muffler change and powerband/mileage gain?

[snowbeard]

wow, I finally have enought experience on my bike to feel a difference in power and handling when I modify stuff!! I'll say right now that I have no experience with performance enhancing mods, so catch me up like I know nothing, cause I do , don't. ?

so I did a pipes mod a year back, cut off an extra set of GS mufflers just where they weld on the cone and baffles. I added a washer on the end of the baffle pipes to restrict it some and threw on some turnout harley pipes.

I took the jets from 110 to 115 and thought I felt a gain in power. but it would idle pretty low, and just drop out if I didn't keep an eye on it at lights, etc.

they were quite loud, and only had one bent slant for a baffle. eventually my ears started to ring at night, so I've changed over to what I think would be some stock slipons from a harley. I found the entire header and pipes in the recycling bin so I have no solid idea what they are.

they are much more restrictive tho, and quieter. what I am noticing is that I am running at a lower RPM for my speed now, but I feel like it's a little choked off on the acceleration sometimes? also it idles right about 1500 most times, which is alright, as I have turned the idle up pretty high to account for the other pipes not holding it up at lights.

so I'm curious, what's happening here? I'm just looking for the theory side of it, the "if you do A, then B should result" stuff. just because I don't know the intricacies of our engines like you guys do in here.

[DanTheMan]

This is on the 650? You do need to have some amount of back pressure from the exhaust for any engine to work properly. No restrictions at all will lead to burned valves as well as loss of power. You could even run straight pipes from the headers if they had a couple of bends or orifice restrictors put in place to maintain the exhaust back pressure, however, the next part you would have to address would be the jetting issues. It sounds to me like the pipes you have on the bike now are much better than those ear splitting things you had before, and they're doing a much better job. Just work on tuning the engine to them.........:-D

[snowbeard]

I did check the plugs a few times with no white ashy color, so I think I had the jetting and backpressure within reason using the washer. but just a little more and it is happier.

so does that change my compression any? does it maybe just keep the gases from escaping as quickly, maybe leading to more efficient combustion? reburning of the exhaust if it can't really flow as freely?

just trying to learn the art, thanks!

unfortunately I think it's my helmet that's deafening me, I still have a ringing after riding...

[DanTheMan]

I did check the plugs a few times with no white ashy color, so I think I had the jetting and backpressure within reason using the washer. but just a little more and it is happier.

so does that change my compression any? does it maybe just keep the gases from escaping as quickly, maybe leading to more efficient combustion? reburning of the exhaust if it can't really flow as freely?

just trying to learn the art, thanks!

unfortunately I think it's my helmet that's deafening me, I still have a ringing after riding...

Compression doesn't really change, but the backpressure does provide mor complete combustion of the volatile fuel mixture as compared to blowing large amounts of unburned fuel out of the exhaust pipes.....And yeah, that Cheshire cat on the back of your helmet is probably howling real loudly the faster you go........:-D

[zig06]

Your mentioned that it felt like it is choked off, which sounds to me like your running lean. Also, how are you doing your plug readings? Plug readings only tell the "last story". Meaning that if you took a 5 minute ride to your "secret test road" did a couple of hard accelerations and maybe even a high speed run, and then spent 5 minutes riding back to your garage. Your plug reading would only be accurate for the last part of your 5 minute ride back to your garage. If you really studied it, you would get some of the high speed run, but again, it won't be that accurate.

If your going to rely on plug readings, you need to clutch and then cut the ignition immediately after the event that your trying to jet for. On the street this can be a challenging and even dangerious condition ~ use caution.

Personally I think that you need to call around and see if you can find a speed shop that has a dyno and can measure air/fuel ratio's. Then load it up and take a drive. And even though it won't be cheap, it will be faster and far more effective. Call for pricing, it may not even be really that expensive.