What type of exhaust for power. (2019)

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I'm not certain of that, but it was done by Jim Comstock. He pops them apart and back together pretty quickly.

Glen
 
Hi Ralph
Your bike looks fantastic ! Love the way you keep looking & progressing. I have one of Nick's 2 into 1 systems to put on the MK4 750. I will catch up with you this season. Good luck at the weekend.
 
worntorn said:
My two pipe/ balanced pipe/Dunstall trials on a stock did not show a massive difference. Once jetted correctly the best combo managed 3 kmh more at the hilltop.
For most Roadriders that wee bit of speed doesn't matter.
It's probably more important for most to have the look and sound they like.
Racing is another thing, an extra 3 kmh is always useful!
I intend to try all three exhaust type plus a 4 th ( 1.5" separate) on the 920.
It has a stock cam, head, carbs and 9.5 to 1 comp. so the info will only be useful to a very small number of Norton owners, maybe just one!
Side note, I found an old discussion of cam types and dyno results from a few years back.
I was surprised to see that the PW3 made 5 HP less than the stock cam at 4500 rpm, same bike same dyno, I believe same day. The PW3 made 3 HP more than the stock cam at 6500.
The owner loved the feel of the new PW3 as the power falloff then the surge gave the sensation of great power.

Glen
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What usually happens when you fit a race cam in place of a standard cam and change nothing else, you gain power both below and above where the power band starts, you get much more above where the power band starts,. But where the power band starts can move upwards 1000 RPM or even more. So if you had a power band from 3000 RPM to 7000 RPM with the standard cam , With the race cam, you now have a power band from 4000 RPM to 7000 RPM, but with more power above 4000 RPM.
When you race, you always stay within the power band. On a road bike, you might use the bit below the power band quite often. If it comes on strong at 4000 RPM, you have to live with it. With a torquey motor, if the power band starts at 5000 RPM, and you drop below it when on the max in a slow corner, you end up slipping the clutch to get out of the corner. That is when you crash.
The 2 into 1 exhaust system softens the process and you can end up going faster more safely. But if there is any restriction in the exhaust, you lose power off the top of the power band. With my Seeley 850 I only use the bit between 5,500 RPM and 7,500 RPM - OOPS ! - (Close ratio gearbox).
But if I get balked in a corner, I am still OK.
I don't like talking about performance, but if I race again in Period 4 historic, I will definitely win. Last time I raced, I had them all beat when the motor stopped. And what was there does not hang around.
 
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With my 500cc Triton, when it was fitted with separate pipes and megaphones, it was unrideable. After I fitted a 2 into 1 system , I lost 1000 RPM off the top , but actually got decent lap times.
 
In the Clymer commando Manual . it shows pipes & megas .

Dual 1 3/4 BORE pipes . Id think these'd sound pretty good .

Used their mega on 2 - 1 set up , Std front to one pipe twice the volume ( X section )
starting under the front of the case . Didnt slow it down any . and wasnt to loud ,
under 1/4 throttle . Bit of a drone over that .

But try Dual 1 3/4 bore SS or S type pipes , for panache & daring . Zero restriction .
Which is a good start .
 
What type of exhaust for power. (2019)
 
I am not sure that just changing the cam and then saying it isn't as good, is a relevant test. A cam with a bigger overlap will significantly reduce the dynamic compression, and compression makes power, for a PW3 to work properly the compression needs to be raised.

I found that a standard cam didn't like a high static compression, it pinked badly.
worntorn said:
Side note, I found an old discussion of cam types and dyno results from a few years back.
I was surprised to see that the PW3 made 5 HP less than the stock cam at 4500 rpm, same bike same dyno, I believe same day. The PW3 made 3 HP more than the stock cam at 6500.
The owner loved the feel of the new PW3 as the power falloff then the surge gave the sensation of great power.

Glen
Click to expand...
 
Chris said:
Hi Ralph
Your bike looks fantastic ! Love the way you keep looking & progressing. I have one of Nick's 2 into 1 systems to put on the MK4 750. I will catch up with you this season. Good luck at the weekend.
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Thanks Chris, have you got any meetings planned for this year?
 
