What type of exhaust for power. (2019)

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Schwany said:
I wrote up a good example of how to ruin a good running Norton with modifications and a 2:1 exhaust, and then what it took flow wise to fix it, but it was so long winded I deleted it.

Storm42... That is one nice looking Norton. Give 'em hell and rubber side down Saturday.
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Thanks, could you re-write your notes? I am like a sponge with info like that.
 
Chris said:
Hi Ralph
Wanted to do Mallory but knew it was to early for me. Just got my eyesight test done & sorting out my licence. Bike needs new throttle cables but should be good to go. Al asked if I would do Darley but again too close. Shame as fun tracks to do.
I am doing Pembrey, birthday weekend! Cadwell Donnington & Goodwood. Although that's been slightly blighted by us ie F750, running with the Barry Sheene event. Tzs in the 80s! Spike Edwards was two seconds a lap quicker than his rivals last time out. I will see a lot of him in a twenty minute race.
Hope the weather is better than predicted & enjoy yourself.
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I am hoping to do Pembrey so will see you there but , those Welsh politicians are a bit unpredictable.

How do you get to race at Goodwood?
 
storm42 said:
Thanks, could you re-write your notes? I am like a sponge with info like that.
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I think everybody that has posted in this thread already knows more than I do about how to bring a motor back to life when a cam change ended up being initially disappointing. It was an Atlas powered P11 with a timed breather off the drive side case. Nothing like the motors youz guys are using. The 2S cam I stuffed in it didn't support the timed breather, so that was the major hurdle for me not knowing much about making a Norton go. The 2:1 pipe I had/still have but modified was cheap, too short, too restrictive, and nothing like what high rollers have on those Seeley framed Nortons. All my flow improvements were shade tree mechanic fixes. Nothing technical was relied upon. I guess you could say I'm a fake it till I make it master mechanic. ;)

I could send the story in a PM, if you still want it. I don't have enough technobabble stored up in my head to defend anything I did in the forum. No measurements were taken or comparative dyno runs. It's seat of the pants amateur hour, but the changes made a significant difference.
 
I asked & Gordon told me what bike he wanted me to ride lol told me he had too many Commandos. Its F750 class bikes Goodwood are keen on originality. However all the Rob Norths had open belt drives & covers. Lots of adjustable mastercylinder & exhaust systems.
Mine will be one of the most basic bikes out there. Saw a Big D triumph 650 & Dave Degans framed bike & an Atlas, mind you that was ridden by a TT rider. Everything else was a bit special.
 
Chris said:
I asked & Gordon told me what bike he wanted me to ride lol told me he had too many Commandos. Its F750 class bikes Goodwood are keen on originality. However all the Rob Norths had open belt drives & covers. Lots of adjustable mastercylinder & exhaust systems.
Mine will be one of the most basic bikes out there. Saw a Big D triumph 650 & Dave Degans framed bike & an Atlas, mind you that was ridden by a TT rider. Everything else was a bit special.
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Sounds like when they wanted to run F750 at IHRO, but the only commandos had to be JPN , Rickman or Seeley. Lloyd said he wanted to ride his featherbed Commando, and was told No, they weren't done in F750 back in the day

His response? You remember Imola 1972 when Paul Smart won etc? Yes Well, I was in that race, on a featherbed framed commando. ;)

As for Goodwood, personally I wouldn't bother. The most successful Rob Norths in CRMC history were told they weren't wanted
 
