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bill said:
Locating pins, perhaps used only for machining?
Head flow testing.
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Locating pins, perhaps used only for machining?
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Size of port, speed of port, amount of 'vacuum' on one side and pressure on the other side has an issue called "Choked Flow", with pressure shock waves as approaches super sonic rates. There are calculators to guessimate perameters to stay close to optimal flows in volume and speed. I was pensive Ms Peel 920 cc fed via 750 CHO head with Drouin would nullify significantly the benifit of boost, but best I can glean it ramps up flow to essentially optimal .7 mach #.
Defined
http://en.wikipedia.org/wiki/Choked_flow
As applies to ports/valves
Calculators
http://www.wallaceracing.com/machcalc.php
http://www.rbracing-rsr.com/machcalc.html
Defined
http://en.wikipedia.org/wiki/Choked_flow
As applies to ports/valves
Calculators
http://www.wallaceracing.com/machcalc.php
http://www.rbracing-rsr.com/machcalc.html
lcrken
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bill said:
The counterbores are for the heads of the two rear cylinder through-bolts. The 920 cylinders I am using with this head do not have counterbores in the cylinders for those bolt heads. The bolt heads sit on top of the cylinder. That helps keep the top of the cylinder liner from distorting around the bolt heads, a common problem with 920 cylinders.
Ken
lcrken
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jseng1 said:
Fair question Jim. I'm sure Jim C has an answer. He put a lot of time into developing the heads for his race bike back in the day. I'll look forward to seeing what he has to say.
FWIW, this particular head has the intake port opened up to 36 mm at the manifold surface. Intake valve is 5 mm larger than stock, and exhaust is 3 mm larger. It's intended for a very short stroke (75 mm x 81 mm) engine built primarily for top end horsepower. Big carbs, big cam, and high red line. Steve ran a similar one in his race bike quite successfully a few years back. I had planned to build it specifically for the AHRMA Daytona race, but now that I'm not doing so much of that, it might get used for a Bonneville lanspeed 750 class engine. In that case, it would use a 79.5 mm bore to meet SCTA and AMA rules. They don't allow the '060" overbore that AHRMA does.
Ken
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jseng1 said:
That is a question that ends up being somwhat of a balancing act. To fill the cylinder efficiently the airspeed needs to be over 300 fps. The faster the airspeed then the more momentum it has to continue filling the cylinder after the relatively short suction pulse has occurred. This has to be balanced out by how long it takes the air to get up to speed when the suction pulse begins.
Since the Norton engine is a relatively slow turning engine with a small bore then there is a relatively long period of time to get the mixture up to speed. The suction pulse is slow and long so a small cross section port is needed to accelerate the air to high speed.
A shortstroke engine with a larger piston and a higher RPM powerband has less time to get the mixture up to speed and a shorter but more powerfull suction pulse to get things moving. A larger valve and port is needed so that the airflow does not exceed the speed where air turbulence begins to plug the port. Once the maximum speed capability of the port is reached then turbulence takes over and the flow will no longer increase or will decrease.
How fast the air can move through the port is determined by the port shape and how much it has to turn the air to get to the valve seat.
With a Norton head with the intake flange in the stock position the maximum achievable airspeed is somewhere around 450 fps. A large radius on the shortside of the valve and careful shaping of the port is required to reach this speed. Modern downdraft ports easily exceed 450 fps and some formula car engines can see 600 fps.
A stock Norton head usually will not allow flow beyond around 300 fps. A 32mm port on a stock 850 motor is large enough that the flow in the port would not exceed 300 fps even if the port shape would allow it. The low CR and slow turning motor does not create a strong enough suction pulse to move the air that fast through a 32mm port.
On a standard bore engine you need a port with the cross section area of 30mm or less to be able to reach 350 fps. At 350 fps things really start happening. The cylinder filling efficiency increases greatly between 300 and 400 fps.
Increasing the bore size along with larger valves and higher CR will increase the pulse strength and a larger port may be needed so the airspeed does not exceed the capability of the port. A larger port will not help without larger valves.
