When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've heard it many times and it makes sense that the factory headers are designed well from the factory for optimized performance as is and just choked up from the cats and EPA regulated tunes. Wondering if anyone has ever taken to the dyno to prove this? Does the factory header with slip ons out perform a 2 into 1?
NO. they will not out perform a 2 into 1. However, if you are comparing apples to apples. Only changing the header part of the exhaust the difference will be negligible.
Why do so many people believe that everything Harley has done from the factory is "optimized"?
If that were true, these bikes would have 200hp. For literally DECADES, Harley has been putting form over function. Their predominant mentality is what something looks like, not how it performs. Case in point, the Cross Bones. It's just that since Indian has been nipping at their heels they're started focusing more on performance, which is a good thing.
NO. they will not out perform a 2 into 1. However, if you are comparing apples to apples. Only changing the header part of the exhaust the difference will be negligible.
I'm not sure that it is that simple. I have dyno graphs for 107 ci. bikes that are set up close to the same. The first one is using a stock decatted header with stock mufflers with Full Sac 2" cores and big sucker air cleaner. The second one is using a Full Sac MX head with stock mufflers recored with 2" & 1.75 " cores and a heavy breather air cleaner. Both are running TTS 100 cams. They are different bikes and different dynos, but the results are very close to the same.
Then there is this from Fuelmoto. A 107 with Jackpot mufflers on a stock header vs. the same bike with a Jackpot header, Jackpot mufflers, and a better air cleaner. The first bike is still running the cats. So again, not apples to apples. The better air cleaner is probably good for 2 or 3 ft/lbs. and the removing the cat would probably gain 2 or 3 ft/lbs. So take that into consideration and they are pretty close. Also, looking at the stock bike dyno and the stock bike with mufflers and a tune, the gain was 3 ft/lbs and 3 hp.
As for a 2 into 1 out performing a 2/1/2, here are a couple dynos of the same bike, same dyno, different exhaust.
So what it boils down to is that a full system, 2 into 1 or 2/1/2 with mufflers, will cost $1000 to $1500, along with a tuning device of some type, $300 to $1000, and maybe a dyno tune, $400 to $600. Mufflers and decatting the stock head pipe, less than $500 and I have done this without tuning. Is the gain worth the cost?
Last edited by $tonecold; Feb 11, 2025 at 07:08 AM.
I'm not sure that it is that simple. I have dyno graphs for 107 ci. bikes that are set up close to the same. The first one is using a stock decatted header with stock mufflers with Full Sac 2" cores and big sucker air cleaner. The second one is using a Full Sac MX head with stock mufflers recored with 2" & 1.75 " cores and a heavy breather air cleaner. Both are running TTS 100 cams. They are different bikes and different dynos, but the results are very close to the same.
Then there is this from Fuelmoto. A 107 with Jackpot mufflers on a stock header vs. the same bike with a Jackpot header, Jackpot mufflers, and a better air cleaner. The first bike is still running the cats. So again, not apples to apples. The better air cleaner is probably good for 2 or 3 ft/lbs. and the removing the cat would probably gain 2 or 3 ft/lbs. So take that into consideration and they are pretty close. Also, looking at the stock bike dyno and the stock bike with mufflers and a tune, the gain was 3 ft/lbs and 3 hp.
As for a 2 into 1 out performing a 2/1/2, here are a couple dynos of the same bike, same dyno, different exhaust.
So what it boils down to is that a full system, 2 into 1 or 2/1/2 with mufflers, will cost $1000 to $1500, along with a tuning device of some type, $300 to $1000, and maybe a dyno tune, $400 to $600. Mufflers and decatting the stock head pipe, less than $500 and I have done this without tuning. Is the gain worth the cost?
Softails and touring bikes have completely different headers. Softails have the cats in the mufflers themselves, and up until now, have been 2 into 2 (with the exception of the sport glide), not 2-1-2.
I'm not sure that it is that simple. I have dyno graphs for 107 ci. bikes that are set up close to the same. The first one is using a stock decatted header with stock mufflers with Full Sac 2" cores and big sucker air cleaner. The second one is using a Full Sac MX head with stock mufflers recored with 2" & 1.75 " cores and a heavy breather air cleaner. Both are running TTS 100 cams. They are different bikes and different dynos, but the results are very close to the same.
