Info on FBO ecu unit
Keep in mind that the max permissable dwell at high RPM isn't very much. At 3000 RPM on a V8, you have 5 milliseconds between spark events. If you give the coil a millisecond to discharge, you have 4 milliseconds for it to fire. Keeping the same 1:4 ratio between discharging and dwell would drop that to 2 milliseconds at 6000 RPM.
Plug in the numbers for an MSD Blaster 2 coil and aim for a max current of 6 amps as a somewhat conservative safe level of current, and you'll find it needs to dwell for 4.9 ms to reach that much current. That 2 ms time at high RPM would only reach about 2.7 ms. At low RPM there is enough time that you would want to stop the charging at a point that limits current. The just isn't enough time to reach high levels of current at high RPM, so at that point any dwell control is aimed at managing the ratio of discharge time to dwell.
The MSD blaster 2 is a cannister style coil
regardless of the turn ratio and the primary resistance I believe the configuration tends to result in less effective flux carrying by the core and a higher resistance in the secondary.
it won't discharge as quickly and more energy wasted heating up the coil
i.e for good reason the original HEI coil is a laminated core transformer style unit, open to the air and clamped by its core to a chunk of mounting bracket
i haven't looked very hard for turn ratios etc for this style of coil, so i could just be spouting BS
BUT I'm inclined to think best results can be had with the right type of coil, GM wouldn't have specified a new one if not necessary, tooling costs, new bracket that doesn't fit a standard coil mount, new connector, different capcitor, traning for the guys on the line all that stuff.
hence my quip about priamry and secondary resistance having an impact on rpm range
Basically i think if you pair a cannister coil with an HEI you get poorer performance in some cases
although the two links i provided talk about the bosch GT40 in good terms and it is a cannister style coil much like the MSD popular in Australia and europe but called different things
MSD do the 8226 which looks more like the right kinda thing
But id rather spend $20 + shipping on an ebay or rockauto filko for a chevy truck, or indeed $40 on the ford version mentioned in another thread, than £120 for the MSD kit
i loose therfore, by not having a big red coil pack sticking out when i pop the hood, but i'm happy if i get much the same spark from what looks like the remains of a broken microwave oven.
i can live with that, looks awful, but it works
Dave
