MG MGB and MGB GT Tech Talk
Moss recommends the distributor 143-110 (Moss Number) from a 62-71 B. Mine is a RB 74.5. It says it needs vacuum advance which mine has, I think. Do I need to change out the dizzy? Will mine be sufficient?
This bolt on idea is wearing thin...seems they want me to change out every other part in the engine bay...
I'm dealing with this right now on mine. the issue with the dizzy is the amount of full advance, and the curve of the advance. here's what I've figured out. You want about 32 degrees total advance (mechanical + initial) with, ideally, 10-12 initial advance + 20 degrees mechanical advance, with full mechanical advance all in by 2700-3000 rpm. The early dizzy's are closest to this spec. Every car differs a little bit, but, apparently, at anything over 32-34 degrees total advance, you get pinging, piston demolition, and a very pricy rebuild.
Having said all of that - I have a 78B with the original dizzy and the moss s/c. My timing is way off - the total mechanical advance is 30+ on my dizzy so the initial timing is set at around 2-3 degrees which makes it run like crap at low rpm. Car runs hot b/c the timing is so retarded, but, if I advance it, I risk blowing it up. Nonetheless, I've put over 600 miles on it mixed highway/city driving since installing the s/c and having blown things up. Since i have a terrible flat spot just off idle b/c of the retarded timing, I'm having an early 25D dizzy rebuilt.
My recomendation, throw your current dizzy on and see how things work. the early dizzy gives optimum performance, but, if you get 90-95 percent of the performance out of your dizzy, it might not be worth it as long as you don't blow things up. If you want to change things, either source an old dizzy and have it rebuilt (John Twist at University Motors does it) or check with Aldon who will offer to send you one specially curved. They quoted me a price of 105 pounds which is about $200 or so, depending on the exchange. Not sure if they have vacuum units though.
One last thing - if you want to compare the curves, check - http://www.mgb-stuff.org.uk/curvestext.htm
There's another site out there that fills in the gaps. Do a google search and you should find it. good luck
Jeremy
Oh, wow...lots of info, and I am not sure I understand any of it. I can do lots with my yengine, but timing is not one of them... I guess I need to read up on this stuff.
Thanks for the input....I will try to make it work as you say...:)
Ed. The SC is a bolt on part. and you'll be happy with it as it is. It's only if you want the absolute maximum performance that you need the different distributor.
Throw on the SC and adjust things only as you feel necessary.
I hope so. I took the B to the pizza place tonight to pick up the dinner. I wound it out, and got to 50 in about a 1/4 mile. Felt like lots of power, and loved te feeling. I can't wait to see what happens after this weekend. :) :)
Will an electronic (pertronix) ignition work well with the SC?
Electronic ignition works fine with the s/c.
run it as is. Enjoy it. In a couple of months, when you get the itch for more power, revisit the dizzy issue.