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Author Topic: Thoughts on exhaust size for larger displacemnt Twin Cams  (Read 396 times)

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WildmanUltra

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Thoughts on exhaust size for larger displacemnt Twin Cams
« on: December 01, 2019, 05:54:55 PM »

Been talking with some people about the size of the header pipes on those of us who have installed larger cylinders.
I have a 2015 CVO that I installed a 117" big bore kit on and the discussion some are leaning towards is that for the larger displacement engines need a larger exhaust.

I'm curious to hear some thoughts on what others think. And then if a larger exhaust is needed who makes a 2-1-2 for our bikes? I've heard that some make a 2-1 exhaust that is larger but not a dual exhaust.

Thoughts?
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FLSTFI Dave

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #1 on: December 02, 2019, 08:34:15 AM »

My twin cam 117, is making 138.5 HP and 140 torque.  A long torque curve.

I am running a Fullsac Head pipe, the DX that he sells for all twin cams.  It flows plenty for the power I am making.

I am running 2.25 inch baffles, and do not need bigger. 

I do not believe a larger head pipe or bigger baffles would produce any better results.  I am sure there are some who feel it would. 

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fastfreddy

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #2 on: December 02, 2019, 06:33:10 PM »

if I remember correctly …. you have a V&H pipe... its ok, you need a more sensible muffler (2 inch baffle, is what I think) and a TUNE other wise your just spending money you don't need too. been there done that  :nixweiss: if your gona run it WFO  all the time then may be a bigger pipe would help, but hey we are ridding 1000 pound baggers not race bikes...  my 2 cents
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ultra13

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #3 on: December 02, 2019, 06:43:23 PM »

2x Fullsac system!
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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #4 on: December 02, 2019, 08:34:27 PM »


Note that Harley sells and promotes a higher flow larger diameter pipe two into one into two system for the M8's, so you're not the only person thinking they need bigger pipes (they don't offer that system for the Twin Cams for some reason, probably due to not having created and certified a an EPA legal version for the TC's)).  But before you go down that road you need to consider exactly how you ride most of the time.  The higher flow system may be fine for those with the head work and cams that support high rpm horsepower, but you may find yourself disappointed if you actually ride your bagger normally and not just WFO all the time.  Talk to one of the highly regarded tuners on the site, give him the particulars of your engine build and your riding style, and see what he recommends.  Bigger is not always better, in a lot of things.

JMHO - Jerry
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FLSTFI Dave

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #5 on: December 03, 2019, 08:03:30 AM »

Note that Harley sells and promotes a higher flow larger diameter pipe two into one into two system for the M8's, so you're not the only person thinking they need bigger pipes (they don't offer that system for the Twin Cams for some reason, probably due to not having created and certified a an EPA legal version for the TC's)).  But before you go down that road you need to consider exactly how you ride most of the time.  The higher flow system may be fine for those with the head work and cams that support high rpm horsepower, but you may find yourself disappointed if you actually ride your bagger normally and not just WFO all the time.  Talk to one of the highly regarded tuners on the site, give him the particulars of your engine build and your riding style, and see what he recommends. Bigger is not always better, in a lot of things.

JMHO - Jerry

That is very true in exhaust for a twin cam.  The 2.5" baffles really hurt low end torque compared to a 2" below 3000 rpm.  Many of the mufflers being sold for twin cams are 2.5 or bigger.  These sell very well, as everybody loves the sound.  I fell into the group until a well know tuner in FL showed my how crappy the Monster Rounds on my 2009 CVO 110 twin cam were compared to fullsac baffles at 2".  The torque difference below 3000 rpm was amazing, no huge dip like the V&H and higher torque by 5 foot-pounds, where you ride with the 2".  No loss of power till over 5200 rpm with the 2" and not as big a loss as there was on the bottom with V&H.

