2 into 1 Exhaust (2015)

Its exciting to read the various successes of 2>1 merged headers, be it mid point or at the end - as long as it helps power delivery. Both sides, ie: lone wolf acotrel vs current race builders, have valid proven points on exhaust successes. Much as I respect and learn from the current racers, acotrel rants about trial/error adjusting collector volume/length - til Eureka! and habit of powering all the way through turns, makes me add a couple scoring points in his favor. Note: I'm not saying acotrel methanol 850 is as powerful as recent gasoline winners, just that he's shown a way to tune a 2>1, if it has a length of common collector to do so. Second point is he's always mentions same slacking of power - till after apexes. I'm like acotrel in that regard, its not my sexual escapades or life saving successes, I flash on most > its obsolete cycle accelerating past everyone else hard on brakes entering turns.

Mz Peel/me humbly seeks-requires advice from both camps, if this is thread space to do so. I want to make a stepped 2>1>mega, one piece if possible, to merge before turning back along R frame tube. I'm thinking, ~8" length of 1 1/2" out of head to bend downward, then slip on 1 5/8" to lead into a bent Y merge, then 1 3/4" out to the 31" long Dunstal hollow mega with my own resonator silencer pulse extractor contained inside the 4" dia 5" long end chamber. The Dunstal has top hat insert to fit 1 5/8" so can suck it out to accept more throaty sounding common pipe. O2 bung and EGT needle placed in the Y merger with the crank case blow by extractor immediately after the merge in the 1 /3/4" section. In late Ms Peel I discovered if down tubes long enough before the merge it allows spreading them enough to snap into the angled out exhaust ports so eliminates need of clunky clamping hardware mass all others require. Should weigh ~ 13 lb complete with mounting hardware. Will wrap headers down to the merge, which takes a lot of the header blast clang out and cooler/safer to diddle stuff around engine.

So how long should I make the stepped lengths before the merge? Would it be better to just go with 1 5/8" out of head to the Y? Collector pipe extends into megaphone as far as I want, so suspect more effect by preventing most the pressure reflections from passing back up pipe, more bounce back out with the rest of the gas pulses. Peel has Norris D cam, D = drag only = greatly over lapped valves open low rpm whimp to compensate for.
https://www.google.com/search?q=stepped+header+calculator&ie=utf-8&oe=utf-8&client=firefox-b-1

Here's a double X-cross over/merge system to ponder

DUAL X PIPES MIGHT SEEM REDUNDANT BUT ITS PROVEN TO INCREASE CYLINDER SCAVENGING

Hobot, just build it and see what the result is, at least you will have a system that you want and wont be relying on what others think or know.
Put it on the dyno and post results.
Otherwise it will all be pure speculation.
Regards Mike

I once made the mistake of racing a short stroke engine in a featherbed frame with separate pipes with megaphones. It was impossible to be smooth in corners, so I ended up going too slow to be competitive. After I fitted the 2 into 1 exhaust system , I started getting decent lap times. The pipe made that much difference. I sold that bike back to the guy who made it in the 1950s. He put it back on petrol, fitted two separate straight pipes without megaphones, a five speed box and decent tyres. I got to ride it like that - it was better but I still had it go sideways in a corner. With the better tyres, I rode through the problem. But in the old days it would have crashed me. The Seeley Commando 850 is a completely different kettle of fish - NO ANXIETY ! - I like everything about it.
If you make up 10 metres in every corner and come out of them much faster than the other guys - that is very hard to beat. You don't need heaps of horsepower.

I once had a friend of mine say to me 'if you keep riding around corners like there is no tomorrow, one day you will fall right on your head'. It turned out he was the reason I had one serious crash when he did something stupid in front of me. But in effect, if you are very fast and very smooth in corners, you are usually safer. When I practise, I always work up to the corners and also work at getting on the gas earlier when coming out, as well as being as smooth as possible. I also count my gear changes. Some guys don't do that.

Ok Brooking will go by guess/by golly and see what happens. I like beating others by handling torque more than top end so thinking to orient Peel's toward low end to help the over lapped cam response down low and hope the blower can over come above that. One thing I noticed on hopped up engines or hi end stereo systems, pretty disappointing, right up to last tiny detail that suddenly blows ya away.

