Exhaust design?

canolman · Nov 15, 2017

628cc
If you were to design an exhaust system from scratch, ideally where would you join the twin header pipes to the collector? How would power and torque change if the join was made close to the head or a long distance away?
Many thanks

paolo6 · Nov 15, 2017

Best person to ask would be the dohc guy ...I read a few thread months ago about it on the Internet there is a lot to talk and also size is involve ...myself personally I would be also adding powerbomb to the list an exhaust with no reversion should be a good one (still diameter and lenght is involve) ....i have thought to have a system similar to aprilia sxv (not now but next year maybe) just love that bike

I am pretty sure akrapovic have the collector with a different lenght, standard one is different (worth looking into that ) or what other manufacturers went

plumbbob · Nov 16, 2017

Hey Canolman,
I've been looking at making headers for my Flat tracker to bring the pipe down the right hand side. There are so many different calculations, options (things to get wrong) I'm going to try and copy the factory dimensions as closely as possible. I reckon those Swedes did a pretty good job.

Carl.

canolman · Nov 16, 2017

Thanks Carl, I'm looking at a few ideas, one being twin outlets down the front of the motor and joining about half way under, just wondering if that is a bit long?
Its all about space on this build, something I have very little of!

plumbbob · Nov 16, 2017

The standard length of header would be close to reaching under the engine, you may need the join just before.
DrC or Bushie must be the guys in the know for this.

paolo6 · Nov 16, 2017

Calo do you live in south Wales? If you need some measurements on mine dual exhaust(sr one) next spring I will be around the area I can show you it ...but mine goes where the starter motor is, shock is a problem as the reservior is the way but I cold help you out with that as I might not need it

TomTom · Nov 16, 2017

Its really difficult to say whats best, normally empirical testing is the cheapest. There are a few softys out there like maxpipe and vannik, if you have the time and patience to put the numbers in with accuracy.

I had the opportunity to try out an mx bike in the dyno with a good customer, I told him to bring an exhaust that you can change the length on and well have a go, and so we did and the longer it got the better results all over the range, we even had it protuding the rear fender.
We directly went back to the reference length and it was spot on power with that, so no illusion (no change of test environment that is).

canolman · Nov 16, 2017

Many thanks to you all. What I'm trying to determine is what effect using long twin outlets would have on power and torque? On our possible redesign making the join under the engine solves so many problems. No space in front of the engine because of the radiator and suspension travel, no room either side because of the bodywork! Overall length is easy to play around with on a track bike.

TomTom · Nov 16, 2017

I dont think any, summed area and their length is it in my opinion.
Pretty much all manufacturers did separate pipes at this time, fashion maybe?

Dr_C · Nov 16, 2017

canolman said:
628cc
If you were to design an exhaust system from scratch, ideally where would you join the twin header pipes to the collector? How would power and torque change if the join was made close to the head or a long distance away?
Many thanks

Well, the fun thing with exhaust design is that it is still involving some "black magic", whereas most other things in combustion engineering have well developed theoretical models.

All other aspects aside, the wizards are stating that the effect you want from the reflected wave will be stronger if kept together. Meaning that joining the pipes as early as possible after the ports, is beneficial. It will not change the characteristics, but make the effect stronger and possibly more focused in the rpm band. Keeping the flow in just one pipe will reduce the media to wall pressure loss, also pointing in the direction of keeping the exhausts in one single pipe for as much of the distance as possible.

Now the Husaberg exhaust ports are pointing in different directions, making it less optimal to join the primaries swiftly, out of pure pressure drop reasons... The best thing would have been to join the ports already in the cylinder head. But then there is sometimes no room for a thick primary tube between the engine and the front wheel or water cooler...

I do not think that the location of the joint (!) will play a key role in the characteristic. At least not compared to the length and diameters of your whole system!

canolman · Nov 16, 2017

Thanks Doc, the system I'm using now the join is very close to the head and because of the angled ports is an absolute bastard to fit! I'm using a 2-1-2 system now, very heavy. The new idea is a single pipe and silencer with the diameter getting larger from the ports onward, ending in a 51mm straight through end can.

plumbbob · Nov 16, 2017

Just need a pipe bender and welder now then Canolman!

canolman · Nov 16, 2017

plumbbob said:
Just need a pipe bender and welder now then Canolman!

Or a local lad who designs systems for rally cars. Fills the pipes with gas before welding, stops the weld from penetrating. Perfectly smooth joins.

Bergfest · Nov 16, 2017

These are dimensions from double muffler made for german racing team by Ricardo engineering. More torque + noise reduction

Bergfest · Nov 17, 2017

Here you can see what some germans made years ago during winter time.
The did what you are talking about. Maybe not a serious help - more a fun comic:

mad mäxla e.V. supermoto & monkey club Kirchheim / Teck

Choose at menu: Projekte Boddle SM
Then: MAD MÄX 4 - 1 till MAD MÄX 4 - 13

canolman · Jan 29, 2018

1.2mm stainless stepping up in size finishing at 51mm into silencer. The pipe was filled with gas before welding, this gives a smooth join on the inside of the pipe.
I've yet to weigh it but it's significantly lighter than what I bodged on originally

TomTom · Jan 29, 2018

Looks nice indeed, if its too loud you can just take the output diameter down without loosing any power and have it more quiet

2x35mm Inner diameter is enough for twice the engine volume without restricting output is what Ive found, take it for what you want.
For a v-twin, but 35 any day for a single.

Rainerio · Jan 29, 2018

Really nice welding job.

plumbbob · Jan 29, 2018

Looking good.

lvspeed · Jan 29, 2018

pipe lore

Hello Cano. Very cool project there. One imagines a racer like that is not overly concerned about low end power. But acceleration is essential. Long headers, as in prior to collector, give better mid-range and up pull. Short headers get you better low rev response. Your crossover or H pipe has to be right where the discolouration from exhaust heat stops. Thousands of rodders and racers run the engine as intended for while, then apply the H pipe in the right place. Gotta service a race bike all the time anyway. A single header pipe thinks the first restriction is the collector, so these work like a long header. Just not near as strong a pull as the dual pipes our Husabergs already have. You want all the volume you can get upstream of the collector. You sure you don't have space for a high pipe? Nice to get hot headers away from under the engine. Good luck, L

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