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Old 05-04-2012, 02:09 PM   #1
Voltaire OP
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Racer Exhausts 2 into 1 VS 2 into 2

I have a 2 into one on my race bike bike mainly as it became available and seemed like a good idea.
Its unequal length and the 'muffler' has been gutted and a plate with holes fitted....its very quiet...road legal quiet.
Last weekend I had a ride on a r100 with 2 into 2 and owner/rider/builder said " look at any pictures of BMW racers and they have 2 into 2.
The bike goes well but it would be good to compare.
Any thoughts ?
I have ditched the filters and am waiting on trumpets from Bevel Heaven.

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Old 05-04-2012, 05:49 PM   #2
motu
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BMW knows more than you and any alteration from stock the bike will lose HP.

I've had the standard system with standard mufflers (rotted, so not something to base my later experiments on) then short mega's, then unequal 2 into 1 with Supertrapp and now equal length with Supertrapp. I'm happy with it now - I get good top end and really good mid range. I don't race, and for my roads operate in the 4,000 to 6,000rpm range, with 7,500 being available if I need it and 8,000rpm for run away wheelspin on gravel.

I think the Supertrapp is the secret - the rest of the system doesn't really matter, you can tune it all out with the muffler.
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Old 05-04-2012, 05:53 PM   #3
Voltaire OP
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Quote:
Originally Posted by motu View Post
BMW knows more than you and any alteration from stock the bike will lose HP.

I've had the standard system with standard mufflers (rotted, so not something to base my later experiments on) then short mega's, then unequal 2 into 1 with Supertrapp and now equal length with Supertrapp. I'm happy with it now - I get good top end and really good mid range. I don't race, and for my roads operate in the 4,000 to 6,000rpm range, with 7,500 being available if I need it and 8,000rpm for run away wheelspin on gravel.

I think the Supertrapp is the secret - the rest of the system doesn't really matter, you can tune it all out with the muffler.
Yes BMW does know more than me 8000RPM
I was hoping to get some Brit bike guys chip in as they are more flexible with specifications...
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Old 05-04-2012, 09:05 PM   #4
Houseoffubar
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A 2 onto 1, or 2 into 2 exhaust have very little difference in HP. The 2 into 2 has the advantage of making good power, while being quieter than the 2 into 1 system.

BTW Supertrapp exhausts make good spark arrestors, they however are the worst muffler made for horsepower. The disc system simply increases back pressure by choking off the exhaust until it is acceptably quiet (usually after losing several HP) It is literally the same as welding a washer to the back of your exhaust to restrict it into being quiet.
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Old 05-04-2012, 09:22 PM   #5
motu
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A race core Supertrapp certainly doesn't reduce noise...maybe with one disc but not with anymore. I've put less on mine until it reduces power, but the noise stays the same. I do noise tests as part of my job - we test at 2,500rpm for a 2 valve twin and it takes an effort to keep mine at 97db. I have to fail over 97db, although 100db is the limit for road use.
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Old 05-04-2012, 09:40 PM   #6
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As a brit bike rider , I would suggest you fit star washers.
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Old 05-05-2012, 01:45 PM   #7
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As a brit bike rider , I would suggest you fit star washers.


And get drip tray?
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Old 05-05-2012, 02:09 PM   #8
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Quote:
Originally Posted by motu View Post
BMW knows more than you and any alteration from stock the bike will lose HP.

If the engine, carbs & ignition is kept standard maybe - but if any performance mods are carried out, such as gas flow, larger valves, bigger bore, decent flatslide carbs, etc; a decent free flow exhaust will aid power - FACT


I've had the standard system with standard mufflers (rotted, so not something to base my later experiments on) then short mega's, then unequal 2 into 1 with Supertrapp and now equal length with Supertrapp. I'm happy with it now - I get good top end and really good mid range. I don't race, and for my roads operate in the 4,000 to 6,000rpm range, with 7,500 being available if I need it and 8,000rpm for run away wheelspin on gravel.

