Programmable MSD 6AL-2 questions

[68Cuda]

Originally Posted by SSLance

Pretty interesting and educating trip to work this morning. I was mainly looking at vacuum and AFRs at cruise speeds.

In 5th gear at around 2200 RPM (70ish MPH) the engine was extremely happy. Pulling 20-22" of vacuum, barely touching the throttle, would pull any hill with no effort...and AFRs at around 15.7:1 and steady.

I didn't have the laptop hooked to the Ignition box so I don't know what the timing was or what the MAP sensor said the vacuum was...but with no Boost Retard Curve installed, it was just Advance Retard working which would have put the timing advance at around 20* advanced.

In 6th gear at around 1700 RPM (70ish MPH) the engine was not happy. Vacuum was bouncing between 10-15", way more throttle input to keep it moving, lugged down on hills...and AFRs got fat, down to mid 12s to 14:1. Timing would have been around 15* advanced.

Engine certainly needs vacuum advance if I want to use 6th gear on the highway.

Sounds like you are starting to get the hang of it and also getting a better feel for things... once you dive in and start tweaking will be the fun part. Testing and observation is where you will learn the most, then you can come back here and tell us how it is done!

[SSLance]

I talked with my carb guy and he's a bit afraid that he's got too much idle air bleed in the carb itself which is a simple repair, but one that he'll need to do at his shop. For now, I'm going to try to turn the idle air mixture screws in a half turn and see what that does to the RPM and AFR at idle, then test on the way home.

It's funny because if going by the seat of the pants feel, the car drives GREAT... No hiccups at all, in the old days we would have left it as is...but by watching the data I can tell it's off in a few places and by dialing those in it'll only get better.

Man... I've had fun driving this thing around the last few days though. HUGE increase in upper RPM power. This was a much needed upgrade over the ignition and carb I was running before.

[Flash68]

Very cool Lance. Who says playing with carbs can't be "techie"?

I have not ran mine yet but my initial program is ready to test out after chatting with a couple of the MSD techs.

[SSLance]

A couple more test drives under the belt, along with several changes...and the car just keeps getting better and better and better.

It didn't like any adjustments to the idle air mix screws, just a quarter turn leaned it out too much and didn't change the idle so I put them back.

I decided to put some more timing in so I set the initial at 9* and bumped the rest of the curve up so it was all in (32*) at 2800 RPM. This put the advance at cruise speed in 6th gear at around 20*. The car really liked this in every way except it idles at around 950 RPM. Awesome power everywhere, no lugging and loading up, VERY smooth off idle on takeoff, no more shudder, and pretty decent pickup on 3000-6000 butt horsepower yet again.

So...still no pinging...lets add more timing!

Turned the distributor to 34* total and adjusted the curve to 9* initial once again with it all in at 2800 RPM. Air fuels are great still, low - high 14s cruising just depending on what I'm doing with the throttle and under WOT it's high 11s-low 12s. Did I mention it's FASTER!!! Man...

I don't think I'll mess with the vacuum advance until I can get some adjustments made to the carb. I've been told I can move the MAP sensor vacuum to a timed port and trick the box to not put any vacuum advance in until the throttle is cracked...but it's so good now, I think I'll just leave it as it is for now until I get some time to send the carb back to Bob. I'd like to get the carb to idle at around 700-750 RPM with as much timing as I can through at it before messing with the vacuum advance.

Thanks for putting up with me through this thread...hopefully some others will try this box as well now that they've seen a noob like me can figure it out. It really is cool to be able to tune the timing with a flick of your mouse. I've saved up a little stash and my next purchase is a back up box which will get loaded with the same tune and always be available it needed.

[68Cuda]

Originally Posted by Flash68

Very cool Lance. Who says playing with carbs can't be "techie"?

I have not ran mine yet but my initial program is ready to test out after chatting with a couple of the MSD techs.

Assuming... you are running about 34 total, that would be the equivalent of running 24 "initial", 10 "mechanical" advance, and an extra 10 "start retard". Not bad. Good performance strategy, and easier to start.

I know some folks that will weld slots in the distributor to be able to limit the mechanical to only 10 so they can run more initial. This makes it pretty easy doesn't it.

Do you have a MAP? Brave enough to try some "vacuum" advance?

[SSLance]

Originally Posted by Flash68

Very cool Lance. Who says playing with carbs can't be "techie"?

