Brooking850 2:1 fitting

Here's the pipe Mike sent me about a year ago for a fully kitted race bike. Its a popular design and seems like a no brainer to me. Go Mike.

I agree with Ken's comments about power requirements for large circuits. I tend to stay away from circuits such as Phillip Island. Partly because of my fear when I hear my motor pulling high revs for long periods of time. That video of Doug MacRae crashing at Daytona when his motor exploded really worries me. I am not prepared to get off at those speeds and my theory is that however fast you go, you have to be prepared to crash that fast. I don't know how anybody can race a Commando at Daytona. Don't you guys ever think about what is whizzing around inside the motor ?

When Herb Becker first built my 750 USS Norton Seeley I provided a new Steve Maney 2-into-1 exhaust but he wanted to try the 2-into-2 approach he successfully used on one of his earlier short strokes. He found virtually no difference. I know this is only one point of data but I find it interesting as sometimes things can be counterintuitive. His current short stroke (longer stroke than my 75 mm stroke) uses 2-into-2 as ridden by Doug Mcrae.

So Brookings850, are you going to offer the Super Trap type stackable disk baffles that Steve had offered?

Hi Dances , not at this stage.
I need to see how the existing 2 x systems on offer sell.
Regards Mike

Brooking 850 said:

Hi Dances , not at this stage.
I need to see how the existing 2 x systems on offer sell.
Regards Mike

Click to expand...

Yep, I was going to ask about anything in the works for:
All titanium version,
Anodized aluminum bits,
Custom engraving,
Stainless steel version, and
Other color selections.....

But I held back. :lol:

All kidding aside, you offer a really nice kit there sir. All the best in this endeavor.

Dances with Shrapnel said:

When Herb Becker first built my 750 USS Norton Seeley I provided a new Steve Maney 2-into-1 exhaust but he wanted to try the 2-into-2 approach he successfully used on one of his earlier short strokes. He found virtually no difference. I know this is only one point of data but I find it interesting as sometimes things can be counterintuitive. His current short stroke (longer stroke than my 75 mm stroke) uses 2-into-2 as ridden by Doug Mcrae.

Click to expand...

That fits with what Steve told me back when he first developed the system. He said it didn't give up any horsepower at the top end and had a much better mid-range. I figured at the time that some of that was marketing hype, but I could certainly be wrong. I still think that if you make as much top end horsepower in a Norton with a 2-into-1 as with a twin pipe system, that something is not right with the twin pipe system. But that's just reasoning from basic principles, and, again, I certainly could be wrong.

Ken

lcrken said:

Dances with Shrapnel said:

When Herb Becker first built my 750 USS Norton Seeley I provided a new Steve Maney 2-into-1 exhaust but he wanted to try the 2-into-2 approach he successfully used on one of his earlier short strokes. He found virtually no difference. I know this is only one point of data but I find it interesting as sometimes things can be counterintuitive. His current short stroke (longer stroke than my 75 mm stroke) uses 2-into-2 as ridden by Doug Mcrae.

Click to expand...

That fits with what Steve told me back when he first developed the system. He said it didn't give up any horsepower at the top end and had a much better mid-range. I figured at the time that some of that was marketing hype, but I could certainly be wrong. I still think that if you make as much top end horsepower in a Norton with a 2-into-1 as with a twin pipe system, that something is not right with the twin pipe system. But that's just reasoning from basic principles, and, again, I certainly could be wrong.

Ken

Click to expand...

I believe that with ay 4 stroke, the optimum for peak power is a 1:1 pipe for each cylinder with a correctly designed megaphone.

However, whether or not that give the best overall optimal set up, or whether of not it is practical to 'package' such a system on a multi cylinder limits its appeal.

Not many of us use correctly designed megaphones!

Whilst I have not yet Dyno tested Mikes pipe, I have Dyno tested one of Steves and it gave a big mid range boost and a top end boost when compared to peashooters.

Brooking 850 said:

Hi Dances , not at this stage.
I need to see how the existing 2 x systems on offer sell.
Regards Mike

Click to expand...

Its a good point though Mike, without more silencing you are pretty much excluding the race market in most countries these days.

