1stVetteFinally

Well, here you go-



I thought is was a little funny and worth sharing.

QCVette

Funny he created a vented Opti.

DGXR

x2

Granted the optispark is not the best distributor with regard to longevity (and sometimes reliability) but many people including myself have never had an ounce of trouble with it. The optispark is an important part of this ignition system which is extremely good at maintaining optimal spark timing, which is why the LT1 Corvette broke new ground with 300HP available standard -- the Vette hadn't seen this kind of power since the early 70's.

Tom400CFI

That was funny.


Well it's obvious, isn't it?? GM stole the idea from Henry Ford's V8!

1stVetteFinally

Never said it wasn't a good system (for the time), but compared to today's ignitions systems...... Personally, I wish my LT1 had a (complete) LS ignition system with individual computer controlled ignition coils and no opti. It rains here quite frequently and it's very humid. I've only been a Vette owner since Sept 2014, and I've already had to replace the Opti.




I honestly had no idea

Kevova

I still don't know why they came with opti spark it's a neat a idea. The gear driven water pump was more of an innovation. GM was already using DIS in the 80's. Crank trigger ignition showed up in the late 70's. IMO if GM would have opted to use DIS with the LT1 it would have eliminated it's only real weakness.

Tom400CFI

^This^.

The opti provides 360 points of reference for each crank revolution, and 720 for each cam revolution. No ignition system that I am aware of can come close to that. The DIS systems of the '80's typically used a crank sensor w/one tooth/2 cylinders, and a 180* cam sensor that provided two reference points/cam revolution (one per crank revolution) only to orient the ECM when #1 was at TDC FIRING. Anyway, even the LS2/LS3 only has a 54 tooth wheel on the crank. 54 pulses/crank revolution is no where near the detail that the opti can provide. So why did they use the opti philosophy? Timing precision and accuracy. And why did they MOUNT it where they did? Packaging. Other cars use the same "opti" system: Mitsubishi 3000GT/Dodge Stealth RT is one...Nisssan Xterra is another. Those are not problematic b/c the distributor is mounted up high, and more spacious inside; the secondary sparks are further from the optical sensor.

Also, multiple coils isn't going to offer a meaningful benefit on a stock or stockish C4 engine; the stock coil can saturate and throw a spark just fine w/in the RPM range of stock or stockish engines.

Kevova

As I said It was a neat idea. I'm sorry, I am not a fan of optical sensors in ignition applications. Magnetic sensors tend to be far more reliable. DIS allows for more precise ignition timing by eliminating distributor cap, rotor, and mechanisms that drive them which can wear. DIS is also based on crankshaft position vs camshaft in the GM opti. One thing in the opti's favor was going from MPFI to SFI a new ECM and a few wires was all that was required. They did add the MAF when the LT1 went to SFI, but I'm not sure it was required

SJW

As Tom correctly points out, the Opti system delivers an ideal amount of information to the PCM about what the camshaft is doing. This permits the PCM to monitor the precise instantaneous position of each piston, as well as the velocity and acceleration/deceleration of the rotating assembly. Given all of this data in combination with inputs from numerous other sensors (ECT, IAT, MAP, MAF, KS, TPS, etc), the PCM can control and optimize spark timing extremely well. This is all to the good.

Unfortunately, the Opti suffered from some major flaws in its original architecture. The Opti not only serves as a camshaft sensor, but also as a distributor of spark. While its placement in front of the camshaft was sensible from a strict performance standpoint (less lash than is commonly found at a conventional distributor gear to camshaft interface, and elimination of any effects of camshaft twisting or harmonics), it was problematic for several reasons. Exposure to moisture (especially escaped coolant) was a big one. Accessibility for service was another. Placing wear items such as cap & rotor where they did was simply foolish from a serviceability standpoint.

And, let's not forget what a nightmare the routing of the plug wires became, from a serviceability perspective. Anyone who has ever replaced the wires on the driver's side of a LTx C4 knows the truth about this.

Poor sealing of the housing against moisture invasion, bearing issues, etc, also contributed to the woes.

Some of these problems were alleviated with the mid-life revision to the Opti's architecture, which appeared in Corvette starting in 1995. These included upgraded bearings, and most notably, active venting. The first-gen Opti relied on passive venting to drain condensed moisture (via three weep holes along the bottom of the housing). This proved to be horribly inadequate, and was a major contributor to the premature failures of many of these units. The active venting that was employed in the second-gen units largely solved this fault, although a heavy dousing of the housing (from, say a coolant leak, a garden hose during engine cleaning, etc) could still wreak havoc. The active venting also pulled out the corrosive ozone that's generated by the arcing between the rotor and the contacts in the cap.

Ideally, if the Opti were to be used, it would have consisted only of the optical sensor, with separate coilpacks to form a distributorless system (such as is created with the LTCC package). This would have eliminated most of the woes associated with the Opti system.

The Optispark ignition system performs wonderfully well when it performs as intended. When it's working right, it's fantastic. Until it fails, or the plug wires need replacement. Then we invent a whole new vocabulary with which to curse it.

Having said all of the foregoing, I can't help thinking that it would have been far better to instead have simply used the distributorless ignition system they already had on the LT5 engine. If it performed well enough for the supercar ZR-1, it should have been judged satisfactory for the LT1 as well. It's a pity that clearer heads didn't prevail when deciding on the ignition system for the LT1.

Now if only we could all have ready access to reasonably-priced replacement units that had a reliable optical sensor, good housing seals and bearings, and active venting, there's be far less anguish among those who suffer with repeated Opti failures. Sadly, that seems to be quite a problem these days. I was fortunate that the Opti on my '94 died back when DTE was still building their superior-quality DynaSpark units, and I keep my fingers crossed that the DynaSpark I bought will continue to perform as flawlessly as it has in the 12 years since I installed it. I wish we could still get these units.

Live well,

SJW