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Been reading and hearing a lot about MSD ignition systems having a hotter spark than the original TI systems of old. Is it worth swapping out a TI system for an MSD or what? Comments please.
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Re: Ignition
Not in my opinion. The MSD is a capcitor discharge system and the TI is inductive. CD systems feature a very intense short duration spark, which is good for igniting the rich, dense mixtures that exist at WOT. This is best for a race engine, but street engines have different requirements.
At idle and low speed, mixture density is low (relative to WOT), and it is diluted with exhaust gas, especially on SHP engines. Such mixtures need a long duration spark since they have poorer ignitability than rich, dense mixtures typical of WOT. The spark duration for a TI is about 180 microseconds compared to about 30 microseconds for a typical CD system. MSD gets around this by generating up to three successive sparks at low engine speed, but, of course, only the first spark is timed properly. The addition sparks are retarded due to the time required to recharge the capacitor.
If you have a TI, my recommendation would be to retain it, and you can increase its reliability by having the modern electronic package installed in the external amplifier.
Like most aftermarket "hot rod" parts, MSD igntions are hyped with a lot of advertising and "word of mouth" testimonials from users who have little real understanding of combustion including the ignition requirements for the differenct mixture characteristics that exist in an operating engine.
GM doesn't spend advertising dollars on 35 year old parts, but in many cases, they are better than "modern" hot rod parts.
If I see one more MSD box on the cowl of a Chevelle at a car show, I'll probably puke.
BTW, the HEI is basically the same design as the TI but features some additional circuitry that adds variable dwell, and it is all packaged in a thick film hybrid cicuit small enough to be packaged in a module (rather than discete parts in an external housing) that will fit in the larger HEI distributor housing. It is completely self contained and only requires a 12 volt power source. HEI replacement parts are readily available and inexpensive, and this along with the HEIs excellent inductive operating characterisitcs make it an ideal ignition system for a street high performance engine.
If the HEI pickup coil wave form is the same as the TI pickup coil wave form an HEI module could easily be substitued for the TI amplifier. The early HEI modules have four pins - two are for the pickup coil input, one is the coil wire and the fourth is 12v power. All you have to do is figure out a dry place to hide the HEI module (I think it's too big to fit in the TI amplifier housing). The wiring harness would have to be modified and the other wild card is the coil as the HEI module might generated more current that the TI coil can handle.
Duke -
Re: Ignition
you can mount the HEI module on a piece of aluminum and hide it under your dist. ignition shielding. the TI coil seems to stand up OK. the HEI module will fit inside a TI case. i have the wiring diagram to do this if any one is interested.Comment
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Re: Ignition
Hey Clem -
I now recall that you adapted the HEI module to the TI system.
Mounting the module in the amplifier box would certainly maintain OEM appearance, but what about the harness? Doesn't it have a resistor wire to the coil which should be replaed with a conventional wire, and wouldn't you have to add an extra ten guage wire for 12v power? I recall that the TI amp has three wires at the connector, but it's been to long since I played with one to remember the schematic and where the 12v power connects.
DukeComment
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You've Learned My Spiel Well Duke!
Right on the money! If anyone needs a wiring diagram or information on how to build a system, just ask. Delco made a tach drive distributor identical to the HEI distributor on the instide. It WILL judge well.
Because of the exceptional rise time and short duration of each spark with all CD systems, cavitation occurs (no hydrocarbon molecule in the vicinity) at part throttle and misfires result. The only thing that makes them work is a series of such sparks in quick succession. (Multiple Spark Duration)
Dale.Comment
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Re: Ignition
duke my systems are not NCRS "legal" but it could be done. you need 4 wires and the TI black box has that if you include the external ground wire. the module does not need 10 gage wire,just the power wire to the coil has to be of heavy gauge because the module controls the ground side of the coilComment
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Re: You've Learned My Spiel Well Duke!
Thanks guys for the usefull info. Seems to me that my type driving only requires an update to the amplifier.Comment
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