Hi Nigel whats the decibel level for classic bike racing in the UK?
I'll run some tests to se where it sits in the decibel range.
Regards Mike

Hi Brooking

Decibel level is 105 however there is a leeway plus or minus.
Steve only used his standard exhaust, warmed the engine up before sound testing & always gently opened the throttle to bring it up to the required revs for testing. Without a warm engine & a steady throttle you can fail! Steve never had any problems & I only failed once spectacularly at Cadwell when my reading was miles over. As it was the same tester & I had seen him at 4 meetings he new the fault was not mine. Saying that I could not stand the stress of going to all that effort to be excluded over a few db. So I ordered Steves end piece with bolt in supertrapp plates. I run it with all the plates in ie the noisest & have always passed at 105.

One thing to note, I used the 750 engine after I blew the 960 engine & the difference in note & coarseness was incredible! a lot more raucious than the big engine.

ps you have made a lovely piece of kit there & I wish you every success with it

all the best Chris

Brooking 850 said:

Hi Nigel whats the decibel level for classic bike racing in the UK?
I'll run some tests to se where it sits in the decibel range.
Regards Mike

Click to expand...

The specific requirement for the test are: Noise meter to be placed 500mm from the exhaust outlet and an angle of 45 degrees from the centre line of the exhaust. Engine to be held at mean piston speed of 11 metres per second. There's a table in the ACU manual of mean piston speed against stroke which allows you to work out the correct rpm to hold the engine at.

From memory ( and this is a very old memory) a Commando needs to be held at either 3800 or 4800 for the test, one of the UK racers will know which .

pommie john said:

From memory ( and this is a very old memory) a Commando needs to be held at either 3800 or 4800 for the test, one of the UK racers will know which .

Click to expand...

I believe an 850 would be running 11 m/sec avg piston speed at 3708 rpm, so your recollection of 3800 rpm is right on.

Fast Eddie said:

lcrken said:

Dances with Shrapnel said:

When Herb Becker first built my 750 USS Norton Seeley I provided a new Steve Maney 2-into-1 exhaust but he wanted to try the 2-into-2 approach he successfully used on one of his earlier short strokes. He found virtually no difference. I know this is only one point of data but I find it interesting as sometimes things can be counterintuitive. His current short stroke (longer stroke than my 75 mm stroke) uses 2-into-2 as ridden by Doug Mcrae.

Click to expand...

That fits with what Steve told me back when he first developed the system. He said it didn't give up any horsepower at the top end and had a much better mid-range. I figured at the time that some of that was marketing hype, but I could certainly be wrong. I still think that if you make as much top end horsepower in a Norton with a 2-into-1 as with a twin pipe system, that something is not right with the twin pipe system. But that's just reasoning from basic principles, and, again, I certainly could be wrong.

Ken

Click to expand...

I believe that with ay 4 stroke, the optimum for peak power is a 1:1 pipe for each cylinder with a correctly designed megaphone.

However, whether or not that give the best overall optimal set up, or whether of not it is practical to 'package' such a system on a multi cylinder limits its appeal.

Not many of us use correctly designed megaphones!

Whilst I have not yet Dyno tested Mikes pipe, I have Dyno tested one of Steves and it gave a big mid range boost and a top end boost when compared to peashooters.

Click to expand...

No doubt peak power is expected with two individual exhausts as opposed to a 2-into-1 arrangement. I don't know the details other than what Herb had said so something may not have been correct in the application. As Jim Comstock may have stated, for most applications, design for area under the curve which makes a lot of sense with these older bikes of relatively long stroke and limited gear selection.

How does one go about designing megaphones correctly? I heard it was approached as trial and error but intuitively think things should boil down to an equation....ah, set of equations....er, series of polynomials of unknown order. Everything I recall reading is more or less cook book in nature (ex. do this for this particular motor) but I want to know why.

When I fitted the 2 into 1 exhaust to my 850, I expected the power to decrease at the top end of the rev range. It did not happen. The set-up gives far more tractable power with no cam spot. So if you get backed off by other competitors getting in your road during racing, the power is there when you need it. With megaphones there is often nothing below the cam spot and as the revs rise, you get everything. The quickest way around a race circuit is often not entirely dependent on the blast down the straights. In any case, if you fatten-up the midrange and increase the overall gearing, aren't you back where you started but faster at the ends of the straights ?

