FA head power curve?

So I wonder what happens with stock cam and stock valves in a 920?
Does it produce more midrange than an 850 and if so at what rpm does the small inlet valve turn it into an 850, then a little higher a 750, as occurs with the 850?

I have a test for this in mind.

Glen

worntorn said:

So I wonder what happens with stock cam and stock valves in a 920?
Does it produce more midrange than an 850 and if so at what rpm does the small inlet valve turn it into an 850, then a little higher a 750, as occurs with the 850?

I have a test for this in mind.

Glen

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I would suggest it does.
The bigger volume still creates a bigger draw.
But the valves are still the bottleneck, and bigger ones would yield gains. Provided the porting and blending was executed to suit.

My result for the 850 as it sits ( balance pipes back on) was 100 bottom 110 top on dyno hill.
The 920 was markedly stronger 100 bottom to 135kmh top, same gearing.

The plan is to add 150 lbs or so to the 920 to make it weigh the same as the 850 then test.

But this only tests midrange.
I am sure that you are correct, the upper range is affected by the inlet size. This starts to happen at some rpm, I'm not sure where. Maybe 5 k?
That is where a dyno would be useful.
It would be great to see dyno charts from stock 750 and 850 bikes as a starting point, same dyno, same cf used, if any.
We have those dyno charts from Mick Walker's book, but people (Rohan)have questioned the accuracy of those .

Glen

I do have the Torque curves compared to the 750, but sadly I didn't dyno my 850 prior to fitting the head and cam. We have a standard MK3 here, I will get that on the dyno in the spring.

Madnorton said:

I do have the Torque curves compared to the 750, but sadly I didn't dyno my 850 prior to fitting the head and cam. We have a standard MK3 here, I will get that on the dyno in the spring.

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That would be interesting. I'm prepped for disappointment! I'm guessing my other bike is three times the power and torque of the Norton, but it's no more fun to ride. Funny that.

How fast a Commando goes in top gear depends in where the motor has to come from. If you have 5 gears and the top 4 are close, when you change from 4th to 5th, you don't lose many revs. Also, you might have the needle set right for high vacuum conditions, but when you change up, you back-off to take the load off the transmission. As you wind the throttle on again, you are into low vacuum again, and the needles in the carbs richen the mixture. If the taper is too quick or the port is too small, the mixture could be richer then the optimum. It does not take much to take the edge off the motor.
I use methanol fuel, so I have slightly more margin for error than I would have with petrol, but even with that - the slightest bit too rich causes the motor to respond slower.
With the Commando engine, I have found that if I gain an improvement, it usually does not become evident until I raise the overall gearing, and the bike gets to the next corner quicker.
There is a part of Winton Raceway which I know very well. The corner at the end of it is more than 90 degrees. If I get down the straight before it faster, that corner becomes more difficult. I use 6D Mikuni needles in a 34mm Mk2 Amals - the slowest taper. It means my jetting stays lean right down the needles as the throttle opens.
I do not use Amal needles and just accept that they are right at all throttle openings. With Mikuni needles you have a sensible needle chart. 6D suits both 32mm and 34mm Amal and Mikuni carbs. 6D is slow taper and 6F is quick taper. The 5 series is for the next two smaller size carbs.
Amal classification of needles is not so simple.
The taper on the needle might be different for bigger ports, but the type of fuel being used does not matter. The taper is there to compensate for loss of vacuum, and with a road bike, it does not matter so much, if it richens a bit too quick, as you open the throttle.
If my needle jets are half a thou of an inch too big, the bike becomes significantly slower, and that is with methanol - petrol is worse.
Modern bikes have fuel injection and probably better mixture and ignition control.

I do not know how you use the throttle when your bike is on the dyno. If you use slower taper needles and wind the throttle on slower, you might get different results. You are probably indirectly measuring throttle response. With my bike, I wind the throttle on a bit slower, but it responds quicker when I do that.

