Fast Eddie
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- Oct 4, 2013
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Same day... different cam...? That’s good going !
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.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
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
Thanks Chris, have you got any meetings planned for this year?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.
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!)Does NRP incorporate a megaphone into his 2:2 systems? I kinda assume he does...
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.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.
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....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.
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.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...?
Anyway Storm... if PW can ride Wagon Wheels I see no reason you shouldn‘t ride Wheelbarrow !!