"Big Bore" head pipes and mufflers

If you took a modern 200 horsepower sports bike, nipped fifty horsepower off the top end and gave it a huge fat torque curve, you would not believe what a ride it would be. It would be outstanding.

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Amen Fullauto, that's exactly what I'm building up in Ms Peel. Well over 100 hp but also torque! In the boosted version I think 1.5" header will give plenty of flow and w/o the blower small ports and 1.5" should tame the drag cam for spunky performance as well. I'm not that interested in top end especially in public. If Peel can run up to say 160 keeping front tire floating then no bike or rider would be able to catch her with the lead gained in even a single turn.
I'm besides myself with insane corner grip and handling not top end. I want to break loose at will up to 100 while leaned to max clearance, likely over 60'.
Yo'all may be picturing straight line tire spin power but I'm going to sleep remembering WOT apex zings. BTW Peel could shift mid turns clutch-less w/o any upset wiggles, as long as not right at apex where a power cut causes hi sides.
Only do that by throttle chops and bike tripped out from under by excess throttle.
Hope is can spin tire at will in 3rd or 4th so never a need to shit up or down on highway fun or rpm distortion/damage.

I want to play with stepped headers, exit head 1.5" headers for ~18" then 1 3/4" from Y to the megaphone. I've put wideband O2 sensor and EGT temp need just beyond the Y junction. Exhaust extractor pipe goes just past these intrusions.
That's mainly what I think 1 3/4" section would help flow past with blue jets out the back. I also try to aim exhaust plume to help lower and lenghten tear drop turbulence of bike-rider. I've actually seen this plume on '71 with dual peashooters. I've seen where the wind is parted or slaps back together or how eddies roll off and expand behind bike.

Fullauto said:

Well, Will, I'll tell ya something. I was in the local bike shop and saw the price of KTM nicnacs and keyrings and little billet covers and stuff. I couldn't afford them so I'd hate to think what spares prices are like. No Norton spare part has ever scared me price wise. On the Buells Down Under forum one of the guys was talking about track days in Queensland and he said one of the local dealers would come out with his Superduke and give it a flogging. The last he heard was that the guy was on his second engine rebuild and third gearbox. I can live without one I think.

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Going on the assumption that everything from the west is more expensive down under I understand where you are coming from.
I wouldn't know about the nicnacs, (motorcycle jewlery for those with too much money), but can tell you the factory option full Ti exhaust is ridiculously expensive here. That said, I beat on my SD regularly and have never had a mechanical problem. My biggest problem with my slightly modded SD is keeping it in tires :lol: I'd stay away from that dealer if they have had that many problems with the bike. The engines are essentially the same as used in the Adventure bike and are well proven for longevity with some easily fixed flaws. They aren't Japenese and require an attentive owner but reward for the trouble of keeping an eye on things. If you ever get the chance to flog one don't pass it up.

Will the way I got some SV650 tire economy is buying used race rubber in 17" 150-170 sizes of the most high end tires made. If not racing around I could get ~4000 miles out of rear. If playing hard maybe 2000. But at $50-60 a tire what the heck. Edges will be ground down some but centers are almost new. After some 100 or so miles of progressively more aggressive leans whole surface is scrubbed to new layer predictable very decent traction security. I go through 4 rears per 1 front on SV650. That's about 16K miles for price of one new rear tire. I often get holes but trust tar cord plugs to any speed, just as long as I remember where in tire patch they are and not to spin tire much or at all to risk pulling cord out as only held in by like 3/16" thick tire case. I'd only gotten 3000 miles this year before goats got me so there's a stack of 4 rear tires still wrapped in plastic just dry rotting away.
Two times I let myself enjoy THE Gravel antics of rooster tailing straights and flat tracking the curves, when tires first put on and when tires mostly showing center cords. If I'd did that beyond 10 miles worth I'd only get 1000 miles a rear or less.
'00 SV rated at ~70 hp/45 lb-ft for 365 lb bike. Its about same as good Combat to 75 then good Combat can take it to over 120. A great Combat leaves it behind by 50-60 mph. Below that wheelie or traction makes em all about equal unless leaning good then SV would wipe out untamed Cdo's but I'd wipe out trying to ride SV as I do Peel in loose or hi grip conditions. Dangerous to jump on SV after Peel d/t a flat. SV out handles my factory Combat in tights and fast sweepers.
Not so Ms Peel no matter on or off road or speed or skipping-drifting or braking or get go or sweet lack of bike sensations.