Nigel, from what my motor does on methanol, I pretty much know what your's will do on petrol. I have used several motors using both fuels. When you are setting the needle jet size with petrol, you choose between 0.106 and 0,107. With methanol, I choose between 0,116 and 0,117. At half throttle, the parallel part of the needles is metering the fuel in the needle jet. As the throttle is opened more than half, the taper comes into play.
With methanol, half a thou of an inch in the needle jet is the difference between fast and slow. Petrol is twice as critical. You can have the correct size needle jet, but if the taper on the needles is too quick the motor will not respond as well at throttle openings above one half.
When you over bore a motor, you effectively raise the compression ratio. It has the same effect as leaning off the jetting or advancing the ignition timing. If you are jetted slightly too rich when you overbore, you get more go. Which you might have got if you could jet close enough to the optimum. Usually a bigger motor delivers more torque, but when you raise the overall gearing to use it, the gains are often not what you think they might be.

Madnorton said:

There seem to be many engines built but very few seem to make it to the dyno which is a shame as it doesn't cost much for a dyno run.

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So far, my inquiries to get a base dyno run on an old positive ground Norton are ignored because all the kids with dynos around here are "dyno tuners". A basic run on an old bike without a computer managing the fueling is a waste of their time apparently. I don't need a dyno tune. I just want a slip of paper that shows where I am as it is. I want to be sure that spending $4K on the motor makes less HP than stock. That way I'll know I'm doing it right, and my butt dyno is broken. lol

Schwany said:

So far, my inquiries to get a base dyno run on an old positive ground Norton are ignored because all the kids with dynos around here are "dyno tuners". A basic run on an old bike without a computer managing the fueling is a waste of their time apparently. I don't need a dyno tune. I just want a slip of paper that shows where I am as it is. I want to be sure that spending $4K on the motor makes less HP than stock. That way I'll know I'm doing it right, and my butt dyno is broken. lol

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Interesting. My experience with most dyno operators is they absolutely insist on snapping the throttle wide open from idle. Which our bikes generally don't like unless the carburetion is already pretty much perfect. They just ignore the fact that the bikes are not computer controlled with fuel injection.

I don't know why but they seem to NEVER listen when you ask (and pay) them to open the throttle at a steady rate. It's really damn annoying.

johnm said:

Interesting. My experience with most dyno operators is they absolutely insist on snapping the throttle wide open from idle. Which our bikes generally don't like unless the carburetion is already pretty much perfect. They just ignore the fact that the bikes are not computer controlled with fuel injection.

I don't know why but they seem to NEVER listen when you ask (and pay) them to open the throttle at a steady rate. It's really damn annoying.

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At least they will take in antiques. I'm getting nowhere with the close places. Thanks for the heads up on the WOT BS. For some silly reason I thought they ramped up. I would imagine they aren't accustomed to not winding the motors up to 11,000 RPM either.

My motor dead cold would not appreciate WOT from against the idle stop. I'm not sure it could do it warmed up. Probably not without a big cough. Throttle is 1/4 turn push pull Motion Pro. It'll take 1/8th (AKA half throttle) from the stop though.

Schwany said:

At least they will take in antiques. I'm getting nowhere with the close places. Thanks for the heads up on the WOT BS. For some silly reason I thought they ramped up. I would imagine they aren't accustomed to not winding the motors up to 11,000 RPM either.

My motor dead cold would not appreciate WOT from against the idle stop. I'm not sure it could do it warmed up. Probably not without a big cough. Throttle is 1/4 turn push pull Motion Pro. It'll take 1/8th (AKA half throttle) from the stop though.

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An upgraded dyno has just been installed near here in Wellington at a place with 50 year history of racing. They actually sold my Commando new in 1975. They are second maybe third generation owners now I think. So with a bit of luck they might be good. A friend with a race Commando is going there next week. But not much use for you in the USA sorry.

The attitude of your dyno owners is a bit hard to understand to be honest. Money is money whether the bike is 6 months or 50 years old.

johnm said:

An upgraded dyno has just been installed near here in Wellington at a place with 50 year history of racing. They actually sold my Commando new in 1975. They are second maybe third generation owners now I think. So with a bit of luck they might be good. A friend with a race Commando is going there next week. But not much use for you in the USA sorry.