You can dramatically increase the static airflow numbers by making the port larger but if the air is not moving fast enough to continue filling the cylinder between the time the suction pulse stops [BDC] and the time the intake valve closes then that volume of mixture is lost back into the intake port. If you have a long duration cam with a large port then the amount of mixture pushed back out of the cylinder before the valve closes can amount to nearly half the volume of the cylinder. That is why a 750 motor with a big cam and big ports feels like a 350 engine until the piston speed raises the airspeed to the point where it is not lost back out the intake. Once the port size is up to 34mm then the longstroke engine will not be able to get the airspeed up to the minimum before maximum piston velocity is reached and the engine will not be able to reach its full potential. Jim
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I hear Steve Maney is currently developing a special performance ignition system to use on his motors! Not likely to mean a head is going to flow any more CFM, but in real world terms poor ignition systems are likely to compromise ultimate performance notwithstanding how well all else might be working.
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For sense of speed values given.
300 f/s = 0.288 mach #. 450 f/s = 0.403 mach #. 690 f/s = mach 0.6.
Speed unit converter http://www.unitarium.com/speed
300 f/s = 0.288 mach #. 450 f/s = 0.403 mach #. 690 f/s = mach 0.6.
Speed unit converter http://www.unitarium.com/speed
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Thanks Jim - well stated.
There's got to be a way to raise the floor and increase the short turn radius? All to reduce port volume to increase velocity and tease more air to hold to the short turn floor.
There's got to be a way to raise the floor and increase the short turn radius? All to reduce port volume to increase velocity and tease more air to hold to the short turn floor.
lcrken
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Nice explanatiion, Jim. As you've pointed out, making Norton horsepower is all about compromises. I already know that this head will work well in Steve's ultra short stroke AHRMA 750 bike, with his cam. It made good horsepower, but the horsepower peak was not much higher in rpm than a really good long stroke engine. To gain significant horsepower, it needs a cam profile to suit the higher rpm limit available with the 75 mm stroke. I'm planning to run it with a Megacycle N480 cam with BSA lifters. This is where the compromise comes in again. Ideally, I'd just dial in faster acceleration on the lobe shape, but with the Norton's long, flexy, camshaft and small lobe size, I can't use something like a Chevy small block racing profile. I'm pretty limited to just going with more duration and more total lift, and a little bit more acceleration, and that's pretty much what the N480 has. In a perfect world I could put in a center cam bearing (sound familiar?) and make room for larger lobes. And then I guess I'd go to smaller valve stems and smaller diameter, shorter springs, weld up the valve seats and re-machinetrhem so I could raise the ports (sound familiar again?). But in the real world, I'd probably get the engine finished somewhere in the next decade. I'm hoping that the combination of readily available parts that I'm using will give me rear wheel horsepower in the 80s, and still have some powerband to play with.
I left out ceramic valves, lightweight maraging steel roller rockers, ceramic/aluminum matrix push rods, roller lifters, and so on. Maybe in my next lifetime.
Ken
I left out ceramic valves, lightweight maraging steel roller rockers, ceramic/aluminum matrix push rods, roller lifters, and so on. Maybe in my next lifetime.
Ken
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Ken, wouldn't it be nice if you could turn the clock back 30 years and still know what you learned in the last 30.
I would hate to try to deal with a cam with faster acceleration than a n480 in a Norton motor. It is fast enough I had trouble keeping the valve train together with it. I got to learn a lot about valve train harmonics and valve bounce when I used it. It needs light valves, lots of spring and stiff pushrods. Valves don't live long when they start bouncing. Jim
I would hate to try to deal with a cam with faster acceleration than a n480 in a Norton motor. It is fast enough I had trouble keeping the valve train together with it. I got to learn a lot about valve train harmonics and valve bounce when I used it. It needs light valves, lots of spring and stiff pushrods. Valves don't live long when they start bouncing. Jim
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bill said:
One would have thought that an ignition system that actually worked rather well, might be something anyone looking for increased performance may possibly have found to be quite useful?
Carbonfibre said:
I don't know or care what your agenda is but it seems to me that it has come down to two things. the first is to push somebody's ignition system that so far is just vapor ware and the other one for some odd reason was to harass another certain member. like I stated, 121 post's and all most nothing positive to help another member. IMHO you don't need to be here and if it continues you should be sent to band camp.
PS Steve Maney has a crank triggered ign. listed
hobot said:
What a great thread, I've learnt loads here!
This is indeed true and important, especially if you're a pilot setting your altimeter (All airports will have their height above/below sea level listed so pilots can adjust their instrumentation to tell them when they're on the ground)
But, as always we have to compromise, not all of us ride at sea level all the time and the speed of sound also changes with temperature, again our motors don't run at a constant temperature so we have to come up with an average figure.
