Carb-intake manifold-intake port matching

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I've downloaded Thinbasic, in the hope that I can use it to unravel the problem of the advance curve for a programmable ignition system. I used basic many years ago, however found it a pain compared with DEC Focal which is almost like programming in English. The old PDP8L computer I used all those years ago was extremely fast because of the lack of programme loops. Extremely easy to use. We had a KV8i storage oscilloscope attached to it for visual output. I was recently reading the book 'The Innovators' and some of the things Bill Gates did , we did at almost the same time. The space game was big, and we wrote a lot of card games as well. Computers are a lot of fun, however I still waste too much time with them.
 
Rohan I haven't gone 'off-topic'. The size of the inlet port on a commando engine is about the size of the models used in the trans-sonic wind tunnels in aeronautical research establishments. If you have any friends in that game it might be worth seeing if they can do a few foreigners with some port models , made in plastic. I'd point out that the sound barrier was unknown until a guy in a spitfire found his controls reversed when in a very high speed dive. And I don't think what might happen at high gas velocities in ports is exactly a choking effect. Something as simple as a slight swelling or depression somewhere in the wall of the port might have a very interesting effect.
 
acotrel said:
Rohan I haven't gone 'off-topic'. The size of the inlet port on a commando engine is about the size of the models used in the trans-sonic wind tunnels in aeronautical research establishments. If you have any friends in that game it might be worth seeing if they can do a few foreigners with some port models , made in plastic. I'd point out that the sound barrier was unknown until a guy in a spitfire found his controls reversed when in a very high speed dive. And I don't think what might happen at high gas velocities in ports is exactly a choking effect. Something as simple as a slight swelling or depression somewhere in the wall of the port might have a very interesting effect.
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Hi acotrel.
I asked about carbys with multi axis mounting earlier. Rather than just the port, could you (i.e. is it possible) model/flow the effect of the carby being oriented differently to the conventional parallel, central, inline location?
Ta.
 
needing said:
I asked about carbys with multi axis mounting earlier. Rather than just the port, could you (i.e. is it possible) model/flow the effect of the carby being oriented differently to the conventional parallel, central, inline location?
Click to expand...

Those sort of things are best done on a flow bench, as a prelim study. ?

It has long been known that the inlet needs to be both offset and downdraft for better high speed performance.
When the race guys heard that new Commando heads might be available, the 1st thing they asked was if they
could be produced with (considerably) more downdraft.
Which would prevent them being used in a stock bike, unfortunately...
 
Some bedtime reading for the more technically-inclined: http://www.pistonheads.com/gassing/topi ... Dyno+Tests

I'm not going to fill this thread with vague deductions of what it means for classic bike motors, but it underlines to me that if you are an enthusiastic amateur thinking of modifying ports on a classic bike, think very carefully. Just to read an interview like this shows the amount of work that the real pros put in before they can achieve their aims, and why it costs money. You are paying for years of experience and know-how.

From what I've read about the Fullauto head, it would seem to be the yardstick for street Commando owners to aim at. I don't know what the differences are in the inlet and exhaust port dimensions. Maybe Fullauto or Comnoz could explain?
 
[quote="Danno"

That's what I thought when I discovered the mismatches; here's something that I can easily correct and at worst, nothing will change. At best, there could be a small improvement.[/quote]

The BSA info kind of says the opposite, at least for that engine. At worst, something did change. Removing the mismatch removed about 10% of the engine's power output.
I have alterred mismatched carbs and stubs in the past and always assumed it had to be better, or as you say, at worst nothing should change.
Turns out that flow and effect is a strange science, or perhaps a black art. Then there is the perfect result on a flow bench which mysteriously does not result in great power. Makes the flow bench guys crazy I'm sure.
So many variables.

Glen
 
A local magazine article on the Horner Bros Vincent Irving twins mentions that they had to build a 1000cc 'stocker' for the Goodwood festival,
so they took some stock Vincent parts "in which the valves are TOO LARGE" and worked from there. Ended up with 98 hp on the dyno.
[Which is about twice ? what a stocker would have produced in it day]

Change of subject from prewar BSA's ports, slightly, but thought that was interesting.
Never assume the stock parts/sizes are the best ?
But actually experimenting/measuring the results is serious stuff....

Of course, as always, this may have been to throw the competion off the scent.
 
I think the Horner /Goodwood engine was at 13 to one and running methanol. So quite an accomplishment, but not much different than the John Edgar/ Rollie free Lightning produced in 1949 and probably less than the Burns and Wright Lightning produced in 1955.
As far as I know, dyno numbers were never given for either of those bikes, but calculating from the speeds attained tells us the horsepower output had to be around 100 HP for the Edgar bike and perhaps 120 HP for Burns and Wright.
Both of those bikes used big valve heads, and standard Vincent valves are already big at 1.875"

Glen
 
BSA was pure accidental like Teflon and no objective reports just race team - we know all lie through their teeth to psych the other Brit competition so obviously foolish to try to mimic hobot either.

