LT1 Questions
08-18-2005, 06:54 AM
#1
Le Mans Master
Thread Starter
LT1 Questions
In my research of LT1 C4 corvettes, and the LT1 SS Impala, there seems to be some issues with the optispark distributor and waterpump. I know nothing about the LT1 engines, so educate a dummy 
What is the problem, and how can it be avoided?
I've seen mention of replacing the optispark with a Dynaspark. What is the difference between the two, and is the Dynaspark immune to the problems the optispark has?
Also, why are the water pumps so prone to leaking? Is this a design flaw in itself?
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
I might stay with the L98s, depending on the outcome of my research.
Thanks in advance for your replies
What is the problem, and how can it be avoided?
I've seen mention of replacing the optispark with a Dynaspark. What is the difference between the two, and is the Dynaspark immune to the problems the optispark has?
Also, why are the water pumps so prone to leaking? Is this a design flaw in itself?
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
I might stay with the L98s, depending on the outcome of my research.
Thanks in advance for your replies
08-18-2005, 07:19 AM
#2
Melting Slicks
Personally, I don't think the OptiSpark is all that bad. It's not as good as direct ignition like the LSx engines use, but I find they are just as reliable as any distributor can be. Now I have a '95 which has the vented Opti, maybe I wouldn't be as happy if I had an earlier one.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
08-18-2005, 08:10 AM
#3
Elite Torch Red Member
Originally Posted by Atok
Personally, I don't think the OptiSpark is all that bad. It's not as good as direct ignition like the LSx engines use, but I find they are just as reliable as any distributor can be. Now I have a '95 which has the vented Opti, maybe I wouldn't be as happy if I had an earlier one.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
As with any car, the ignition system needs maintainence, anyone with a L98 will still have to change the rotor and stuff. With the LT1, I've heard of folks changing the cap and rotor, but most replace the whole thing.
Average life span is about 65,000-75,000 miles, some have made it over 100,000 and many have made it much less than 40,000 miles.
As for the waterpump, I'm not sure about the design and any faults, but since it sits in front of the opti, when the water pump blows, it is possible(especially pre 94) that the opti can(note I said can, not will) fail.
The 95-96 stands a better chance of surviving, but if you have to replace the water pump anyway, you might as well change the opti. Same as if you blew your tranny, would you keep the old clutch in there or replace as long as everything is apart?
08-18-2005, 08:20 AM
#4
Your research may show you that the people who are afraid to drive their cars tend to have more problems with these two components. The water pump is designed to move, letting it sit in a garage for years without being driven is murder on the bearings. Once the water pump fails it will begin to leak onto the distrubtor. The distributor then has no chance in hell of surviving because the car barely ever gets warm enough to dry it out.
Just keep in mind if you're buying an LT1 that it needs to have "acceptable" mileage. It doesn't have to be driven 10,000 miles a year, but it doesn't need to be a garage queen either. IE if you find a 12 year old car with only 5000 miles on it you may have a lot more trouble out of it than one with 80,000 miles on it.
Just keep in mind if you're buying an LT1 that it needs to have "acceptable" mileage. It doesn't have to be driven 10,000 miles a year, but it doesn't need to be a garage queen either. IE if you find a 12 year old car with only 5000 miles on it you may have a lot more trouble out of it than one with 80,000 miles on it.
08-18-2005, 09:53 AM
#5
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I have to agree with the advice that has already been given...heed it. My Opti crapped out at 25,000 miles. 
The water pump bearings (the few that were left) went south and took the Opti with it. Had the plugs and wires done at the same time.
If you don't do your own work for something like this, expect to spend a minimum of $1,000.00.
As far as how to avoid this problem....don't buy an Opti-equipped vette.
The water pump bearings (the few that were left) went south and took the Opti with it. Had the plugs and wires done at the same time.If you don't do your own work for something like this, expect to spend a minimum of $1,000.00.
As far as how to avoid this problem....don't buy an Opti-equipped vette.
