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EXCELLENT WRITE UP BY :
Oklahoma Corvette and Performance Specialist
Opti-Spark. Sounds like something from the new transformers movie, eh? If you have had one fail, you may think it was out of a horror movie. Well the truth behind the opti has been told a few times here and there. It basically boils down to a great idea and bad follow through. I am sure we have all been guilty of this before, but we don't manufacture cars, so we get spared of our mistakes. So lets get that out there first...
Why does everyone run screaming from an opti-spark? Why is it a POS?
Well GM engineers fathomed up this brilliant idea for a low maintenance distributor that was very accurate, and for the most part they did a damn good job. The problem lies in the rest of the design that caused the failures.
1. Ya see, a water pump has these seals on the spinning shaft. When the seals fail, coolant is bypassed though the seal housing and out of a weep hole in the bottom of the water pump. This is on virtually every water pump out there. GM kinda didn't realize that the weep hole was above the opti-spark, or they overlooked it, or just said screw it... no one knows for sure.
2. After 1994 all of the opti-sparks became vented. Why? Ozone. Ozone is a gas that is created when there is a spark of electricity. Inside of this tiny arc that occurs from the tip of the rotor and on to the distributor cap there is basically a lightening bolt that cooks the air around it. When you “cook” the air, you produce the gas ozone. Also, if there is moisture in the air (look up to see where the water is coming from) you create steam. Ozone and steam do not play well with optical sensors, because they are “looking” at each other. If you fog up your buddies glasses, he cant see you any more...
3. Sealing the cap and the bearings... The pre 95 had an unsealed distributor cap and the bearings were subject to letting fluids past. This did not help the dripping water pump.
4. Heat kills.... And in this case, heat weakens the electronics that are inside of the 'optical' side of the house, causing heat related failures which often mimic a failing ICM or Fuel Pump.
5. Printed distributor cap... Uhhh yeah, electronic conductive ink was used to print the pattern on the inside of the distributor cap. This unique design prevented cross-fire of cylinders and allowed for a great layout to get even and odd plugs to their corresponding side of the block. But you guessed it, when it gets old or overloaded, electricity will always find the shortest path to ground... That may be the next fancy line of conductive ink- which leads to the next cylinder. Try diagnosing that misfire.
So you can see, there were some flaws. So what? Its not like you have to pull apart the front half of the engine to get to it once it got wet... Oh, right, you do. And this is why people hate the optispark. Even if you only have to change it once every 120,000 miles, it still looks like a worthless chunk of crap once you have dissected your engine to get to it. Because of this, “opti-spark sucks” is the common chant.
Well if its such a hunk of crap, why don't they come up with a fix?
GM tried in 95-97 by venting the cap and using incoming filtered engine air to supply and a one way check valve on the intake manifold to pull vacuum on the inside of the distributor. They also made other changes to the drive mechanism. The end result? Its pretty water proof if maintained... meaning as long as you dont take your LT-x through the next big flood, you should be good to go. Well so long as the foam seal thats around the distributor doesnt rot away...
Bailey Engineering created the LTCC to eliminate the high voltage side of the optispark. You can google it.
Deltec made a solution too.... again google
And to follow a few others (including myself) have designed ways around the Opti. We wont discuss that here, but just know that if you have had enough, then you can source your own solution.
Many of you out there are not ready to make that great leap ($$$$) for a different approach. I don't blame you. I think the Opti is an amazing design! And to convey that message, I will explain how the Optispark works...
PART 2:
Oklahoma Corvette and Performance Specialist
How the Opti-Spark works...
First off, lets look at what it does-
It provides a signal to the computer (ECM/PCM) about where the engine is rotationally in respect to where it has been. Basically, what degree of rotation is the engine at, and what is coming next as far as firing events are concerned.
Well thats easy, eh?? Not exactly...
