4 into 2

[fredintoon]

My XS11SG's stock exhaust has PO re-welded muffler to collector joints that have recently cracked completely open.
I did a temp fix each side with muffler paste overwrapped with muffler tape under a split muffler sleeve held closed by 3 hose clamps.
Hey, it works. But it won't last for ever.
I can get a 4 into 2 MAC exhaust from Dennis Kirk for ~$330.
The MACs siamese 1&2 together and 3&4 together just like the stock system but the MACs don't have a crosspipe.
Now other aftermarket pipes (the ones nobody makes anymore) make that spaghetti crossover to siamese 1&4 and 2&3 together
and they presumably wouldn't have uglified the system that way without a reason.
So, will the MAC's lack of a balance pipe give me any grief?
I can always remove the 3 hose clamps and use a polished stainless T-bolt clamp instead, eh?

[Radiation]

I have that

I bought the Mac 4 into 2 with the turnouts about a year ago. I like them. I was told that the crossover pipe helps to balance out the sides with each other. Mine seems fine. One of the oldtimers that I work with said he doesn't like the crossovers because they can mask a out of sync carb. Just my $.02

[Crazcnuk]

I have 4 into 2 turnouts, probably MAC How could I tell?) and the bike runs fine.

[randy]

I'v also had the MAC 4-into-2 since day one with this bike and it works fine. In fact, I'm on my second set (5 yrs of parking near the ocean)

[Poprock]

I'm running stock headers with Harley Sportster muffs, crossover eliminated. Works fine for me, sounds like a stocker only lower pitch, and Sportie muffs can be had for real cheap. Just takes a 1 3/4" adapter off the end of the stock headers and a steel strap from the muffler mounting point to your stock muffler bolt. I had a Mac 4/1 on a Maxim 650. I liked it, especially above 5500 rpm when it got on the pipe. Carbs were stock. It really lit a fire under the 650.

[mstic2000]

The 78 I have has the mac 4 into 2 tappered exhaust. Runs fine. Make sure your carbs are dialed in good and not running hot before you put the macs on or they'll change colors on ya quick.

[TopCatGr58]

Hey Folks,

With Fred's Sidecar rig I don't think he's worried about upper rpm performance! What I think he's getting at is a possible loss of low end grunt with the non-crossover style pipes vs. the OEM's.

Any aftermarket pipe is going to probably flow a bit more than the stock ones with stock mufflers, so there's a little risk of running a bit leaner with the MACs. You may have to fatten up your pilot jet settings....ie. more turns out of the pilot jet screw, or even 1 size up larger pilot jets, but would be best to get the pipes and do some test riding and spark plug analysis as well as seat of the pants feel before making any jetting changes.

I have a 4-1, and have noticed that it doesn't have quite as much grunt in the very low rpms, like 1500 or so, but then again, I don't run it down there, rarely dropping below 3k usually, and that's where my pipes start to perk up!

Fred, any chance you could take the pipes to a muffler shop or such to have them rewelded, fitted with proper extensions to fit the slip ons!?
T.C.

[T99Ford]

Fred--
I believe the advantage of the 1/3 2/4 split was for cylinder scavenging as a performance idea (which does work). Most 4-2-1 pipes connect this way as well. The stock system does not take advantage of the scavenging, but then also does not have the fat midrange problems, either. 1/2 3/4 works well to make smooth power across the entire range. With the other system, in the rpm range just before the tuned (come on the pipe)range, the sonic exhaust waves which create the big boost when the engine comes on the pipe are working at a frequency below optimum (actually moving toward the cylinder on the intake stroke) which will actually blow back through the carb. This creates a double negative for the following reasons: First, the exhaust gas passes through the carb, picking up fuel as it goes (a carb works in either direction on the venturi principle). Then, since that particular cylinder is on the intake stroke, the "fresh" air (which is already diluted with exhaust and rich in fuel) passes again through the carb, picking up fuel again. So now your intake mixture is twice fueled, and loaded with exhaust gas. This is seen as a huge rich spot on a A/F ratio, just before the big power boost usually seen around 5K rpm (and worse with an airbox). Most guys will tune this with the midrange needle to an acceptable level, or shift around the dead spot. In the "on the pipe" range, the sonic exhaust waves in the pipe are travelling out, (not in, as previously) effectively creating a vacuum in the cylinder drawing in only fresh, once fuelled mixture, and lots of it, creating the big power gain.
The 1/2 3/4 system places your exhaust strokes so far apart, that this problem is eliminated, since the exhaust strokes of the two cylinders tied together never line up with an open intake valve. It makes smooth power all the way through, though slightly less on the top end. But you will never have to deal with the dreaded "mid range bog" of the other system. It is much more rideable and tuner friendly, which is probably why Yamaha went that way in their production bikes.
Tyler

[T99Ford]

Just read TC's message. I agree that the stock exhaust (or a 1/2 3/4 like the Mac) will give more satisfactory low end performance. Tuned pipes are made for power hungery riders (like me) that ride in at the upper end of the RPM range. Tuned pipes can be made for lower RPM ranges, but there is not much market for that...
I would bet that the Macs are a bolt on, since they are configured like the OEM pipes.

[Guest]

crossover

hey fred on my 81 project the po put 4-2 mac's on said he couldn't get to run right till he cut holes in the mufflers welded on 3/4 nipples and put them together with a union [ugly] I'll let you know which way runs better as soon as i get it on the road an run it both ways but the pluming has to go !!!!!!!!

[cywelchjr]

Just read TC's message. I agree that the stock exhaust (or a 1/2 3/4 like the Mac) will give more satisfactory low end performance. Tuned pipes are made for power hungery riders (like me) that ride in at the upper end of the RPM range. Tuned pipes can be made for lower RPM ranges, but there is not much market for that...
I would bet that the Macs are a bolt on, since they are configured like the OEM pipes.

My Jardine spaggeties (sp) put 1-4 and 2-3 together. Seem strange but I will admit that the brute is pretty even tempered. I know I need to sync the carbs a bit, but I'm not touching them till I change the engine. Hopefully it's gonna stay cool enough this weekend to crack the cases on the replacement so I can prep for installation.

[fredintoon]

Hey Folks,
Fred, any chance you could take the pipes to a muffler shop or such to have them rewelded, fitted with proper extensions to fit the slip ons!?
T.C.

Hi TC,
there's pretty plain evidence that the dreaded PO welded the muffler joints back together with the system still on the bike but no real indication to suggest the system has ever been off the bike from new.
If I took the chance that I could take the stockers off without wrecking them I could weld up cuffs and extensions to make a slip joint where the weld was myself.
That'd lead to a semi-matte hi-temp paint job on at least part of the system and I was lusting after new chrome.

[Dragon Tamer]

Fred,

I have the Jardine system on the Dragon and it came with a crossover. Some years back the crossover pipe started to work loose and would work to one side or the other and come loose so I removed it and made two plugs for the ports. So my crossover has been effectively removed. It made absolutely no noticeable difference in the system. If anything I would have to say that there may be a slight boost in the lower end torque. Made no difference at all in the top end. YMMV.

[Crazcnuk]

By blocking the x-over you effectively added back pressure.

Adding backpressure moves the power curve lower in the rpm range, to a point.

[Dragon Tamer]

Craz,
Yup, that would seem to be what happened alright. Thanks for putting in better terms.
At the time I did it I was not concerned with the fine points, just needed to get rid of the leaking, rattling, irritating piece of metal. I did it in such a matter that I could install a new one if it caused a major change in the performance but it changed nothing except like you pointed out so I never looked back!