What is the inside diameter of the pipe, if it’s 2-1/8 you can put Big City Thunder Monster baffles in. They reduce down to 1-3/4 are smooth not perforated and have a built in gun sight, or lollipop as others call it.

 

Thry are 2 1/4”, but I have not measured the inside diameter. I am going to drill th holes for the baffle screws before I mount them.

 

How far from the inside of the pipe should I drill the hole to hold the baffles in?

 

The phenomenon of "reversion" occurs when these pressure waves travel back toward the combustion chamber during the valve overlap period—the brief window when both the intake and exhaust valves are open. A positive reversion wave is detrimental to engine performance; it acts as a physical barrier, pushing spent exhaust gases back into the cylinder or preventing the fresh intake charge from entering efficiently. This results in "dilution" of the incoming air-fuel mixture, which reduces volumetric efficiency, increases combustion chamber temperatures, and can lead to engine knock or detonation.

Conversely, a negative reversion wave (often called a rarefaction wave) is highly beneficial. When timed correctly, a negative wave arrives at the exhaust port during the overlap period, creating a localized low-pressure area. This suction effect helps to scavenge the remaining exhaust gases from the cylinder and can even assist in pulling the fresh intake charge into the combustion chamber, a process known as "exhaust scavenging." The goal of high-performance exhaust design is to manipulate these wave reflections so that the negative wave arrives at the exhaust port precisely when the exhaust valve is open, while simultaneously creating a physical or fluid-dynamic barrier to block positive pressure pulses from entering the cylinder.

 

A fiberglass wrapped louvered baffle will give really good all around performance with a nice tone but not ear cracking and if it's too quiet you can always remove the fiberglass.. As for pre drilling the pipe, I wouldn't do it till you have the baffles in.. To help with Reversion you can always install a bolt that goes the full width of the opening on the pipe where the screw would go to secure the baffle.. They are known to interfere with the atmospheric pressure wave coming back up the pipe when the exhaust valve closes991.. Not a 100% fix but does make a difference..

EDITED: If possible I would try to install the baffles 2-2.5" from the end of the pipes..

 

/\ This all the way. Torque cones don’t work at all for shovels… like at all, but oddly enough they do make a small difference or help with reversion with an EVO… All that said, do as Hotrod98 says above. This is your best balance. Personally I’d buy two sets of baffles. Wrap it tight for a deeper sound, wrap it lose for a less deep sound… but take the first set and start cutting them shorter. Experiment an inch at a time all the way down to 3” long.. then whatever sounded and worked the best, cut the second pair to that and re-wrap.

In the above scenario, Bob chose the best baffle with that dividing bolt at the end. That bolt is what you want. If you buy baffles without, you can add a 3/16 bolt across but that bolt is the real key for reversion, over baffle design. With baffles “just holes” are better for midrange. Flared sticking into the exhaust pressure path with help bottom end while sacrificing top end. Pick your compromise, you don’t get both. It’s very Subtle so not a big deal though.

One last thing… with pipes that big on a motor that small, hopefully they are at minimum 36” long? If you’re willing, tape one end shut with duct tape on each pipe and poor water into one pipe right to the tip. Then very carefully without spilling any poor the full pipe into the empty one and see if they are identical length (volume). You can cut the longer to match the shorter and gently smooth with a fine file.

 

Do they still make the baffles with the ball shapes? You can cut them if too quiet.

 

Not wanting to steer away from the topic, just hitting the top. 2 into 1 exhaust was designed to clear unspent gases to prevent from being pulled into the cylinder, back pressure or timed collision balance is needed tho to make a Harley engine work properly, can see your point. If you ever run a digital Wego on the street with free flowing exhaust during closed throttle deceleration, the reading goes scary off the chart lean from reversion. My 127" with a 3" baffle 2-1 Drago's is brutal lean on deceleration but needs the baffle size at WOT, offset with more than normal larger low jet and rich screw mixture to kill the lean pop off idle throttle after a decel, bike has been streetable for many years.

Yes exhausts are mostly theory, live and learn applications.

 

Torque cones are snake oil. They do nothing. Might be better off with lollipops.

 

Setting hypothetical or the math aside… How do we measure what’s best? What is Best for one person is a poor compromise to another. Your Math while not wrong… might do poorly reaching a particular goal.

A persons goal might be a blend of looks and sound… he’ll sacrifice a little performance to meet his goal… therefore that pipe is better for him.

A person might have a goal of being super quiet while still wanting a measure of performance.

Another might be building a dedicated drag bike and the goal is all in mph/ET.. he doesn’t cared about looks, street manners or gas mileage.

Then there is Rains2much. He wants maximum mph/et blended with street manners blended with looks….

The “Math” and exhaust theory is great until you actual install tune and compare based on your own goals.

All things considered, step tuned drags are the real ticket. But you can’t just one size fits all.. the formulas get you close, to minimize the trial and error you now need to embark on. Pipe diameter and length will always have a bigger impact on the results from any other smart guy tech. As I’ve always said, there is no such thing as a magic pipe. There are pipes that are wrong for your parts/goal/purpose and pipes less wrong for your parts/goal/purpose.

And by all that’s sane, pick your goal first, then acquire parts to reach that goal. For any given motor size, compression… heck chassis the pipe is last… it has to handle the rpm range and air volume… meaning it comes after cam and likely once your close you’ll fine tune gearing and still go back to pipe being last. Those two kinda fight to be last.

To your point you do get that “magic” after careful trial and error. When pipe length, intake length, overlap are just right, gearing is sorted, you do find that eureka like you just turned on a turbo charger… It’s the difference between two guys with almost the same build sheet and yet one guy is clearly consistently faster. Meanwhile back in reality, nobody cares on that poker run… so still back to goals and compromises.