08-18-2005, 10:25 AM
#6
Race Director
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I agree with Atok and Nathan... the opti isn't the greatest design, but at the same time it isn't all bad either. The main problem with the earlier style was that it wasnt' vented so moisture would build up under the cap causing premature failure. On the flip side, my friend has an LT1 Camaro with 186k on the heartbeat and it is still running strong... and I have seen later LT1's and LT4's puke an opti in less than 20k miles. That said, I agree with Nathan that you have to drive the car and use it regularly so things don't just go bad with age.
08-18-2005, 10:50 AM
#7
Le Mans Master
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Water pumps wear out and when they do they leak.
Some brilliant engineer put the ignition under a water pump.
Why is unknown.
There are + and - with both models. Lt-1's are nice cars with thier own set of problems the L-98 has its draw backs also.
If you want a LT-1 but a 95 or 96 they're as good as gets for the C-4.
L-98's can be built to run with the LT-1's. AFR offers a set of L-98 heads claiming 80 horse power over the stock head.
www.airflowresearch.com
Of course a modified LT-1 is a another story.
If want a L-98 90-91 is your best bet.
Anyway you go a Corvette isn't just a car its an expierence.
Some brilliant engineer put the ignition under a water pump.
Why is unknown.
There are + and - with both models. Lt-1's are nice cars with thier own set of problems the L-98 has its draw backs also.
If you want a LT-1 but a 95 or 96 they're as good as gets for the C-4.
L-98's can be built to run with the LT-1's. AFR offers a set of L-98 heads claiming 80 horse power over the stock head.
www.airflowresearch.com
Of course a modified LT-1 is a another story.
If want a L-98 90-91 is your best bet.
Anyway you go a Corvette isn't just a car its an expierence.
08-18-2005, 12:11 PM
#8
Melting Slicks
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St. Jude Donor '06
Originally Posted by Atok
Personally, I don't think the OptiSpark is all that bad. It's not as good as direct ignition like the LSx engines use, but I find they are just as reliable as any distributor can be. Now I have a '95 which has the vented Opti, maybe I wouldn't be as happy if I had an earlier one.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
I think they get a bad rap because when they do wear out they are expensive and difficult to replace. But they are designed to last much longer than your average distributor.
I'm sure someone will disagree, but hey - that's Ok.
08-18-2005, 06:24 PM
#9
Le Mans Master
Originally Posted by Randy93
Not to hi-jack the thread, but can an LSX ignition be used on an LT1?
I'm in the process of cleaning up all the wiring now, but this is the LTCC kit that allows you to use the LSx coils, it is still fed by the optispark though so they know when to fire. However, I completely gutted my opti when I installed this kit. The rotor is not just a small piece of plastic, no metal on it anymore.
08-19-2005, 12:09 AM
#11
Le Mans Master
Originally Posted by Shotgun
In my research of LT1 C4 corvettes, and the LT1 SS Impala, there seems to be some issues with the optispark distributor and waterpump. I know nothing about the LT1 engines, so educate a dummy
The Optispark was a huge evolutionary step that took engine controls to the next level beyond what was possible with HEI. It works extremely well until something goes wrong with it. The Optispark is a distributor, but rather different from any other distributor. It has two sections:
The optical section uses two optical sensors that read holes in a rotating disc. These sensors furnish the ECM with exact camshaft position, velocity, and acceleration/deceleration data. This data is extremely useful to the ECM, as it allows the ECM to custom tailor the spark timing to optimize it for all operating conditions.
The high-voltage section of the Optispark is conceptually no different from the high voltage section of a conventional distributor, however it differs in how it's implemented. The Optispark lives on the front of the timing cover, directly ahead of the camshaft, and is directly coupled mechanically to the camshaft. Because of its placement, and the diameter of the cap & rotor, as well as the fact that the plug wire towers are not in order (relative to the firing order), and are not spaced equidistant around the cap, the cap uses conductive ink to make the conductive path to the wire towers.
What is the problem, and how can it be avoided?
There are two basic problems with the Optispark:
1. It has some durability issues (especially the passively-vented first-generation Opti, which was used on Corvettes from '92 through '94). The actively-vented second-generation Opti was a significant improvement. Sealing was a big problem with the OEM Optis, and a leaking water pump can quickly kill these units, as can cleaning the engine with a water hose.
