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Post by headcase on Sept 6, 2013 23:40:18 GMT -5
The original double-wall pipes on my '79 are finally getting a bit too ugly and the mufflers are about shot, so I need to start shopping soon, but before that happens I have a few questions for the Gurus of Growl.
1- We all know the diameter and length of the pipes before mufflers affect tune, power, sound etc. The factory inner pipe diameter is pretty small (not sure what the exact size is offhand), yet all single wall replacements are the same diameter as the factory outer tube...or close to it. I've read how sensitive these engines are to exhaust mods, so how is it you can replace the stockers with larger tubes and not throw everything off? Other than aesthetics, why aren't the aftermarket pipes the same size as the factory inners? I would think the low-end torque would take a good hit with larger diameter tubes right out of the ports.
2- Exhaust diodes/inserts...I understand the theory behind them, but being so short, do they really help bring the low end back? Would it help even more to have another set at the ends of the pipes just at the muffler entry? I'm thinking velocity vs. flow vs. scavenging/tuning.
My goal when I finally do the replacement is to keep the great low rpm power as is or even better if possible. I don't want a loud rapping exhaust note, and if possible reduce the sharp puffing/pulsing air sound out the back, like the stock mufflers have. I don't mind a low rumble or growl at speed, and the volume at wide open isn't a problem either, just want it to idle quiet enough not to see any shotguns out the neighbors windows at me at 7am. I'm thinking decent size muffler inlets/outlets to keep the puffing down, but the diodes and smaller i.d. inserts in the pipes and muffler entry. I know it sounds like I might be over-thinking this, but if I'm gonna get into it anyways, I'm gonna play with the insert idea...crunching up a set on the lathe is pretty simple.
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Post by grizld1 on Sept 7, 2013 12:25:51 GMT -5
Right, 1-1/2" single wall aftermarket pipes increase the effective ID a bit but put it about where it needs to be; you won't screw up the breathing of the motor with them. With freer-flowing muffs on the pipes you may need to jet just a touch richer. Exhaust port inserts operate on the same principle as the velocity cones that have been used in racing exhaust systems for decades. In addition to impeding exhaust gas reversion, the restriction they cause out of the port increases velocity into the first bend of the pipe, improving flow. There is no need for inserts at the outlet in 1-1/2" pipes. Their diameter is consistent with the power characteristics of the motor, and you won't feel loss of low-end pull in the seat of your pants unless your seat is a lot more accurate than mine, and you should feel strong gains past 6K.
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Post by headcase on Sept 7, 2013 18:22:17 GMT -5
Thanks, Griz. The reason I'm fine with smaller pipes is that I rarely wind it past 6 grand anyways. I go easy on the old goat since it does make some rattly noises around 5k or so (no tach presently). Maybe I'm just getting old, or maybe I'm not thrilled with the idea of tearing into it yet again to replace broken parts...wonder which it is  The reason I'm thinking of inserts downstream is mainly for noise control. Small enought to kill some noise with free-flowing mufflers, but bigger than the stock outlets to keep the huffing n puffing down. |
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Post by grizld1 on Sept 8, 2013 17:34:41 GMT -5
Outlet reducers won't do much for noise reduction. Emgo wide-mouth bell megaphones quiet things down to approximately the level of the OE muffs, flow about the same, look similar to the originals, and are good value for money. You can make a pair of exhaust port inserts that will serve you well by cannibalizing your old headers. Cut off the end that mounts in the port plus 2 or 3 inches of pipe, then cut off the outer layer of pipe. Turn down enough of the weld on a grinder to enable a hard tap fit into the new pipe. A word to the wise: the mounting plates on many aftermarket pipes are flimsy and will deform under enough torque to seal. Cut spacers or stack washers to prevent that, or install your old finned flanges on the new pipes.