So lets break it down some. You should know that your engine crank will spin 720* for a complete rotation. The camshaft is driven at half the speed of the crank, so it will go 360* per full event cycle. The Opti is driven by the camshaft. So it has to spin once and give enough information to complete 720* worth of events.
How does it do that?
The Opti has a shutter wheel inside of it. The wheel is about 2.5” in diameter and thinner than a credit card. The wheel has 360 holes cut into it on the outer most “ring” and the inner ring has 8 holes of varying size cut into it. (more about these holes later) This is mounted on the center shaft which is supported by some bearings that are pressed onto the shaft and then into the metal housing of the Opti. The camshaft has a dowel pin pressed into it, and it sticks out of the cam a certain amount, which varies depending on year. This dowel pin slides into a slot on the Opti. Supposedly only one way, but actually it will go about ¾ down the wrong hole and she screams. (!) The opti wont completely bolt on if you have it in the wrong slot, which is slightly frustrating. Anyway, when the cam turns, it spins the shaft in the opti, which in turn spins the shutter wheel and the rotor. The holes that are in the shutter wheel are the vital pieces of info here. To read this vital information the Opti has OPTICAL sensors (that moment when they say the name of the movie in a movie...) These optical sensors are actually a matched pair of LED transmitter/receivers. One transmits infrared light at a certain wavelength. The other sees only that same wavelength of light that the other is transmitting. And there are TWO pairs of these LEDs. One reads the outer ring with the high number of holes, the other reads the one with low number of holes. When the infrared light from one transmitter is seen by its receiver through one of the holes, it essentially becomes a switch and allows current to flow through it. As this current passes through the LED it is then sent though a transistor and amplified to a high enough voltage so that it can be sent to the computer. When the wheel moves, the space between the holes does not allow the infrared light to pass through, so the LED turns off, which turns off the transistor and the signal is zero. While the wheel spins and the holes pass quickly in front of the LEDs the signal turns off and on quickly. It creates what is called a square wave pattern, because it goes from high to low instantly and is held high or low for the amount of time it takes for it to move to the next hole or not. If you were to draw that represented by a line it would make a wave that is squared off...
This square wave is taken by the computer and it means shit.
What does it all mean!?
I am glad you asked, cause this is where the accuracy of the optispark comes into play. I wont go into how other ignition systems work, but lets just say they suck in comparison. Because what the opti provides for information is 90 times better than what existed at the time, and still better than what the LSX uses.
These holes on the outer ring... there are 360 holes. So that means there are 360 filled areas. So it can go low to high (two different states of logic) 360 times each, or 720 times. Wait a sec, there are 720* in a full engine cycle... so if the wheel turns once, that means the cam turned once, which means the crank turned twice.... by golly they found a way to tell the computer where the engine is DEGREE BY DEGREE. Holy crap, thats accurate. They call this bit of information the HIGH RESOLUTION SIGNAL. Sound familiar?
Onto the 8 slots on the inner part of the shutter wheel... There are 8 slots which have a unique design. Their function is to tell WHICH cylinder is passing. The way they did this was kind of ingenuous if you ask me. They made the holes different sizes, but only 5 sizes. Wait a sec, whaaa? If there are 8 cylinders and only 5 different sizes... WTF bro? Welcome to the computer age, we can do a lot with a little. The signals are provided by the length of the hole. 4 of the holes are the same length, between these holes are 4 different sized holes. I hope you understand when I describe the holes' length by degrees... The holes correspond to a cylinder. They go in the firing order according to rotation of the engine. Since its a small block, you should have this memorized, 1 8 4 3 6 5 7 2. Since every other hole is the same size, cylinders 1, 4, 6, 7 all have a 2* long slot. Cylinder 8 has a 7* long hole, 3 has a 12* hole, 5 has a 17* hole and 2 has a 22* long hole. (I will post pics) These signals are all, of course, 45* apart.
