CuttyShark

Running an MSD Atomic with Timing Control. I need to input the RPM the timing is All in, the total Timing and Total Vacuum and RPM where advance starts from. The computer takes care of rest.

what is a good TOTAL? i am finding some threads that say 34 and some up to 42. Is 34 too little?

anyone with a Holley Sniper or FiTech?

the specs of the Cam are Duration 280/290, Lift .448/.472

the Heads are Aluminum ProComp

Magnum 1.6 rockers

keith black pistons Bored 060 over

stock spec Eagle Crank

redbaron442455

Not sure the difference between the atomic and sniper system, i have the sniper system and it allows input for idle, wot and cruise, i found that idle works best for me at 40, wot 35. And total 45.
but you really just have to experiment and find what works best.

Fun71

Most of the time full mechanical advance is in the 32-38 degree range. Vacuum advance is separate from that.

joe_padavano

Just to be clear, TOTAL timing is typically in the 32-38 deg range (and typically around 34 deg for an Olds). Total timing includes initial plus mechanical. Assuming about 10 deg initial, that means the mechanical advance only provides 24 deg. And since manifold vacuum is near zero at wide open throttle, you get zero vacuum advance under those conditions.

cutlassefi

I find it hard to believe that your idle vacuum continues to climb all the way to 40btdc. I’ll bet it doesn’t.
To the Op, best idle Timing with that cam and out of the box Procomp heads will most likely be in the high teens. That’s a very mild cam. The duration numbers you gave were advertised, not @.050.
Unless they’ve changed it, one bad thing about the Atomic is you only have so much to play with, cold start timing etc.
Cruise timing is normally best in the mid 40’s. WOT is good at about 34 as mentioned. I’ve had dozens of 455’s on the dyno and NONE of them made anymore power at 36 than they did at 34.
And when you set your desired air/fuel remember if you’re running today’s pump gas with 10% ethanol, your stoich number is no longer 14.64, it’s now 14.1. You’ll need to take that into consideration when setting that table.
Hope this helps.

CuttyShark

Yup I used 14.1 when it was on the Non-Timing control.

So if I set..
All In Advance at sat 2800 RPM
Total "mechanical" at 34
Vacuum at 10
for a total of 44 is that ok?

OR Do I set mechanical at 24 and Vacuum at 10 for a total of 34 at 2800? Sorry it is a little confusing. I am used to the Stock set springs that came on the mechanical advance stock non computer controlled Distributor.

cutlassefi

It’s no different than a mech dist. 0 your vacuum advance settings and just do initial and mech advance. Grab a light and run it up to whatever rpm you need to in order to check total. See what it’s at and go from there.
You might be over thinking this, just sayin.

CuttyShark

there is no initial with the MSD. It uses the timing and IAC to hit the desired idle speed. Also MSD don't recommend using a dial back gun as it won't be accurate since the computer is constantly changing the timing.

cutlassefi

Computer shouldn’t be changing timing once it’s off idle. It only changes timing at idle to stabilize it.once I t’s beyond that it should be rocksteady just like anything else.
Run it up to whatever RPM you have your full mechanical advance set at. So, if you have it programmed to have 34° of total mechanical Advance at 3000 RPM then run it up to that and see what you have. Again make sure you zero out your vacuum advance side before checking it.

CuttyShark

I am not trying to check the timing. I am looking for info on what the timing settings should be. I don't think I am making myself clear.

Let me rephrase:

at what RPM is the mechanical advance maxed out on a stock distributor? Typically. with a more or less street cam.

Assuming 8 degrees is where the engine idles, at what degrees should timing start to advance off idle? Immediately? 10? 12?

What is the normal max amount a vacuum can advances the distributor?

what is the max all in total timing recommended for same engine? How much is TOO much, and how much is too little? And what is the usual margin of error or standard deviation on most stock engines?

Answers to these questions will let me program the basics the MSD needs. The only time the timing gun is needed is Phasing the distributor.

danktx

I've got a MSD ready to run dist. in a mild 455 with 15 deg initial, 19 deg bushing in it for a total of 34 deg all in by 2900 rpm. I have the vacuum advance limited to 11 deg. It runs good to me with no pinging using premium fuel. Anything increase I tried to any of these settings and I would get pinging somewhere as the engine rev'ed. Increasing the initial beyond 15 deg would sometimes cause the engine to hold back when starting. The car has a 700r4 with 3.08 rear gears. Without limiting the vac adv it is generally around 20 deg. When I did not have the vac adv limited it would surge at freeway speeds. This should give you a place to start, adjust as needed.

bw1339

What about retarding timing at the upper end of the RPM range, as volumetric efficiency drops?

cutlassefi

You’re comparing apples and oranges here and approaching this totally the wrong way.
You can set your timing with way more detail than a std dist. Set the idle spark wherever you get the best vacuum. Set the “vacuum advance” wherever you get the best vacuum while driving etc. You have infinitely more control than a std dist yet your trying to mimic one. I don’t get it.