The attitude of your dyno owners is a bit hard to understand to be honest. Money is money whether the bike is 6 months or 50 years old.

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I keep meaning to take my bike to Mike's (half-owner) dyno in Paeroa. They should know what they are doing with it re. Nortons. I just never get around to it.

johnm said:

The attitude of your dyno owners is a bit hard to understand to be honest. Money is money whether the bike is 6 months or 50 years old.

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I spoke too soon. Found one that will do the baseline. I have to schedule over the phone. Thanks for the information.

The confusing thing with a dyno result is the correction factor. Correction factors are rarely shown on the chart but often used.
Supposedly the most commonly used North American standard today is SAE J1349. That standard corrects for temp, humidity, and barometric pressure plus it adds 15% to the rear wheel result to allow for drive train loss. In Europe DIN is often used. It gives a slightly higher number than J1349.
There are many other standards in use as well.

Owners tend to report all results as " rear wheel horsepower" but many are not.
Sometimes the 15% friction factor gets added twice, once by the Dyno program then again by the proud owner.

For tuning though, the correction factors should be helpful , as long as the same dyno and same standard are always used.
If you do a baseline on a 60f day then come back months later with a modified engine but temps are 90f, the cf should correct to the standard and give a useful result.
Raw data is not really helpful in that situation.

Glen

worntorn said:

The confusing thing with dyno results are the correction factors used. They are rarely shown on the chart but often used.
Supposedly the most commonly used North American standard today is SAE J1349. That standard corrects for temp, humidity, and barometric pressure plus it adds 15% to the rear wheel result to allow for drive train loss. In Europe DIN is often used. It gives a slightly higher number than J1349.
There are many other standards in use as well.

Owners tend to report all results as " rear wheel horsepower" but many are not.
Sometimes the 15% friction factor gets added twice, once by the Dyno program then again by the proud owner.

For tuning though, the correction factors should be helpful , as long as the same dyno and same standard are always used.
If you do a baseline on a 60f day then come back months later with a modified engine but temps are 90f, the cf should correct to the standard and give a useful result.
Raw data is not really helpful in that situation.

Glen

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Thanks, I think you saved me some time and some lunch money. One baseline run sounds pointless without pre-modification numbers other than those in a Haynes manual. Besides I don't have an FA head. I have an FBS ported head.

If you don't have any future engine mods planned then might as well use the dyno money for tires etc.
Sounds like the bike runs strong now.

Glen

worntorn said:

If you don't have any future engine mods planned then might as well save some money for tires.
Sounds like the bike runs strong now.

Glen

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I appreciate the logic.

It runs well. I'd say it's reliable, but that might jinx it. I do need a new rear tire. I only seem to go hard in straight lines apparently and the rear is all squared off in the middle after 2100 miles. Fronts last forever on the street for me anyway.

Only thing I may do in the future that makes a dyno run now useful is send the spare head I have off to Maney, and put it on next year in place of the head I am using. Probably not talking big HP differences, but it could still be interesting to do a before and after.

With my Seeley 850, I have found that steering geometry is more important than any power considerations. When you can power through corners, immediately after getting into them, you become much faster at the ends of the straights. When your bike stays more upright in corners, tyres are less critical. When all the bikes in a race understeer, they are usually all out wide on full lean in corners and nobody has any advantage. This probably does not apply to extremely powerful motorcycles - they need to understeer.
If you ride an original Manx Norton, you will find they oversteer slightly - they are faster in corners than most other bikes of that era. And better than any Triton. I think you would find a Molnar Manx is different. These days 19inch race tyres are hard to get.

Schwany said:

Thanks, I think you saved me some time and some lunch money. One baseline run sounds pointless without pre-modification numbers other than those in a Haynes manual. Besides I don't have an FA head. I have an FBS ported head.

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Could be.

I used the same dyno a lot to develop a race bike but I have never had my street Commando on one.

But the race bike experience did teach me that carburation can be both more difficult and very rewarding to tune and many bikes are running too big a main jet for example. So a dyno with a reliable mixture analysis could be very helpful for a street bike as well.