If you try to race a commando using the standard 4 speed box, the acceleration up through the gears is disgusting. So close ratios are the norm. If first gear in the close box is as high as 2nd gear in the standard box, and you have a savage cam spot at 4,000 RPM due to megaphones - how many race circuits don't have a tight corner which you cannot get around without slipping the clutch ? While you are doing that, you are getting thrashed and it is also more likely that you will crash. Nearly every Japanese bike from the 70s has a 5 speed box and most have very smooth power delivery.
In some of the American classic racing videos, there are shots of CR750 Hondas whizzing by on the straights. Most of the CB750 Hondas which race in Australia use 4 into 1 pipes and are very much over-capacity. If you want a fright - fit four pipes with megaphones to a big four cylinder Jap bike. With them, top end power was never a problem. On a tight circuit they can be beaten.

Dances with Shrapnel said:

No doubt peak power is expected with two individual exhausts as opposed to a 2-into-1 arrangement. I don't know the details other than what Herb had said so something may not have been correct in the application. As Jim Comstock may have stated, for most applications, design for area under the curve which makes a lot of sense with these older bikes of relatively long stroke and limited gear selection.

How does one go about designing megaphones correctly? I heard it was approached as trial and error but intuitively think things should boil down to an equation....ah, set of equations....er, series of polynomials of unknown order. Everything I recall reading is more or less cook book in nature (ex. do this for this particular motor) but I want to know why.

Click to expand...

There are software programmes available that work out exhaust pipe length and diameter, and megaphone length and taper, for given engine configurations. I don't know of them myself though, its all way above my head, but I did play around with some such thing a little while ago...

I came across one such programme a few years ago, an ex F1 guy had a programme whereby he would take your cylinder head, and bore & stroke (can't recall if he needed anything else) and from that, would then specify the optimum inlet port length, diameter, taper... ex pipe length and diameter, megaphone length and start / end diameters... optimum cam profile... valve sizes... etc. We built a few motors as close as we could to this spec, close enough to be convinced it gave a good start point at least. This was in the late 90's. I imagine such programmes have improved massively since then.

Its still a 'double edged sword' to me though. The above mentioned programme said that a 1:1 pipe into an open megaphone is the best theoretical design. But its also evidence of how difficult it is to get right. Which probably therefore means that many (most?) megaphones in use are actually a long way from being optimal.

Fast Eddie said:

Its still a 'double edged sword' to me though. The above mentioned programme said that a 1:1 pipe into an open megaphone is the best theoretical design. But its also evidence of how difficult it is to get right. Which probably therefore means that many (most?) megaphones in use are actually a long way from being optimal.

Click to expand...

I'm not sure that there is such a thing as an ideal megaphone. It's my understanding that generally a wider divergence angle gives better top end power ( up to a point ) and a narrower angle tends to spread the power down the rev range, so what you want from the megaphone can change which one you choose.

Depending on the motor, sometime it is impossible to take the edge of extremely harsh power delivery even with reverse-cone megaphones. What I dislike is the power bump when the motor comes back on song as the revs rise. My old short stroke Triton would step out and go sideways, often at about 70 MPH even on a dry road, when it came back onto the megaphone. You need that like a hole in the head, particularly in the wet.
There is a theory in classic racing that big is better, however high top-end power is not the be-all and end-all. If you give some away, often the bike is all-round better. When I fitted the 2 into 1 exhaust to my Triton in place of separate pipes with 4 inch megaphones, the top of the rev range dropped from 10,500 RPM to 9,500 RPM, however I started getting respectable lap times because the bike was not always trying to kill me. It actually had some TORQUE !

When you talk about exhaust systems with megaphones being 'optimal', optimal probably only means best power over a very narrow rev range. In that respect a 2 into 1 system is much better. If your power band is very narrow, you need a gearbox which will allow you to play it like a musical instrument. With my old Triton, I never had more than 4 gears close ratio. I rode it later when a friend had it and it was fitted with a 5 speed box - it was better, but I still had it sideways in one corner.

There was a question raised on the decibel levels for the 2 into 1 exhaust system, here is the NZ standard , its a lengthy document, although you can scroll to the relevant areas with regards to motorcycles.

http://www.lvvta.org.nz/documents/stand ... ssions.pdf

Rev range for testing in this article is 2500RPM , twin cylinder 2 Vv's per cylinder. Altough there are some clauses depending on when the vehicle was first registered in the country, if its a low volume ground up build etc that allows for a bit of wiggle room!
Ill carry out some tests using my race bike system ( remember this is a race motor) using the NZ test specs and guidlines to see what levels we come up with.
Testing parameters seem universal