^ Good stuff. Thanks for taking the time to explain. So back to the initial question. Is there any point in buying a "performance" HEI module? Do they really offer any benefits over a standard HEI module? Or are they just putting a cool sticker on these things and doubling the price?

Only a dyno can really answer your question.

Personally, I think theres a bit of hype going on with a lot of these HO HEI and
coil claims. I also think for a non-track car that stays below 7k rpms most of the
time you may not be able to tell the difference.

I think that the answer to your question depends on how effective the stock HEI ignitors are.

I know that adding power to the ignition system can produce huge amounts of power you would never know was there (as I saw with the Transistor Trick mod), but there must be a point of diminishing returns that you're going to hit sooner or later.








.

Do you have any autocross videos that show your car with and without the transistor trick installed? Your car definitely rips, but I just wondered if you had videos with and without that we could watch for reference.

Oh, and looking at that chart again, the PS scale is talking about engine output, not ignition system output.

The 8 PS difference highlighted equates to a 7.89HP gain at 8000rpm by using the CDI system through the same (air gap) plugs. (1 PS = 0.99 HP)

The text at the bottom seems to be saying that even when they boosted the HEI voltage to match the CDI, the CDI still outperformed, which they attributed to the CDI's different output waveform (fast rise, short duration) and higher current.

What they don't show in that graphic is just as interesting. I'm betting at the
lower rpms the HEI meets or beats the CDI system. In more lay terms I expect the
drivability would be better with the HEI; faster starts, stronger low end etc. This,
BTW is what I experienced from the HEI.

And before anyone says I'm biased towards HEI because I did a writeup yadda yadda yadda.
I'm not, CDI has its place and its clearly better at the higher RPMs and would
be the ideal ignition for a tracked car. It costs a heck of a lot more as well.

Also how many of us run around at 8k rpms consistently? I still maintain that the
bang for the buck is better with the HEI vs. CDI.

Now back to the OP topic, are the HO HEI parts worth their extra price? I suspect
not but someone needs to prove it. I'm happy so far with my junk yard coils and
cheap 4 pin HEI modules.

A couple things about the HO HEIs:

1. It looks like they are designed to increase dwell (charging time). What this does is help to ensure that the coil is fully saturated and contains the full energy when the spark occurs. With the TT, the problem is that the 1st gen dizzy when hooked to a small load (like the TT box), the dwell went very high. This means that the coil was fully saturated at any rpm. The problem is that after the coil saturates, the ignitor has to go into the current limiting mode. The ignitor is still trying to charge, put the coil is "full" and cannot hold any more. Without the current limiting, it would be almost like a short circuit at that point. Since the coil can't hold any more at this point, the energy that is still flowing has to be dumped as heat (in the ignitor). This is why the TT had problems with the ignitor get so hot.

2. It looks like the HO HEI have a more precise current limit (and possibly a little higher current limit) than the regular HEIs. Really this doesn't mean a lot. Depending on the design, it might mean being able to drive more than 1 coil or be able to drive a single coil with less effort, but really you won't see anything from this.

So, it is hard to say if they are worth the money. You probably wouldn't notice the difference for the most part. If I had more info (dwell vs. RPM for stock HEI vs. HO version, we may be able to see what the benefit may be).

For coils, the output voltage doesn't mean much either. The actual output voltage will be whatever it takes to jump the gap. This depends on the gap itself, but also pressure, temperature, mixture concentration, etc. in the combustion chamber. A higher output voltage means that it will still be able to spark at larger gaps or under more harsh conditions (boost, etc.), but mostly you won't see a difference.

One more point about the GM HEIs; the "perfect highest performance" HEI will conform to the 'scope charts at: http://www.megamanual.com/ms2/GM_7pinHEI.htm regardless of tempature and RPM. All the ignitor is doing is changing a sine-ey wave from the magnetic pickups to a square-tooth on/off signal that the coil uses to fire.

All that is to say that a "better ignitor"'s only benefit is keeping the spark where you put it with initial timing and advance. That is-> Until you use the ignitor's ability to advance/retard the timing. But... That's not answering the question the OP asked.

Answer for OP: No. :P (As long as quality components are used in the first place.)

Now how about that oscilliscope data for the electronic dizzy?

