Ransom GRM+ Memberand UltimaDork
3/25/20 12:25 a.m.

Is there any difference?

My Internet meanderings suggest that the 45D is just the newer model of the same type as the 25D, but that at this point they both fit many of the same applications, and that both have been built with many curves, meaning that which curve you need probably tells you nothing about which distributor you need... Among other examples, it sounds like the MGB was fitted with the 25D until the mid '70s, then got the 45D, but not necessarily in line with any specification change that called for a different distributor.

My specific situation is that I bought a 25D thinking I needed to replace the dizzy in my '73 MGB GT, but like a complete dolt hadn't actually pulled the old one first. I knew mine had Pertronix guts, but I didn't realize it was actually a 45D-style Pertronix Flamethrower (with a dead vacuum canister). I've since returned the 25D since it turns out that unlike the Lucas units, you can get a replacement vacuum canister for the Pertronix dizzy for $20 or so, and I'll just be repairing my existing unit. But it did leave me curious about what differences I hadn't managed to unearth in the catacombs of British-car Internettery...

Robbie GRM+ Memberand MegaDork
3/25/20 9:48 a.m.

I think in general mgb people prefer the 25d since it had better factory curves. Of course that all can be fixed, but the preference remains.

I have no idea why BL switched, but it could have been any number of reasons I guess. Being able to replace one part and not the while distributor is a pretty good reason to switch by itself.

Ransom GRM+ Memberand UltimaDork
3/25/20 9:58 a.m.
Robbie said:

Being able to replace one part and not the while distributor is a pretty good reason to switch by itself.

That would absolutely be true; is that a general 25D vs 45D thing, or based on my canister story? Mine seems more like a Lucas vs Pertronix thing. I don't actually know how much Lucas 45D there is in the Pertronix unit. All I know is that a vacuum canister for a 25D, while available, cost nearly as much as a whole 25D ($62 for the canister or $65 for the dizzy from my local vendor). Meanwhile I can get the Pertronix canister for $20, though I don't know whether it's interchangeable with a Lucas unit.

Anyhow, that's quite interesting about the preference, and sounds all too plausible. Thanks!

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