SteveA said:
The days of Megaphones as such are long over....
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Good point. Back in the '70s when I started racing Commandos, the best exhausts were pretty well cut and dried. I used Axtell megaphones and pipe dimensions, developed with hours of serious dyno time and lots of real time testing in flat track racing. Nobody worried much about sound levels then. The factory did a lot of dyno development on the same design, dual exhausts with reverse cone megaphones. I have dimensions of several different designs they used, some for 750, some for 850, with comments on which were good for top end and which were good for mid-range. Not really very complicated to come up with a suitable system. The early sound limits at tracks weren't too difficult, and the AMA inspectors tended to be pretty liberal in interpreting them :rolleyes:. I recall the first time I had to go through a sound tech measurement, at Laguna Seca, and the tech guy managed to pass the bike even with the 1 5/8" pipes and open mega, but he liked seeing a Norton competing, and there was a lot of "wink, wink" sort of dialogue involved. It got a lot harder when the tracks and racing clubs got serious about sound limits. By the early '90s, when singles racing was getting pretty serious, I was running a Ron Wood Rotax with a Axtell twin reverse cone mehaphone exhaust with a pair of silencers tacked on that Ron had designed to pass sound tech but still make good horsepower. They worked great, but they were huge! I thought about trying to fit them to my Norton, but always managed to get past the sound requirements with the open mega system, so never bothered. I haven't run the Norton at a road race since about 2007, so it might have more trouble with current sound limits.

This picture shows the megas and silencers. The silencer design used a perforated tube in a zig-zag shape wrapped with fiberglass packing, similar to a design used by car racers at the time. It is large, but that seemed to be what it took to pass AMA sound requirements without seriously degrading performance.

What type of exhaust for power. (2019)


Ken
 
I wanted a Wood Rotax like that, and almost talked myself into building one with bits and pieces off my ATK 604. That would have been unapproachable in the California hills. And not just for posing at Alice's.

Only reason I bought a Norton was I had to have that sound after seeing the Red Norton on the San Jose mile. That was before they had to put those big cans on the exhaust. Those really were the good old days IMO. Of course the people living close to the fair grounds didn't see it that way, and that's how things ended up like they are. Darn leaf blowers are louder than GP bikes.

My Norton is quietish idling, but I don't think the 2:1 would pass track inspection for sound with 21 SuperTrapp plates in a gutted 25" megaphone. Shrug :rolleyes:
 
John
That is just legend!
Eligibility sorted.
Me? I just want to ride the circuit. Shame about the Tzs being out with us.
 
The frame steering geometry and suspension determine how much power you can put down on the ground in corners when you have good torque. And the gearbox is also important. If you think you can build a top end Commando motor and out run four-cylinder bikes and two-strokes down the straights, you are kidding yourself. The quicker you get around and out of the corners, the quicker you will be towards the ends of the straights. You accelerate slower, but start faster. It does not depend on outright horsepower. Separate pipes with megaphones give you more top end power, 2 into 1 gives more torque. The gearbox is a torque converter. As you raise the overall gearing you end up in the same place as the guy with the top end motor, but at lower revs - so the exhaust system needs to be different.. Close ratios with a torquey motor and high overall gearing are excellent. But your strengths are are in different places on any race circuit, when compared with the guys with the top end motor..
Nothing can beat my Seeley 850 around a corner. It is not me, it is the bike. If you have got the run at the start of the straights, the other guys need massive horsepower to accelerate past you. And then they need to stay in front in the next corner.
 
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Chris said:
John
That is just legend!
Eligibility sorted.
Me? I just want to ride the circuit. Shame about the Tzs being out with us.
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That's Lloyd, straight talking :)

It was the organiser of GW that put us off, and now we're selective enough to just not go to meetings we don't want to
 
acotrel said:
The frame steering geometry and suspension determine how much power you can put down on the ground in corners when you have good torque. And the gearbox is also important. If you think you can build a top end Commando motor and out run four-cylinder bikes and two-strokes down the straights, you are kidding yourself. The quicker you get around and out of the corners, the quicker you will be towards the ends of the straights. You accelerate slower, but start faster. It does not depend on outright horsepower. Separate pipes with megaphones give you more top end power, 2 into 1 gives more torque. The gearbox is a torque converter. As you raise the overall gearing you end up in the same place as the guy with the top end motor, but at lower revs - so the exhaust system needs to be different.. Close ratios with a torquey motor and high overall gearing are excellent. But your strengths are are in different places on any race circuit, when compared with the guys with the top end motor..
Nothing can beat my Seeley 850 around a corner. It is not me, it is the bike. If you have got the run at the start of the straights, the other guys need massive horsepower to accelerate past you. And then they need to stay in front in the next corner.
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My 750 will run with TZs and 1000cc post classic bikes all day, but then it doesn't run 7-1 compression, nor run on methanol........