On the exhaust note- when I shot out two .38 cal holes by 6 shots of .22 cal - SV got deeper almost real motorcycle sound and a bit more spunk torque response.
I can't hear note after 90 but friends I've passed tell me they can hear it screaming before the pass and liked it. It stock engine and carb tune.
Prior darn thing sounded just like any other utilitarian ATV 4 wheeler.
I can not tell difference between straight pipe Harley and hick's cherry bomb dual 2" exhaust chevy V8's.

Hobot,

Pirelli Supercorsa SC1 dot race soft compound 180/55. I'll be surprised if I get 1000miles out of this one. Metz.Z6 before did 3500 miles, Corsa IIIs almost 3000. 110-120hp at the wheel after last mod. I haven't got back to the dyno since the PCIII went on but it's running leaner now. When cash permits I'll get my own map made but the one I'm running now is close. Was better without baffles but kept setting off car alarms.

Notice big bore exhaust in photo :lol:

Yep Will, I saw the full ti system for the KTM was over 5 grand in Aussie dollars here. Leaves me scratching my head. Along with 800 dollar rearsets for just about anything, Japanese or otherwise, just to have your heels shoved even further up your arse. Tee hee.

[Well said.

I guess my problem is that, although I've owned Commandos since 1971, my other current bike is an 08 CBR1000RR. I took them both out for a track day. Man oh man was the Commando a droner . . . fun, lots of compliments on "how fast that relic goes" . . . but . . . . and that wide ratio 4 speed . . . ugh . . . . but the thing is I love her . . . . far more than the CBR . . . . I just want a little more out of her . . . . . that's why I'm askin about 1.5" head pipes.[/quote]

Watch the video of jim Schmidt doing over 100 in third gear and pulling wheelies on the bike during the acceleration...then think about doing the JS pistons and rods and a Fullauto head. The expertise is here to get more out of your bike. If that is the direction you want to go, ask these guys and get out your check book. I think the stuff they are doing is terrific.

Russ

Nice job of polishing off the very edges Willi. Tearing the rubber fabric not melting or abrading it gives me the most fun too. Still I'm scared of fat tires now and amazing to me is how well Peel's rear lasted even though shoving me around turns harsher than moderns whose tires resembled yours afterwards. That fact that we both can use up to cords in ~1000 miles but I hardly ever do should give some sense how moderate I am vast majority of time. More often than road hazard revealed in a hwy blinds - is running up on police at go to jail speeds. Don't remember if I had digi camera during Peel's prime time.

Personally like anyone else I like big deep sounding pipes as still allows good performance or even enhances it. Size of muffler matters a lot sound and zoom wise too.

Resurrecting this thread.

I got the 1.5" headpipes.

Can't say that I lost mid range or that I got top end. The bike runs stronger than any of the other Brit twins I've ridden with . . . . so far. A friend's 696 Monster walks away from me though. I weigh 270 naked, so I'm close to 300 pounds in full gear.

20 tooth, the head's ported, stock valve sizes, Jim Schmidt's PWKs, TriSpark from CNW. Indicated 110 at 7000 at 2700 feet el so not spectacular speed but she was willing to pull past 7000.

The 1.5" head pipes flow into OEM peashooters which have an average ID greater than 1.5" and I say that because some peashooters have smaller IDs than others.

To spank small size Monsters took a 2 into 1 1.5" pipes and some messing with the muffer baffle toweards more open - then only the 900 Monsters could out run Peel, once they got full upright that is.

I did a lot of pipe experimentation when I was building my race bikes and found my old notebook. On the first racer using a ported head, stock valves, 4s cam and 34mm Amals I did back to back checks with pipes. Baseline was 1 3/8 stock pipes with reverse cone megaphones.
Next set was 1.5 inch pipes with the same megaphones. After playing with the length a bit I got about 2 more horsepower above 6000 rpm and lost everywhere else.
Next set was 1 5/8 and I didn't see a gain till over 7000 and lost a lot from 4 to 5500 rpm . I was up around 3.5 at 7500. I had to make the pipes 3 inches longer to get around a bad case of "Megaphonitis"
Next set was the 1 3/8 set cut off just before the second bend and joined to the 1.5 inch pipes. That got me back to the same up to 6000 with a couple horse gain at 6700.
Next set was all the same dimensions starting at 1 3/8 and stepping to 1.5 but built high similar to SS pipes. For some reason they made almost 5 more than the stock pipes. I have seen similar gains since when the exhaust pipe bends to the side after it leaves the cylinder instead of down.
All these were done with the same megaphone and with a slip fit pipe at the front of the megaphone so I could adjust the length. I wouldn't say that all the testing was real thorough and I have found I can do better with 2 into one now. I still stick with 1 3/8 for the first 18 inches or so. Jim

On the other, feed side of my 1.5", 2-1, megaphone, slight back pressure reflected, a standard 28 mm head kicked my ass while a CHO head with Dreer 6mm K/W kit was kinda dull from bottom to top end, even with the same exhaust.
Go figure - I've speculations only but plan to try same accidental set up on a factory Combat as its just bolt on stuff, head, carb and pipes. Prior I thought megaphonitis meant clogged up head flow, but to me it now means Hot Red Swollen Painful flow.