What does this do? Well depending on how long the computer sees the LOW RESOLUTION signal determines which cylinder it is on. This is also used for the sequential injection. Now the engine knows exactly what cylinder its on. The low resolution signal tells the computer which cylinder its on, and the high resolution tells the computer how many degrees are passing while it is on which ever cylinder. Woah. If you crunch some numbers, you can see that this is an amazing amount of information. I know it takes me a few mins to find out which cylinder is at top dead center, and if its on its firing stroke or exhaust stroke... this puppy can tell you in 1/100th of a second. And its always right. Thats accurate.
Well thats all fine and dandy. What good it knowing when and where the engine is? For starters, I can tell you that the computer is smart enough to know that on cylinder 1 it should take 2* to get its signal and should see 90 total high and lows for that cylinders firing event, and if it sees too many or not enough it knows that something has happened. It compares this with a multitude of other info and it can reason that there was some knock. Oh yeah, its smart. Ever wonder why the LTX was so sensitive to knock retard and why there was an updated LT4 knock module? There is your answer! This is only a small reason for the fancy opti... the biggest reason was cold starts and emissions. With the computer now able to know exactly when and where the engine was, it was able to start from a dead stop much faster. This enabled the use of less fuel on startup, which decreased initial cold start emissions to the point it was hailed in the engineering community. Ill be damned, the opti was a good idea for something.
This is just what the shutter wheel does... the high voltage side of the opti is, well basically a distributor. The computer takes all the info from the shutter wheel, makes its decision when to fire the next plug, and sends a signal to the ICM (ignition control module). The ICM takes that info, amplifies it to 12v, calculates dwell time, applies 12v to the coil, removes the 12v and a large inductive spike occurs in the coil and magically 30,000-50,000 volts are blasted out of the coil and sent down to the optispark. It comes in and touches the center of the rotor and is distributed to which ever cylinder the rotor is pointing towards. Then down the fancy conductive ink, to the plug wire, into the plug where It bridges the gap to the electrode ground and SPARK!
THANK YOU TO: https://www.facebook.com/OklahomaCor...anceSpecialist and LTxTech.com
Oklahoma Corvette and Performance Specialist Opti-Spark. Sounds like something from the new transformers movie, eh? If you have had one fail, you may think it was out of a horror movie. Well the truth behind the opti has been told a few times here and there. It basically boils down to a great idea and bad follow through. I am sure we have all been guilty of this before, but we don't manufacture cars, so we get spared of our mistakes. So lets get that out there first...
Why does everyone run screaming from an opti-spark? Why is it a POS?
Well GM engineers fathomed up this brilliant idea for a low maintenance distributor that was very accurate, and for the most part they did a damn good job. The problem lies in the rest of the design that caused the failures.
1. Ya see, a water pump has these seals on the spinning shaft. When the seals fail, coolant is bypassed though the seal housing and out of a weep hole in the bottom of the water pump. This is on virtually every water pump out there. GM kinda didn't realize that the weep hole was above the opti-spark, or they overlooked it, or just said screw it... no one knows for sure.
2. After 1994 all of the opti-sparks became vented. Why? Ozone. Ozone is a gas that is created when there is a spark of electricity. Inside of this tiny arc that occurs from the tip of the rotor and on to the distributor cap there is basically a lightening bolt that cooks the air around it. When you “cook” the air, you produce the gas ozone. Also, if there is moisture in the air (look up to see where the water is coming from) you create steam. Ozone and steam do not play well with optical sensors, because they are “looking” at each other. If you fog up your buddies glasses, he cant see you any more...
3. Sealing the cap and the bearings... The pre 95 had an unsealed distributor cap and the bearings were subject to letting fluids past. This did not help the dripping water pump.
4. Heat kills.... And in this case, heat weakens the electronics that are inside of the 'optical' side of the house, causing heat related failures which often mimic a failing ICM or Fuel Pump.