Fast Eddie said:
Does NRP incorporate a megaphone into his 2:2 systems? I kinda assume he does...
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The days of Megaphones as such are long over....the pipe increases in diameter between the end of the primary pipe and the entry to the silencer, where the perforated section inside the can remains at that diameter until the exit. (old picture but the exhaust is wrapped these days, clearer to see here. The join primary to rear section is right behinds the frame tube in this picture, so in truth the primary runs pretty much to the bend!)
IMG_1412.jpg
 
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storm42 said:
I am not sure that just changing the cam and then saying it isn't as good, is a relevant test. A cam with a bigger overlap will significantly reduce the dynamic compression, and compression makes power, for a PW3 to work properly the compression needs to be raised.

I found that a standard cam didn't like a high static compression, it pinked badly.
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I am pretty sure if Jim Comstock did it he was making a point, the point being just changing a cam doesn't make sense, you will be disappointed.

You have to 'accommodate' the cam with some compression and some flow.

We know that, but there are many out there over the years who have suckered themselves into installing a 'hot' cam only to find out what Jim and others will have been telling those who will listen for years!
 
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Yes, it seems there are a lot of hot cams installed in otherwise stock or near stock engines and that is a detune.
A very popular one! I recently watched Mick Hemmings do just that on the engine assembly DVD. stock pistons, head, carbs and an upgrade to a "sports Cam", a PW3. It'll work but it will leave a big hole. Thanks to Jim and his dyno, we know just how large the hole is.
Jim's owner was thrilled with the PW3 as it gave a 2 stroke zing at the top, magnified by the midrange hole.
On the question of best exhaust, the answer seems to be dependant on the other components installed in the engine. Change one thing and everything changes. I can say with certainty that the Dunstall 2 into one does not perform as advertised, that is it did not turn my 850 into an 11 second bike! In fact it slowed the bike down a bit. Change one thing and everything changes.

Glen
 
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SteveA said:
...the pipe increases in diameter between the end of the primary pipe and the entry to the silencer, where the perforated section inside the can remains at that diameter until the exit.
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Cool. That IS a megaphone Steve, albeit a shallow one. I think it’s ’proper’ reverse cone megas that seem to be out of vogue these days.

So long as the perforated tube in the silencer is at least the same diameter as the outlet of the megaphone, it has no effect. The megaphone effect is taking place in the megaphone and before the waves reach the perf tube.

Long, shallow, megaphones are generally the way to go as I understand it.

Out of curiosity, when Nigel makes a custom system like yours and Ralph’s, what info does he ask for; bore, stroke, CR, cam details...?
 
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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Anyway Storm... if PW can ride Wagon Wheels I see no reason you shouldn‘t ride Wheelbarrow !!
 
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.
 
Fast Eddie said:
Long, shallow, megaphones are generally the way to go as I understand it.

Out of curiosity, when Nigel makes a custom system like yours and Ralph’s, what info does he ask for; bore, stroke, CR, cam details...?
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There are long shallow megas around, more or less the whole length of the pipe, and yes they seem to work at least on some single engines, but they aren't the only thing that is being used, check out some much longer pipes people like Snotzo have been involved with for example.

Not Nigels approach on the Norton isn't a long 'mega' it is a few inches of conical shaped section to step up to the larger diameter, that is as I see it, but maybe it is too subtle for me!

And yes, Nigel asks for all of that data, valve timing seems the most critical. He has some software to confirm what is happening, but is working from quite a bit of experience these days on top of what the software can tell him. He has made systems based on the Maney 2 into 1 design, particularly for Watson/Thwaites on the big banger, but he also made the separate pipes were on the 750 short stroke 270 crank, which as I understood it was mainly because the 2 into 1 just won't work with the crank. Nor did those pipes look too much like mine, smaller ID I think!

I have 3 pipes, 2 on the Norton and 1 on the Fury Yamaha single. Seems to me they work!
 
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