Sorry for not providing full context for this chart. The paper is Muroki, "Recent Development of High-Powered Rotary Engine at Mazda," 1984. PM me if you want a copy. It's mostly about 6 port induction, the 12AT, and some race engine stuff.

https://www.rx7club.com/attachment.p...1&d=1281647862
https://www.rx7club.com/attachment.p...1&d=1281586932

Surface discharge plugs have a ring around the outside and the electrode in the middle. These are actually used in marine applications and were factory plugs up until series 5. Here is how the series 4 FSM shows them:

https://www.rx7club.com/attachment.p...1&d=1281648369

The "Air Gap" plugs are really just modified surface discharge. The gaps help reduce the chance of fouling. This was used from the factory on Series 5 FC (copper) to Series 6-8 FD (Platinum), and have since been replaced with a different design on the Rx-8 which is also irridium.

https://www.rx7club.com/attachment.p...1&d=1281648369

The PS is actually engine horsepower from a 12A race motor. I'm not sure if it's turbo or not. You can see they picked up 8ps, which is basically 8 horsepower, from using the CDI system over the HEI in this case. But this is a race engine. The paper also talks about two other things on this race engine: strengthened rotor gears and 1 piece carbon apex seals.

The ignitor does a bit more than that... the magnetic pickups could never withstand the charge current the ignition coils require, even if their signal was of sufficient pk-pk voltage, which its not. The signal out of the pickups is quite small potatoes; just a tiny variation in coil current as the reluctor blade goes by.

The ignitor provides signal amplification/waveshaping of the pickup signal & high-current switching of the coil charge/discharge current. It's got to quench the primary-side current fast enough to let the magnetic field collapse fast enough to generate peak secondary output, then provide full charge current for the next firing cycle.

So do you think these HO HEI modules may offer the benefit of the TT modification (keeping the coil fully charged) without the drawback (burning up ignitors)?

BTW, this is why I love the 1st gen section. Anywhere else a thread like this would turn into a giant argument with everyone being the authority. Everyone chips in their 2 cents here, and builds on what was discussed by others. Maybe that's why we figure out so much cool crap around here. :D

I still think they should call them "HEI HO," just for the lulz that are in it.

I spent the evening testing an electronic dizzy in front of the scope and I found no difference whatsoever between a (tested, known-good) junkyard HEI module of unknown OEM-age, a brand-new Autozone ignitor and two brand-new "high performance" modules (Accel and Pertronix.)

Crosstalk... or some other failure became evident in the lot around 20krpm. Barring that, each module performed identically. (Which makes sense, considering one ignitor handles eight sparks per turn of the engine in its natural habitat.)

But... testing with non-rotary spark plugs the "hi-pro" modules were able to keep-up with each other with increased spark gap. So, my BUR7EQs are set at what... .05? Sticking in "standard" plugs that had a gap of .07 or... .09 (lol) differenciated the ignition modules from one another, with the "hi-pro" having reliable spark above 6krpm@ .09 gap.

So-- I guess the question becomes "What spark plug can I use (reliably) to take advantage of high-performance GM HEI ignitors?" Which begs the question to be asked... "What COIL should I use to take advantage of ____Larger-gap rotary friendly plug____ and hi-pro GM HEI Ignitors?"

Can't figure out how to upload a picture. Bleh.

Okay, quick question. What do you gain from increasing the gap on the spark plugs? I know that increasing gap will make it harder to start the engine, and you will need better coils to help firing across the increased gap. But what is the payoff?

Increasing the gap increases the size of the arc, increasing the amount of heat energy transferred per unit time and thus the size of the initial flame front during ignition.

It'll also make the plug run hotter, which will reduce fouling but shorten life as the electrodes will burn away faster.

If the FC and FD service manuals are to be believed, the platinum (BUR7EQP) plugs have a tighter gap than the copper (BUR7EQ) plugs. Page G-19 of the FD FSM says the platinums have a gap of .044" , while page G-27 of the S5 FC service manual says the gap of the copper plugs are .056" . Platinums were standard on the FD, coppers standard on the S5. The S5 was the first generation to have the BUR7EQ ("air gap") plugs that we are used to.

That makes sense to me. The platinums probably require less gap.

Hammy, I probably do have videos with/without the TT. But to be honest, it wouldn't show much. I was making so many changes back then, sometimes even on a daily basis, that they could show just about anything in any of the videos. Sorry.

And on top of that, there's my Sterling carb. That is easily my most valued posession performance wise, so you can't compare my performance to anything else because of that. In fact, I've been running stock ignition for the last year, which is why I'm paying such close attention to this thread. I'm looking for a good option for my next ignition system. :)

I have to run a stock keg, no porting allowed in my race class. I've already got the carb, I've got the exhaust, lol. There's not too many places I can turn to get more power if I want it. But I know that there is huge room for improvement in my ignition system. I dream about the days when I had the TT up and running, before I ran out of 2nd gen coil/ignitor packs. That was when the car really ripped!

kentetsu, do DLIDFIS. I've always handed out good advice on clutches. Now trust when I say it's the most effective and cheapest ignition solution, and darn easy the way I installed it in PercentSevenC's car... at night in the dark. :D He previously had 2GCDFIS which burned out the stock ignitor. Before it died, it was only a minor improvement over stock. When we went back to stock, again it wasn't much of a difference. Then with DLIDFIS it actually improved the startup and cold running, the low RPM response and part throttle smoothness, and driveability noticeably. His setup has a weber 45DCOE and huge streetports with a blow through S5 turbo. The carb isn't perfectly tuned yet because he just recently got his wideband together and working, so in its partially tuned state, DLIDFIS shines through. It's pretty amazing actually. Exhaust stinks less too.

