Exhaust modification

[molokaimike]

While I have the rear end out so that I can install the new IRS suspension I'm looking at the exhaust. At the end of the stock head pipe the diameter reduces quite a bit as it works its way top the muffler. I would think that this would cause some restriction of the exhaust flow. Now would be the best time to redo the exhaust and go with a larger diameter pipe. My question is would this reduce the back pressure to the point where I would feel a drop in performance. Or would I be OK with leaving the exhaust system alone. I have a stock 2020TG with a gutted head pipe and V&H slip ons. My down stream plans are to add a torque cam, air cleaner and tuner.

[Jack Klarich]

Forget back pressure, think exhaust gas reversion and speeding up the hot gasses flowing.

I would straighten out that flattened connector pipe for better reversion and scavenging of the exhaust. Exhaust likes heat and straight flow to create the low pressure scavenging.

D K Customs has these to help with exhaust gas reversion

[rhino 2]

While I have the rear end out so that I can install the new IRS suspension I'm looking at the exhaust. At the end of the stock head pipe the diameter reduces quite a bit as it works its way top the muffler. I would think that this would cause some restriction of the exhaust flow. Now would be the best time to redo the exhaust and go with a larger diameter pipe. My question is would this reduce the back pressure to the point where I would feel a drop in performance. Or would I be OK with leaving the exhaust system alone. I have a stock 2020TG with a gutted head pipe and V&H slip ons. My down stream plans are to add a torque cam, air cleaner and tuner.

You need back pressure how much ?.....Thats the 64 thousand dollar question..

Just an example when i opened the headers [Tuned Spaghetti Headers] on my 68 Charger at the strip...I had to advance the timing or bog at the bottom end...Then when i closed them for street use i had to reset the timing...With my 2011 Tri-Glide as soon as i added rush 1.75 slip-ons i lost bottom end and in order to get the bottom end back and then some i used DK's Thunder Torques.... You can see it with kids putting on Soup Can muffler on their Hondas...They make noise but can't get out of their own way from a traffic light..

[ROAD DOG]

While I have the rear end out so that I can install the new IRS suspension I'm looking at the exhaust. At the end of the stock head pipe the diameter reduces quite a bit as it works its way top the muffler. I would think that this would cause some restriction of the exhaust flow. Now would be the best time to redo the exhaust and go with a larger diameter pipe. My question is would this reduce the back pressure to the point where I would feel a drop in performance. Or would I be OK with leaving the exhaust system alone. I have a stock 2020TG with a gutted head pipe and V&H slip ons. My down stream plans are to add a torque cam, air cleaner and tuner.

Look at D&D trike exhaust they have a 2 into one exhaust that has the extension pipe off of the headpipe that is 2.5" it's a $195.00 I think it will fit on the stock head pipe ? you would have to cut the end off your muffler and weld in a piece of 2.5" exhaust pipe , like I did with the flex pipe I used on mine . I want to buy one and try it , to busy right now trying to get my motor back together , I cant find a clutch hub bearing H D says sometime in June ?

[molokaimike]

The IRS unit is built to work with the stock exhaust routing with ample clearance. Plus, in the area where the OEM swingarm is located the IRS unit will not have any up and down moving parts. With that in mind my thought is to take the crossover pipe and the extension to it off and go to a muffler shop and have them build a copy of it with a larger diameter pipe, maybe around 2". I will also do the same with the short extension on the right side. Both will have to be reduced to 1 3/4" at the end to fit into the muffler. I thought about having the inlet of the muffler enlarged but the inside of the muffler is a smaller diameter so I don't see a need to enlarge the inlet unless I'm missing something here. This will at least open up the exhaust system for most way and should help with the scavenging. That is the beauty of the IRS unit, the parts that move are outboard of the mufflers. Once I get the IRS unit mounted I will have a better idea of what I can do.

[molokaimike]

Here is a photo of the OEM crossover pipe. As you can see it is flattened for clearance reasons, this has to be somewhat restrictive. My thought is to have a muffler shop make a copy of it but using a larger diameter pipe. The owner of IMC where I'm getting the IRS unit said that he will loan me the bracket that mounts where the swingarm was so that I can make sure that my new pipe will clear. Nothing moves in this area so clearance should not be a problem.

[Jack Klarich]

Here is a photo of the OEM crossover pipe. As you can see it is flattened for clearance reasons, this has to be somewhat restrictive. My thought is to have a muffler shop make a copy of it but using a larger diameter pipe. The owner of IMC where I'm getting the IRS unit said that he will loan me the bracket that mounts where the swingarm was so that I can make sure that my new pipe will clear. Nothing moves in this area so clearance should not be a problem.

That bottle neck begs to be fixed

[DK Custom Products]

It is highly unpopular, and much like discussing which oil is best, which is why I don't bring it up much....but, I will dive in (since I am leaving and won't be back online much for the next week)

It is a myth that back pressure is good or needed on Harley Exhaust. There is a pretty comprehensive write up on the Facts and Myths about Harley Exhaust at this LINK.

Here is just a little excerpt from the above link, for full explanation, see above link.