I have not ran mine yet but my initial program is ready to test out after chatting with a couple of the MSD techs.

That should work...but did they teach you the trick of starting the curve at 0* and then bringing it down to 20* at 200 RPM or so? This gives the engine advance for initial starting and reduces the chance of the engine kicking back (or something like that). That probably comes into play more with a higher compression, larger cam engine than mine, but I put it in mine anyway.

Let us know when you fire yours off and get to play with it a bit.

[68Cuda]

I'm still trying to figure out what I will be doing with mine. I bought it assuming I was going to run a carb.

Shortly after I bought it I ran across my dream intake up for sale that I had been keeping an eye out for a few years. They are kind of rare, I did not think I was going to find one honestly. Considered by many to be the best cast intake ever made for this engine. Of course this intake was developed for super stock racing in the mid 70s and never was intended to go on a street car. It has some nasty idle mixture problems due to the design of the upper plenum. One way to solve that issue is to not put fuel into the upper plenum, no way for it to come out of suspension and puddle in that instance. Of course that means eight injectors at the base of the intake, AKA EFI. And, since this is a street car of course it needs to have traction control. The EFI system does this through spark retard. So, now I have an EFI system that can do all the same spark control that the MSD box is capable of and traction control.

So, I will have a locked out distributor and the program for the box will be set for 0 everywhere. I guess my back up box does not need to be a programmable unit. I guess I just keep the programmable as a back up box.

[Flash68]

Originally Posted by 68Cuda

Assuming... you are running about 34 total, that would be the equivalent of running 24 "initial", 10 "mechanical" advance, and an extra 10 "start retard". Not bad. Good performance strategy, and easier to start.

I know some folks that will weld slots in the distributor to be able to limit the mechanical to only 10 so they can run more initial. This makes it pretty easy doesn't it.

Do you have a MAP? Brave enough to try some "vacuum" advance?

30 degrees total here. This is an SB2.2 headed engine. Highly efficient combustion chamber.

And I was just gonna run a locked out distributor with standard 6AL again like on my 377 before, but a friend talked about using one of these so I kinda decided to just try it. And you nailed the goal -- performance with easier start up.

No MAP and no bravery here.

Originally Posted by SSLance

That should work...but did they teach you the trick of starting the curve at 0* and then bringing it down to 20* at 200 RPM or so? This gives the engine advance for initial starting and reduces the chance of the engine kicking back (or something like that). That probably comes into play more with a higher compression, larger cam engine than mine, but I put it in mine anyway.

Let us know when you fire yours off and get to play with it a bit.

I should be firing it for first time in the car in the coming couple months.

Do you mean starter kickback? That is all the MSD tech mentioned being aware of. Here is his final comment on my baseline tune:

-------------
Yes, that's near the money. You could play with the cranking timing up to the point of starter kickback: 10-15 degrees, and your idle timing: 12 - 20 degrees for idle quality.

Eg: you may end up at 13 cranking so it starts well, and 18 idling.

[David Pozzi]

Here's my cheat sheet for PSIA to Vacuum conversion.
On this one, I was trying to leave 4 deg more advance available in software so I could try adding more later without having to re-set the distributor.
Another good trick is to set up the retard wire to a rocker switch so you can pull out 2 to 4 degrees if you ever get some bad/low octane gas and hear pinging.
I mounted the MSD in a place where I couldn't see the L.E.D. but found a fiber optic flashlight extension and used that to "pipe" the light to an area I could view it.

[SSLance]

Thanks David, you always bring great tech to any thread...

I love how people take what this box gives them and then try to figure out ways to trick it do even more than MSD suggests with them. All great ideas...

I wonder why my vacuum gauge and MAP sensor via the MSD screen vary so much from your cheat sheet? Mine very clearly shows 20" of vacuum corresponding with 7.00 PSI.

I currently have the vacuum gauge hooked to a timed port on the top front of the carb (same as goes to the choke pulloff) and the MAP sensor hooked to a manifold vacuum port at the back of the carb base next to the brake booster port. I guess I should rearrange one of both of them to really see what is going on... Where should I put each connection for the best info gathering source? This is a 1977 mechanical quadrajet with an electric choke.

I also noticed the other day that my heater controls aren't working properly so I'm going to cap those vacuum ports off for now as well as I might have a vacuum leak there that could be affecting things.