As long as weather has been freezing, a question about freeze plugs

[SkipII]

Yes, I know its a well-worn topic, and I've searched a bit, but hoping to condense a few things here from a group that I consider best at technical.

My set-up is mostly stock and will be staying that way. I did remove the cat. I also run PVCX.

I'm not looking for a change in sound, although if it were to change I would like it deeper, not necessarily louder. My bigger question is the impact on exhaust velocity (sometimes called back pressure).  If I do this, I plan to drill them out.

Sp...

1.Sound ?
2. Measured effect on torque and performance ?

Enzo on indianmotorcycles.net installed aftermarket baffles at the tips of the silencers after removing his cat. I'll have to ask him what that achieved.


 

[Senior Chief Vintage]

Well my friend, I did not like the sound after I knocked out the plugs. Sounded tinny to my old ears. Sound "sounded" better, deeper, after I had American Customs re-do the baffles. I was happy with that until Vance & Hines went on sale! Without doing a dyno, can't say if it had any effect on torque and performance, except my mine says it did!

[SkipII]

Thanks.

A few things I'm still trying to figure out or learn.

Deduction leads me to conclude that the freeze plugs are simply designed to block the exhaust gasses from going straight out the pipe, essentially forcing them around and through whatever glass fibers they use in the wall of the silencer. If that is true, removing the freeze plugs would allow gasses to go through uninhibited, which also means loss of restriction or back pressure. That would suggest the need for a baffle.

I'm still trying to figure out the right diameter of the Cobra Silent Care baffle I plan to use. Hard to get a micrometer in there but the pipe appears to be about 1 5/8."  (I may just keep wrapping a 1" OD piece of PVC pipe with duct tape until it starts to fit tightly. 

[133]

SkipII,

Your reasoning about the freeze plugs sounds correct and I would agree, except for one other fact:  I removed the freeze plugs back in 2013 and it made no difference to the way my bike ran, although it did change the sound a tad.  I later completely dismantled my OEM mufflers and, then seeing the design, can say that you are also correct that the plugs force the gases through small holes drilled in the center pipe and that, without the plug, the gasses can flow a less-restricted path straight out the center pipe.  What you have missed is the natural back-pressure created by the resonance (frequency) of the pressure generated by our particular engines.  It is all very involved (we need the professor from Gilligan's Island to explain this), but with our pipes and our engines, the presence or absence of the plugs seems to make little difference.  So why did Indian even bother putting the plugs in?  Eh - I have no idea.

As mentioned, what I eventually did was to disassemble both pipes (after first removing the plugs a year or so earlier) and completely remove all packing material and even the end plate of the mufflers.  My mufflers now are completely open.  This did change the resonance and did require that I install a fuel regulator to add a bit more fuel to the ratio, but the end result of all of this was a much more powerful engine (a 15 - 25% increase in power, as judged by the seat of my pants), a cooler-running engine, a small increase in gas mileage, and a bit of an increase in sound volume and lower-end rubble.

I hope this helps.

[SkipII]

Cowboy,. thanks for your thorough note and experience.

Yes, I have learned just enough to know there is a lot more to learn about exhaust flow dynamics. Pressure waves, pulses, exhaust stream velocity, exhaust scavenging, all that. I think there is a tendency to think that all exhausts are somehow inadequate, but of all things an engine manufacture can do today under air regulations to improve3 engine output, exhaust systems are open range. 

Net out, I plan to take out the freeze plugs, but likely install some baffles -- partly to reduce volume levels, maybe a deeper, tone, and maintain some back pressure.

[TOMCENTRAL]

Yes, I know its a well-worn topic, and I've searched a bit, but hoping to condense a few things here from a group that I consider best at technical.

My set-up is mostly stock and will be staying that way. I did remove the cat. I also run PVCX.

I'm not looking for a change in sound, although if it were to change I would like it deeper, not necessarily louder. My bigger question is the impact on exhaust velocity (sometimes called back pressure).  If I do this, I plan to drill them out.

Sp...

What Senior Chief Vintage recommended.The American Custom record is a real nice upgrade for the money.I'm sure Cowboy will testify the doing a self mod is not that easy.
That's just my opinion,I could be wrong....

Regards,Tom
1.Sound ?
2. Measured effect on torque and performance ?

Enzo on indianmotorcycles.net installed aftermarket baffles at the tips of the silencers after removing his cat. I'll have to ask him what that achieved.

[Chftn405]

For your reading pleasure....

https://www.rbracing-rsr.com/exhausttech.htm

Tony

[SkipII]

For your reading pleasure....

https://www.rbracing-rsr.com/exhausttech.htm

Tony

Yeah, I read that article a while back. Part of what led me to conclude there is way more to exhaust flow dynamics that most of use come close to understanding. Logically, a engine manufacturer will want to get the absolute most out of the exhaust system first, since the EPA is standing on their head for everything upstream of that.