Then there is this from Fuelmoto. A 107 with Jackpot mufflers on a stock header vs. the same bike with a Jackpot header, Jackpot mufflers, and a better air cleaner. The first bike is still running the cats. So again, not apples to apples. The better air cleaner is probably good for 2 or 3 ft/lbs. and the removing the cat would probably gain 2 or 3 ft/lbs. So take that into consideration and they are pretty close. Also, looking at the stock bike dyno and the stock bike with mufflers and a tune, the gain was 3 ft/lbs and 3 hp.
As for a 2 into 1 out performing a 2/1/2, here are a couple dynos of the same bike, same dyno, different exhaust.
So what it boils down to is that a full system, 2 into 1 or 2/1/2 with mufflers, will cost $1000 to $1500, along with a tuning device of some type, $300 to $1000, and maybe a dyno tune, $400 to $600. Mufflers and decatting the stock head pipe, less than $500 and I have done this without tuning. Is the gain worth the cost?
This is the kind of stuff I was looking for. Just a fun thought experiment I was toying with in my mind looking at new exhaust systems and the crazy costs they've gotten to. With forced induction so much can be left on the table because of exhaust design. It would make sense from factory and engineering points of view that any manufacturer would produce and exhaust system that maximizes the engine output within the constraints of the EPA. Look at the difference between the yamaha R1M or BMW S1000RR in europe vs NA. A simple tune change unlocks a huge potential even with stock components. Also just seeing the gnarly torque dip that happens with some inferior 2 into 1 designs also sparked this curiosity. I simply wanted to see if anyone has done the horsepower science of taking two identical bikes with the same cam and engine configuration and seeing the difference of what factory header and slips vs a full system would be.
Softails and touring bikes have completely different headers. Softails have the cats in the mufflers themselves, and up until now, have been 2 into 2 (with the exception of the sport glide), not 2-1-2.
While they may not be 2-1-2 like the touring models, where the exhaust goes into a large single chamber and then splits off into the separate mufflers, they are not true 2 into 2 exhaust either. They all have crossover pipes that allow the exhaust to equalize between the two pipes and mufflers.
Originally Posted by pgreer
I believe the cat converter is in the mufflers on FXBBS. M8 Touring bikes have the cats in the header.
Paul
Yes this is correct. The easiest way to get rid of the cats in a Softail is to change to aftermarket mufflers without cats. The '25 model Softails with the 2 into 1 exhausts have the cat in the header.
I have a 117 FXLRST with the stock head pipe and good louvered slip on mufflers. I do not see the big torque rise that some of the other dyno charts people post up with the same cam/air cleaner throttle body setup and a 2:1. The curve with the stock header is much flatter, and I'm seeing around 15 ft lbs less peak torque. The max hp on MY dyno is about 5 less than what everyone else posts too. I don't give that much credence, since they (dynamometers) all seem to vary, I'm more speaking to the shape of the curve. This previous statements are only pertinent to softails. I think touring bike exhaust is a different deal. I did test the stock header with cat vs a Jackpot header with the same mufflers on my 24, and I saw basically no difference with just the header change.
The stock M8 head pipe with the cat removed, for a fact, is a solid performer. Sheffer Performance HD has many dyno sheets even with 124-128 builds using the stock decatted head pipe with great peak numbers and torque curves. Of course the muffler/cam selection and tune also play a part in that. Will it make better numbers than some aftermarket units? Maybe not. But it makes sense from a financial standpoint if you don't want to pay a vast sum of money for 5-6 extra HP that you won't be thinking about while riding anyways. But some people will spend that to post dyno numbers on Facebook.
I'd have to do some digging but could find my own dyno sheet since my bike uses the stock head pipe. It runs great.
Slideshow: Jason Momoa's latest restoration project blends 1920s Harley-Davidsons with modern electric technology, creating some of the most unusual hybrid motorcycles ever built.
Harley-Davidson Fat Boy Becomes a Dark, Decepticon-Inspired Custom
Slideshow: Killer Custom's latest build relies on styling changes rather than performance upgrades, giving the cruiser an entirely different personality.
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Slideshow: The bar-and-shield logo shows up on far more than motorcycles, some of the company's most unexpected products have nothing to do with riding.
Slideshow: From the troubled AMF years to modern misfires, these bikes earned reputations for reliability issues, questionable engineering, or disappointing performance.
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Slideshow: The Swiss custom shop has taken a Harley Softail and stretched it into something so long and low that it looks closer to a rolling sculpture than a conventional motorcycle.
OEM Headers performance
