Rodbr Posted April 22, 2020 Report Share Posted April 22, 2020 Hi Bob, Possible to fit a pair siamesed Lap joint or similar inside these? Quote Link to post Share on other sites
stuart Posted April 22, 2020 Report Share Posted April 22, 2020 3 minutes ago, Rodbr said: Hi Bob, Possible to fit a pair siamesed Lap joint or similar inside these? No theyre a sealed unit with crimped over edges. Stuart. Quote Link to post Share on other sites
Lebro Posted April 22, 2020 Author Report Share Posted April 22, 2020 Anyway they are much too shiny You would have to do similar to my method. Cut and bend away a tab of steel from the inside plate big enough to squeeze a bellmouth through, then put it back again. The bellmouth would need to be secured in the right position. I used M3 screws. Bob. Quote Link to post Share on other sites
Ian Vincent Posted April 22, 2020 Report Share Posted April 22, 2020 Alternatively use the cheapo items flagged up by Pete earlier in this post and sandwich them between the carb and the filter. It means you would have to enlarge the hole in the filter to match the OD of the bell mouth. Rgds Ian Quote Link to post Share on other sites
Ian Vincent Posted April 23, 2020 Report Share Posted April 23, 2020 On 4/20/2020 at 3:23 PM, Hamish said: I tried those Peter and they are cheap for a reason. Smaller than 1 3/4 and very rough. They are rough and the diameter is only 39mm but when I measured my HS6 carbs, the internal diameter of the inlet throat is only 41mm. By the time you have removed the ovality of the cheapo items and polished them the diameter will be 41mm Rgds Ian PS Does anyone know why the inlet diameter of a 1 3/4" SU (HS6) is only 41mm and not the full 44.45mm? Is it to do with velocity across the bridge? Quote Link to post Share on other sites
Motorsport Mickey Posted April 23, 2020 Report Share Posted April 23, 2020 (edited) Read the writing in the pic on the front of the bellmouth blank on my previous post made for my 1 3/4 HS6 carbs, I made it 1 5/8th or 40.9mm for the inlet of the carb. Yes the inlet needs to be a smaller dia to accelerate the gas speed over the bridge and exit at the 44.45mm (1 3/4) dia into the inlet manifold. The SU is a seemingly crude design often maligned by mechanics or tuners who prefer other designs, often with more exotic sounding names or a penchant for being bolted upon cars as part of a "tuning" package. However it performs extremely well delivering both reasonable economy and good performance for a fraction of the price of other named carbs. Skinners Union completed an excellent development and production package with these carbs and care needs to be taken when trying to tune them. After an evening with Peter Burgess (Automotive Engineering) one of the best SU tuners in the country back in 1987 on a flow bench testing various configurations of butterfly and throttle spindle mods and piston leading edge radii modifications including changing the bridge approach and depart angles benefits could only be found by butterfly and spindle mods (about 5% from memory) any changes of the carb bridge by altering angles or changing the piston leading edge etc inhibited the flow and cost HP. There are other mods which include boring the bridge out completely leaving the jet as a pillar which I understand are supposed to improve HP but at the cost of flexibility for road use, I've not tested this myself so am unable to provide info on it. Mick Richards Edited April 23, 2020 by Motorsport Mickey Quote Link to post Share on other sites
DRD Posted April 24, 2020 Report Share Posted April 24, 2020 On 4/19/2020 at 9:03 PM, Hamish said: I have considered these instead of trumpets https://www.med-engineering.co.uk/ancillaries/stub-stacks/med-stub-stacks I tried to order these but they are out of stock at the moment, apparently there are more being made. Quote Link to post Share on other sites
Lebro Posted July 14, 2020 Author Report Share Posted July 14, 2020 On 4/22/2020 at 1:01 PM, Rodbr said: Hi Bob, Possible to fit a pair siamesed Lap joint or similar inside these? Rod. I have now moved on to a different style of bellmouth to fit inside some commercial pancake filters, you are welcome to these two , removed from my earlier effort, if you are still interested, will cost you the postage ! Bob. Quote Link to post Share on other sites
Rodbr Posted July 17, 2020 Report Share Posted July 17, 2020 Hi Bob, PM sent Quote Link to post Share on other sites
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