...and if its pinging or has too much advance the tuner can pull it via the tune and if its retarded he can advance it...
IMO if you try to fix things by moving the advance screw you will be chasing your tail......

 

You are not trying to set it. Just see what it is.

 

Well how would he know if it's advanced or retarded if it's not going to show up on a log?

 

Whatever...I'll feel better checking it so that's what I'll do. Thanks guys!

 

For the PCM, timing is a simple look-up function with the main parameters being load and rpm. There are a few "modifiers" internal to the programming, but at the end of the day it all boils down to what's in the timing table.

The datalog is nothing more than a report regarding what value in the timing table the PCM is using.

Since the MSD Opti adjusts the timing outside of the PCM and there is not a timing advance feedback mechanism to the PCM, the PCM has no idea what the MSD distributor is doing. Therefore the PCM goes about it's merry way using what is programmed in the table. Since the datalog gets its info from the PCM, it has no way to see or report the effect of a change generated by the MSD Opti screw either.

So, in theory the timing tape would allow you to see the effect of changing the MSD setting. Adjust the screw clockwise all the way and take a reading. Then adjust counter-clockwise and take a reading. Split the difference and you know where zero is relative to the MSD. Of course this assumes you can actually see the balancer which can be challenging on an LT1/4 when it's running due the the accessory bracket, etc.

At the end of the day....way easier to just set the MSD at zero by having the timing screw in the middle of "full clockwise and full counter-clockwise", and then tweak the tune. Takes 10 minutes and you have none of the hassle.

I will also add that you have nothing to gain by making a gross adjustment. 99 times out of 100 you will gain in one area and lose in another.

Like I mentioned before....pointless gimick.

 

I understand Jim but going back to post #17.... what if the screw is not doing what it's supposed to be doing inside the opti. How would I know besides doing the tape? How would the tuner know since the opti is after the PCM? He can't know. The PCM is assuming the opti is in a certain position, correct? I'm with you on pointless gimmick and I wish that screw wasn't there but it is. According to some post in threads I have read. Some guys have actually checked where the screw is supposed to be at from the factory and it is not where it's supposed to be. In reality isn't this kind of like the conventional distributor? You loosen the clamp to fine tune it to a certain point. In the MSD's case you adjust the screw to do the same thing you would be doing by rotating a conventional distributor.

I believe for this one test removing the fans or something else to be able to see the damper would work just fine. Is all of this a lot of trouble? Yes it is, but once again how can you make certain without doing it. I just don't believe you can.

Thanks for everyone's input.

 

It doesn't matter where the MSD is set. You leave that alone and then adjust the timing tables in the PCM to maximize the operation of the engine. You validate those results via real world driving and the chassis dyno. Who cares what the "real" value is. You plug numbers into the timing tables to get you the best results. Since you don't know where the MSD is set, it just means some of the values could end up looking funny.

Regarding it being like a conventional distributor...yes, but it's not "fine tuning" by making an adjustment that affects every single rpm point. It is a gross adjustment. You're doing surgery with a hatchet. Fine tuning is when you adjust individual timing cells....a degree here, two degrees there, no adjustment somewhere else. That is fine tuning. It's also why computer cars make more power and are more efficient than the old non-computer cars. You can optimize every area of the timing map.

I understand the desire to "know" and if you have the time to do it, great. However, it's nothing more than interesting information and will do nothing to increase the performance that you couldn't already do via the timing tables in the PCM.

 

Alright Jim, I'll take your word on it but it still seems strange to me. I'll just have to think on it until it clicks I guess.

Thanks

 

You did a great job of explaining why it really doesn't matter...... and how datalogging / changing the tune can easily set the best timing curve/parameters

 

Ok, just so I won't be completely wrong here. IF I was just replacing the opti with a MSD with this adjusting nut thing and the car was stock with no intents and purposes of getting a performance tune. Just a everyday DD. There would be issues with the timing, correct?

 

No issues if you left it at set at zero....advance or retard..


IMO the factory vented opti can't be beat...I even helped a buddy convert from non vented to factory vented... Back in the day I was going to install one of the two coil on plug conversions and the each of the two different tuners I used told me to stick with my factory OPTI....


Mike

 

Ok, good enough unless it's set wrong at the factory to begin with. That's it I'm done!

 

..... and even if factory set it wrong....during your datalogging, driving/ dyno/ track etc
You'll/the tuner will figure out that it either needs more or less timing and the tuner can tweak it........

Go out and drive that sucker....

 

Thought I'd come back and finish this thread.

I ended up installing the timing tape on my damper. No room for a pointer but I was able to mark the face opti at TDC to do the check I wanted to do. The timing was 5* advanced at idle from what my tuner said it should be at with the screw two turns out as suggested by MSD for the factory setting. I ended up screwing the adjustable screw on the opti all the way in to get the the timing to what he said it should be. I also checked it at 2K rpm also and with MAP readings given to my tuner. It was off 3* advanced at that rpm before I screwed the screw in. I have no idea what my margin of error would be with any of this but I do know the car idles a hell of a lot better than it has in quite some time so it wasn't a total waste of time as some have said it would be. MSD actually recommends doing this with this model opti on their website.

http://www.msdignition.com/uploadedF...structions.pdf

 

Doesn't your camshaft have 5* advance built in?

 

Ignition timing Vs Valve Timing = Two different animals.

Jake

 

OK, I get confused by the two.

 

Really? That would be true on an L98 with a distributor that can be moved, but lets say we are installing a stock opti with no provision for timing adjustment. Base spark timing is determined by the camshaft dowel pin so if the cam is advanced or retarded so is spark timing relative to crankshaft position.

 

I was mildly surprised at how many folks actually think as you do on this issue. We hashed this out a few months ago on two different Forums. This one and LS1LT1, IIRC, which began with the OP posting about advancing his cam (LT engine) using an offset bushing.

ELLWEIN was the only person I was able to find who had actually done it. He had tolerance stack and needed to rephase his cam using an offset bushing. He and one magazine Tech Author (HIB?), in addition to Forum members also gave their concurring input.

No need to get into it all over again. It would take us way off topic.

Jake

 

I would be interested in viewing the thread if you can direct me to it rather than hijack the one Mike has going here.
Understand Mike did not move his cam with an offset bushing, he used the crank key method, but no matter how you move the cam relative to the crank it has to change ignition timing as well on an LT1.
The only cam and and or crank reference input to the PCM on the LT1 comes from the opti, the dowel pin has to set TDC as base.