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MG MGB GT V8 Factory Originals Technical - Pertronix

Dear All,
I have just installed pertronix Ignitor II electronic ignition plus Flamethrower II coil in my MGB V8. Simple installation, even I -a complete novice- finished the job in 2 hours including setting the timing. A lot of that time was getting the HT leads the right way on the new dizzy cap. The idle speed dropped from 900 to 650 and she sounds very nice, drives better than ever.

My questions are, should I use the manual recommended advance- 8 BTDC, or should this change now I have the Pertronix fitted?
I have standard '35 gap plugs fitted, but I have heard that '40 gap are recommended for Pertronic II systems. Would this help? If I did changed from a '35 plug gap to a '40 plug gap should I also change the advance from 8 BTDC? If so, what should I change it to? Are there any other tweaks I should consider?

Thanks in advance for any advice.

Why did the idle drop? Most people claim fitting a Pertronix *increased* the idle. Did you check the timing before you started and restore it to that or just do the changes and then use the book value (my book says 8 degrees at 1000 rpm and 26-30 at 2000). The timing could well be retarded now to what it was before. IME the V8 is very resilient to pinking, unlike the 4-cylinder where you have to be careful not to over-advance. Even so I can't see any good reason for advancing it.

PS. Carry points and condenser as a spare and be able to retro-fit them at the roadside.
Paul Hunt

Dear Paul,

I don't know enough about it to explain why the idle dropped. I did not check the timing before I started personally, -presumed the garage set it at book value- but I did check it myself afterwards. Is it possible to optimise the timing for a particular vehicle?

On 4-cylinder engines the book value assumes the use of 4-star leaded petrol 30 years ago and factory fresh and all to spec components. Even so individual engines varied quite a bit depending on how the tolerances on each component interelated and the factory had to be sure that the worst combination didn't suffer engine damage from pinking, so the book figures are quite conservative. In those days I got significantly better performance and economy out of my BL A-series engined car by tuning to a vacuum gauge rather than the book. These days, primarily because of unleaded petrol, I suppose, even Super, plus 30 years of wear and tear on the engine and its components, I have to adjust so that I just don't get any pinking, which is actually slightly less than the book figure. But as I say the V8 seems to be able to take quite a bit more advance without pinking, even on standard unleaded. But rather than push things too far and cause damage I stick to the book figure.
Paul Hunt

This thread was discussed between 24/05/2004 and 25/05/2004

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