Heads: 1928 Ariel vs. 1963 Gold Star

Anything about Ariels
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cmfalco
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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby cmfalco » Wed Jul 10, 2019 5:52 am

david.anderson wrote:But a 3 angle valve job would certainly help.
The set of Neway cutters I bought for my 1928 Ariel allowed me to do a 4-angle valve job: 15, 30, 45 and 60 degrees. I have to install a new intake valve seat so will be doing the same with it once I find the time to install it.

p.s.
david.anderson wrote:From memory Superflow gives us a formula that suggests that for every extra cubic foot of flow there is an extra half horsepower.
The SuperFlow manual gives the formula HP = 0.35 x (flow in CFM at 15" H20 test pressure) for a "well-tuned racing engine."

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby PeterW » Wed Jul 10, 2019 7:52 pm

Recently read an article in The Motorcycle on this. Will try and find it...

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby PeterW » Wed Jul 10, 2019 9:28 pm

Found it!
From Feb 1945, tiny writing as paper supply was restricted so you'll need to zoom.

Image (1).jpg


Image (2).jpg


Image (3).jpg


And while I had the scanner out - anyone fancy painting their WNG white?

Image (4).jpg

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby cmfalco » Wed Jul 10, 2019 11:31 pm

This thread already has gone off track and there's no real reason why it shouldn't have. With that in mind, my original point was that you can look at the two inlet ports in the first post and know that one flows more air than the other. However, if I can be presumptuous and summarize David's posts, his point is, the details are complicated.

Perhaps a simple illustration of both of our points is in the attached photograph, upon which I'll first base a quiz. Which of these Gold Star pipes, with the same ID, flows more air?....

.... You failed the quiz. The significantly longer Catalina pipe flows 3.2% more air than the shorter Clubman pipe. I checked each pipe twice so I'm sure of the measurements. Our intuition often fails when applied to air flow. In this case, without a flow bench there wouldn't be any way to know that the extra resistance due to the longer Catalina pipe is more than matched by the sharper bends of the Clubman.

My point would be that just looking at either pipe tells you they flow a lot of air, and (again being presumptuous) David's point would be that you can't know the details just by looking. Although the details of the flow aren't so important for the exhaust, they are important for the inlet tract.
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SuperFlow_ExhaustJig_03.jpg

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby PeterW » Thu Jul 11, 2019 11:04 pm

Yep, and added to that is the back-pressure caused by the length of the exhaust being important in keeping the correct flow of the gas through the head so a too free flowing exhaust can just lead to more mixture disappearing.
And talking about inlets, my car has adaptive inlet tracts so you get a different length at high revs to provide more torque or more bhp depending on how you were driving. It was the designers way of adjusting the tract to bring more top end bhp without a cost lower down the range.
I guess it depends on whether you are tuning for racing or normal road use. A friend of mine is running a Gold Star at the moment. It uses higher compression than a Red Hunters, can be um "challenging" to start and is heavy on juice. Lovely though it is to look at and listen to, and it is fast, he can keep it :¬)
Going back to tuning, I think the point of the diagrams in that article I posted was that the Joe Craig wanted to convey that the direction of the flow was also important and having large ports that just allowed the gas to be sucked straight from inlet to exhaust was less efficient than having some downdraught to encourage the gas into the swept area. Its possible that they had a similar idea in mind when building these inlets the way they did.
Either way it will be interesting to see the results.

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby cmfalco » Fri Jul 12, 2019 12:27 am

PeterW wrote:Yep, and added to that is the back-pressure caused by the length of the exhaust being important in keeping the correct flow of the gas through the head so a too free flowing exhaust can just lead to more mixture disappearing.
Since I have my 1928 Ariel's exhaust system off the bike at the moment PeterW's post prompted me to see what my flow bench had to say about it. For other reasons I've converted all my other exhaust measurements to a pressure of 20.4" H2O so I did so with the Ariel as well. The Ariel header pipe + silencer flows 99.3 CFM. For comparison a Gold Star Clubman exhaust system flows 165.4 CFM.

I was a bit surprised the difference isn't larger, given the at least the 2x higher h.p. of the Gold Star, plus the fact the Ariel's silencer, ahem, silences a lot more effectively.

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby PeterW » Fri Jul 12, 2019 1:24 am

Interesting :¬)
I guess the other things to consider are the pressure in the pipe, the speed of the gasses and the length before it hits a point where the pressure can drop. In the article they talk about megaphones allowing a 42inch pipe even though the racing rules said it had to reach to the rear spindle. I don't know but I guess a large silencer (e.g. a "Brooklands Can") would have enough volume so the pressure in the pipe can collapse as it enters the increased space at the right time even though it might be ultimately more restrictive than a straight pipe. As I understand it the point is to get the pressure to drop in time for the reduced pressure to get back to the exhaust valve after most of gasses have left but while the valve is still open thereby sucking more charge in. A longer pipe would produce the drop too late and a shorter pipe too soon (i.e. while the first rush was still happening). Too large a pipe, while offering greater overall flow would have slower flowing gasses and lose this effect.
Complicated stuff for this time of night! My 350 RH was scrambled by a previous owner and the exhaust has a 45 deg kink followed by a shortened burgess silencer. I'm not interested in more power but getting it quieter without losing bhp would be good. Various oil leaks & decent tyres are higher priorities though at the moment.
I guess the thing regarding flow is how many CFM an engine would produce if not restricted.

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Re: Heads: 1928 Ariel vs. 1963 Gold Star

Postby cmfalco » Fri Jul 12, 2019 2:06 am

PeterW wrote: a shortened burgess silencer. I'm not interested in more power but getting it quieter without losing bhp would be good.
FYI, I measured two aftermarket Burgess-type silencers:

Burgess-type #1 90.9 CFM
Burgess-type #2 184.4 CFM

I don' t know what either sounds like but I strongly suspect there might be a difference.


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