4 into one exhaust header design

[LakeWylieJoe_imp]

Has anyone else noticed the header pipes on the 2014 standard, equipped with a four-into-one collector system, are intentionally designed to have uneven lengths?

With a standard crank design of an inline four, a cylinder fires every 180 deg of crank rotation. The most efficient exhaust scavenging would result from headers that were equal length. The pipe for the #1 cylinder, which has the longest run to the collector on the far side of the bike is intentionally made even longer than it needs to be, with an out-of-path bend. #2 has been made longer as well.

In an equal length setup, the #3 & 4 would be bent to add a little length so as to match #1 & 2.

Any thoughts?

 

[Lord Popgun]

Helmholtz resonator

Sorry, that's all I know about exhaust theory

 

[LongRanger_imp]

Form, not function.

 

[Frulk_imp]

I trust the engineers at Honda explicitly. I can’t imagine that they didn’t consider what the impact on performance and reliability the pipe lengths would have on their design. Based on that I’m guessing the impacts were negligible.

 

[GoldOxide_imp]

If there was a noticeable issue, it would have failed at Design Verification. Maybe it did, but they addressed the issue in one or more best know methods (e.g. popgun's resonator remark).

 

[SportsterDoc]

Perhaps for oil filter access?
With 0-60 in 3.3 seconds, I would not be concerned.

 

[LakeWylieJoe_imp]

That's probably the reason, as engine output wasn't the chief goal with the 1100. In any event, the 4 into 1 set is vastly superior in exhaust scavenging compared to the 4 into 2 with a crossover pipe of the other CB1100 models.

 

[SportsterDoc]

HP was not the prime objective, but overall performance is very pleasing.

Just before I replaced stock tires at 10,579 miles, I did a few hole shots. Above 4,000 RPM, full throttle, the rear broke loose and went a bit sideways...more than once...and the stock Dunlop was not slick...quite a bit of tread left. Hitting over 60 MPH in first gear in 3.3 seconds may not match a crotch rocket, but still a thrill.

86 HP @ 7500 RPM
65.6 ft lbs @ 5700 RPM
0-30 1.2 seconds
0-60 3.3 seconds
0-90 6.8 seconds
0-100 8.6 seconds
1/4 mile 12.11 seconds @ 109.25 MPH

 

[LongRanger_imp]

Hi Doc, we've missed you. Hope you're doing well.

 

[alprider]

it can be a desing-construction thing (examp. access to the oil filter)

but

an exhaust is a highly complex matter ( not just in terms of sound)!

different gas pressures or flow velocities resulting from different pipe lengths and shapes....and bringing them together in the right place , like 4into1

or why is the 4in1 considered sportier sometimes (power) ? why for what we have sometimes a "interference tube" at the exhaust, my honda VTX 1300 had it ?

well i cant find a english site...but with the online translater

https://www.motorradonline.de/zubeh...leistungsvergleich-bei-akrapovic-volles-rohr/


and I quickly found no scientific page on gas flows (speeds/pressures) in (exhaust) pipes.....

 

[alprider]

or short

i consider the original / stock exhaust to be the best compromise from all factors ; design , constructive/ functionality , power , sound, consumption....

bcos i hate absolut extra louder and i need no halfe hp more bcos i drive on racetracks wehre is every 1/1000 sec top important

 

[jtopiso_imp]

it can be a desing-construction thing (examp. access to the oil filter)

but

an exhaust is a highly complex matter ( not just in terms of sound)!

different gas pressures or flow velocities resulting from different pipe lengths and shapes....and bringing them together in the right place , like 4into1

or why is the 4in1 considered sportier sometimes (power) ? why for what we have sometimes a "interference tube" at the exhaust, my honda VTX 1300 had it ?

well i cant find a english site...but with the online translater

https://www.motorradonline.de/zubeh...leistungsvergleich-bei-akrapovic-volles-rohr/


and I quickly found no scientific page on gas flows (speeds/pressures) in (exhaust) pipes.....

maybe because it is lighter

 

[LakeWylieJoe_imp]

For an inline four with a standard firing order (no cross-plane trickery with the crank), the 4 into 1 provides the most efficient exhaust scavenging. The pressure pulses of exhaust gases travelling down the pipes at regular intervals creates a venturi effect at the collector which helps draw the last of the spent gases out of a cylinder that is completing an exhaust stroke. An optimally designed system will be a bit more efficient and/or powerful over a given rpm range.

As a bonus, a 4 into 1 has less mass than a comparable 4 into 2 system made of similar materials.

For turbo or supercharged engines, this is not a concern. The boosted intake charge blows the spent gasses out during the short valve overlap that occurs at TDC. In such engines, the individual pipes don't even need to be joined as no scavenging is needed.

See this excellent video:

 

[emptysea]

Helmholtz resonator

Sorry, that's all I know about exhaust theory

You have an exhaustive knowledge, PG.

 

[Lord Popgun]

I LOL'd at work MTC. Now my co-workers are looking at me...

 

[alprider]

buuuuut we have no superrcharged/turbo engines..and so its just a bit science how you get the best header/collector - air flow, suction effect ...aaand the back pressure (right term ?) also plays a role in relation of torque...
isnt?

 

[alprider]

but i spreak from the pressure in the headers and not in the endpart of the exhaust , yes there its better if is nothing more inside

in the text ( my link) from this exhaust company Akrapovic is it some explained too

 

[LakeWylieJoe_imp]

That's a good video.

 

[SportsterDoc]

Hi Doc, we've missed you. Hope you're doing well.

Very kind of you!
Doing very well...lots of trips to ranch with grandsons.
Still have a double image when looking very far right, but not an issue.
Trip after snow storm of Nov 29 was first time in 19 years I had to chain-up 4WD the last 1/2 mile.

 

[alprider]

MORE DETAILED EXPLANATION.

well yes It has been a long time since I have dealt with the topic...amongst other things I now got a little mixed up the 2 + 4 stroke too ...

now yesterday evening i took time and browsed the net and sorted the individual puzzle pieces again...

too terms like : low rpm-engines and thin tubes, interference pipes, the importance of valve timing.......

the little fresher has done well..