Here's an formula to work out the speed of sound (in m/s) at any given temperature (in °C)
V ≈ 331.4 + 0.6Tc
So, for example lets say our motor is running at 40°C
331.4 + 0.6 x 40 = 335.4 m/s
Now, let's up it to 80°C
331.4 + 0.6 x 80 = 379.4 m/s
Doe's anyone here have an idea of what temperature our motors run at?
I would also like to add another variable into the equation (please bear with me, I'm no expert in engine tuning!)
What about the inlet tract harmonics? That is, just like an exhaust system for ideal performance the inlet should be a tuned length (there's quite a few Triumphs out there with long intakes fitted), here's the formula:
L=aC/RPM
Where L = Inlet length, C = The harmonic and a = wave speed (the speed of sound)
On a four stroke engine there are 4 values used for the harmonic.
8900 - 1st Harmonic (This is not practical as it would create an overly long inlet)
6600 - 2nd Harmonic
5150 - 3rd Harmonic (I believe this is the most widely used figure)
4150 - 4th Harmonic
I forgot to mention that the inlet length is measured from the valve seat to the bell mouth in mm.
I measured an old Triumph head fitted with some AMAL velocity stacks that were claimed to increase top end power.
The total length of the tract measured out to be about 10"
Now using the formula 345 (speed of sound at 20 something degrees) x 5150 (3rd Harmonic) / 7000 (max RPM of these old tarts) = 253.82mm
Which is pretty close to 10"
What do you engine gurus out there think? Doe's this really make any difference in the real world?
Thanks
Webby
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bill said:
Seems strange that the mere mention of something thats currently being developed, and may well be of great interest to anyone serious about looking at serious performance, is firstly not likely to assist anyone using this forum, and that this also suggests I have something to gain commercially from this!
I have nothing whatsoever to gain commercially from this, and maybe I was wrong to think there were people on here who are looking to improve their bikes noticeably?
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What do you engine gurus out there think? Doe's this really make any difference in the real world?
Thanks
Webby[/quote]
Intake and exhaust length tuning is something I certainly do on race engines. It can increase power or move it around and help get around bad spots in the powerband.
There are a lot of variables that need to go into determining the lengths and the formulas will only get you in the area. From there you just need to cut & try to come up with the best combo. It's pretty common to have different velocity stacks and exhausts for different tracks or even weather conditions. Jim
Thanks
Webby[/quote]
Intake and exhaust length tuning is something I certainly do on race engines. It can increase power or move it around and help get around bad spots in the powerband.
There are a lot of variables that need to go into determining the lengths and the formulas will only get you in the area. From there you just need to cut & try to come up with the best combo. It's pretty common to have different velocity stacks and exhausts for different tracks or even weather conditions. Jim
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9 -1/2" to 10" intake track is what I've used on the track. This is longer than most racers used - one of the reasons my motor was faster than most others. The impractical longer length you mentioned is not a problem if you lower the oil tank. Peter Williams used about 12" but I think the ideal is around 15" to get the ideal primary wave. No one bothers with this and I think its a big hole ignored in development. See the Leo Goff & Ron Wood intakes below.
As for ports - I ridden some average Norts with stock ports but I'll never forget my first ride with an Axtell head and Axtell #3 cam with 102 deg lobe centers (not easy to fit without valve clash). Raising & tilting that port toward the vertical in the guide/bowl area so the charge is directed straight down and all around the circumference of the valve makes a world of difference. You can start with a 28mm head and do everything you can to raise but not lower. At the other extreme - the 850 head was ruined as supplied with a hogged out & lowered floor.
You might as well weld up the combustion chamber to lower it an 1/8" and then reangle the valves.
Jim
As for ports - I ridden some average Norts with stock ports but I'll never forget my first ride with an Axtell head and Axtell #3 cam with 102 deg lobe centers (not easy to fit without valve clash). Raising & tilting that port toward the vertical in the guide/bowl area so the charge is directed straight down and all around the circumference of the valve makes a world of difference. You can start with a 28mm head and do everything you can to raise but not lower. At the other extreme - the 850 head was ruined as supplied with a hogged out & lowered floor.
You might as well weld up the combustion chamber to lower it an 1/8" and then reangle the valves.
Jim
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