Dyno run (2017)

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The biggest surprise I have had with my Seeley 850 is that it is fast enough to be competitive against 1100cc methanol-fuelled Honda CB750s. I never expected that and that is why the bike stat un-raced for 20 years. The motor in my bike has got almost nothing done to it except for a 2 into 1 pipe and methanol fuel. Most of it's advantage has come from it's steering geometry. It turns quicker and under most other bikes, so I almost always have the run on them. I only found that advantage by accident. I never run wide in corners, stand the bike up and indulge in a drag race down the next straight. Commandos are not good for that.
 
Nigel, I have never understood how a pumper carburettor can provide more power. Usually if the mixture is even slightly too rich, the motor becomes sluggish. Best power always seems to be when the motor is just prior to destroying itself by detonating and burning pistons and valves. I suggest the shape of the needle in a normal carburettor is about coping with the loss of vacuum which leans the mixture off.
 
acotrel said:
Nigel, I have never understood how a pumper carburettor can provide more power.
Click to expand...
You're right; it doesn't. What it does allow you to do is to jet for the best power level at any throttle position. Normally, this would cause the engine to bog as the throttle is opened, but the accelerator pump adds fuel for a predetermined amount of time until the fuel through the jets can "catch up" with the air increase. With the jetting now leaned for best power rather than to cover a lean bog, you're now producing more steady-state power.
 
Full Auto said "Now, to my (opinionated) point. I rarely use the top end. I trundle around town or the open road, using the low end and fat midrange that Nortons are known for, with somewhat more in my case because of the changes made. When on the road, you use the low end and midrange ALL THE TIME, not occasionally like the top end."

Ken, I know where you are coming from here. My Commando gets used differently than yours or Nigel's, but the midrange is more important to me than the very top.
Doing long distance touring, generally in mountains, the loaded bike has to pull up some long steep grades, often for many miles.
I don't expect it to overheat, ping, nip up or to bog even in top Gear on these grades (7-8percent) . With the bike heavily loaded 2 up + gear, its easy to climb at 70-75 mph on about 1/3 to 1/2 throttle, top gear.

So midrange is king and it has lots ( near stock bike, just open peashooters)
As good as you say the midrange of your motor is, it would improve with a stock cam. It has to.
The stock cam and twin carbs also gives nice power between 5 and 6 k, just not as much as a well matched hotrod like Nigel's will.
But I would wager that Nigel's hotrod motor would not be so good for climbing the Salmon -Creston (BC) or White Bird Pass ( Idaho) on a hot summer day in 4 th gear, bike fully laden.
Happily for him, it probably doesn't matter!

Glen
 
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Fullauto said:
Hey Nigel. I just call it as I see it. I can hardly call it as somebody else sees it. Absolutely no offence intended. Except to those "cool" cowboys!
Click to expand...

Zero offence taken here Ken, it’s all healthy debate in my book.

Now about your unwarranted attack on cowboys...
 
worntorn said:
Full Auto said "Now, to my (opinionated) point. I rarely use the top end. I trundle around town or the open road, using the low end and fat midrange that Nortons are known for, with somewhat more in my case because of the changes made. When on the road, you use the low end and midrange ALL THE TIME, not occasionally like the top end."

Ken, I know where you are coming from here. My Commando gets used differently than yours or Nigel's, but the midrange is more important to me than the very top.
Doing long distance touring, generally in mountains, the loaded bike has to pull up some long steep grades, often for many miles.
I don't expect it to overheat, ping, nip up or to bog even in top Gear on these grades (7-8percent) . With the bike heavily loaded 2 up + gear, its easy to climb at 70-75 mph on about 1/3 to 1/2 throttle, top gear.

So midrange is king and it has lots ( near stock bike, just open peashooters)
As good as you say the midrange of your motor is, it would improve with a stock cam. It has to.
The stock cam and twin carbs also gives nice power between 5 and 6 k, just not as much as a well matched hotrod like Nigel's will.
But I would wager that Nigel's hotrod motor would not be so good for climbing the Salmon -Creston (BC) or White Bird Pass ( Idaho) on a hot summer day in 4 th gear, bike fully laden.
Happily for him, it probably doesn't matter!

Glen
Click to expand...

Where I live, all we have is quintessential English rolling countryside. Which, of course, is lovely, but we certainly don’t have the dramatic country you enjoy. We do have a little of that up North where I’m originally from, and I do miss it!

So, you might be right Glen. When I read your logic, and recall what Comnoz has said in the past, I agree. But then I remember how my bike felt back to back with my mates near stock mk3 (with peashooters). It basically left it for dead in every regard apart from the fact that his was (even) smoother than mine.

I forget the exact figures now, but mine showed near 50 foot lbs torque from around 3k to over 6k. I can easily imagine yours outperforming mine below 3k, after that, I honestly don’t know.

But as we know, dyno figures are only useful as comparitive, not absolute figures. I will try even harder to persuade my mate to bring his near stock mk3 to the dyno next time I go as it would be really interesting to use his as a baseline against which to compare the effect of things I’ve done.