Quote:
a standard 28 mm head kicked my ass

Boy, been there done that. Bigger don't mean faster was a hard thing to get through my head. Jim

Hm, yeah heard that on some of my dates too : )
The over ported CHO for a 750 may work out just right for a 920.
Interesting the rpm ranges of you pipe experiments as I found the stock Combat seemed to gain an extra piston about 6800 but then floated valves about 7200 : (
On a factory Combat I found that open headers developed more seat of pant power than with factory peashooters. It was not the mass loss as they were still tied to bike on seat.

comnoz said:

Quote:
a standard 28 mm head kicked my ass

Boy, been there done that. Bigger don't mean faster was a hard thing to get through my head. Jim

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Ha.

Last year Mr. Comstock insisted on going with stock-sized valves on my Fullauto head. I fought him hard, as I'd been running (quite successfully) a big valve head up to that point. But he and persevered, did some flow tests, and insisted I bolt it on and go. I did, and away I went.

I have numbers to back it up. Bigger is not always better.

I also saw a bolt-on 5 bhp 5mpg increase with standard SS pipes and Dunstall mufflers on my '72 Combat--a close second would be the Dunstalls with the stock 850-style crossover pipes.


Tim Kraakevik
kraakevik@voyager.net
Three Commandos

Hm the scope of reports on this is giving me some insights to exploit in Ms Peel. In her case the intake side is a non issue as not much more can be done to gain more packing in d/t blower and drag only cam and 10.5 CR. Its the exhaust side that most help blowers of various sorts get more power and heat relief. Seems the jets out of the head 'prefer' a straighter path at the beginning. Sideways aimed pipes would align better with the splayed out exhaust ports. By most engine logic it should not make that much difference and even Dunstall himself found that lots of sharp bends didn't affect flow but size changes and lengths did. Putting on a 2 -1 is worth at least over a hp benefit just by the loss of 1/3 the mass of a dual system
~6 to 9 lb depending on what and how much removed and replaced with.

The hard part is that it is so expensive in time and money to create hard data, let alone arrive at conclusions.

And then, its apples and oranges - for instance, I'm running 1.5s into stock 1.5 inlet peashooters and all the racers' experience on here is with megaphones and with engines built to handle more RPM.

On a close to stock motor ridden on the street Norton did a good job of getting the exhaust right. Not much room for improvements in the tuning of 1 3/8 pipes and peashooters unless you are making big changes in the engine. The one exception is the fact that SS pipes will make a little more power in the stock RPM range than downpipes.
Of coarse I love custom exhaust for weight savings and personalizing one's bike. Jim

For just plain wonderful delightful low effort sane joy riding and routine commuting on an English bicycle with 13 sec 1/4 mile turbo fan smooth noise maker I can't imagine a better motorcycle than basic factory Combat. Its so fine and easy operation refreshing to me Trixie Combat is what I'll likely end up with forever after smashing Ms Peel to smithereens. Norton sure got it right for the price and tooling of the era, just not up to modern sport performance is all.

Then I die.

But before I go I plan to explore to the max - insane flings on you know who.
White folks can't dance and Norton can't spin, so power equation must add torque not rpms. So upping displacement and forcing mix in via smallish passages is Peel's path. Big block grunt down low but before ports/valve restrict any, boost overcomes. At Norton rpm limits and Drouin air curve, her port venturi velocity only gets to .7 mach number @ 8000, about ideal for max flow in w/o the sonic shock nozzle interference. Peel should come on drag only cam pretty darn quick. 20% bigger engine, 10.5 CR, small ports/valves/ chamber, wide squish bands with boost assist should tame wild cam for easy legal-ish operation too. Study of what's been done on sets up like Peel, use asymmetric cams that emphasize exhaust flow. Past Peel did not really wake up till I got pissed royally and shot out supertrap blockage in her 2-1 mega. That and the links transformed my emotional/glandular/mental life. I will not have to rev to red line to be smashed back long as I can take.

I have to cut up old 2-1 to put on trapped Al exhaust nuts and landings on turned forks foul fender on LH header bend to RH, so opportunity to do something to help head exhaust. Anit-reversion cones, re-angled initial 8" or so?