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+--- Thread: H1 SU versus Ruby Zenith sidedraft (/showthread.php?tid=1197)
H1 SU versus Ruby Zenith sidedraft - JonE - 17-05-2018
Was reading on old forum thread on the H1 SU and I've seen various people rave about them. But does the 1" H1 yield anything powerwise over the Ruby 17mm Zenith for cars which are already converted from the 15mm updraft?
Someone then mentioned that ALL the parts/bodies are still available from Burlen. I see the body is just over 250 quid now. Has anyone actually gone down the route of pricing up a new one rather than fiddling around restoring an ebay purchase with broken this and worn that...?
RE: H1 SU versus Ruby Zenith sidedraft - Hugh Barnes - 17-05-2018
For what it's worth, I'm a big fan of an SU. I run both the Austins and the Riley on 1" OMs. I love them. The one thing you can do with an SU is adjust it. Lets face it, a second hand Zenith is likely to be just as worn but at least with an SU, you can replace the worn out bits - new jets and needles if required..
As long as you start with a known complete article (assembling different bits can create problems of 'tolerance' particularly with the dashpot and piston), it should be fairly straight forward. The only thing that I would get Burlen to do it bush the spindle. The tolerances there are really quite critical and require a jig...
my two penne'th...
RE: H1 SU versus Ruby Zenith sidedraft - Chris KC - 17-05-2018
For me the big advantage of an SU is once set up you can forget about it. Mine came from a jumble sale for £1, was cleaned up with paraffin and went on the car. Thus I must say £250 sounds an awful lot to me.
RE: H1 SU versus Ruby Zenith sidedraft - AustinWood - 17-05-2018
They are also much less sensitive to dirty fuel. No little jets to block.
RE: H1 SU versus Ruby Zenith sidedraft - Alan - 17-05-2018
I just wish the vscc light car section loved them as much as I do.
RE: H1 SU versus Ruby Zenith sidedraft - JonE - 17-05-2018
(17-05-2018, 12:09 PM)Chris KC Wrote: For me the big advantage of an SU is once set up you can forget about it. Mine came from a jumble sale for £1, was cleaned up with paraffin and went on the car. Thus I must say £250 sounds an awful lot to me.Chris, I'm happy to pay a quid commission too if you manage to find another one....
THanks all - very useful.
So what about the comparison though - I now understand they are 'fit and forget' and enable you to run on dirty fuel, but what is the physical difference in character? And how efficient are they in comparison? Is the advantage because of their variable nature.. i.e. that they have more range?
RE: H1 SU versus Ruby Zenith sidedraft - John Cornforth - 17-05-2018
Hi JonE
The H1 is a 1 and 1/8 inch carb, the 1 referring to the number of eigthths of an inch above 1 inch. I run a fully refurbished original one (From a M****s 8), with a '37 head and a sidedraught alloy "log" style manifold not too different to the Nippy style downdraught but without the hotspot. Power and all other aspects of running are an improvement on the Zenith, but this may be due in part to the less restrictive manifold. I use a GG needle which seems to work well, but I make no claim that this is optimised. This carb has a weighted dashpot but no spring, so one less thing to fiddle with. I suspect that the carb is a little oversized for a road engine with only a standard cam and valves which maxes out at about 4000 RPM, so a 1 inch type might also be a worthy contender if you can find one.
Cheers, John
RE: H1 SU versus Ruby Zenith sidedraft - FodenK - 17-05-2018
(17-05-2018, 04:42 PM)Alan Wrote: I just wish the vscc light car section loved them as much as I do.
Agree Allan, this years LC&E Event starts just down the road from my daughter and it would be so much fun to join in. I’ll try again
RE: H1 SU versus Ruby Zenith sidedraft - Bob Culver - 17-05-2018
This topic was covered at length in the old website and the virtue of the various SUs was agreed. Besides, a polished horizontal (not semi dd) SU looks neat.
The piston and aperture of the 1 and 11/8 are the same; the former may give a more progressive throttle action . The horizontal 1 1/8 with dashpot ex postwar Morris is relatively common.
Where I lived involved a mile pull every evening up a road constructed for the early trams so had a uniform grade which matched the Seven flat out in 3rd. So every day was a road test. A carb bored to 19mm was a slight improvement but the 1 1/8 SU better still. Made as much difference as the later head so must represent a couple of hp or so. Also very smooth in stop go traffic. Curiously a larger manifold seemed to not assist. The needle size can be checked by manipulating the start enrichment.
I retained the Morris needle and did 38 mpg flat out everywhere. In earlier times as original driven at 40-45 a carefully checked 50 mpg was routinely attained on trips and presumably could with the right needle.
RE: H1 SU versus Ruby Zenith sidedraft - JonE - 17-05-2018
(17-05-2018, 08:51 PM)Bob Culver Wrote: The piston and aperture of the 1 and 11/8 are the same; the former may give a more progressive throttle action . The horizontal 1 1/8 with dashpot ex postwar Morris is relatively common.
Thanks. I'm curious now as unsure what the 1" one is called if its not technically an H1, from John's point?
And what IS the difference between the 1 and the 1 1/8 if piston and aperture are same...? trying to get my head around where the extra flow comes in (or rather the potential for the flow hesitating, perhaps)