Why do these VF bikes have a collector box? why not just pipiework 2 into 1 or something simple? Does anyone know know? Also can anyone tell me which other exhaust systems will fit these bikes. My neta cans were knackered so I put these black standard ones on but it just sounds too tame now . Yes I know some people are just never happy .

If I remember correctly it has to do with back pressure in the exhaust system.
it increases the low end torque from the engine to give the engine a smoother power band through the rev range.
back pressure is important

Lloyd in Norwich[:)]

I’ve been wondering the same thing, here’s an article I found on exhaust theory that seems to explain it quite well, looks like the Honda stock collector is mainly for baffling and also to help with scavenging.


Crookys stainless collectors do away with the baffling and have a link pipe to help with scavenging.

The Delkevic cans and two inch link pipes with stainless collector I have on mine sound very deep and thumpy.

Always plenty to think about with these![:)]

I was told that the collector box was purely for noise regs as its the easiest way to get noise down before the silencers without needing a lot of extra tubing and then cans that stick out the back of the bike.


I am bumping old thread so I do not have to start another one. I searched for this topic on this forum and this thread seems like the place to share my thoughts.

On the picture above you can see two exhaust setups, one from my f2 with stock collector box and one from f1. I have ridden both bikes, F1 has different jets front and back and the bike generally did not loose any torque in comparison with my f2. Well as I felt it it had noticeably more power. Even with f1 fuel pump dead and f2 with working fine. This could be also due to different gearing of two bikes as I can finish the rev range on the f1 whereas the f2 struggles to achieve even its top speed at the moment. Both sets of carbs were rebuilt by the same guy.

In Subaru world people throw in unequal length headers to get that Subaru rumble sound and report no loss of power. And the f1 sounded amazing with that setup, much beefier than the f2 even with an aftermarket backpipes.

I will be throwing the f1 setup on the f2 without rejecting the carbs to see how the power and changes. I have no dyno except the butt dyno :wink: Next I will be testing f1 carbs on the f2.

It is a common misconception that opening up an exhaust system will increase horse power. Most modern engines rely on some degree of scavenging partiality burnt air fuel mix back into the combustion chamber. Just removing back pressure will increase noise, if that’s your thing, (in which case can I point you towards your local Harley dealer) but without appropriate adjustment to compensate for the lost air fuel mix you will NOT gain any power.

1 Like

I am looking at Ducati Pagnalve V4 and it does not have collector box. All back pressure is realized in the muffler. Akrapović does not know what they are doing? I do not think so. I will try to mimic that setup later, much later. Now I play with what I have.

I have 3 sets of mufflers that I will test.

And you are right - without fueling changes no loss or gain of power should be achieved. But I have set of carbs tuned for this exhaust and my f2 runs super rich even though it is setup by the book.

My F2 is quieter than a 250cc Kawasaki, I do not like that at all. At idle it is nice, rumbles up to 2.5k rpm nad than it goes quiet again. F1 without collector box was much better but not super loud.

Here is a video of sound comparison before and after collector box delete.


I have recorded 6.2G vs 5.8G acceleration on Yamaha My Ride application on my phone same day.
My butt dyno says the bike revs better above 7k rpm. Loss of torque is noticeable only in 5th gear below 4k rpm - I can live with that. And I like the sound aswell.

1 Like

Great video - the Sankei’s sound cool.

Now you just need to figure out how to attach a sofa to the back seat, foot rests to the handle bars and you can grow a beard, lie back and pretend you have a Harley! :smiling_face_with_three_hearts: :crazy_face:

The bike does not sound even close like a Harley. Sounds more like Moto GP bike now. Especially reved out to redline. Sound is unique and it is hard to record on a phone. There is no rumble which was present before at 2.5k RPM exactly.

FTR I do no like Harleys :slight_smile:

Hi pablo, like the sound of the sankie`s but all sound quiet compared to my 4 into 2 into 1 system that has the neighbours cursing at 5am as I leave for work! Not liking Harley’s is a sign of good taste.