Info on FBO ecu unit
Hi Dave , good post . Do you know amplitude of GM pickup at some rpm and mopar stock pickup at some rpm ?
then we know dwell control rate from V/ rpm .
No need to reduce dwell until under ~ 3 k rpm to avoid coil overheat is why , and how they can eliminate ballast R So may do nothing till that area down ?
I thought chip in HEI looked at time between pulses not amplitude but either can work . But if amplitude , you might be screwed up with wring mopar vs GM pickup volts .
By the way HEI is a lot better conceptually than mopar , so those saying “ just a hei “ are leaving 1 k rpm on the table . Nothing wrong with early dual point either from old dodge v8 to 57 . more dwell , i think 55 back fits A block ( shaft length) .
Saw a dyno test where msd died on dyno 56 hemi , guy put dual point and ballast R he had on it exact same HP right to 6000. Nothing electronic to punt , 400 still in pocket too
I don't know the amplitude that the dwell control is triggerd, never found it and don't have the equipment to work it out....
i think it will be module specific, linked to original application, and it will be to do with the supporting components the manufacturer uses with the Motorola chip that is embedded in all of them. subtle changes to capacitors and resistors around that chip, allow the module to be matched to specific pickups and specific igition coils.
however the dwell control is used at low rpm not at high... you would assume the opposite
basically, due to HEI systems running a 0.6 ohm coil at 12-14.5 volts
at low rpm the coil would overheat so the HEI module reduces the dwell dramatically.
However due to running the coil at this voltage and its very low primary resistance
the total dwell time to get the coil up to max flux regardless is tiny in comparison to the time period between the necessary spark events to run a v8 at higher rpms
as RPM increases the peak of the reuluctor signal increases and dwell is extended until it reaches this maximum dwell figure which fits nicely with an rpm that is at redline or more on a v8.
so what you have is the exact reverse of all other igntions.
HEI has short dwell to protect coil at low rpm and maximum permissable dwell at High rpm
obvioulsy with everything else that has a coil that has a high resitance primary
the time to get it FULL is way way longer
and as the RPM increases the necessary dwell for a good spark is not possible because the necessary dwell time is longer than the time between each spark event,
anyway some good reading below
first link
A discussion of the benefits of HEI, some words on pickup coil and dwell control etc, and how to convert a lucas distributor...
second link
A comparison of CDI Vs MDI or magnetic igntion, such as HEI. Mainly all the bits about transistor zener clamped MDI
the HEI module has a modern interpretation of a transistor zener clamped set-up
basically in conclusion he says CDI and HEI are much the same spark power in more or less all cases applicable to road and affordable race engines
http://nebula.wsimg.com/5956cdbfbf7...E22DE049163134A29&disposition=0&alloworigin=1
http://nebula.wsimg.com/88a559cc1e6...E22DE049163134A29&disposition=0&alloworigin=1
i use a mopar pickup. all seems to work well to 6000 rpm
documents above hint at why some people seem to run into a problem at lower RPMs than that....
all to do with coil primary and secondary resistance
Dave