Only 2 dyno people I know about is comnos and Herb Becker, so will cost couple grand to do in a year or so. I spent a few months calling every dyno equipped shop I could find almost nation wide to have them all say can't/won't do a Norton. I spent more time looking into my own dyno to give up on that too. Mean time buying tube and learning wire feed welding. Have new set of ceramic aluminized inside and out 1.5" headers to slice off 8" of flange end to get started.

Doesn’t a blower override exhausts?

Fast Eddie said:

Doesn’t a blower override exhausts?

Click to expand...

I was just thinking the same thing. A blower turns tuned inlet tracts and tuned exhausts into decoration. Perhaps a 2 into 1 pipe feeding through a turbocharger might be effective - would not use so much horsepower to run the blower ?

Well yoose guys are half correct about boast not much effected by exhaust scavenge tuning but ain't up to speed on characteristics of centrifugal blowers, which significantly differ in the low rpms and slow throttle opening - from compressors delivering set amount of boost no matter the rpm. Study of mechanical boosted engines reveals most their hop ups involve opening up exhaust path, even thought they also benefit from head/valve work like any engine, exhaust matters more. Most the time Mz Peel will not be on boast but dependent as normal on exhaust tuning trying to enjoy surviving in public.

In Mz Peel case she must creep on steep low traction conditions when blower rpm and throttle opening speed not boasting at all, but still needing good torque to keep climbing w/o accelerating, so configuring exhaust for those grunting lugging yet responsive conditions seems my best bet. Also may not always want a big ass blower just to commute around on a race type 920 carb engine. I don't think will give up much top power this way, if any. Thot I could just re-use late Ms Peel's headers but the hard points for crash cage fouls them so must do another custom hassle, maybe even better. Remember Ms Peel almost got sold off, especially after incomprehensibly ruing out from under twice from one last little desperate exhaust modification til realized just open throttle slower, sheeze. I love the long dong ridiculous ray gun/rocket look of long exhaust.

acotrel said:

I once made the mistake of racing a short stroke engine in a featherbed frame with separate pipes with megaphones. It was impossible to be smooth in corners, so I ended up going too slow to be competitive.

Click to expand...

Sounds like a personal matter. This is a response I would expect from someone attempting to race a poorly prepared and poorly tuned bike. By your own admission, the short stroke you attempted to ride was not in a state of decent tune.

You could tune it any way you wanted, the result was always the same. It was a vicious piece of shit, especially when it was fitted with 4 inch megaphones. The 2 into 1 pipe made it sane. I raced it for 12 years, then sold it. I was glad to see it go - it badly needed a six speed box. But who needs to live with the continual fear of being bitten ? That 500cc short stroke Triumph that Percy Tait used to ride, would not have been easy. A good Manx makes that sort of idiocy look stupid. I dare to say that on a short circuit a decent 500 cc Manx might give 750cc Commando a fright. In the old days in Victoria there was a guy with a 1000cc Norvin who used to win A grade races which were full of the top guys riding 500cc Manxes. That is history - what historic racing is supposed to be about ?

I think there is a tendency amongst road race guys to look at an ace riding a similar bike to their own, and fantasise that they can be equally as successful. The guy who originally built my short stroke Triumph certainly knew about Percy Tait and Geoff Monty. However I suspect there were major differences between the circuits being raced on in the UK and what we had in Australia. On a big flowing circuit such as Phillip Island, the short stroke Triumph was excellent - it had so much top end that at the ends of the straights, you would be passing guys as though they were standing still. On a short circuit, with the four speed close box - unless you dropped the gearing far too low, it would not get out of corners fast enough. And the megaphone exhausts made it savage. With the drum front brake, it was an accident waiting to happen. There was only one good thing about that bike - it taught me what NOT to do. I haven't raced much in recent years, but when I have, I've found myself well up front in races - especially when it rains. The young guys are very tyre-dependent these days.

Ah yes, here we go with that "vicious piece of shit" tale of woe.

As you say, it apparently was a piece of shit so no wonder it was not good - hardly a gold standard.

Try riding a reasonably well sorted out short stroke and then chat it up a bit.