2. It has major accessibility issues, as a result of its physical placement on the front of the engine, below the water pump. The designers placed the Opti where they did in order to couple it more directly to the camshaft. This reduced the mechanical slop between the camshaft and distributor and increased the accuracy of the feedback of camshaft data from the Opti to the ECM, which is a good thing. Unfortunately, the price for this was a major penalty in accessibility, and given the durabitilty issues with the OEM Optisparks (first-generation Opti in particular), it proved to be a painful trade-off.
To avoid the problems related to the Optispark, either buy a car that doesn't use the Opti, or upgrade it after you buy one. The Opti-equipped cars should not be feared.
I've seen mention of replacing the optispark with a Dynaspark. What is the difference between the two, and is the Dynaspark immune to the problems the optispark has?
The DynaSpark is an aftermarket replacement for the Optispark. The designer and manufacturer of the DynaSpark (DynoTech Engineering) pulled out all the stops to try to solve all of the deficiencies associated with the OEM Optispark (visit their website for details). They did a very nice job. The DynaSpark is a high quality piece, and goes as far as is possible to solve the problems. It is so well sealed that DynoTech actually encourages you to hose it down. I installed a DynaSpark in my '94 last year, and I'm very pleased with it. My Opti-related paranoia is now history.
Also, why are the water pumps so prone to leaking? Is this a design flaw in itself?
I have seen nothing that leads me to believe that the LT1/LT4 water pumps are more prone to leakage than any other OEM pump. I suspect that the reason you've heard so much about water pump woes on these engines is because they so often take the Opti south with them when they do leak.
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
The LT1 was a big step forward from the L98. The L98 was a great engine -- torquey, hard-working, and tough. Its long intake runners caused it to run out of breath ~4500 RPM in stock trim. It used HEI, which was relatively simple and reliable, but could not manage spark timing anywhere near as well as the Opti-equipped engines that followed it. The LT4 was an improved LT1, good for at least 30 more HP in the top end. Lower RPM performance was very similar to the LT1.
I might stay with the L98s, depending on the outcome of my research.
The L98 was a good engine. But, I chose to get an LT1 or LT4 (ended up with an LT1), because of its more advanced design, and because that's what came in the later C4s. I bought a '94. If I had it to do over again, I'd buy a '95 or '96, because they came with worthwhile improvements over the earlier model years (bigger brakes, revised Optispark, etc). The early C4s with the L98 were great cars. The later C4s with the LT1/LT4 are even better in many ways. The C4 was steadily improved over its lifespan, and I feel that the '95 and '96 were the best of the lot.
Does this help?
Be well,
SJW
Thanks in advance for your replies
The Optispark was a huge evolutionary step that took engine controls to the next level beyond what was possible with HEI. It works extremely well until something goes wrong with it. The Optispark is a distributor, but rather different from any other distributor. It has two sections:
The optical section uses two optical sensors that read holes in a rotating disc. These sensors furnish the ECM with exact camshaft position, velocity, and acceleration/deceleration data. This data is extremely useful to the ECM, as it allows the ECM to custom tailor the spark timing to optimize it for all operating conditions.
The high-voltage section of the Optispark is conceptually no different from the high voltage section of a conventional distributor, however it differs in how it's implemented. The Optispark lives on the front of the timing cover, directly ahead of the camshaft, and is directly coupled mechanically to the camshaft. Because of its placement, and the diameter of the cap & rotor, as well as the fact that the plug wire towers are not in order (relative to the firing order), and are not spaced equidistant around the cap, the cap uses conductive ink to make the conductive path to the wire towers.
What is the problem, and how can it be avoided?
There are two basic problems with the Optispark:
1. It has some durability issues (especially the passively-vented first-generation Opti, which was used on Corvettes from '92 through '94). The actively-vented second-generation Opti was a significant improvement. Sealing was a big problem with the OEM Optis, and a leaking water pump can quickly kill these units, as can cleaning the engine with a water hose.
