Norton intake ports compared to Harley XR 750 (2013)

The RD 400 box is for a roadster, has a big gap between 3 and 4th and the 6th top gear is a bigger jump from 5th than the water cooled TZ 350 E/F/G which has a close ratio to suit the 4500 rpm all top end power band of this grand prix winning machine, with only a couple of hundreds rpm drop between 5 and 6th.
You very rarely want, say, a 3 1/2 gear for a corner for this machine.

Bernhard said:

The RD 400 box is for a roadster, has a big gap between 3 and 4th and the 6th top gear is a bigger jump from 5th than the water cooled TZ 350 E/F/G which has a close ratio to suit the 4500 rpm all top end power band of this grand prix winning machine, with only a couple of hundreds rpm drop between 5 and 6th.
You very rarely want, say, a 3 1/2 gear for a corner for this machine.

Click to expand...

There are a few articles about the RD400 in recent magazines which mention the gearbox. The RD400 is much less likely to bog down in corners because of the better ratios. The RD400 has more torque than the RD350, yet still has the closer ratios. I will go through my magazines and it I find either of those two recent articles, I'll post a reference to them. Ay least one of them was in 'Motorcycle Classics' - which I think is an American magazine. Close ratios means the revs have to come up less distance when you change up. With a Commando, the bike is noticeably less sluggish when you use a close box. I tried racing with the standard box - it is appalling. However I am probably a bit more sensitive to the differences than many people. I raced for too many years with a severe disadvantage in machinery.
Just in straight line acceleration out of any corner, the close ratio box makes the bike faster than it would be with wider ratios. On the circuit on which I normally ride, I know how long it takes to get from one corner to the next. If I get there quicker, I know it.

When I was building the Seeley 850, a friend said 'if you have a torquey motor, you don't need a close ratio gear box'. He was just showing his ignorance - I don't think he had ever used one. My 500cc Triton had a close box, but desperately needed 6 gears. If I set the overall gearing low I could beat most of the large 4 cylinder bikes around most of Winton, but get passed towards the ends of the straights. If I set the overall gearing high, I would be too slow out of corners, but fast enough at the ends of the straights. I usually set the gearing high. - With 4 speeds, there was never a happy medium. My Seeley now has a 6 speed TTI box.
With my bike, there are five things which make it fast - the steering geometry - the gearbox - methanol fuel - the front brake - and it pulls like a train.
To my mind, it is a very silly motorcycle. With what is in the motor, it should be slow.

edgefinder said:

Hi Christian, I'm glad you brought this up and offered help with welding. I've been using a small tig for years on steel and got pretty good. It doesn't have input for a pedel so have to scratch start. I was recently given a Lincoln square wave 355 and reading up I see everybody's gone to Inverter machines. Your saying I need to get a modern inverter machine and I'm wondering what specific features i'm looking for and why.

Click to expand...

Yo hi there,

Gladly done, I'm happy that my current edu as IWE is at least good for something.
Please send me a pm so I can if needed give you further assistance which I more than gladly do.
Even without pedal one should not need scratch starting as usually a Tig welder has hi frequency arc starting and Zeroline transfer.
If not try scratching on a nearby copperplate that way at l AST you don't (or at least less) contaminate the needle

@acotrel

I can assure you that you will not hear a Transsonic port on the usual SF, send style flowbench.
What one hears on whistling ports is in my experience Eddy disatachment on corners or heavy deviation from the perfect shape, thus disturbing the smooth (not really laminar despite what gets often stated since it's not honey) flow and making quite some ear-piercing noise.
Furthermore I'm the opinion that not wanting to offend (not ment personally) you, that concerning the usual www and racecircuit circulating bull, that one does not need outrageous pressure differences on the intake as it is imho just not needed if sufficient delta P exists.
Some of the best heads have been developed on 10" water column (might even have been Axtell and Branch while smokey went up to 28").
It's by far more important to pay very very close attention to pressure distribution within the port, local airspeeds through various valve piston displacements regarding cam timing.
And last but not least to always remember that gas follow different inertia paths than lower density air .

For the pulsing and everything else I already mentioned that some SAE documents exist with mathematical correction factors but that it is possible to hypothize that one can consider it "quasi static"
What I feel is by far more important is to calculate immediately the coeff of disch in order to be able to see how efficient are the various parts of the port.

Of course one could break it down to incremental steps but it is simply not needed in 99,99% of the cases to run havoc on semi agricultural engines, with lots of other weaknesses (triumph by far more than Norton or beezas)

All the best and kind regards

Christian

Hi there,
I just welded and roughed out last week a D-exhaust port, thus with a gentler SSR curve.
If somebody could tell me how to insert pictures without using a external hosting site I would be very happy to show 'em.
Kind regards
Christian

Hudriwudri said:

If somebody could tell me how to insert pictures without using a external hosting site I would be very happy to show 'em.

Click to expand...

You would need VIP membership for that.

Uh don't have that pitty
Thanks for the info though

Kind regards

Christian

Ps: oh wait a minute, I guess I could also url link from another forum

Engine development is subject to the law of diminishing returns. A good Commando engine on petrol, would probably be one which delivers 60 BHP and 60 newton metres of torque. - Just my opinion - I wonder what others think is a reasonable expectation ?
When you look at horsepower and torque curves, they always cross over at 5000 RPM, but the scaling on the vertical axis might be deceptive. There is no measure of cause and effect and the gearbox is a torque multiplier. - In short, when I look at a torque curve from a dyno, I don't know what I am looking at.

acotrel said:

Engine development is subject to the law of diminishing returns. A good Commando engine on petrol, would probably be one which delivers 60 BHP and 60 newton metres of torque. - Just my opinion - I wonder what others think is a reasonable expectation ?
When you look at horsepower and torque curves, they always cross over at 5000 RPM, but the scaling on the vertical axis might be deceptive. There is no measure of cause and effect and the gearbox is a torque multiplier. - In short, when I look at a torque curve from a dyno, I don't know what I am looking at.

Click to expand...

Your last sentence is the first think you've said that I agree with

Try 75 RWHP and 60+ft/lbs from a 750 on petrol

acotrel said:

When you look at horsepower and torque curves, they always cross over at 5000 RPM, but the scaling on the vertical axis might be deceptive. There is no measure of cause and effect and the gearbox is a torque multiplier. - In short, when I look at a torque curve from a dyno, I don't know what I am looking at.

Click to expand...

5252 is the cross over point.

Of course there is a measurement of the effect of the gearbox.

Im surprised Al is posting dyno videos as he doesnt believe in dyno data going by his earlier posts???