The phrase ‘short stroke’ is a relative concept. It means, the stroke is shorter than it was, or shorter than another derivative of the same engine.

That’s all.

Neither a short stroke Norton or short stroke Triumph would be considered short stroke against a modern short stroke engine.

So, there’s is really no point, at all, in trying to compare a short stroke 500 Triumph to a short stroke 750 Norton Al. Just no point at all.

However, I’d also like to add that Monty and Ward built VERY successful short stroke Triumphs, and they were successful on very tight U.K. short cuicuits. So, as has been pointed out already, mainly by yourself Al, yours clearly wasn’t a very well executed attempt.

We’ve all had duff bikes from time to time. Not many of us kept them for 12 years though...!

I kept it for 12 years because I liked the adrenalin rush and the technical interest, but in the end I did not like the injuries - I still carry them. 63mm is short stroke for a Triumph. The unit Triumph 500s were 65.5mm stroke. When you reduce the stroke of a 750 Commando from 89mm to 82mm, you create the equivalent of a Triumph 650 with a slightly better head. It is still a big motor, so not so peaky. Triumphs are not a good way to go racing - the cost/benefit does not stack up. Better to buy yourself something decent - like a Paton and sell it when you are finished. For historic racing, a Jawa two-valve speedway engine in a featherbed frame with a 5 speed box is hard to beat. Much better than any 500cc Triumph.

One thing which really crags me about historic racing, is that in the old days the Senior class was the biggest at 500cc. Triumph 650s were not eligible and weren't fast enough anyway. These days everybody is into the 'big is better' - just silly stuff. Most guys cannot ride a Manx to the limit. And what they now race are often not race bikes anyway. When I was racing, it was always in the Allpowers Class with bikes up to 1300cc, and I could just stay with them with a 500. There was once race per year which had the 500cc capacity limit - the Harvey Wiltshire. I rode in it once and found out what the real racers (like Tom Phillis ) do.

Here's a link to all the classes we currently race in the NZCMRR.
Next round this coming weekend.
The class I race in is the Open Classic 70's
http://www.nzcmrr.com/results/2018

I'm glad expert racer people responding to acrotel semi civilly as he's earned his wisdom the hard way on his own so seems just trying to make sense of practical applications once exhaust is kicking butt. I can relate to him on lost years thinking obsolete Commando was too antique POS compared more proven common breeds, to be flabbergasted rest of life how wrong we were. Keep in dark deep back of minds, his remarks about the lack of increasing noise entering turns on antique to modern video, is exactly same reaction I have to all pavement racer video, freaking counter productive no matter what excellent power on tap, can't apply it to matter - til essentially upright safe, which by then pecking order power planting road test done did.

I didn't know what was possible til Peel was shooting blue jets some inches out long exhaust path and shocking small children to scared crying if standing a few yards too close at stops. It was a treat to startle , stun, stumble racers and general public back with a really effective 'accidental' system I seek to improve on soon.

Fast Eddie said:

The phrase ‘short stroke’ is a relative concept. It means, the stroke is shorter than it was, or shorter than another derivative of the same engine.

That’s all.

Click to expand...

For reference and context, the stock 750 stroke is 89mm. The factory short stroke was 80.4mm (with an 850 bore). Steve Maney developed, raced and marketed a 75mm stroke 750 which was deadly effective when properly set up. There were other bore stroke combinations out there. A Gary Denucci (RIP) out of Minneapolis/St. Paul did a short stroke back in the early to mid 80s that was somewhere around 75mm so the variations have been around for quite some time. I think a Jim Moser did much of the work for Gary's bike which was set in an authentic Colin Seeley Mk3 frame. Notable on Gary's bike was a huge main journal billet crank for durability.

I guess 75mm I’ll be what this stunning looking machine has in it then...

https://www.ebay.co.uk/itm/NORTON-S...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

Yep, it's a piece of high performance art. Steve's endeavors sent me down that slippery slope around 2003. Have a nice picture of Rob McClennon on my Seeley beating out Jay Springsteen on an XR750 about 10 years ago. Unreal how trackable these 75mm motors are. I built it with a five speed, switched to a six speed but realized it was unnecessary and somehwhat counter productive so switching back to a five speed. The initial motor work was by Herb Becker.