On my built 110, to 117 with 11.4 compression, bigger throttle body, bigger injectors, head work, and so on, build is in signature, 2.25 baffle is plenty, still smaller than the  popular baffles for sound.
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2018 FLTRXSE Gunship Gray  Traded
2017 FLHXSE  Starfire Black / Atomic Red  Traded
2015 FLTRUSE Abyss Blue / Crushed Saphire Traded
2013 FLHRSE5 Diamond Dust 117 Cylinders  Heads By HD Street performance, Comp 11.4,TW-9B-6 cam, 55 HPI tb, 5.3 injectors, woods Alpha directional lifters, Fullsac "D" pipe and 2.25 cores, TTS Tuner
2012 FLTRXSE White Gold Pearl / Starfire Black  Traded
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WildmanUltra

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #6 on: December 03, 2019, 05:44:09 PM »

I'm erroring on the side of all of your experiance as opposed to these few who are saying that the Twin Cam needs a bigger pipe.

Yes I'll be the first to admit I was stupid in listening to the parts guy at HD when he was selling me the parts for my bike. I should have waited and read more and asked questions from all of you who already had done all this. Trying to use the SEPST was my biggest mistake. I am already seeing a PV in my future again. I had one on my old bike and liked it a lot so I see no reason to go a different direction as far as that goes.

The Khrome Werks mufflers at this point are working since I installed the baffles but will have to wait until spring to see what they do with the PV tune. If they are the problem at that point then I'll swap them out for something else.

Yes I have the V&H Power Duals head pipe which is how this discussion got started on another forum. The poster said that the issue was my head pipe and that I needed a larger diameter pipe.
While I can say this theory might work when dealing with V-8 engines as many have pointed out here I don't see the reason in our exhaust.

As for the M8 engines having larger pipes I wonder if part of that has to go with the 4 valve heads? They need to breathe different from our Twin Cams? I don't know enough about this to be able to offer any experiance or knowledge.

Thanks for all the feedback and real world experiance.
 
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FLSTFI Dave

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Re: Thoughts on exhaust size for larger displacemnt Twin Cams
« Reply #7 on: December 04, 2019, 08:03:43 AM »

As for the M8 engines having larger pipes I wonder if part of that has to go with the 4 valve heads? They need to breathe different from our Twin Cams? I don't know enough about this to be able to offer any experiance or knowledge.

Thanks for all the feedback and real world experiance.

Stock M8 heads flow better than stock twin cam heads.  In fact a stock set of M8 heads flow very close to as good as my twin cam heads that were ported by Don at HD street performance. 

I am still trying to learn about what is need for exhaust on a built M8 motor.  I know some where there is a youtube video comparing M8 cams and two exhaust systems, one being the Fullsac again.  It did very well.  2.25 baffle and his MX head pipe. 

Steve has done a build with a M8, with his MX head pipe and 2.0 baffle and it was 114 HP and 150 torque.

So not sure yet that the M8  requires big exhaust either.

https://www.cvoharley.com/smf/index.php?topic=118283.0

What I have learned is there is no magic cam, or exhaust or intake or so on.  With a twin cam, its critical to select parts designed to work well with each other, cam and compression have to be matched, heads and intake have to be able to support the air flow needed, exhaust has to have enough back pressure.

I know enough to be dangerous, but am smart enough to ask professionals advice, and recommendations.  Like many will point out the the HD-259E cam is no good in the HD 117 kit for the 110 motors.  Its actually a very good cam, but the kit compression is way to low.  I built a 110, not bored over with that HD-259E cam and 10.8 compression, it was 121.8 HP and 121 torque.  Again Fullsac DX head pipe and 2.25 baffles. 

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2019 FLTRXSE Red Pepper / Magnetic Gray
2018 FLTRXSE Gunship Gray  Traded
2017 FLHXSE  Starfire Black / Atomic Red  Traded
2015 FLTRUSE Abyss Blue / Crushed Saphire Traded
2013 FLHRSE5 Diamond Dust 117 Cylinders  Heads By HD Street performance, Comp 11.4,TW-9B-6 cam, 55 HPI tb, 5.3 injectors, woods Alpha directional lifters, Fullsac "D" pipe and 2.25 cores, TTS Tuner
2012 FLTRXSE White Gold Pearl / Starfire Black  Traded
2009 FLTRSE3 Silver/Titanium  Traded
2003 Fatboy, real fire paint set, 95"
 

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