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Discussion Starter #1
Ok, question here for the HK 3'' owners that are running straight through baffles.....Did anyone notice any issues with loss of back pressure?

Next....did you notice a change in how the bike ran?

Next....how do you like the sound on decel?

Next....did you rejet with a stock airbox?

And.....ARE YOU HAPPY????

Give me your feedback my brothers...(and sisters too :shock: )
 

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dogtownz said:
Ok, question here for the HK 3'' owners that are running straight through baffles.....Did anyone notice any issues with loss of back pressure?

NO
Next....did you notice a change in how the bike ran?

To me it didn't feel as peppy but could have just been me

Next....how do you like the sound on decel?

Sounded like a 18 wheeler deceling

Next....did you rejet with a stock airbox?

I didn't re-jet

And.....ARE YOU HAPPY????

I am now, I sold the baffles and put the stock baffles back in. It was WAY to loud for me and I like it loud but not that loud.

Give me your feedback my brothers...(and sisters too :shock: )
[/b]
 

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ditto to what BadX said!!!! Especially about the part of being TOO LOUD. I seriously felt like I should have been lined up at the christmas tree at my local 1/4 mile drag strip!!!! I like them loud too but not that loud!!WHOA!!!!
 

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Discussion Starter #4
hmm.....I LOVE the deep throaty sound, but hate the poppy decel noise ( i think it is the lack of backpressure ). Am going to put thumbscrews in just to check it out, but will most likely get the Thunders with the 2 1/8" ID.
 

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Dogtownz
If you are doing the thunders on the HK Big 3" Straights you need the 1 7/8 inch thunders. That is what I have.......
 

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Discussion Starter #6
Txvtx, I called Big City Thunder and spoke with Gail....she told me that I could use any of the sizes that they offered. She also sent me a CAD drawing to help with the mod. Maybe, the reason you went with 1 7/8 is based on the straight through's that you got from HK?? I thought you had told me that you bought those before...?

Either way, considering that there is 3" of pipe to work with (or heat shield) you have to make sure that you have the 1 3/4" swedged into the 2 1/8" in order to make this happen. The 1 3/4" goes onto the head pipe.

At least this is my school of thought....maybe I am wrong?
 

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Discussion Starter #7
bump...
 

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I don't follow your logic. I pulled the baffles and the 1 7/8 slid right in with no room to spare. If you hold it to the end of the baffle it is the exact size therefore fits the pipe. I don't know where the 2 1/8 would fit since the pipe is not that large anywhere to get it in.
I am pulling the pipes and stripping down the bike to the engine in the next few days, hopefully starting tomorrow. I'm off for the next 5 days so it is mod time. I will try to take some pics for you to show you what I mean. Maybe that will help.
Did you buy them yet? Gail was the one that pushed me to the 1/78. I actually talked to her last week and ordered another set for my bro's bike.....same HK 3". The theory is to have the thunder monster tighten the air current to create back pressure. The smallest part of the 2 1/8 could hardley be much smaller than the pipe so I don't see how it would create backpressure which = torque in this case.
 

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Discussion Starter #9
Tx...I agree with you....you have done the mod, I haven't. We better confer on this and I will certainly consider your advise.

Let me explain my logic though. Consider the fact that the heat shield is what surrounds the whole thing right? The baffle goes onto the head pipe with a 1 3/4'' diameter. The stock baffles measure out at 1 7/8'' (if I am correct), maybe 2''?? So in theory, within the heat shield I still have around 1'' to play with. I figure that the 2 1/8'' diameter baffles should fit perfectly within the 3'' heat shields.

I took the stock baffles that came with the pipes, and cut off both ends, the cap (where the screw holds it to the heat shield) and the other side that goes onto the head pipe. The spiral material is gone now. So in effect, I have a set of straight throughs right now. There is little back pressure at this point. So tonight I will put thumbscrews in and try to "tune" the backpressure and regain my torque.

To answer your question, I have not bought the baffles yet, but as Gail pushed you to the 1 7/8'', she also told me that the 2 1/8'' would work as well and that it was my decision on what diameter to go with.....

So for now, I am not going any further with the Thunders, even though I will get them when I am sure that everything will work right. I am going to use the thumbscrews to get my backpressure for now....
 

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I guess the question is what are you trying to achieve? Performance, louder sound, lower tone?
Sounds like you are cutting down the baffle and putting in a thumbscrew like the TM baffles have since you said you got the cad drawing of the TM's. Seems as if you will make it louder by cutting down the baffles which increases the air (whooshing) sound since no baffles (cheese grater section at least) are there to diffuse it but with the thumbscrew you hope to defeat the air sound by diffusing the current. The backpressure won't increase noticeably so no torque gains will be noticeable. The smaller pipe section in the hourglass shape of the TM's is where the majority of the backpressure comes from.
Sounds like you'll come out with louder pipes and the last foot being blued from the exhaust dumping early into the heat shield b/c of the shorter baffle.
BTW if you read the HK warranty....they don't warranty against blueing if you pull the baffles.
 

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Discussion Starter #11
My general thing was to create a lower tone. I really didn't like the higher pitch the stocks create. I didn't cut the baffles in length at all. I left them the same 10'' that they came, I just removed the "cheese grater" material inside.

So, my bottom line is a good tone (deep) with little to no loss in performance. If that is even possible. But right now, I can really tell the difference in performance, it is not the same as it was. I can't wind the gears out like before.

The thumbscrew will hopefully like I said before create enough back pressure to eliminate the "sucking" sound on decel. And my hope was to gain back a bit of the performance.

If you talk to Gail again, confirm my idea on the 2 1/8'' diameter and if it will work with these pipes. She told me that they would give the lowest possible tone and that I would enjoy the performance that is promised from TM's. If you think about it, it does make sense. Think of how a tuba sounds vs. a trumpet.
 

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I took the stock baffles that came with the pipes, and cut off both ends, the cap (where the screw holds it to the heat shield) and the other side that goes onto the head pipe. The spiral material is gone now
I thought you shortened the baffle......my bad. I didn't screw with the baffle enough to try to get out the cheese grater. I dropped the tm's in forward of the baffles because I wanted the backpressure for torque. If they go in past the baffles the backpressure is not making it back to the jugs but escaping at the flange where the pipe meets the baffles. I guess you could weld that to seal it but it would be hard to get the weld all the way around b/c of the chrome shields. I guess I went the easy route but it works great. Good luck!
 

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Discussion Starter #13
I read the theory on shortening the baffle length, with a larger diameter tube vs. the opposite. I def want that deep note (tone) that I know these puppies are capable of. See I thought you were running straights, but it sounds like you aren't, but have the TM's...is this right?

I will let you know how it fairs....be sure to post pics of your project, whatever you are doing.
 

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Discussion Starter #14
Well it worked..my theory was correct. I put in the thumbscrews and got the back pressure "back"....the midrange torque came, along with some of the high end. So now, I have straight through's and back pressure.

I will still install the TM's down the road when $$ allow.

Just thought I would drop this in for those who might be following this thread.

Peace.
 
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