5. Printed distributor cap... Uhhh yeah, electronic conductive ink was used to print the pattern on the inside of the distributor cap. This unique design prevented cross-fire of cylinders and allowed for a great layout to get even and odd plugs to their corresponding side of the block. But you guessed it, when it gets old or overloaded, electricity will always find the shortest path to ground... That may be the next fancy line of conductive ink- which leads to the next cylinder. Try diagnosing that misfire.
So you can see, there were some flaws. So what? Its not like you have to pull apart the front half of the engine to get to it once it got wet... Oh, right, you do. And this is why people hate the optispark. Even if you only have to change it once every 120,000 miles, it still looks like a worthless chunk of crap once you have dissected your engine to get to it. Because of this, “opti-spark sucks” is the common chant.
Well if its such a hunk of crap, why don't they come up with a fix?
GM tried in 95-97 by venting the cap and using incoming filtered engine air to supply and a one way check valve on the intake manifold to pull vacuum on the inside of the distributor. They also made other changes to the drive mechanism. The end result? Its pretty water proof if maintained... meaning as long as you dont take your LT-x through the next big flood, you should be good to go. Well so long as the foam seal thats around the distributor doesnt rot away...
Bailey Engineering created the LTCC to eliminate the high voltage side of the optispark. You can google it.
Deltec made a solution too.... again google
And to follow a few others (including myself) have designed ways around the Opti. We wont discuss that here, but just know that if you have had enough, then you can source your own solution.
Many of you out there are not ready to make that great leap ($$$$) for a different approach. I don't blame you. I think the Opti is an amazing design! And to convey that message, I will explain how the Optispark works...
PART 2:
Oklahoma Corvette and Performance Specialist
How the Opti-Spark works...
First off, lets look at what it does-
It provides a signal to the computer (ECM/PCM) about where the engine is rotationally in respect to where it has been. Basically, what degree of rotation is the engine at, and what is coming next as far as firing events are concerned.
Well thats easy, eh?? Not exactly...
So lets break it down some. You should know that your engine crank will spin 720* for a complete rotation. The camshaft is driven at half the speed of the crank, so it will go 360* per full event cycle. The Opti is driven by the camshaft. So it has to spin once and give enough information to complete 720* worth of events.
How does it do that?
The Opti has a shutter wheel inside of it. The wheel is about 2.5” in diameter and thinner than a credit card. The wheel has 360 holes cut into it on the outer most “ring” and the inner ring has 8 holes of varying size cut into it. (more about these holes later) This is mounted on the center shaft which is supported by some bearings that are pressed onto the shaft and then into the metal housing of the Opti. The camshaft has a dowel pin pressed into it, and it sticks out of the cam a certain amount, which varies depending on year. This dowel pin slides into a slot on the Opti. Supposedly only one way, but actually it will go about ¾ down the wrong hole and she screams. (!) The opti wont completely bolt on if you have it in the wrong slot, which is slightly frustrating. Anyway, when the cam turns, it spins the shaft in the opti, which in turn spins the shutter wheel and the rotor. The holes that are in the shutter wheel are the vital pieces of info here. To read this vital information the Opti has OPTICAL sensors (that moment when they say the name of the movie in a movie...) These optical sensors are actually a matched pair of LED transmitter/receivers. One transmits infrared light at a certain wavelength. The other sees only that same wavelength of light that the other is transmitting. And there are TWO pairs of these LEDs. One reads the outer ring with the high number of holes, the other reads the one with low number of holes. When the infrared light from one transmitter is seen by its receiver through one of the holes, it essentially becomes a switch and allows current to flow through it. As this current passes through the LED it is then sent though a transistor and amplified to a high enough voltage so that it can be sent to the computer. When the wheel moves, the space between the holes does not allow the infrared light to pass through, so the LED turns off, which turns off the transistor and the signal is zero. While the wheel spins and the holes pass quickly in front of the LEDs the signal turns off and on quickly. It creates what is called a square wave pattern, because it goes from high to low instantly and is held high or low for the amount of time it takes for it to move to the next hole or not. If you were to draw that represented by a line it would make a wave that is squared off...