Ralphs 920 makes a bit more power so shouldn't have a problem if he really went for it either. Gary Thwaites never had a problem and when he rode the triple even TZ750s couldn't get within a second a lap of him.

Maybe it's just yours that is slow?
 
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For me why Goodwood is for the ride!
Graham higlett won the 77th members meeting F750 race in 21minutes 26seconds for the race. Best lap 1.26 Looking at the mid pack best laps 1.35
I will hope for a 1.40 lol

Spike Edwards meanwhile on a 79 TZe in the 75th members meeting posted a race time of 20 minutes 10 seconds
With a best lap of 1 25.155 ie 101mph lap.

With a joint grid Graham would have finished in 13th place 1 minute & 16 seconds down.

I'll be lapped twice 10 seconds short of being lapped a third time. "IF" lol I can run 1.40s & the bike lasts.

Class field of riders embarrassing to be sure but I'm still smiling lol
 
Chris, your position in the field is irrelevant... you race the track, and your own limits, like Jonathan Livingstone Seagull ...
 
Chris said:
For me why Goodwood is for the ride!
Graham higlett won the 77th members meeting F750 race in 21minutes 26seconds for the race. Best lap 1.26 Looking at the mid pack best laps 1.35
I will hope for a 1.40 lol

Spike Edwards meanwhile on a 79 TZe in the 75th members meeting posted a race time of 20 minutes 10 seconds
With a best lap of 1 25.155 ie 101mph lap.

With a joint grid Graham would have finished in 13th place 1 minute & 16 seconds down.

I'll be lapped twice 10 seconds short of being lapped a third time. "IF" lol I can run 1.40s & the bike lasts.

Class field of riders embarrassing to be sure but I'm still smiling lol
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Different races, 2 years apart though. Was the track faster on one day? What if Spike rode the triple? He'd probably be lapping in 1:23

Graham is a good rider, but he's no Spike (and Spike is a fantastic rider, no matter what some Youtube racers think)

Don't forget, the TZ750 guys spent 5 years trying to get the North banned from post classic races because it was unbeatable....they even used the excuse "It's unfair because it's too old"
 
There were a few versions of the TZ750 iirc. As things go, the bike gained power and lost weight through the 70s.
Somewhere along the line they jumped from 90 bhp up to 120bhp.
It was one of the 120bhp models that Joey Dunlop used to raise the IOM lap record with.
118. something mph.
Not hanging about!

Glen
 
worntorn said:
There were a few versions of the TZ750 iirc. As things go, the bike gained power and lost weight through the 70s.
Somewhere along the line they jumped from 90 bhp up to 120bhp.
It was one of the 120bhp models that Joey Dunlop used to raise the IOM lap record with.
118. something mph.
Not hanging about!

Glen
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Correct these were all upgraded to full spec over the years. Nobody races a museum piece. There were no twin shock early ones left, and Rob Hall and Roy Flower (to name just 2) could certainly ride them, and they were making closer to 145RWHP by then. But, they could still be outridden.
Their big problem was that an "old banger" made them look silly, even at the power circuits like Snetterton and Silverstone....after all, no matter how long the straight, there will still be corners.

The last time we raced with CRMC was at Silverstone. Cormac still won the "Race of the Year" on the triple after having a race long duel with a newly built, no expense spared TZ750. I think they were about 30 secs ahead of the third placed rider
 
Seeley920 said:
The last time we raced with CRMC was at Silverstone. Cormac still won the "Race of the Year" on the triple after having a race long duel with a newly built, no expense spared TZ750. I think they were about 30 secs ahead of the third placed rider
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Wudda loved to have watched that race !
 
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