Neil Smith Posted September 27, 2023 Author Report Share Posted September 27, 2023 Good evening all! Having worked on the car today, and taken on board all your comments, we removed the vacuum and sure enough the dynamic timing went down to approximately 10 degrees BTDC We are assuming that if we keep the car in line with its original spec. and fit a Lucas 22D6 distributor with a retarding vacuum we will get close the the recommended TDC I haven’t run this past the person who is helping me yet but from the various posts I assume my other options are to either fit a 123 distributor or, unless I’ve completely misunderstood, to keep the distributor I have and connect it’s vacuum advance to the port on the top of the front carb? Unfortunately we didn’t get to investigate further as we now have to resolve an intermittent sparking issue which is preventing the car from starting but I guess that’s classic cars for you! Thank you to everybody who contributed and helped solve our timing issue ….. I’ve learnt more about my car’s engine in the last few weeks than I have in the 30 years I’ve owned it. Thanks again …. it’s much appreciated! Neil Quote Link to post Share on other sites
Peter Cobbold Posted September 27, 2023 Report Share Posted September 27, 2023 Neil, Assuming you have a stock, unshaved,USA compression head ( 8,5 or even 7,75 in the final year or two) you need more statci ca 15-18 BTDC risng to ca 35 ATDC at 3000 rpm. Low comp head have much less turbulence and the flame spread is slowed, hence need for more advance. The vac advance capsule will come into operation at cruise when the butterfly is less than 30deg open. It improves fuel consumption, but is tricky to establish the ideal extra advance. The original vac-retard was aimed at NOx reduction rather than performance. Usually with carb butterflies with over-run valves. Combustion talk from IWE, slides here: https://supertrarged.wordpress.com/2016/07/21/iwe-2016-technical-seminar/ Like you I drive the 6 for thirty years without knowing the basics ! Peter Quote Link to post Share on other sites
harlequin Posted September 27, 2023 Report Share Posted September 27, 2023 Hi Neil It's good you are getting somewhere with your distributor issues. Before spending money on another distributor why not continue running your AC Delco unit with the vacuum advance connected to the top of the carb, if it works well then that's great. If the setup is no good run the car with the vacuum unit disconnected, this is how PI cars left the factory, As Peter said the vacuum advance is only an economy measure, and the vacuum retard is only to reduce emissions when the car is idling so you won't notice any performance differences. George Quote Link to post Share on other sites
Neil Smith Posted September 30, 2023 Author Report Share Posted September 30, 2023 Thank you both again for your advice! We’ll be working on it again next week and will let you know how we get on, assuming we get it to fire up! Many thanks Neil Quote Link to post Share on other sites
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