This square wave is taken by the computer and it means shit.
What does it all mean!?
I am glad you asked, cause this is where the accuracy of the optispark comes into play. I wont go into how other ignition systems work, but lets just say they suck in comparison. Because what the opti provides for information is 90 times better than what existed at the time, and still better than what the LSX uses.
These holes on the outer ring... there are 360 holes. So that means there are 360 filled areas. So it can go low to high (two different states of logic) 360 times each, or 720 times. Wait a sec, there are 720* in a full engine cycle... so if the wheel turns once, that means the cam turned once, which means the crank turned twice.... by golly they found a way to tell the computer where the engine is DEGREE BY DEGREE. Holy crap, thats accurate. They call this bit of information the HIGH RESOLUTION SIGNAL. Sound familiar?
Onto the 8 slots on the inner part of the shutter wheel... There are 8 slots which have a unique design. Their function is to tell WHICH cylinder is passing. The way they did this was kind of ingenuous if you ask me. They made the holes different sizes, but only 5 sizes. Wait a sec, whaaa? If there are 8 cylinders and only 5 different sizes... WTF bro? Welcome to the computer age, we can do a lot with a little. The signals are provided by the length of the hole. 4 of the holes are the same length, between these holes are 4 different sized holes. I hope you understand when I describe the holes' length by degrees... The holes correspond to a cylinder. They go in the firing order according to rotation of the engine. Since its a small block, you should have this memorized, 1 8 4 3 6 5 7 2. Since every other hole is the same size, cylinders 1, 4, 6, 7 all have a 2* long slot. Cylinder 8 has a 7* long hole, 3 has a 12* hole, 5 has a 17* hole and 2 has a 22* long hole. (I will post pics) These signals are all, of course, 45* apart.
What does this do? Well depending on how long the computer sees the LOW RESOLUTION signal determines which cylinder it is on. This is also used for the sequential injection. Now the engine knows exactly what cylinder its on. The low resolution signal tells the computer which cylinder its on, and the high resolution tells the computer how many degrees are passing while it is on which ever cylinder. Woah. If you crunch some numbers, you can see that this is an amazing amount of information. I know it takes me a few mins to find out which cylinder is at top dead center, and if its on its firing stroke or exhaust stroke... this puppy can tell you in 1/100th of a second. And its always right. Thats accurate.
Well thats all fine and dandy. What good it knowing when and where the engine is? For starters, I can tell you that the computer is smart enough to know that on cylinder 1 it should take 2* to get its signal and should see 90 total high and lows for that cylinders firing event, and if it sees too many or not enough it knows that something has happened. It compares this with a multitude of other info and it can reason that there was some knock. Oh yeah, its smart. Ever wonder why the LTX was so sensitive to knock retard and why there was an updated LT4 knock module? There is your answer! This is only a small reason for the fancy opti... the biggest reason was cold starts and emissions. With the computer now able to know exactly when and where the engine was, it was able to start from a dead stop much faster. This enabled the use of less fuel on startup, which decreased initial cold start emissions to the point it was hailed in the engineering community. Ill be damned, the opti was a good idea for something.
This is just what the shutter wheel does... the high voltage side of the opti is, well basically a distributor. The computer takes all the info from the shutter wheel, makes its decision when to fire the next plug, and sends a signal to the ICM (ignition control module). The ICM takes that info, amplifies it to 12v, calculates dwell time, applies 12v to the coil, removes the 12v and a large inductive spike occurs in the coil and magically 30,000-50,000 volts are blasted out of the coil and sent down to the optispark. It comes in and touches the center of the rotor and is distributed to which ever cylinder the rotor is pointing towards. Then down the fancy conductive ink, to the plug wire, into the plug where It bridges the gap to the electrode ground and SPARK!
THANK YOU TO: https://www.facebook.com/OklahomaCor...anceSpecialist and LTxTech.com
357ci LT1, cammed, stalled, and driven. 
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