Aftermarket exhaust and fuel efficiency

[BigGinger]

Hi guys,

I want a louder exhaust; probably Scorpion.

what affect will it have ok my fuel efficiency?

thanks

 

[bigbird]

Depends on how you twist the throttle.
Otherwise, the back pressure reduction is negligible.
Most of the restriction is in the 2 into 1 exhaust header and the cat converter.
If you want slightly more efficiency, get an aftermarket link pipe with the Scorpion.
That will eliminate the cat, but still has the O2 sensor bung so you won't mess up the ECM.

 

[BigGinger]

Thanks for the answer!
Why would a set up with less restriction improve mpg?

to be honest I’m only worried about negative impacts. If the slip on won’t hurt the numbers then that’s fine by me.

 

[bigbird]

Why would a set up with less restriction improve mpg?

I'm no engineer, but having less exhaust restriction improves an engine's efficiency (mpg) and also increases power output.
That would be the reason that any competition engines have no mufflers, as well as using tuned exhaust pipes (headers).
A slip-on won't harm anything, including mpg, on your NC.

 

[BigGinger]

I think I’ll bite the bullet eventually then. Once I’ve upgraded the suspension first.
Thanks a lot

 

[bigbird]

I think I’ll bite the bullet eventually then. Once I’ve upgraded the suspension first.
Thanks a lot

I have a Delkevic 9" stainless steel on my NC.
Highly recommended.

Click on this link to some pics and a sound clip: ----> #32

 

[BigGinger]

I like the look and sound. It’s hard to decide because all videos sound different as different devices are used for recording. Based just on looks I like the scorpion titanium. I’m able to source parts at cost too so will pay under £250 if I remember correctly.

 

[bigbird]

Delkevic also makes other styles for the NC. From what I've read Scorpion is a popular slip-on in Europe.
Not so much in N. America.

Slip Ons - Honda - 2018 Models - NC750X - Page 1 - Delkevic

delkevic.com

 

[BigGinger]

I really like their titanium oval. I have a delkevic on my CBR600. Still looks new so that speaks to their quality.

 

[showkey]

Bigginger, no MOT inspections in Wales ?

 

[TheIronWarrior]

I'm no engineer, but having less exhaust restriction improves an engine's efficiency (mpg) and also increases power output.

Not strictly true, it depends on the engine design. Without Honda's TDP for this machine I can't say for sure what the impact of a change in exhaust would be.
In some cases, the restriction of the exhaust and exhaust length are important parameters affecting engine performance. The restriction and length can be intentionally selected so that the exhaust pulses (pressure waves) harmonize with the engine cycles at specific RPM to actually improve overall exhaust flow.
What I mean is that exhaust isn't a steady stream, it comes in pulses, one pulse per cycle (4 strokes) per cylinder. It is possible to set up the exhaust to work with these pulses to ensure a negative pressure in the exhaust header during the exhaust stroke, and more specifically during any valve overlap where both intake and exhaust valves are open, helping draw out more of the exhaust gasses. The more exhaust that comes out of the cylinder, the more air and fuel can enter on the intake stroke. Look up "exhaust scavenging" for more information if interested.
Exhaust design is only one part of it, too. The whole system from intake to muffler can be so designed to optimize efficiency and power.
Keep in mind the pipe diameter is going to affect the speed and pressure as well. In general, a larger diameter is going to slow down flow and increase pressure, so going too big will start to have negative effects on overall flow. Eventually the reduction in restriction is overcome by the negative impacts of the larger diameter.
It is also impossible to design the system to be optimized at ALL engine speeds, so there is likely a design speed (I'd guess somewhere around 5000 RPM?) that they used for system design and then just checked to make sure the system still worked decent enough throughout the rest of the rev range.

It's likely this engine isn't so finely tuned that you'll make too much of a negative impact with aftermarket exhaust components, but I don't think you'll see much of an improvement either.

Somewhat related, I've also seen it claimed that the most restrictive part of the system is actually the intake header. The theory follows that no matter how "free" or "optimal" you make your exhaust, the overall flow is still limited by the intake therefore negligible (if any) benefits even from a full aftermarket exhaust. I have seen nothing to back this up, though, and I expect Honda isn't in the business of sending their engine analysis and design out for free, so we may never know.