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Re: Twin SU Spacers & Getting A Filter On
Fascinating topic with no easy answers - here's my rambling tuppen'orth...
Whilst I'd like to fit twins (and have already reconned a set ready) I'm still holding back on the grounds that the performance gain will not be significant whilst the hassle-factor is doubled. I think the best compromise is probably a single HIF6 on a custom inlet manifold, with a standard MGB exhaust manifold to improve gasflow.
As for what causes the unreliability of the TC setup it could be different in every case...however I'm not convinced the thinner spacers are necessarily the main cause. My SC runs a thin spacer and no heatshield, albeit it is a little further from the block/exhaust than the TC-setup. Thermal characteristics of cast iron vs alloy may also have a bearing, but I wonder whether the main area is general engine set-up.
Timing and mixture will all affect the amount of heat generated and unleaded engines will run a little hotter than leaded...also consider the carb needles and jets...I recall when I first started driving my Roadster the performance was appalling. Despite setting things up by the book I resorted to a rolling-road session where a worn carb jet was diagnosed...this manifested itself in periodic hesitant running and occasional cutting out. New jet and the problem disappeared.
As for needles, if running K&N or pancake filters you'll need richer needles than standard...I think I have AAB in the SC and I put AAA in the twins (per Moss recommendations)...more air flow means you need more fuel. If you don't richen the needle then you'll get poor running and problems which might, at casual glance, seem like vapour lock.
Also be interesting whether the problem-cars still retain the engine fan or whether they have thermostatic setups. At least the engine fan keeps the heat moving around the engine bay...
Other ideas might be to use a braided fuel feeds rather than the cheapo rubber versions from the Marina. Also an electric fuel pump with the pressure regulator turned up should help...bring the fuel feed in low (as heat rises) and keep it routed well away from the manifold/downpipe.
Fascinating topic with no easy answers - here's my rambling tuppen'orth...
Whilst I'd like to fit twins (and have already reconned a set ready) I'm still holding back on the grounds that the performance gain will not be significant whilst the hassle-factor is doubled. I think the best compromise is probably a single HIF6 on a custom inlet manifold, with a standard MGB exhaust manifold to improve gasflow.
As for what causes the unreliability of the TC setup it could be different in every case...however I'm not convinced the thinner spacers are necessarily the main cause. My SC runs a thin spacer and no heatshield, albeit it is a little further from the block/exhaust than the TC-setup. Thermal characteristics of cast iron vs alloy may also have a bearing, but I wonder whether the main area is general engine set-up.
Timing and mixture will all affect the amount of heat generated and unleaded engines will run a little hotter than leaded...also consider the carb needles and jets...I recall when I first started driving my Roadster the performance was appalling. Despite setting things up by the book I resorted to a rolling-road session where a worn carb jet was diagnosed...this manifested itself in periodic hesitant running and occasional cutting out. New jet and the problem disappeared.
As for needles, if running K&N or pancake filters you'll need richer needles than standard...I think I have AAB in the SC and I put AAA in the twins (per Moss recommendations)...more air flow means you need more fuel. If you don't richen the needle then you'll get poor running and problems which might, at casual glance, seem like vapour lock.
Also be interesting whether the problem-cars still retain the engine fan or whether they have thermostatic setups. At least the engine fan keeps the heat moving around the engine bay...
Other ideas might be to use a braided fuel feeds rather than the cheapo rubber versions from the Marina. Also an electric fuel pump with the pressure regulator turned up should help...bring the fuel feed in low (as heat rises) and keep it routed well away from the manifold/downpipe.
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