2. It has major accessibility issues, as a result of its physical placement on the front of the engine, below the water pump. The designers placed the Opti where they did in order to couple it more directly to the camshaft. This reduced the mechanical slop between the camshaft and distributor and increased the accuracy of the feedback of camshaft data from the Opti to the ECM, which is a good thing. Unfortunately, the price for this was a major penalty in accessibility, and given the durabitilty issues with the OEM Optisparks (first-generation Opti in particular), it proved to be a painful trade-off.
To avoid the problems related to the Optispark, either buy a car that doesn't use the Opti, or upgrade it after you buy one. The Opti-equipped cars should not be feared.
I've seen mention of replacing the optispark with a Dynaspark. What is the difference between the two, and is the Dynaspark immune to the problems the optispark has?
The DynaSpark is an aftermarket replacement for the Optispark. The designer and manufacturer of the DynaSpark (DynoTech Engineering) pulled out all the stops to try to solve all of the deficiencies associated with the OEM Optispark (visit their website for details). They did a very nice job. The DynaSpark is a high quality piece, and goes as far as is possible to solve the problems. It is so well sealed that DynoTech actually encourages you to hose it down. I installed a DynaSpark in my '94 last year, and I'm very pleased with it. My Opti-related paranoia is now history.
Also, why are the water pumps so prone to leaking? Is this a design flaw in itself?
I have seen nothing that leads me to believe that the LT1/LT4 water pumps are more prone to leakage than any other OEM pump. I suspect that the reason you've heard so much about water pump woes on these engines is because they so often take the Opti south with them when they do leak.
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
The LT1 was a big step forward from the L98. The L98 was a great engine -- torquey, hard-working, and tough. Its long intake runners caused it to run out of breath ~4500 RPM in stock trim. It used HEI, which was relatively simple and reliable, but could not manage spark timing anywhere near as well as the Opti-equipped engines that followed it. The LT4 was an improved LT1, good for at least 30 more HP in the top end. Lower RPM performance was very similar to the LT1.
I might stay with the L98s, depending on the outcome of my research.
The L98 was a good engine. But, I chose to get an LT1 or LT4 (ended up with an LT1), because of its more advanced design, and because that's what came in the later C4s. I bought a '94. If I had it to do over again, I'd buy a '95 or '96, because they came with worthwhile improvements over the earlier model years (bigger brakes, revised Optispark, etc). The early C4s with the L98 were great cars. The later C4s with the LT1/LT4 are even better in many ways. The C4 was steadily improved over its lifespan, and I feel that the '95 and '96 were the best of the lot.
Does this help?
Be well,
SJW
Thanks in advance for your replies
Last edited by SJW; 08-19-2005 at 12:33 AM.
08-19-2005, 06:25 PM
#12
Safety Car
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Originally Posted by Shotgun
Also, why are the water pumps so prone to leaking? Is this a design flaw in itself?
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
I might stay with the L98s, depending on the outcome of my research.
Thanks in advance for your replies
Are there any other issues with the LT1? Do they really offer an advantage over the L98? I plan to mod whatever car I buy, so horsepower is a moot point.
I might stay with the L98s, depending on the outcome of my research.
Thanks in advance for your replies
As far as the LT1 vs L98, each has its advantages and disadvantages. The LT1 makes more power in stock form and the torque curve peaks quickly and stays flat over a broad range of RPM. However, this engine shares very little in the way of parts with earlier SBCs and nothing with the LSx engines that followed it, so when doing a build up you have to make sure you specify that its an LT1. This is especially true with the cylinder heads.
Remove the intake manifold and FI unit from a L98 and you're looking at basically the same engine that has graced the engine bay of millions of Chevys (and a fair number of rodded Fords and Mopars as well.) Parts are plentiful and if you've worked on any Chevy built before 1992 you can work on this engine. It has great bottom end torque (in fact stock vs stock it will take a LT1 off the line) but around 4500 rpm it runs out of steam due to the long tube intake runners.
Last edited by 6t9l4t6; 08-19-2005 at 06:28 PM.
08-19-2005, 06:36 PM
#13
Melting Slicks
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St. Jude Donor '05
mine got a 125,000 before it crapped out i guess i was one of the lucky ones but when it does go your not going anywhere. i drove mine to work went to go home at the end of the day and all it would do is crank over no fire whatsoever. i did mine in about three hours that included new wires and a new waterpump 
