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TR4/4A Lucas 23D4 vs 25D4 Distributor

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dgaldrich

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So I'm restoring my 63 TR-4. Before I started, I noticed that my distributor had no vacuum advance and there was no easily seen vacuum port on the bottom of the carb. Now that everything is apart, I find I have a Lucas 23D4 distributor (that worked pretty good) instead of the factory specified 25D4 and the vacuum port on the bottom of the SU is plugged. The question is whether I should rebuild a 25D4 (there is a spare in a parts box) and resurrect the vacuum advance lines or just keep the 23D4. The car is going to be a regular driver and I'm not ****-bent on originality but would like at least factory original performance. I'm guessing that the previous owner may have done it to get some small improvement in performance but he's not around to defend himself.

If the 23D4 performs at least as well as the 25D4, then I'll keep it. If it's worse, then away to eBay it goes and Moss gets another order but I have no information on which to base a decision. I'm hoping this august group has some expertise in the matter. Thanks.
 
A 23D4? I didn't know Triumphs ever used it. If you can find the 5 digit model/curve number on it you can look it up in the PDF linked below. You may find out some details about its advance curve along with that of the 25D4 that you have.

If you are uncertain about which would be better, it might be worth a phone call to Jeff at Advanced Distributors to see if he can make a recommendation. He can also recurve either to be a good fit for your engine configuration.

https://www.starchak.ca/tech/pdfs/lucas.pdf
 
For a "driver", I would definitely try to get a vacuum advance. It doesn't do anything for full power, but will reduce fuel consumption by 10-15%
 
It would seem that the 23D4 came out of a Austin "A" block car, maybe a 1275 Sprite or something similar. Will take a critical look at the 25D4 cores and see what can be done with them.
 
Hmm... A-series... Please look at the 23D4 for the 5 digit number beginning with "4" and send me a PM telling me what it is.
 
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