"Back-pressure fights AGAINST performance. Back-pressure holds back power, not unlike a 350 lb. rider will reduce acceleration more than a 150 lb. rider.

The reason some folks think that back pressure is good, is because when they put a baffle in (which creates back-pressure) the bike runs stronger. BUT, it is NOT running stronger because of the back-pressure, it is running stronger in spite of the back-pressure, because it is reducing Reversion."

Kevin

[Jack Klarich]

It is highly unpopular, and much like discussing which oil is best, which is why I don't bring it up much....but, I will dive in (since I am leaving and won't be back online much for the next week)

It is a myth that back pressure is good or needed on Harley Exhaust. There is a pretty comprehensive write up on the Facts and Myths about Harley Exhaust at this LINK.

Here is just a little excerpt from the above link, for full explanation, see above link.

"Back-pressure fights AGAINST performance. Back-pressure holds back power, not unlike a 350 lb. rider will reduce acceleration more than a 150 lb. rider.

The reason some folks think that back pressure is good, is because when they put a baffle in (which creates back-pressure) the bike runs stronger. BUT, it is NOT running stronger because of the back-pressure, it is running stronger in spite of the back-pressure, because it is reducing Reversion."

Kevin

Back pressure can lead to the negative pulses pushing exhaust back thru open valves, thus impeding complete intake cylinder fill. Think , back pressure = backing up the exhaust. Now think why would anyone want this

[molokaimike]

Kevin & Jack

Thanks for the clarification on backpressure. Once again I'm reminded of how being on this forum and getting good information from those who know more than justifies the cost of the Gold Membership.

Mike

[Wmitz]

The IRS unit is built to work with the stock exhaust routing with ample clearance. Plus, in the area where the OEM swingarm is located the IRS unit will not have any up and down moving parts. With that in mind my thought is to take the crossover pipe and the extension to it off and go to a muffler shop and have them build a copy of it with a larger diameter pipe, maybe around 2". I will also do the same with the short extension on the right side. Both will have to be reduced to 1 3/4" at the end to fit into the muffler. I thought about having the inlet of the muffler enlarged but the inside of the muffler is a smaller diameter so I don't see a need to enlarge the inlet unless I'm missing something here. This will at least open up the exhaust system for most way and should help with the scavenging. That is the beauty of the IRS unit, the parts that move are outboard of the mufflers. Once I get the IRS unit mounted I will have a better idea of what I can do.

I wonder if by using a a larger pipe extension, you couldn’t just use a regular touring muffler for the two wheelers. Why reduce it to fit the old style muffler. You could use like a 2” pipe, then have the muffler end stretched to fit the regular touring muffler. Ultimately it is the baffle that controls the exhaust, not the inlet. Or I could be mis understanding the clearance issue. I thinks that is what D&D did. They probably use their regular touring muffler on the right side, I didn’t see any special muffler for the trikes.

[molokaimike]

I installed the IRS mounting bracket that the shop loaned me so that I could check for exhaust crossover pipe clearance. It looks like I will have ample room to change the pipe to a round one instead of the flattened shape of the OEM. I can also straighten out some of the bends all of which should improve the exhaust gas flow. I thought of enlarging the pipe which would also mean changing the inlet to the muffler but decided to go with the stock diameter. I think that if I did all of the enlarging modification I would only gain maybe 1 or 2 horsepower.

[Jack Klarich]

Sounds like a good plan. Let it flow

[molokaimike]

I made a mockup of the new crossover pipe using PVC. I should be able to take it to a muffler shop and have them bend one up for me. It looks a little off in the photos but that's because I can't get the PVC fitting to slide onto the head pipe straight and the fittings might not be aligned 100% but I'll correct all that before I get the real on made. I was able to eliminate the flattened section of the OEM pipe and get rid of a few bends. It should breath better now.

[ROAD DOG]

I made a mockup of the new crossover pipe using PVC. I should be able to take it to a muffler shop and have them bend one up for me. It looks a little off in the photos but that's because I can't get the PVC fitting to slide onto the head pipe straight and the fittings might not be aligned 100% but I'll correct all that before I get the real on made. I was able to eliminate the flattened section of the OEM pipe and get rid of a few bends. It should breath better now.

That was a good idea

[molokaimike]

That was a good idea

Thanks Road Dog, every now and then that one brain cell I have kicks in.

[ROAD DOG]

Thanks Road Dog, every now and then that one brain cell I have kicks in.

I No that feeling ! some days I walk to the tool box and ask myself What the F an I doing hear ?????????????

[molokaimike]

I finished the mockup now I'm just waiting for the IRS unit to arrive. I want to bolt it on and do one last test fit of the pipe before I go the the muffler shop to have it made. Here is a photo of the mockup and the OEM pipe.

[Fearless]

I No that feeling ! some days I walk to the tool box and ask myself What the F an I doing hear ?????????????

Add me to the list as well LOL

[ROAD DOG]

I finished the mockup now I'm just waiting for the IRS unit to arrive. I want to bolt it on and do one last test fit of the pipe before I go the the muffler shop to have it made. Here is a photo of the mockup and the OEM pipe.

I took my cross over pipe to a friends shop , he could not make the tight bends ? If it works make 10 of them I sure you could sell them all .