Kentetsu

I missed this thread the first time around, but just finished wading through all of the arguments and technical data. Overall, I'd say this was a pretty good discussion, with a lot of information to back up your individual claims.

Now, having said that, it has always been my opinion that there is a lot of power to be had in ignition mods. Stepping up to the 2nd gen coil mod gave me a slight improvement in power, but just barely noticeable on the butt dyno. However, smoother idle, better gas mileage, and easier starting were definitely there.

Later, I moved up to Kent's Transistor Trick ignition. And that was like living a miracle! The power increase was undeniable.

Taking all of the arguments into consideration, I believe that the increase was due to a more reliable spark at the high end of the rpm band. With the stock ignition, I think it starts falling off at higher rpms and the increase in engine speed slows down a bit as you near the redline. But with the TT, it rips right up to the redline and beyond in a much smoother and faster manner.

So, despite the fact that some of you have vast experience, and others have degrees, I will stand by what I said. There is a tremendous amount of power to be found in the ignition system. Or, if not "found", at least it will allow you to utilize it in a more efficient and complete manner.

Thanks for shaking the dust off this thread.


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BeenJaminJames

Well, since we're bringing back this thread, I figure I'll add my experiences with ignition mods. A friend and I once built an '84 12A RX7 with a garett turbo and a Holley commander throttle body running about 28 inches of boost on a good day shifting at 12,000. We ran stock ignition, stock with Blaster2 coils, SLIDFIS, DLIDFIS, and full-computerized CD. The stock ignition on the NA setup, with new cap and rotor, gave us essentialy the same power output and fuel consumption as all the other inductive discharge ignition systems, untill we started shifting above 7000 rpm. However, the DLIDFIS did make for a better burn on the low side of the tach. We did'nt spend alot of time studying the performance below 4000, but we did notice a slight improvement in cold starts and were able to run a leaner idle mixture. (The aftermarket throttle body allowed us to connect a laptop computer to program the fuel maps and monitor exactly what the mixture was doing in real time.) When we installed the turbo, we saw a very large improvement in horsepower, about 30 rwhp, by going to the more powerful coil. We also saw another 10 rwhp with the direct fire. We could find no measurable difference in power or fuel burn between the single and dual leading ignitor setups. When we started turning higher revs, we saw a vast difference in peak horsepower with the CD box. The power curve peaked at about 6800 rpm and 422 rwhp with the inductive discharge system, but once we went to CD it kept following the same climbing trend all the way to 12,000 rpm and 496 rwhp. It is worth noting here that we ran two ignition boxes. I have no idea what would have happened running only one.

If I were going to recommend an ignition system to someone driving a naturally aspirated car and shifting at the stock 7000 rpm redline, i'd have to go with DLIDFIS. For boosted, stock redline cars, get a high performance coil too. However, if you want to turn higher revs I can only advise the CD box. A coil just cant build up that fast. Period.

I offer this information because not only did we have frequent (and super cheap!) access to a chassis dyno, but also since we installed the throttle body from the get go we were able to study exactly what our mixture was doing at all times, and compare it to our O2 sensor readings. Now I don't proffess to know a whole lot about ignition systems, (Mark hooked everything up) but I like to think I know the basics. Any comments or input would be appreciated. (That's what we're here for is to learn from each other, not prove why we're right and the other is wrong)

Kentetsu

Man, shifting at 12,000 rpms? You must have some pretty impressive engine mods. Can you elaborate?

BeenJaminJames

Well, she wasnt mine, a friend bought the car and parts, and I helped him build it. It took 3 years, about $15000, and LOTS of work and tuning. If you have ever programmed fuel maps, where you actually have to tell the computer how much gas to put in for every throttle position/rpm/engine load/air temperature/O2 sensor reading combination you ever might use, you will know what I mean by work and tuning. And then came the rebuilds, 5 of them on one engine. Street porting, super-lightweight rotors (they weighed about half what the stock ones weighed), a holley throttle body conversion kit, a garrett dual ball bearing turbo, mechanical bov hooked to the throttle, and tons of other stuff. The turbo was pushing less than 15 pounds of boost, but we got almost 500 horsepower to the ground. Oh yeah and the ford 9 inch rear end with independent suspension that we narrowed down from under a Thunderbird. And a carbon fiber drive shaft. There was more, but it's late, and I cant remember anyway. The car was great fun, when you went WOT in second or third gear you could hear the weaker parts of the body flexing under the torque. And then the idiot parts it out, sells what's left of her, and moves to florida. He should at least have kept the car to teach Directfreak a thing or two about 12A's. hahaha But it really was VERY fast, and the main reason I started liking rotaries. I had prior expierience with them, and didnt much care for them, untill we built that monster. I have no intention of building one that fast for myself due to how much work it was when I was just helping. Yes, I kinda claim it as ours, and not mark's, but with as much work as I put into it, I should have that right.

[edit] Oh yeah, and I have heard of one guy shifting at (I think) 15000 rpms, but it was a pure racecar. And what's Kent's Transistor Trick? Sound's interesting, is there somewhere I can go to read more about it?

Kentetsu

There is a huge thread on it. Just search "transistor trick" and choose the biggest thread. I think it's like 50 pages or something...

fastorlast

I'm reviving this tread because its something everyone should read and witness. i don't post on here often but certain things should be remembered. The main reason for direct fire is for a more powerful spark and reliability. But a more powerful spark is only needed for high compression or high rpm application, such as boosted applications. The higher the compression the more it takes to get the fuel/air mix to ignite, because you use higher octane fuel and the compression for some reason makes it harder for a spark to jump the gap on a plug. Engine masters(it's a muscle car magazine) had a very detailed Q/A about a supercharged V8 lossing all power at high rpm, they discovered that the problem was that the spark wasnt strong enough to jump the gap on the spark plug at a stock compresion ratio with 14 pnds of boost revving above 3500 rpm(I think thats the rpm and psi, its been a while since i read the article). As for reliability, i can't say for better or for worse, if this mod makes for a more reliable ignition for the fact that i haven't done this mod yet. There are a large number of people the say it helps gas milage, and people that say their cars idle better... on the reverse side you can also find a large number of people saying they saw little to no differance at all. So make of it what you will, i'm probly going to do the mod for the chance of better fuel economy. The bottom line is that unless your revving really high... i think 12k is a little excessive, but lets say 8.5 or 9.5k rpm its not neccesary for making power.

On a second note at 12k i would have to agree that a coil wouldn't have time to charge enough power to release a decent spark, its simple, electricity has to travel from your ignitor to the coils then to the plug then finally across the gap back into the motor via grounding. thats a large distance to move and while coils are nothing more than fancy capacitors they can only do so much.

Also, a weak spark causes the air/fuel mix not to ignite well meaning that it wont burn all the mix and you end up getting backfiring out the exhuast similar to a very rick condition. At least on V8s. i'm not sure about rotaries, there like a new puzzle that i haven't put to gather yet.

I'm guessing, that the people who say they experienced a gain on there butt dyno, and such is because they needed to replace there dizzy caps and rotor so they weren't getting a good enough spark to ignite the fuel well anyway.

PercentSevenC

Dunno about NA since I've never compared it back-to-back, but it definitely makes a difference with a turbo. I was dropping spark at high RPM before switching to DLIDFIS. No other changes, same cap and rotor, wires, plugs, etc. Also, at idle the exhaust note got smoother and it's a little easier to start now. Seems to smell a little less, but that could be my imagination. Anyway, good mod all the way around.