Well just got news that the my new motor is done.

I helped pull the old one, but my buddy did the reinstall for me since i am up at school during the week,

Anyways, used a MSD crab cap distributor, run from the stock ECM and coil. Left the high/low res wheel part of the opti in tact, and pulled out the rotor.

So my find. Physical distributor timing in reference to the crank doesnt really matter on the lt1. I know you all will flame me for this, but by doing things few people have done, you learn.

Started with the distributor with about 6 degrees advance. Turned the key and the car started instantly, idles etc. Put a light on the car. ECM was feeding a 25 degree idle, the car was actually seeing about 20. Turned the distributor a tad, and nothing. Turned some more, nothing. You had to turn the thing about 90 degrees before any actual timing difference was observed, and at that point the car just died. The only way you could make the observed timing change is if you spun the distributor very quickly, and the timing would jump for a second, and then return to the 20 degrees.

Somehow, it seems as if the ECM self adjusts itself. Any ideas? Im not worried about it at all, the car is running fine, just trying to understand why its doing what it is doing.

 

I take it you just ran a longer coil wire from the LT1 coil to the rear mount dis. No differant than the opti function since the ecm is still in control as you found.
Thats the 360 degree function of the opti to correct each side of TDC per hole at work.

 

By doing this would spark KV be weaker or stronger?

Might it be using the coil saturation time to fire differently in order to keep cam and crank signals inline.

Very interesting question!


Who drilled your intake for the distridutor? I like that idea.

 

Correct. The distributor is basically just taking the place of the opti rotor. Doing it this way, it wont fling the rotor apart, wont break up at higher RPMs etc. Basically a cheap way to eliminate many of the opti's shortcommings.

Can you elaborate on your last sentence please? Thats what i am trying to learn about or find out how it actually adjusts itself. I know what you meant by the 360 knotches inthe wheels, but how does that affect TDC firing?


The intake is a single plane super vic converted to EFI, so the distributor hole was there It shouldnt affect voltage output of the coil, a slightly longer coil wire is needed so you will have some extra resistance there. The main benefit is to get rid of scatter spark up top. Running a 6al box too. Poor mans delteq

 

The computer only has controll over the coil, but it references signals from the cam and crank. By decreasing duty cycle of the coil, I would think you'd get a weaker spark and it would change the fire time. Weaker spark = poor combustion, which might equate to a slower crank speed to keep cam and crank sensor synchronized.

 

So you left the opti stuff running in the stock opti distributor on the front of the motor but you're using the aftermarket one at the back to do the actual spark-distribution duties?

If I have that right then there is NOTHING the rear distributor can do to alter timing. All you're doing is altering the distributor phasing by twisting it back and forth. It'll run the exact same timing no matter where you set it until the phasing gets so bad the spark won't jump to the correct terminal under the cap, at which point it will die.

 

Ha!!! I must be missing something here but right now I'm drilling a hole in the lt1 intake manifold. Actually, I've already drilled it out. Hopefully it is lined up dead center. I just have to make a collar and TIG it the manifold, slap the manifold back on the block and drop in the MSD dist. Are you using a low profile MSD??

Just incase someone was wondering this is just a motor with the cam, heads, and intake on. The mock up motor I'm using is going to be used for anything inless I have the collar and hole for the distriobutor dead on b@lls. If it is, I'll clean up the tacs and reweld the rest of the collar on. Pending if everything else is okay.

 

Yes you got it. I just thought that i would be able to influence the timing a tad by rotating it, just by making the spark jump sooner/later. Is there a way to perfectly phase the rotor inside the distributor?

I am using the low profile billet crab cap MSD. Its mainly used with crank trigger setups, nothing to it except the cap/rotor/shaft. You can get a fist above it and the windshild overhang, may be possible to even pull it out without dropping the motor.

 

Sweet, I'm headed in the right direction then. Like I said as long as if it lines up straight. I'm tired of opti blowin up.

 

Hope I'm not all wet here with this...

Low res pulse fires inj phasing and the high res pulse [360 degrees] allows the ecm to add or subtract timing per hole [cylinder] up to what 32 er 28 degrees each side of TDC for each cylinders firing sequence. This is why you didn't get much "reaction" out of advancing or retarding the rear mount DIS...
...the ecm was doing its thang
We talked about doing this a few years back for kicks as we knew it would work fine as long as the rotor was in phase with TDC.

 

HRH-
Got it i think, basically i have 28-32 degrees on both sides of TDC per cyl of which the ECM can compensate.

Now for rotor phasing, should i just phase it with absolute TDC and let the ecm take care of the rest? In that case wouldnt 32 degrees be max timing advance? That being correct, i would want to phase it 6-8 degrees advanced for a max of about 40 degrees total advance possible?

 

Man I'd put it in dead on. The deal with the correction is "IF" knock is picked up or if it's not then we know the ecm will adjust "optimizie" timing to the base setting for the cell your operating in, wither it need retarded or advanced based on the KS operation working with "attack" amount or min advance tables. ..... Hence Optispark.
It takes those windows eachside of tdc to work all together in the mix.

 

Sounds like good advice to me.

 

I need the SPECIFICS on how to do this conversion, sites anywhere? I did a search....BTW our new search function sux.


David

 

Wouldn't going to the LTCC or DELTEQ be a much simpler solution instead of hacking up the intake?