changing pipes

[theswede]

I'm considering changing the pipes on my 1980 special and I was wondering if I was to install torque tubes could I avoid having to re-jet the carbs.

[grizld1]

What kind of pipes? "Torque tubes" are used to match torque peak (determined by ID of pipe) to power peak (determined by length of pipe) in large diameter systems. If you're using 1-1/2" pipes (~1-3/8" ID), torque peak is already appropriate for the engine; I don't know of a torque tube made to fit that application anyway. If you're planning on using 1-3/4" pipes (~1-5/8" ID), you'll need to rejet no matter what you do. Rejetting is needed whenever flow is significantly improved. Stock pipe ID is around 1-1/8"; 1-1/2" pipes make a significant difference.

[theswede]

Thanks grizld1 I think I'll save the pipe change for winter when I have time to tinker with re-jetting. I'm adding the 2-1 pipes from mikesXS with maybe a cherry-bomb glass pack.

[sixxfiftyboy]

I know this question has probally been answered a million times but I have custom exhaust on my bike (stock 79 motor) they are 1-1/2 diameter what is the best thing to do In my situation? I was hoping to keep the straight pipe look to it so maybe baffles or something? I was wondering how long the pipes should be and what not, also what do I have to do to my carbs? sorry again for the question but I dont know anything about exaust. thanks

[grizld1]

1-1/2" pipes with baffle inserts are more restrictive than the OEM mufflers. Pipe length is one of the factors (along with cam timing and intake length) that control where the power peak of the engine occurs: shorter pipes move the power peak higher in the rpm range, longer pipes move it down. The convention is to measure length from the exhaust valve along the center line of the pipe. Michael Morse shared this measurement shortcut: on these bikes, length of the pipe as measured from its inlet on the outside line is approximately equal the center line measured from the valve face. In practice, a pipe length anywhere from 34" to 38" works well on the street, and that's the range in which commercially available 1-1/2" pipes usually fall.

As to the rest, you'll make your choice based on looks or on performance. I like a free-flowing glass pack muffler, and currently use Emgo 17" reverse cone megaphones--they need new packing right out of the box, but the baffle design is really nice. Re. jetting, my advice is to learn how or put the OEM system back in place; there's plenty of material out there.

[XS Rod]

Oh slammin baffles into a straight pipe... did it. Yep yet another back in the day story ...
Was running straight aftermarket headers back in da day ... Everything was running great so heck gotta play with something and see if I can screw things up a bit. Found a set of baffles that fit my pipes and slammed em home. Room mate walks by and mumbles about how I'm gonna regret that. Started the bike... it was quieter than stock all I could hear, pretty much, was the motor internals. Thankful that I was able to snatch them outta the pipe cause they didn't stay a minute.

[sixxfiftyboy]

So would I run into problems if I have 34'' pipes 1-1/2'' diameter and no baffles? besides being loud.

[XS Rod]

Just a rejet...
I don't recommend installing those baffles that are an interference fit inside the pipe. Personally I liked running straight headers... performance is on that's for sure. A little bit older now and will probably run the MAC 1 into 1's I've been storing for all these years, even tho I have been advised they are not optimum for performance... down the road? well we'll have to see.

[sixxfiftyboy]

So a rejet is getting a different jet for my carb or is it an adjustment?

[boots]

Jun 21, 2010 8:08:58 GMT -5 grizld1 said:

1-1/2" pipes with baffle inserts are more restrictive than the OEM mufflers. Pipe length is one of the factors (along with cam timing and intake length) that control where the power peak of the engine occurs: shorter pipes move the power peak higher in the rpm range, longer pipes move it down. The convention is to measure length from the exhaust valve along the center line of the pipe. Michael Morse shared this measurement shortcut: on these bikes, length of the pipe as measured from its inlet on the outside line is approximately equal the center line measured from the valve face. In practice, a pipe length anywhere from 34" to 38" works well on the street, and that's the range in which commercially available 1-1/2" pipes usually fall.

As to the rest, you'll make your choice based on looks or on performance. I like a free-flowing glass pack muffler, and currently use Emgo 17" reverse cone megaphones--they need new packing right out of the box, but the baffle design is really nice. Re. jetting, my advice is to learn how or put the OEM system back in place; there's plenty of material out there.

hey grizld1;
right now, i have a set of roadhawks on the bike; but i like the look of the shorter pipes. if i was considering putting on a shorter set (about 19"), i would have to rejet?

[grizld1]

Boots, do you mean 19" muffler length? It's flow, not length of muffler, that will determine whether or not you'll need to rejet. If you're just changing aftermarket mufflers on OEM pipes I doubt there would be a major effect on tuning, but you'll have to determine that for yourself. See www.amckayltd/carbguide.pdf for some basic tuning tips.

[boots]

thanks man