Carb-intake manifold-intake port matching
 
If you want to estimate inlet port velocity, needless to say you can find online calculators for it.

I've no idea how accurate it is, but it puts a Commando on full song up around 0.6 Mach which is ( according to them) right on the limits for volumetric efficiency.

http://www.wallaceracing.com/machcalc.php
 
Aw poo ya can not test sonic choke on bench testers and doubt any Norton can approach sonic choke hinderance w/o boosting a ridiculous cam. Some obvious things work good while some un-obvious non common sense work better. Guess how they found out, trial and error with measuring by seat of pants or clocks. See what ya make of American V8 pushrods findings. Article also has examples of intruding gasket stealing power so who knows til on purpose planned or by accident. My Swami Nitjsanda Saraswati (Nity Gritty) told me to always watch for the exceptions as its the exception that test the rules and can reveal deeper principles.

then there are other times when you can install a Big Block Chevy rectangular port Intake manifold on an Oval Port BBC head and make more HP and TQ even with a tremendous port mismatch
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http://speedtalk.com/forum/viewtopic.php?t=860
 
hobot said:
Aw poo ya can not test sonic choke on bench testers and doubt any Norton can approach sonic choke hinderance w/o boosting a ridiculous cam.
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How do we know, o swami ?
Has anyone ever tested the flow speed in the ports ?,
or tried for supersonic max hp ??

Or is this pure guesswork !
 
The www has plentiful references on flow bench misdirection and limits of testing. So see if ya can find a statement that contradicts flow benches not measuring sonic choke. Generally if sonic choke hinders more flow at top rpm its indication to open port up to slow flow loses down, but then may need accelerator pump to rev up off idle. Norton should be so lucky to worry about super sonic shock wave compression.
 
i recoil at stepped obstructions in flow like anyone so disappointed when i switched mis matched manifold for matched-blended no gasket intrustion dual Amals and even more so putting them on refreshed Combat head, ugh. On the flip side against common sense the exhaust can benefit with head lip too.

https://books.google.com/books?id=OTOYH ... rts&f=true
 
hobot said:
So see if ya can find a statement that contradicts flow benches not measuring sonic choke.
Click to expand...

So is that an admission that its a no, o swami....

BTW, for Alan, the V2 rockets in WW2 explored the sound barrier and associated steering solutions,
well before pilots happened across this. We just didn't get to hear much about it, and its still probably on the secret list...
 
Hi all.
Thanks for that 4-stroke tuning book link hobot. I read it in the 80s and was inspired then too.

This topic of Norton Commando 'Carb-intake manifold-intake port matching' must have reached an illogical conclusion now that the 'secretive Nazi rocket science' card has been dealt.
Ta.
 
Supersonic still hasn't been explored here... ?

You and Aco must have gone to the same trolling school
 
Hi rohan.
May I suggest you actually start your own thread entitled, say, 'Secretive Nazi rocket science and my practical application this research to my supersonic Norton Commando'.
Ta.
Goodbye.
 
Aw Rohan you are always upset with me because you know your cycle can not turn so harsh all its controls reverse and love it. Seems you do not understand there is not a sudden sharp choke down effect nearing super sonic just less and less flow increase even with more and more pressure. You imply an objective engine background so see if you can locate a vacuum powered engine head flow bench that can test even approaching sonic choke inefficiency. hobot would use a fire cracker or brust barrier to mimic fast valve opening rush. To some degree a step in the flow path can work like the flats on front of lower fairings on some famous fastest vintage racers. OK had my snack break so back studying useful stuff but leave another brain teaser mis-match.

Re: intake port to intake manifold. match or mismatch?h
Postby Ted » Thu Jul 22, 2010 8:49 am
Recently dyno tested a street 454 BBC that had the 119 oval port heads with a variety of intakes. The rectangular port dual plane (factory Winters intake) easily outperformed the oval port Edelbrock Performer RPM. The intake port mismatch was beyond bad but both the lowend and topend numbers were better with the large rectangular port intake. Just FYI and shows that almost every combination has to be tested.
Ted Eaton
Click to expand...
http://speedtalk.com/forum/viewtopic.php?f=1&t=22539
 
hobot said:
Seems you do not understand there is not a sudden sharp choke down effect nearing super sonic just less and less flow increase even with more and more pressure.
Click to expand...

We are struggling to see that you have any solid knowledge of this subject.

And I made no such statements anywhere Steve.
If you are going to fabricate what others are (not) saying, your usefulness here is about zero.

How can there be 'pressure' in the inlet manifold when it is a (partial) vacuum that is pulling it in.
Lets get even the simple facts somewhat straight here, to begin with.
Science = measured stuff.
hobot = ??
 
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