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Post by headcase on Apr 19, 2015 12:17:24 GMT -5
Welp, it's been a while, but I finally got the replacement tubage on, along with the Dunstall replica mufflers I put on last year (packed with as much fiberglass as I can get in them). Good news: It didn't seem to kill any torque down low, in fact my keyster says it's just a tad up, and seems to smooth things out at low rpm too. The clutch slips just a bit now at lower rpm and w.o.t., seems like that's all the power it's gonna put up with. I know the tone of the exhaust it a LOT deeper at idle and cruising, and the puffing out the ends is almost gone. I kinda like it  The lack of a crossover tube didn't affect things like I thought it would. In fact it helps make carb balancing a lot easier. I now know the left cylinder isn't as strong at idle as the right one. Occasional miss/fart here and there while the right is bang-on each time. Hmmm....valve lash too tight? Bad news: I had to remove my nifty little crash bar to get the pipes on, and it won't go back on now. The pipes are bent different than the stockers, and are directly in line with the front engine mount bolts....one of which is used to mount the crash bar. It's just a bit unsettling now to see that there's nothing in the way of my footies and the pavement should the thing get horizontal. I had the diodes underway on the lathe using a piece of 6061 aluminum bar and planned to finish them off after the pipes were on so I could compare the difference. Not sure I even want to bother now. The carbs were set just a tad rich to begin with, and it seems to be doing just fine so far. As long as the chrome doesn't go blue I'll call it good. So begins Season 6 of Tojo's Revenge. Now if I could just get those d**n needles and seats to stop fuel dribbling out of my air filters.... |
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Post by grizld1 on Apr 22, 2015 8:51:10 GMT -5
If the motor is properly tuned, single wall pipes are going to blue for about the first 8", and there's no way around that. Take your pick--jet so fat that the valves and head choke up with carbon, learn to like the looks of a well-tuned exhaust, or rig "heat shields" and pretend they do more than add weight and cover what really ought to be there. Re. crash bar--did you really trust that thing to keep the bike off your leg?
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Post by richard on Apr 22, 2015 17:25:56 GMT -5
Yep they're going to blue. In the old days we used to pour a heat coating paste inside then roll the pipes around to coat everything, but it never lasted and eventually burnt off at which point the pipes turned blue anyway. Once I realized that my goal was to just have the bluing on the pipes be even so that no cylinder leads more than any other. As far as valve being tight my experience is that there is not a whole lot of advantage in running tight valves on an XS650, so the old saying better to hear them than not hear them applies. At least for me. I like Grizld1s philosophy about the crash-bars, they have their limitations at speed.
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Post by grizld1 on May 1, 2015 21:29:04 GMT -5
Re. the crash bars, Richard, I'm not philosophizing, just empiricizing. Back in 1967 I observed a very, very tight spot between an 18-wheeler that turned too fast off an Interstate ramp and crossed up in front of me on the left with his trailer across the median, and the curb and rail of the overpass on the right. I was doing around 80, and my only option for survival was to whack the throttle hard and try to get through the gap before the SOB closed it on me. The crash bars on my 55 c.i. HD flathead made the spot even tighter. As soon as my hands stopped shaking enough to hold a wrench, those curb catchers came off!
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Post by richard on May 10, 2015 13:43:58 GMT -5
I can see you point. I've been in a lot of close calls, but none like that.
Being merged into it is the most common for me. A pickup making a no signal left turn in front of me, on a crowded and risen two lane, which pushed me out into oncoming traffic was my closest call. I have never forgotten it.
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Post by headcase on May 14, 2015 23:45:06 GMT -5
The crash bar really wasn't in the way at all, it's a smaller piece that looks halfway decent... maybe the pegs bolted to it stuck out a bit. But they fold up for those tight maneuvers between cars. They stuck out about as far as the sides of my boots on the factory pegs. I just like that theres a bit of metal that might help the feet get less smashed should it ever go down that way.
And the pipes are still silver after about 100 miles. Not sure how long it takes to have any blueing show up, but so far so good. Sheeza sound really nice now at 3500, not the cutesie puffer sound like it used to be. I can't believe I haven't cracked WOT once this year....haven't needed to, the power is so much better down low. Next step: rear shocks and springs. Yay.
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