Blah blah I know. These are typical improvements if your mixture isn't 100% perfect, but when is it ever 100% perfect? Especially with a carb? You'll probably notice a difference for the better, even if your Sterling is tuned perfectly at that very moment for weather conditions, elevation etc.

You should try the TFIDFIS system and see if it compares to the TT. You are one of the very few people who actually ran the TT ignition, so who better to do the comparo for us? Looks like junkyard parts are readily available, and you can get the HEI ignitors at Autozone brand new for $20. On top of that t_g_farrell already has all the wiring diagrams on his thread ready to go for you. I say give TFIDFIS a try. I know I will be.

Jamie

(BTW the TFIDFIS is basically an adaption of Jeff's DLIDFIS. There probably isn't a whole lot of difference between the two except for what ignitors and coils are being used.)

I will be doing something like this. I haven't figured out if I'm going to use the MSD Blaster2 Coils, the TFI coils, or something else. This is mostly because of what we've diggled up in this thread. It "SOUNDS" like TFI based dual fire produces more reliable (and therefore more...?) power, but I haven't seen a dyno shot comparing TFIDFIS, stock and Jeff's setup.

I would like to compare the output(s) of the TFI coil, the can(s,) and some newer-er coil-on-plug setups, but I'm at a loss in trying to figure out a plug with a wider gap than what I'm running now-- And of the lot, the spark plugs are almost the most expensive (and most... unreusable) part of this whole operation. (When testingand using junkyard parts, blah, blah blah.)

No scope data but I have real world experience data. Make sure you use the dizzy
from an 81-85 12a. Do not use the SA eletronic dizzy. The relucter wheel for 81 and
later was redesigned and will give a cleaner signal to the HEIs. The 80 dizzy gives a
less defined signal and will cause misfiring above 6k rpms. Ask me how I know :)

Iteresting info regarding plug gaps and plugs in general. I've never run the air gap
plugs and now I want to try them out and see how they perform.

This has turned into a very interesting thread on 1st gen igintions. BTW, go DFIS
of whatever flavor, its the cheapest best bang for the buck you can get.

Now, that's another interesting tidbit... I didn't know the reluctor was changed when the ignitors were moved to the sides of the dizzy.

I wonder if the 81 reluctor would fit into an 80 dizzy, thereby improving the signal quality without having to sacrifice my engine bay's authenticity?

The 80 dizzy has issues with crosstalk, due to the long distance the low-level signal from the pickups has to travel, over to the fender where the ignitors are. Anything that cleans that signal up couldn't hurt it at all.

Anyone up to doing machinist-grade measurements on the 81 reluctor and shaft? I'll reciprocate with 80 measurements.

I don't think it is just crosstalk. If you look in my TFIDFIS thread I have pictures
comparing the 2 reluctor designs and its obvious that the shape and strength of
the signal changes for the better in the 81+ dizzy. I think you might be able to
just pull the old reluctor off and press on the new but it may affect the ignitors
as the J105 may internally expect a different trigger form that the J109.

Knowing mazda they used the same dizzy internals and
just swapped reluctors and the casing to get the J109s mounted. Also if
you look in the parts fiche for the dizzy shaft, if it is the same number between
the years then you know it will fit.

DD, swap the upside-down T-shaped shaft instead. Much easier, of course this is assuming they are compatible, which I beleive they are.

If you must swap reluctors, that's pretty easy too. I've found that if you list equally on both sides it comes up off the shaft well enough. Remove the roll pin once it's off but before installation on the other shaft. Once reluctor is fully seated, tap roll pin in.

The shafts are probably the same, but you never know until you measure. I might get some time to measure an '81 today. We know the upper length is the same (same dizzy cap and rotor). I'll measure across the round section for diameter and a second measurement on the flat machined part. IF I get around to it. :) No promises.

I've not experienced cross talk with DLIDFIS regardless of signal wire length. They've all been with the '81-'85 dizzy and its better reluctor design.

Thats what I'm sayin', the FB dizzy fixed a bunch of signal issues when I was
doing the HEI thang.

Make sure you twist the wires good that come across to the
ignitors if you make your own. That helps cut down on interference issue.