Head flow testing.

Indeed.............surely though if this is the case, then it would be a good idea to outline exactly what you have achieved through flow testing and developing heads, which are then used on road or race machinery?

Carbonfibre said:

Indeed.............surely though if this is the case, then it would be a good idea to outline exactly what you have achieved through flow testing and developing heads, which are then used on road or race machinery?

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That is the reason I am doing this. I am hoping to be able to get a more thorough understanding myself of why some heads work and some don't so I can apply what I have learned to future projects.
I have been working in this field for many years and I know what I have made work and what has not worked for me but I like to see what other people have done. I might even learn something new.

You can never learn to much comnoz, When you stop learning you become a know it all. Its hard to live with a know it all.
Phil

Norton-Villier said:

You can never learn to much comnoz, When you stop learning you become a know it all. Its hard to live with a know it all.
Phil

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A friend of mine sold a brand new set of encyclopedia's because his wife knew everything :lol:

That is the reason I am doing this. I am hoping to be able to get a more thorough understanding myself of why some heads work and some don't so I can apply what I have learned to future projects.
I have been working in this field for many years and I know what I have made work and what has not worked for me but I like to see what other people have done. I might even learn something new. [/quote]

Just interested to learn what you have actually achieved with your development work to date? Must be very hard to make a head with ports that already seem much too big for road or road race type use, to offer any really useful performance increases, without some very careful reshaping and making the ports smaller in the areas which are obviously overly large.

Sumarize what I have learned so far. I could write a book. Maybe I should.

1. Air velocity becomes useful in efficiently filling the cylinder at about 300 FPS @ 28 inches depression.

2. I like to see airflow reach 300FPS at around 75% of the maximum valve lift.

3. The more velocity the better as long as you do not sacrifice so much flow potential that you can not make the horsepower [RPM] required. Providing more airflow potential than the engine can use kills the power fast because the air will not reach a workable speed.

4 Big flow numbers do not mean the cylinder is going to be efficiently charged. You have to keep the mixture in the cylinder or it doesn't do any good. After the piston reaches bottom dead center on the intake stroke and begins to rise ,the pressure in the cylinder goes up. If the pressure in the port is lower than the pressure in the cylinder then the mixture just flows back out of the cylinder into the port until the valve closes. The inertia of the air in the port is what can keep the pressure in the port high and keep the air from escaping or in some cases continue to charge the cylinder after the piston stops pulling it in.

5. Port velocity over 400 FPS is hard to get in a Norton head. There is too much angle from the port to the seat for fast moving air to make the curve. Re-angling the valve makes it worse so then you must make the port larger to keep the velocity down. Once the air reaches that critical point and begins to break away from the floor on the short side it will flow across the back of the valve and mess up the flow.

6 For a performance street engine where power under the curve is more important than power peak- velocity is more important than max flow. For peak power you need both velocity and enough flow to provide for the target horsepower but Without adequate velocity you will never reach the target horsepower.

6 Norton should have stayed with 30mm ports.

7 Bigger valves are nice. Re-angled valves are not.

8 Norton exhaust ports are too big and the short side radius is too short.

9 Flow benches are worthless for testing exhaust ports except for low lift flow to find the best seat angles.

10 Increasing the intake valve diameter by 4mm and decreasing the exhaust valve by the same amount makes more power than re-angling the intake guide to get the 4mm os valve in there. It takes a new exhaust seat and some port filling to make it work though.

11 Big cams trade off pulling power for rev-ability. You can then get the pull back by gearing lower but high rpms and Nortons don't mesh very well on the street.

12 Revving a longstroke Norton over 8200 RPM is a waste of energy. Even if it is built well enough to handle it mechanically you can't beat the velocity vs friction equation. Any horsepower increase from the increased RPM will be more than eaten by friction once 8200 RPM is reached. Horsepower loss from friction is the main reason a short stroke Norton will outrun a longstroke Norton.

13 If you really want to go fast buy a crotch rocket. If you want something that stretches your arms and puts a grin on you face ride a Norton.

Torque is what we really want! But we have been sold on Horsepower so long we don't know it. Long live the long strokes, ie. Norton's and Buell's. :wink:

In regard to Norton heads modified by you, what increases in torque and power have been recorded on the dyno, when a bike fitted with one has been tested?

Hi Jim, many thanks for those valuable informations........but to stay on a more simple ground what do you think of the difference between the std 32mm heads : combat , RH5, RH6, about flow ? we know the difference about the ratio, but is there some heads which flow better for the hot street, or must we stay with the 30mm?? Pierre.

As a rule of thumb intake port dimensions for race use need to be approximately 75% of valve diameter, and a little smaller for road use. Use of much bigger ports, which may well provide impressive numbers on a flow bench, will in most cases mean reduced torque, and power shifted very high up the rev range.

marinatlas said:

Hi Jim, many thanks for those valuable informations........but to stay on a more simple ground what do you think of the difference between the std 32mm heads : combat , RH5, RH6, about flow ? we know the difference about the ratio, but is there some heads which flow better for the hot street, or must we stay with the 30mm?? Pierre.