Or, you and I will have to arrange that drag race one day!

One way or the other, I’d certainly like to accompany you on those roads one day as you do really ‘sell’ them Glen.
 
Horsepower generally wins drag races and of that you have more!
It's heat that is the enemy in the Mountains. Bikes that rip around perfectly at lower elevation suddenly develop strange new problems, like seizure.
Last trip out we nipped up two bikes, a hotrodded 10 to 1 cr 636 Comet and a very nicely restored plunger Gold Flash. Both bikes were well broken in at lower elevations and on easier terrain. They seized within 100 yards of each other near Washington Pass Summit, just when I was thinking they were doing ok pulling up there at a steady 65 mph or so.
Very high compression engines can have detonation problems in such places. On the other hand, a working squish band might be the saviour.
It's a bit of Roulette!
Glen
 
worntorn said:
But I would wager that Nigel's hotrod motor would not be so good for climbing the Salmon -Creston (BC) or White Bird Pass ( Idaho) on a hot summer day in 4 th gear, bike fully laden.
Click to expand...
+1 on the White Bird Hill! Nine miles nearly straight up with no level spots in between. "Averages" a 6 percent grade. Four escape ramps for the semi's coming down. 2750' rise in upper 90-degree summer weather. That's a road dyno to be reckoned with!

The old Hill was a lot more fun (on a bike or with the right car).
Dyno run (2017)

Nathan
 
I suggest that with most commando engines torque is more important than top end power because of the heavy crank. You can have a motor which produces a lot of horsepower at high revs, but what does it matter if the revs never get to high levels ? With some motors which have light cranks, they almost stall when they encounter slight head winds. If you have the heavy crank and a close ratio box, the revs are usually always well up the rev range. With a light crank, the close box is essential. With the heavy crank, the acceleration is still faster with a close ratio box than what it is with a wide ratio box. In theory a light crank in a top end motor will be faster, but that doesn't necessarily happen in practice. On most race circuits and on public roads, there are corners. How fast you get around them and get back onto the gas, determines how fast you go down the next straight bit of road.
 
worntorn said:
Full Auto said "Now, to my (opinionated) point. I rarely use the top end. I trundle around town or the open road, using the low end and fat midrange that Nortons are known for, with somewhat more in my case because of the changes made. When on the road, you use the low end and midrange ALL THE TIME, not occasionally like the top end."

Ken, I know where you are coming from here. My Commando gets used differently than yours or Nigel's, but the midrange is more important to me than the very top.
Doing long distance touring, generally in mountains, the loaded bike has to pull up some long steep grades, often for many miles.
I don't expect it to overheat, ping, nip up or to bog even in top Gear on these grades (7-8percent) . With the bike heavily loaded 2 up + gear, its easy to climb at 70-75 mph on about 1/3 to 1/2 throttle, top gear.

So midrange is king and it has lots ( near stock bike, just open peashooters)
As good as you say the midrange of your motor is, it would improve with a stock cam. It has to.
The stock cam and twin carbs also gives nice power between 5 and 6 k, just not as much as a well matched hotrod like Nigel's will.
But I would wager that Nigel's hotrod motor would not be so good for climbing the Salmon -Creston (BC) or White Bird Pass ( Idaho) on a hot summer day in 4 th gear, bike fully laden.
Happily for him, it probably doesn't matter!

Glen
Click to expand...

Funnily enough, Glen, in reality, the only change to the motor during the rebuild was the cam, and it leaves the stock cam so far behind at all revs it's not funny. Also, because of the overlap. I get no pinging, no matter what the rating of the fuel is. The difference in acceleration between 50 and 70 MPH is really noticeable. Strange, but true. I would make the PW3 cam standard on any build I would do from here on in.
 
Ken, Your comment about getting no pinging because of the performance cam ties in with what I said on this forum about fitting race cams to engines, causing them to run with less distress. I fitted race cams to many standard 650 Triumph engines. The first noticeable change is the pronounced power band - operating from 4000 to 8000 RPM with more grunt below 4000 than with standard cams. With a Commando engine, I don't think anyone ever fits 'full race' cams, because the bottom end won't cop the revs and the cam followers are probably too heavy. However there would be benefit for anyone in fitting a performance cam to one as long as it did not raise the rev limit above 7000 RPM, to get more power.
 
Glen a well-worn motor can make good power as long as the rings are OK and the valves are seating properly, and the cam is not buggered. You might think that because a motor is all brand-new inside, it must perform well - not necessarily the case. Sometimes a sloppy old heap of garbage can be faster. It depends on how it is set up.
 
I never doubted you. You obviously know what you are talking about. That cam interests me. It would be easy to have a 'full race' one ground up, but it might become very self-defeating. One thing that many people do not know, is that with the big four cylinder Japanese bikes - top end was never a problem. So Yoshimura cams and similar, were designed to improve mid-range. If you fit a 'full race' cam to one of those, they really get up and go, but the bottom end power becomes difficult to manage. We got a Z1R going like that in the 1970s - quickest in it's class at Bathurst that year.
 
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