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+--- Thread: A different kind of Ulster! (/showthread.php?tid=854)
RE: A different kind of Ulster! - Bob Culver - 26-02-2018
the virtues of the equal length 4 into one pipework, much favoured for drag cars, and common generally from the 1960s, were not widely realised in the 1930s. Does anyone know any period car which used?
I have yet to find an explanation of exactly why superior to separate pipes.
RE: A different kind of Ulster! - Erich - 26-02-2018
Bob, I'm not an expert by any means, but I seem to recall from reading a couple of tomes that it has to do with back pressure. We know that for the intake, equal length pipes allow for better equalization of fuel. It may have been David Vizard, the Mini Wizard, or a book on tuning two strokes, but I recall the idea was to extract exhaust gases equally, so there is equal room in the combustion chamber for new fuel mixture. Manx Nortons often ran with a megaphone which acts to pull more exhaust out of the chamber by creating a depression. Unfortunately, that also pulls some unburned mixture out. And it tends to be pretty peaky. The fix, to create better midrange, was to fit a cone to the back of the megaphone to stuff some unspent fuel back in the chamber. Sorry for the long explanation, but I relate this to the idea of a tuned exhaust. Here is something I found online which explains it far better than I have.
https://www.wemakeyoufly.com/tuned-vs-equal-length-exhaust-systems/
With piston port two strokes, a megaphone was found to pull fresh mixture out of the exhaust ports, spa reverse cone was added that essentially send a shock wave back up the exhaust to stuff the fresh mixture back into the combustion chamber before the piston blocks it.Having the right diameter of the expansion chamber is important, and sort of mimics a cam on a four stroke.
Best,
Erich
RE: A different kind of Ulster! - Mark Dymond - 26-02-2018
As it happens I was just watching a you tube post about exhaust scavenging. Seems to be a plausible, well thought out, explanation
https://www.youtube.com/watch?v=jjPeP_Nn2B4
RE: A different kind of Ulster! - Mike Costigan - 26-02-2018
(26-02-2018, 01:00 AM)Bob Culver Wrote: the virtues of the equal length 4 into one pipework, much favoured for drag cars, and common generally from the 1960s, were not widely realised in the 1930s. Does anyone know any period car which used?
I have yet to find an explanation of exactly why superior to separate pipes.
I don't believe any pre-war car used such a system. Even well in to the 1950s Grand Prix cars did not have such a sophisticated exhaust, either relying on stub exhausts or unequal length primaries.
RE: A different kind of Ulster! - Nick Salmon - 26-02-2018
Frankly, having just the one AM is a tad lacking. You really need one for weekdays and a best one for weekends.
A few years ago I snapped Nick Mason at Goodwood driving my dream car. And just behind him came his daughter, Holly, driving his other one... It is indeed another world. And if I had just the one I think I'd look a lot happier than Mr M did in this pic!
mason.JPG (Size: 84.92 KB / Downloads: 502)
RE: A different kind of Ulster! - Mike Costigan - 26-02-2018
Perhaps Holly had just informed him that she wasn't handing it back
RE: A different kind of Ulster! - Alan - 26-02-2018
The real reason you need two Astons is you need one to use while the other is being mended. A bit like Austin’s really. Well, that how I justify my lot.
RE: A different kind of Ulster! - Edward Bradley - 06-03-2018
Hello. I was very interested in this thread - I'm lucky enough to be the present custodian of AKU 991. I swapped it for another car and some cash back in 2015. My wife and I have a joint bank account. There is no way that the cash could have been anywhere near near GBP1,000,000! I have known AKU 991 for many many years - and raced against it in my Austin 7 for a lot of those. The Ulster is very original and I have confined myself to repairing and rejuvenating. We are only custodians of these cars and I don't want mess this one up. It will never be shiny - not even Rod's bits. The exhaust manifold did require a lot of head scratching. It does give a power advantage (mainly for the scavenging reasons mentioned above) but the 1,500cc Aston's didn't use them in period. Interestingly, some of the later two litre Astons did. However, I race the car in VSCC events with my son. A lot of other VSCC cars use these manifolds (including the other Ulsters) and we took the view that as this is only a bolt on modification we would use the new manifold for VSCC events. We will be doing the Le Mans Classic later in the year and will revert to the original manifold for that. I asked Rod to make a new panel for me so that we did not have to mess up the original one. Needless to say, Rod made an excellent job of it but I am looking for an antiques dealer to age it for me! The engine was built by Aston guru Alan Brooke but Alex (PigSty) did help with the tuning. I raced with his dad for many years. I hope to get my Austin out this year and race with him again. The CCK figures are a bit misleading. When we went to see them we knew that the mixtures and timing were all over the place - that's why we went. They did do an excellent job and we left with very good results. I would say that the manifold, when the engine is set up properly, gives another 8 or 9% in bhp terms.
RE: A different kind of Ulster! - merlinart - 07-03-2018
Listen to it on the rolling road here!
http://www.cckhistoric.com/1935-aston-martin-ulster-23-gain-rolling-road/
Arthur
RE: A different kind of Ulster! - Colin Swinbourne - 07-03-2018
Edward, glad to see it’s all better after it’s problem at Snetterton.