i'm a little confused by the opti replacements people are using. for the ones where the opti is retained, why not save money and just use a regular distributor? am i missing something?

here's my thought: drop in a sbc distributor and use it only to distribute the spark. it would only need to be phased within ~20 degrees to work properly, if even that closely. leave everything else hooked up normally, but connect the coil output to the new distributor.

if you used a distributor with its own trigger, then the added bonus is that it would later be exceedingly easy to use a megasquirt efi setup and bypass the opti altogether. (megasquirt can even go wide-band O2 closed loop at wot now.)

the only hole i can spot in this idea is, uh... the hole. you'd need to have an LTx intake machined to fit the distributor. still, the total outlay would be less than any other alternative that's on the market, right?

- distributor
- new plug wires
- possibly one custom wire to reach distributor from stock coil
- machine intake
- new intake gaskets to reinstall intake manifold

in my case i'm switching to a single-plane intake, so i don't even have to machine the intake. and, i do plan to switch to megasquirt, and this completely solves the problem of the MS not correctly sensing the signal from the opti.

i'd greatly appreciate any info, comments, or certainly objections to see figure out what i'm missing. thanks!

-michael

 

There is a real lack of room at the rear of the motor and the firewall and the overhang where the hood sits to install a distributor. The LT1 oil pump is driven by a shaft that has a specific gear assembly up at the cam to drive it. This would have to be modified to have the distributor driven by the cam gear and a separate driveshaft to drive the oil pump like the earlier motors.

You might be better off using an earlier L98 type of short block that is already set up for a rear distributor. But that means the water pump would be driven by a serp belt instead of the LT1 cam-driven water pump. And that would probably require using an entirely different serp belt system.

 

If you are going to use the original ECM/PCM that came with the LT1/LT4 motor, it has to have the optical signals generated in the Opti-Spark.
These signals are used for fuel injection as well as spark.

The L98 ECM is different.

Tom Piper

 

Installing a conventional distributor is seriously a step backwards.

For all the faults of the opti, it's strengths outweigh them. The unit is very accurate, and, actually, rather durable and predictable.

The DynaSpark and MSD units look like good options, as would be converting over to a Gen II unit.

The LTCC and DelTeq both use the opti for its optical portion, the part that is truly reliable.

The opti in my car has been there for over 90k miles without a code. What does that say? I am running LTCC...

 

maybe i didn't explain myself properly...

the opti remains, it must in order to drive the ecm. the "distributor" part of the opti isn't inherently better than any other kind. they all still work the same way for EFI cars, the spark has to jump whatever gap necessary since the cap terminals don't move.

the oil pump drive on an LTx is exactly like a distributor at the bottom. the pump driveshaft is identical for both regular SBC and LTx, i don't believe physically fitting a distributor is a problem.

fitment with respect to the cowl... is the LTx cowl different than for the L98 cars?

thanks.

-michael

 

Forum member "lcvette" is using a conventional style distributor on his turbo Vette.

 

This ought to be interesting..

 

the local machine shop guy that did the ''hole'' thing on my lt1 manifold actually got started doin it for the 4x4 truck guys...apparently its a bellybutton thing to put a lt1 from a caprice,etc in an older pick-up but use an early tpi ecm and an hei...big problem for the off-roaders in the low slung opti catching water, mud ,rocks, etc.,and its lack of durability, big $ repairs

 

Now I've seen everything

 

i believe it's a basically sound idea, then. now i just need to figure out which distributor to get!

i probably wouldn't bother if not for wanting to try megasquirt.

thanks.

-michael

 

I really don't want "two" distributors.

The Opti-Spark has 1* crankshaft resolution for spark timing-- I don't think the L98 setup is that accurate.

I took the high-voltage out of the Opti-Spark with the Delteq (LTCC does the same thing), and I still have 1* of crankshaft resolution for the Delteq spark timing from the Opti-Spark signals.

Plus, the LT1/LT4 crankshaft hub does not have a key.
And, it isn't easy to use a timing light on it because there are no timing marks.
In addition, unless you have the heads off, it isn't easy to find TDC, with the accuracy needed, to put your on timing marks on.
Using a piston stop in the spark plug holes doesn't work well in aluminum heads because it flexes too much to be accurate.

Tom Piper

 

no where close.

The entire concept seems rather silly to me... leave the Opti to manage timing and fuel delivery, use the LTCC or DelTeq to manage spark.

 

I've actaully used the low side of a opti to drive a traditional tach signal with no problems. It worked pretty good but I didn't trust it because of the uneven pluses to signify TDC.

I've read where another guy used a 97 F-body timing cover, reluctor wheel, and crank position sensor to fire a megasquirt. IT worked for him and he posted the offset required to get you back at a TDC reference.

 

that would solve it! do you remember where you saw this?

thanks.

-michael

 

i'm not sure if you're trying to say my proposal would be less accurate. if that's what you're trying to say, i would maintain that the opti sensor still controls the spark. i don't see how there would be any difference between the optispark's cap/rotor and a regular distributor's cap/rotor to distribute the spark.

or did i misunderstand and you meant about the case where i'd use a megasquirt driven by a regular distributor vs keeping the opti for timing?

thanks.

-michael

 

I guess it is a misunderstanding.
I am thinking you want to use the electronics in the L98 distributor for ignition -- so, I am now assuming you are just going to use the highvoltage section (cap and rotor).
Still, this would require the Opti-Spark along with a conventional distributor.
Why not go the DIS (LTCC or Delteq) route?

Tom Piper

 

Gotta argree with Andy and Tom here. If you're going to go to all the trouble and expense of getting the high-voltage ignition section out of the Opti, I can't imagine why you'd not want to go DIS. It makes so much more sense to me than to try to get a cap & rotor running behind the intake, which would be a huge step backward as compared to a DIS setup.

Be well,

SJW

 

how could the dis be used to trigger megasquirt if the opti were eliminated? is that possible?

-michael

 

The Delteq and LTCC DIS conversion setups do not eliminate the optical section of the Optispark. All they eliminate is the cap & rotor, in favor of four Northstar wastespark coilpacks (Delteq) or eight LS1 coilpacks (LTCC). Either of these systems is triggered by the stock ECM, which relies on the high- and low-resolution timing pulses from the Optispark.

Be well,

SJW

 

Everybody whines about the optispark. I don't know what year your car is, but if it is an early model, you can always switch to the later model. If kept reasonably dry, the opti-spark works just fine! The original should work fine for 50-150K miles.