Interesting exhaust comparison ..

Fast Lane

Fast Lane

Club Member
Here's a chart from the dyno today that shows the difference between exhaust systems. The build was a 103" Twin Cam, Cycle Rama 570-2 cams set at 10.25:1, my Street Port Plus heads, stock throttle body and injectors and the stock 2007 header pipe (no CAT) with a pair of Vance and Hines oval mufflers. I also did exactly the same build a few months ago, the only difference being the exhaust system. The earlier build had a Vance and Hines Power Duals header system and Bassani Mufflers. We thought it would be interesting to overlay the two charts. There's a difference of 4.84 in torque and 7.73 HP in favour of the Power Duals. Not just the numbers though. You can see how the exhaust influences the position of the peak TQ and HP. The Power Duals and Bassani mufflers bring in the peak TQ 340 RPM earlier and the peak HP occurs 360 RPM later. The build is EXACTLY the same, the only difference being the exhaust systems and the temperature and humidity in the dyno room at the time of tuning. These two builds will feel very different to ride. Never underestimate the influence your exhaust system has!
Exhaust comparison labelled.jpg
 
Re: Interesting exhaust comparison ..

Typical Glen, younger, better looking, faster rider and more bloody power, I going for a sulk now.
 
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Yes glen, and I was hoping to at least see you in the distance, as you pull away....bloody youngsters..
 
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So essentially Harley is giving customers a poorer-performing design of exhaust than the aftermarket..... for EPA reasons? Before your comparison here, I would have anticipated the results to be near identical ESPECIALLY with the cat gone.

It would surely take some work to do that deliberately......
 
Re: Interesting exhaust comparison ..

Like everything on stock bikes Dave - built to a price and not a performance standard.

The EPA compliance is taken care of by the weak (14.6:1) tune that all new bikes leave the factory with. The combination of the weak mixture and the CAT keeps the pollution police happy which allows the bikes to continue being sold. I doubt that any gas flow research goes on when designing a stock system - the aforementioned compliance and aesthetics are more important to the masses than performance. Saying that the FXDR exhaust team must have been tripping when they designed that thing. For example most riders like the symmetrical look on the Tourers so to achieve that the rear header pipe splits into two via a 'Y' shaped profile where it attaches to the rear exhaust port. This was the case on this bike. Could anything be worse for flow? Onto that in a minute.

An immediate doubling of the cross sectional area as the exhaust pulse enters the pipe so the gas velocity immediately halves in speed and pressure as it leaves the port. You won't see a mess like that on any aftermarket system. Similarly again on the Tourers, some of them have the front pipe leaving the cylinder and running along the frame rail towards the rear muffler. Just before the muffler they then have a point where the rear cylinder header joins the same pipe. This is the opposite of the last situation as you have a 1.75" pipe discharging gas from one cylinder and then another 1.75" pipe discharging the same amount of gas at the same pressure is dumped into the existing flow path causing an instant doubling of pressure at that point. None of this kind of stuff is conducive to performance.

Others have a pipe that goes underneath from the right side to the left of the bike that attaches to a bracket behind the transmission. Here, the pipe goes from 1.75" round to nearly flat so that it fits in the bracket before opening up back to round to accept the left muffler. Exhaust design has a HUGE effect on the performance characteristics of a performance built engine. Not so much a standard engine as all of the components are so mild that the best pipe in the world can't improve on low lift, low duration cams, low compression and poor head design but once these factors are improved then the exhaust becomes more of a major player and can either make or break the build.

There are good and bad in aftermarket designs too though. The majority of V & H systems are all designed and tested on stock engines. You have to look further to the likes of D & D, Rush, Burns, RB Racing, Bassani and a few others to find something that is tested and designed for use on higher output engines. Throw a pair of V & H Short Shots onto a 117" build and see what happens. Milwaukee 8 heads are extremely sensitive to exhaust efficiency. Much more so than the conventional two valve heads ..
 
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Re: Interesting exhaust comparison ..

I don?t know if any of you follow Blockhead on YouTube but he is currently posting videos of his Low Rider S 131 build. What I find interesting is that he has installed the 131 kit and run it on the dyno with a 2 into 2 Bassani exhaust. He is using the H-D tuner. He is then going to run it again with a 2 into 1 and a Thundermax tuner. Will be interesting to see the difference in numbers.


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Looks like a much better initial throttle response on the V&H set up. I can understand how that would feel better on take off. That power climb around 4k is interesting.
 
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The courier delivered my ultra today, so had a 20 mile ride, what a transformation, if this is what its like with a poor exhaust system it will do for me ,112 tq and 92.5 hp best money I have ever spent on a bike, top marks to alex at fastlane, cant recommend him enough. may even go as far as to buy him a beer at the lakes sometime in the future.
 
Re: Interesting exhaust comparison ..

Fast Lane said:
Like everything on stock bikes Dave - built to a price and not a performance standard.

An immediate doubling of the cross sectional area as the exhaust pulse enters the pipe so the gas velocity immediately halves in speed and pressure as it leaves the port. You won't see a mess like that on any aftermarket system. Similarly again on the Tourers, some of them have the front pipe leaving the cylinder and running along the frame rail towards the rear muffler. Just before the muffler they then have a point where the rear cylinder header joins the same pipe. This is the opposite of the last situation as you have a 1.75" pipe discharging gas from one cylinder and then another 1.75" pipe discharging the same amount of gas at the same pressure is dumped into the existing flow path causing an instant doubling of pressure at that point. None of this kind of stuff is conducive to performance.

Others have a pipe that goes underneath from the right side to the left of the bike that attaches to a bracket behind the transmission. Here, the pipe goes from 1.75" round to nearly flat so that it fits in the bracket before opening up back to round to accept the left muffler. Exhaust design has a HUGE effect on the performance characteristics of a performance built engine. Not so much a standard engine as all of the components are so mild that the best pipe in the world can't improve on low lift, low duration cams, low compression and poor head design but once these factors are improved then the exhaust becomes more of a major player and can either make or break the build.

There are good and bad in aftermarket designs too though. The majority of V & H systems are all designed and tested on stock engines
Click to expand...

thought pressure and speed of gas due to volume changes had an inverse relationship so doubling one reduced the other??

the under cross pipe on tourers is a snake in the grass. As Alex says, flattened to make space so flow characteristics all limited by this bit of pipe. Stock Harley touring silencers are not flow symmetrical. The left side has a much smaller baffle internally. The intention is not to have too much flow take this route, the journey via the left is also crazy long and way off desirable equal length header before the mufflers objective. I believe the whole thing is designed to block the flow taking that hard right turn and follow along to the right muffler and operate as a 2:1.

Aftermarket slipons are symmetrical flow (same size baffles) but often have the flattened cross pipe. Just swapping mufflers with stock headers will improve looks and make a ?big boy pants? sound. Performance? Nah.

i also think one of the reasons the MOCO restricts flow to the left is to keep rear tire temp under control, this is likely to be an idiotic fantasy but seeing the temp and corresponding pressure rise since fitting a TPMS under all riding conditions started the worms wriggling in my head and I blame the non flattened cross pipe from the Power Duals which along with the less restrictive silencer on the left creating a BBQ effect on the tire. Hence the cupping challenges I have been facing. But could just be all in my head

will confirm after I fit my Bassani 2:1 over the winter

V&H have confirmed many times their design philosophy is not about performance but satisfying the large market made of of people that care about show, not go. They design great looking pipes (I still look at pictures of the V&H Propipe on my Softail thinking how much more pretty they were compared to the Supertrapp now fitted and providing far improved performance) and are extremely well put together. Perfect for those where that is all that counts.
 
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