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Actually the Norton heads all flow pretty similar numbers in stock condition. There seems to be as much variation from one head of the same number to the next of the same as there is from one series to the next.
The 30 MM port head has the cleanest [least port turbulence] but it is limited at about the same flow as the 32mm port. The 32 mm port will not carry as much velocity as the 30mm port because the short side radius on the 32mm head is worse.

The better head to use for an easy port job is the 30 mm head. Remove nothing from the floor except to make sure the short side radius is smooth and meets the seat without a step. Using a flame shaped carbide burr widen the port 2 or 3 mm starting from about 1 inch in front of the guide and going all the way to blend in with the seat. Use caution where the oil drainback goes near the port. Clean up the protrusions around the guide. Clean up any step from the bowl to the seat. Do not increase the port diameter unless you are over 900cc. A 30mm port does not hinder high rpm and making it larger only delays when the powerband starts.
A large part of making a Norton head flow is the valve seat. The seat needs to use at least 3 angles, preferably 2 below the seat and 1 above and the 45 degree cut needs to be no more than 1mm wide. The width of the valve seat is probably the single biggest mistake made.
This makes a good head for performance street or roadrace use and will be better than any stock head . Taper the manifold up to the carb bore. Use a 32 or 34 mm carb. PLUG - Or buy a Full-auto head for the max benefit. Jim

Carbonfibre said:

In regard to Norton heads modified by you, what increases in torque and power have been recorded on the dyno, when a bike fitted with one has been tested?

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Well I am not going to quote numbers here because there are way to many variables but the only time I have replaced a RH4 on a stock motor I saw the powerband start 800 rpm lower. IE -the power at 5000 rpm with the stock head was now there at 4200 rpm with the Fullauto. Power at 5500 was up about 10% and power at 6200 was up about 2%. It felt strong on the street. Jim

comnoz, Could you give me your opinion on why in 73 they put an RH10 head with 30mm ports on an 850? Did it have anything to do with some of the things you mentioned above? Do you think it would better to go with 30mm carbs and 30mm to 30mm carb specers rather than 32mm to 30mm carb spacers with 32mm carbs? Hope this makes sence.
Phil

Public demand and bigger is always better attitude was why they went to 32mm ports. The RH10 head will work best with the tapered manifolds and 32mm carbs. Jim

Jim, I have a Maney Stage 2 850 head packed and ready to ship to you Monday. I'll be interested to see how it compares to the Stage 3.

Ken

The "venturi" effect in relation to cylinder head design is something that appears to work extremely well, but often when the port sizes are too big there is a need to reshape and make the ports smaller, rather than removing material to achieve the highest possible numbers on a flow bench.

Carbonfibre said:

The "venturi" effect in relation to cylinder head design is something that appears to work extremely well, but often when the port sizes are too big there is a need to reshape and make the ports smaller, rather than removing material to achieve the highest possible numbers on a flow bench.

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Precisley, A small port that is correctly shaped can flow as much as a big port that is a poor design. The small port then has the advantage of inertia from velocity. Jim

I agree with Jim C and he has obviously done his work. I'm suprised that (when I was racing) I came to most of the same conclusions. I would try to get a 1mm larger intake valve in mainly to shape the area near the seat to get more flow at low & med lift. Starting with smaller ports allowed reshaping in an upward direction (until you ran out of material) to get the gas charge to turn dowwards in a more effective manner .

The idea was to get the full charge to come straight down and go in all the way around the seat with no dead areas - better than going to a bigger valve which weighs more. The most important area was around the guide and leading up to the seat (bowl and floor).

It was a balancing act - pushing high RPM hsp up to the point where it was still usable. The ports did measure 32mm at the mounting surface but tapered down on the way in. They were offcenter - raised in relation to the bolt holes

The limiting factor was heat. When the motor was cooking it literally cooked the interals and heat treated everthing all to pieces.

So I went to alchohol- another story.

JimSchmidt

For anyone who thinks 30 mm will not flow enough air I did a simple test. It is a 6 inch long piece of acrylic with a 30 mm hole through the center and a 1 inch radiused inlet and outlet. [nowhere near the optimum for flow]

On the flowbench it flowed 190.5 CFM at 28 inches which is enough to produce 64 horsepower per cylinder according to Superflow's formula. Do you think you need more air than that? Jim

comnoz said:

For anyone who thinks 30 mm will not flow enough air I did a simple test. It is a 6 inch long piece of acrylic with a 30 mm hole through the center and a 1 inch radiused inlet and outlet. [nowhere near the optimum for flow]

On the flowbench it flowed 190.5 CFM at 28 inches which is enough to produce 64 horsepower per cylinder according to Superflow's formula. Do you think you need more air than that? Jim

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Stick a bend and a valve stem and crap in the middle of that tube and then see. :mrgreen: