Misspelled Opti-Spark?

[sorcerer]

Is there anyone with a f-body '93-94 that went 100,000 miles without Opti problems? Should be renamed Opti-scrap...

[Rob B (shoebox)]

It's a distributor. It doesn't last forever. Does a regular SBC cap and rotor last 100k? Not even close. The opti does a pretty good job in comparison. It's just mounted in a funky place.

I have read lots of threads with people over 100k with the original opti, if that is your question.

[TraceZ]

It's a distributor. It doesn't last forever. Does a regular SBC cap and rotor last 100k? Not even close. The opti does a pretty good job in comparison. It's just mounted in a funky place.

I have read lots of threads with people over 100k with the original opti, if that is your question.

I've never seen one go bad in person. This is my 3rd LT-1 car sinse 1995. It's not really that big a deal. So if it goes bad, you replace it.

[azkkn]

106,000 on the odo, had to clean it once, but knock on wood its still good. car also has original plugs and wires. i do have a new opti sitting here, and plugs and wires also. just to get a water pump and headers before i dive in.

[lt1redz]

My 93 Camero lt1 has 135000 with original opti..No real problems so far. It does stumble last time it went thru car wash.. Don't use car washes now.Use Zanio and hand wash..

[alenstein]

My 93 Camero lt1 has 135000 with original opti..No real problems so far. It does stumble last time it went thru car wash.. Don't use car washes now.Use Zanio and hand wash..

I have noticed the same occurance, every time I go through car wash, towards the end it starts to rough idle, and stumbles a little.

[sorcerer]

Well, everybody i've speak to that own one f-body 93-up with opti around here ended up replacing it. At $1056.00 retail, plus the work involved to get it, it's no small affair. I'm about to replace it AGAIN ( lasted 13 months) so don't tell me it's a great piece of engineering.

[Mikeyboy]

The Opti itself is A great piece of engineering yes, Where it is placed on the motor, is not. That water pump, as we all know, isn't indistructable, and when it goes, the opti goes. I've had to put 3 on mine, and can't even remember how many I've done at work, and most were from the pump leaking.

[Rob B (shoebox)]

Well, everybody i've speak to that own one f-body 93-up with opti around here ended up replacing it. At $1056.00 retail, plus the work involved to get it, it's no small affair. I'm about to replace it AGAIN ( lasted 13 months) so don't tell me it's a great piece of engineering.

If you are paying that price plus labor, I can see why you are upset. A non-vented opti is only $300. If you do your own labor, the only other cost is a pair of water pump gaskets.

It is possibly the best distributor ever put on a small block engine, IMO.

[sorcerer]

The concept is hi-tech,no doubt about it, but the engineering to make a durable is not. That's too bad because you loose confidence of the car.

[AmericanZ28]

It is possibly the best distributor ever put on a small block engine, IMO.

Interesting comment, Rob. I dont think I've ever heard anyone say that before. Can you elaborate?

[Injuneer]

When it was first introduced in the 92 Corvette, the Optispark was the subject of an Society of Automotive Engineeers (SAE) paper that cited unprecedented levels of spark timing accuracy. The accuracy was measured in terms of "spark scatter".... the ability of the unit to provided a spark at precisely the required point. When you plot the actual spark timing for a large number of events vs. the intended spark timing, you get a "scatter" diagram (statisticians will know exactly what this means). The closer the actual spark event is to the intended event, the better the combustion. Reducing scatter reduces emissions, improves power and improves fuel efficiency.

Several of us have been using the optical section of the Optispark to feed the cam position to an aftermarket engine management system (ECU) and using that signal for timing the injection and spark. The high voltage function (cap & rotor) section of the Opti is not used, but external drivers are used for spark. I use a MoTeC M48Pro ECU, with their 8-channel ignition driver, through 8 LS1-style coils. The MoTeC is capable of programming precise and variable injector timing based on a table of load and rpm. Each cylinder is individually adjustable. Ditto for the spark timing, with individual cylinder offsets. This system has been used on LT1 engines making up to 1,125HP and turning up to 8,000rpm.

Getting the high voltage function out of the Optispark case seems to make it much more reliable, and there are now two "black box" add-on systems that allow the Opti to function in this manner - optical section only - using the stock PCM. Do a search on "LTCC" and "Delteq" to learn more about these options.

The Optispark is NOT a GM invention. It was first used by Chrysler/Mitsubishi in late 1980's 3.0L V6's that were used in various Chrysler and DiamondStar products. That application suffered of the problems inherent to the GM design, most likely because Chrysler/Mitsu had the sense to put the dirstributor on top of the engine, where any other "conventional" distributor was typically located.

Opti = great idea, poor execution.

[Rob B (shoebox)]

Interesting comment, Rob. I dont think I've ever heard anyone say that before. Can you elaborate?

Fred has indicated how accurate it is for timing detection. Because of the large diameter cap and rotor section, it is less prone to any "crossfire" in the secondary ignition portion (remember when GM went to the HEI distributor? It had a larger diameter cap to reduce crossfire and improve accuracy).

It is just unfortunate that all of them are not sealed so well and not more protected from the elements.

[AmericanZ28]

Ok, that definetly cleared things up. Its hard to believe that location would be the thing to make such a great design a bad idea. Didnt the fact that it was driven via- the cam dowel pin contribute to its accuracy though?

[Injuneer]

Obviously direct coupling the Opti to the cam dowel (or using the splined shaft in the cam gear, as in the 92-94 unvented units) will be more precise than using a gear set on the end of the cam, with its inherent "lash". But the main feature of the Opti is the use of the 360 slots in the disc, allowing the PCM to know EXACTLY where the cam is at any point in time. Most systems use eight impulses per cam revolution, meaning that the ignition system is "blind" for a large part of the rotation between impulses. If the cam is accelerating or decelerating, there is error (= scatter) during the "blind" period.

The Opti, on the other hand, increases or decreases the pulse rate to tell the PCM exaclty where the cam is, and how its rotational velocity is changing. The weak point of the control system for the LT1 is the lack of a true crank position sensor. While the Opti low res pulse pattern effectively identifies the correct cylinder to fire, any play in the timing chain can affect the cam's postion relative to the crank, and throw off ignition and timing events relative to TDC. It isn't any different in this respect than a reference signal using a conventional cam driven distributor. One can only assume that any inaccuracies introduced by timing chain play are more than offset by the PCM knowing whether the engine is accelerating or decelerating in close to "real time".