For anyone interested in upgrading to the '96 LT4 ignition coil and coil driver module:
http://forums.corvetteforum.com/zerothread?id=597629

Tom Piper

 

:sleep: :sleep: :sleep:

 

Tom-

I think what you were getting at is summarized in the chart below. It's my understanding that the two systems stack up something like this:

LT1 early coil: approx 8 mH primary; Module approx 6.5? amp current limit
LT4 & Vortech coils: approx 4 mH primary; Module approx 7.5? amp current limit

(Note: I haven't measured either one personally - these are my best guesses taken from GM literature & other's tests. I plan to measure an L98 module sometime this summer, but it hasn't gotten done yet. If anyone has better numbers I'm interested in seeing them.)

If you compare the spark energy of the two systems on the (approximated) basis above, using the B&G simulator*: http://www.bgsoflex.com/igncoil.html

you get an illustration of spark energy something like this: http://temp.corvetteforum.net/c4/doc...oil-module.jpg

If my understanding of the system is correct, the older-style ignition makes more spark at low RPM - where you don't need it. The newer-style makes a lower energy number overall, but carries that energy out to higher RPM's - where you do need it. By way of comparison, an MSD 6 box throws off about 125 mJ per spark over the same range.

What does that mean? Dunno. I've tested similar systems to both (and a CD box) on my L98, and my datalogs aren't showing any gross mis-firing with any of them up to 6000 RPM.

What the logs DO show is that, compared to a stock L98, my present system (crank trigger + single coil ignition like the LT4 design above) has less 'RPM Scatter' on a WOT pull. That is to say, the RPM vs. Time curves are smoother with the new system. My dyno calcs aren't sensitive enough to attribute any significant power gain to that system, but they do show the N/A engine is more stable ('happier') with it than without.

Most of that change is probably due to the crank trigger - but hey. If GM spent the money to upgrade the LT4 spark system, why should I throw rocks at it? They are probably better engineers than me (well, at least there are more of 'em) and if they thought the new coil was better, I'll agree even if I can't put a number on it. Directionally, it should be a design improvement for a performance engine... Whether it really makes more power is something that I may find in further testing... maybe not.

That's my take on the design trade-offs - of course I could be wrong. YMMV. etc. etc.

DrJ
*Supporting design & source info was here: http://forums.corvetteforum.com/zerothread?id=419893

 

Thanks Tom, I might just do that when I take my engine apart later this year/early next year.