2 into 1 Exhausts

My race BMW currently has a rather horrible 2 into 1 on it, previously I was running a 2 into 2 with Commando mufflers.
I have not done any back to back testing but have kept the 2 into 1 because its lighter and sounds frikken awesome with no internals.
I'd like to make up a proper 2 into, my Triumph mate had his racebike dynoed and the guy said to ditch the 2 into 2 as it was holding back 6 2 into 1 HP.
Mate says that all the Triumph guys say a 2 into 2 is best. Dyno guys said its the best they know.

Any thoughts from the panel?
From what I have gleaned from the the net the stock 38mm should go to 41mm out of the head and then into a 50mm collector at " a certain distance", then into a muffler. Details are light.
Engine is 1000cc, 42 inlet, 38 exhaust, revs to 8000.
Picture does not show the muffler, but its a gutted Emgo reverse cone with no insides.
Pipes are uneven length and with a 90 degree bend....it was lying around. :roll:

Without back-to-back testing, who can say what is best for YOUR bike ?

Unequal lengths doesn't sound optimal either.
Hedging your bets ?

By and large, 2into 1 are made by most aftermarket exhaust manufactures because they are cheaper to make.
As a general rule and I believe this was discovered by Dr. Gordon Blair a 2-1 can work; but this involves a lot of experiment in combination with a dyno to obtain the results.

blair-into-into-exhaust-system-t17077.html

Many different bike makers have used different methods like the big and cumbersome one on the Honda CX500 which has 2 internal pipes Inside the collector box feeding some of the exhaust gas into the opposite silencer – a real work of art, if I may say so. This supposedly boosts mid-range power but you will have to compare them back to back with a 2-2 on a dyno to see the difference.

The Factory JPS Nortons all used 2 into2 with long taper meggas,the Dunstall system were 2 into 1 and back into 2,with decibel silencers that were designed by Dr Gordon Blair at Queens University Belfast ,and these guys did a lot of two stroke expansion development work and porting work for Yamaha works racers,that was one reason Ray McColough was so quick,he did race the development hacks.
Dr Gordon Blair was a genius on all exhausts,he did work with Colin Seely G50/7R racers.
One thing I found out talking to an exhaust specialist was when an exhaust pipe enter a collector box they must protrude about an 1"into the box.
Coming back to the JPS Norton Racers they tried various methods of the exhaust systems but they all were 2 into 2.

Norton did supply a 2-into-1 exhaust for their FIM F750 racer kit.



Ken

Nortons also supplied a 2-1 exhaust for the circa 1961 and thereabouts (road) dommies.
Vic Willoughby tested such a bike against a twin exhaust bike (at MIRA) and found the 2-1 gave it some more mph.
Nortons claimed more hp for it on the dyno too, but only above 4500 rpm.

2-1 are very fussy about the length to the join and the total length too.
Much dyno time to find the best lengths ?

It depends a bit on what you want out of your motor. I always try to avoid megaphonitis and the really sharp cam spot, they make the bike harder to ride especially when you are going very fast around tight bends with the gearing not quite right for the circumstances. There are three main parts to the two into one - the header pipes, the collector and the tail pipe. I believe the tail pipe resonates at twice the frequency of one header pipe. I obtained the header pipes on my system are from a friend of mine who was making after market pipes for the Z900 Kawasaki - the lengths seem right. A most important thing is that the size of the outlet of the collector and the tail pipe must not the smaller than the total cross sectional areas of the two header pipes, and the lengths of the header pipes should be almost identical to each other. I use header pipes in which the ID exactly matches the ID of the exhaust stub, and the stub has no taper - it matches the ID of the outlet of the port in the head. My two into one exhaust actually works very well.

Unequal lengths of header pipes is sure to introduce unequal power output from the cylinders....leading to an induced vibration.

Slick

Boy Howdy did Peel's 2-1-long mega work a Trip on me but only after disappointing results trying this and that on guts in and out of mega and type of exit, 3" wide open, super trap and end cap with big hole, that finally did the trick for Peel. Need equalish headers in a 360' twin so the bounce of sonic waves is similar side to side so can actually tune for each jug's exit pulse extracts the following one as well as help intake not to blow though or exhaust back out carb. One less muffler and mounts and couple feet less tubing helps about a hp of mass lost. Peel lost ~ 9 lbs this way from the heavy DS. Interesting details Alan on the x-sections and volumes to keep in mind on trial and error sink or swim attempts. Another pleasing thing I obtained with Peel 2-1-mega-end cap hole was a deepening and mellowing of the notes - At Less than WOT plud not stalling or hesitating to lug at hi throttle low rpm though loud jets of purple-orange flame roared out on WOT.

On my Triton I kept cutting back the outlet of the collector and matching the outlet to the megaphone with larger diameter pipes welded in until the bike regained power in the mid-range (8000 RPM). I'd lost a bit off the top but at least I started to get decent lap times. I don't know much about the theory. It might be smart to find a pipe that works, and then work backwards.

Being involved with Norton Racers I found that The Norton is quicker in lap times if you use the Torque of the motor and found a standard flywheel to be better and
a Norvil 2 to 1 exhaust,good porting a pete williams race cam,and vernier cam sprocket,using a Rickman frame,with metalastic swing arm bushes instead of taper roller(this gives the rider warning when on the limit) this is on advice of John Hartle who did a lot of development work on a rickman G50 at mallory park leicestershire in 1967.and an important one this an Oil tank instead of oil in the frame,all this gave very good results.word of warning on Rickman frame they break where the left hand swing arm gusset to frame bend behind the clutch breaks,another reason to use an oil tank,this was a frightner when it broke at Donnington at speed.

This looks like someone may know a thing or 2.
Or not - that zorst would scrape just in my driveway !

Here's a search on this and suggest tagging RBRacing first to keep ya interested in 2>1 experiments.
https://www.google.com/#q=two%20into%20one%20exhaust

yes Mr Ritmo sure builds to a high standard.

The race class must have more er flexible rules than here.
As mentioned above equal lengths, collector and muffler....its probably going to be trial and error, good welding practice.

I would have though the header pipes would be too long. I suggest you should consider a rev figure at the middle of the effective range, and calculate the wavelength for that. The tail pipe will always resonate in sympathy, as long as there is no back pressure - however I think the header pipe length is more important. It will always be 'suck it and see' anyway. I use to change my pipe and mu cam timing progressively over several race meetings. Even then it should be done without a change of venue. The gearing changes to suit the circuit. You need to keep the number of varying factors to a minimum.

they are long!!!, The ones I am looking at by a German racer meet up under the motor.
This guy has been giving me tips on reducing the squish band by machining the pistons and base of cylinders.
Certainly seems more powerful.
he suggested one of his cams and made up an exhaust similar to this

He says some of his 2 valve racers are over 100 hp.

I think I have the gearing right, just about full revs in top at the end of the long straight.
My mates BMW, I can do it in 4th as he's running a higher FD ( but I'm not going to tell him this)