Every bike will differ with production tolerance variance, wear & tear differences, etc, so what may suit one engine will not necessarily be good for a similar bike which had had years of different conditions.

I think the Supertrapp is the secret - the rest of the system doesn't really matter, you can tune it all out with the muffler.

Not 100% true! The length & diameter of the pipes is critical to ensure correct resonance to suit the required power output: either low end torque or top end bhp, or good mid range.

Basically, soon as you start messing with any part of the engine it will have a knock-on effect and to get it running right will need more time & money spent matching the unit as a whole. But isn't that what makes bikes fun
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Old 05-05-2012, 02:21 PM   #9
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Quote:
Originally Posted by Pigford View Post
Basically, soon as you start messing with any part of the engine it will have a knock-on effect and to get it running right will need more time & money spent matching the unit as a whole. But isn't that what makes bikes fun
true, I've only had the bike running for what amounts to a few hours on the track, It runs fine considering so much was changed at once when we rebuilt the $275 engine..... heads skimmed 1mm, sports cam, inlets opened from 32 to 36 with some Dells fitted.
It is fun looking at all the what ifs and maybes.
Sorting out the programmable ignition I got for it recently this week .
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Old 05-05-2012, 05:34 PM   #10
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Quote:
Not 100% true! The length & diameter of the pipes is critical to ensure correct resonance to suit the required power output: either low end torque or top end bhp, or good mid range.
Yeah, I do all those calculations too - my exhausts aren't something I slap together with some scrap pipe. I've just worked out what size 1/4 wave resonator I need to cut noise at our 2,500rpm test speed....and it needs to be over 2 metres long!
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Old 05-05-2012, 05:40 PM   #11
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Depends how much you want to spend, but getting a decent system designed according to the rest of what you've done with the engine's always the optimum. Wobbly designed not only the 2-stroke systems on my TZ Yamahas, but also the 4-2-1 on my CB1100, and for this last we have 6hp more on the dyno from the exhaust alone compared with a yay whizzo brand one from the USA.

In general terms, on all my Norton twin race bikes, we always had the best power on the dyno from 2-2s, but the most even spread from 2-1s.
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PJay screwed with this post 05-06-2012 at 02:27 AM
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Old 05-05-2012, 06:49 PM   #12
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Volty has a cross tube on his headers as does a certain British bike, are these a help or hindrance. My understanding is they help midrange but do they detract from the top end ?.
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Old 05-05-2012, 07:29 PM   #13
Voltaire OP
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Quote:
Originally Posted by PJay View Post
Depends how much you want to spend, but getting a decent system designed according to the rest of what you've done with the engine's always the optimum. Wobbly designed not only the 2-stroke systems on my TZ Yamahas, but also the 4-2-1 on my CB1100, and for this last we have 6hp on the dyno from the exhaust alone compared with a yay whizzo brand one from the USA.

In general terms, on all my Norton twin race bikes, we always had the best power on the dyno from 2-2s, but the most even spread from 2-1s.
hmmm Wobbly does exhausts too....I just got an ignition off him.Must ask him.
Hey Motu /WOF man...why is my almost empty muffler so quiet?
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Old 05-05-2012, 10:05 PM   #14
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You get out what you put in - you are not putting much into the exhaust....so not much comes out.
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Old 05-06-2012, 01:59 AM   #15
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I have run my modified BMW engine with both a 2 into 1 and now a 2 into 2. The 2 into 1 was a siebenrock sgs2 system super light well made and provide good power and torque it cost about 900. I now have sold that and fitted a 2 into 2 from Kiehen (about 600) its a sports system for my dakar replica. I have not run this far yet but the short test ride I done with it seemed to give excellent power and torque. I had advise from Klaus at HPN and he stated that in their experience the airhead generally worked better and gave better performance on a 2 into 2 system. I should be doing a 500 mile ride in two weeks time to run the project bike in so should be able to report back on the comparison between the two bikes. I may even get another Dyno test run then I would have a direct comparison between the two exhausts. As I have the results for the 2 into 1. Jake.
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