gain you get for a street bike.

[Joe Nardy]

Yes, exhaust alone won't give much performance gain. You will likely lose a bit of mid-range and gain top end. If you don't want to go with PODs, opening up the airbox and adding a Stage 1 jet kit will liven the bike up noticeably. You will also lose some weight and gain noise. Even adding a Stage 1 jet kit to a stock bike will liven it up as they came from the factory lean to meet EPA regulations.

Thanks,
Joe

[Road Rash]

Thanks for all the input, guys. Yes, I understand having to tune for the mods made, and I also understand about other components being a bottleneck, as well (I'm a bit of a gearhead from about 20the years back, wrenching on my 89 Camaro and 68 Chevelle. This bike is my second foray into the 2-wheeledmovie world.). So, most everything mentioned have confirmed what I felt. I just don't like to assume that what I think is going on, really is, until I speak to others.

Thanks, so much!

[Nessism]

Contrary to what many think, installing a header and pods won't add a whole bunch of power. Figure on about 3-5% on the top end, with some possible loss in the mid-low range. Most headers, like V&H, hang low below the engine and can snag on curbs and such; you will rarely find a used header without bashed in header pipes. They are lighter, which can add some performance. Most aftermarket headers are also poorly finished and will rust quite easily. Not a fan.

[koolaid_kid]

Thanks for all the input, guys. Yes, I understand having to tune for the mods made, and I also understand about other components being a bottleneck, as well (I'm a bit of a gearhead from about 20the years back, wrenching on my 89 Camaro and 68 Chevelle. This bike is my second foray into the 2-wheeledmovie world.). So, most everything mentioned have confirmed what I felt. I just don't like to assume that what I think is going on, really is, until I speak to others.

Thanks, so much!

The thing to remember is that it is a system. Ignore one part, and the gains will be minimal, at best. The quality of the aftermarket systems also seems to vary. My Kerker exhaust system is ~30 years old with no rust, but it is also ceramic coated inside and out.
The main thing to realize on this forum is that when you start to mention intake and exhaust mods, all sorts of flags are set off. Those that have done all their homework, with quality components, with lots of time verifying the results, have no misgivings. Those that attempt to cheap things out encounter issues which are not easily or cheaply resolved.
If all you are concerned with is replacing a faulty stock system with an aftermarket system which is more readily available, with no regards to a performance increase, all you have to do is rejet accordingly and you will be fine.

[koolaid_kid]

Contrary to what many think, installing a header and pods won't add a whole bunch of power. Figure on about 3-5% on the top end, with some possible loss in the mid-low range. Most headers, like V&H, hang low below the engine and can snag on curbs and such; you will rarely find a used header without bashed in header pipes. They are lighter, which can add some performance. Most aftermarket headers are also poorly finished and will rust quite easily. Not a fan.

Sorry, Ed, but this is far too general a statement. Lots of things enter into the performance equation, carb mods, cam timing, cam lift, ignition curves, tuning precision, etc. Please do not generalize what should be a specific topic. BTW, the Op never mentioned an expected performance increase. Not sure why anyone is so concerned at this point.
AFA fitment, for example, my Kerker 4-1 exhaust has none of the issues you report, especially the "bashed in header pipes". And yes, I have both my center and my side stands intact, and there is no rust on the 30+ year old exhaust.
Peace.

[Road Rash]

All I really wanted to know was if aftermarket header pipes were single or double walled. Well........that and what the factory muffler inlet size was.

[koolaid_kid]

All I really wanted to know was if aftermarket header pipes were single or double walled. Well........that and what the factory muffler inlet size was.

That is all I saw in your question also. Aftermarket are single walled for price and for weight. Not sure on the inlet size, however.

As you can tell, this is a controversial subject on this site. Many apparently do the mod expecting a 60 hp increase (not gonna happen) or find it falls flat on its face (not done correctly). Regardless, if you install an aftermarket system you will need to rejet slightly to compensate for the added air flow.

[Road Rash]

Yeah, I guess so. I didn't think I'd be opening up a can of worm with such a simple question. I fully expected to have to rejet, too. Any recommendations for good jet sources?, or is THAT gonna cause a debate, too?

[Joe Nardy]

Yeah, I guess so. I didn't think I'd be opening up a can of worm with such a simple question. I fully expected to have to rejet, too. Any recommendations for good jet sources?, or is THAT gonna cause a debate, too?

Just my opinion but I think the Dynojet kit is the way to go. I'm not sure what bike you have but many of the Dynojet kits comprise of stage 1 and stage 3 kits. The stage 1 kit is for stock bikes and stage 3 is for bikes with aftermarket pipe and PODs. They come with several different main jets for different applications and the instructions are pretty good. Even a stock bike will run better with a stage 1 kit. Dynojet claims the shape of their needles make the biggest difference. Also, as stated earlier, these bikes were jetted lean from the factory for EPA requirements. Richening them up a bit helps performance. There is a world of jetting experience and some others here can give you ballpark jet sizes for your particular bike.

Thanks,
Joe

[posplayr]

Just my opinion but I think the Dynojet kit is the way to go. I'm not sure what bike you have but many of the Dynojet kits comprise of stage 1 and stage 3 kits. The stage 1 kit is for stock bikes and stage 3 is for bikes with aftermarket pipe and PODs. They come with several different main jets for different applications and the instructions are pretty good. Even a stock bike will run better with a stage 1 kit. Dynojet claims the shape of their needles make the biggest difference. Also, as stated earlier, these bikes were jetted lean from the factory for EPA requirements. Richening them up a bit helps performance. There is a world of jetting experience and some others here can give you ballpark jet sizes for your particular bike.

Thanks,
Joe

Joe,
Having jetted my bike for a 4:1 which is pretty standard around here and then using a WBO2 sensor to calibrate a 4:2:1 it is pretty clear that the DN kit is primarily needed because of the needle. The carburetorIon reversion around 4-5k doesn't need as much flow as a stock pipe with cross over. The 4:1 needs more gas at the high end which you czn probable mostly adjust for with the main. So as has been the d period car of many here a 4:1 needs a needle different from stock.