[Greg T]

Howdy folks! Just wondering if someone has any info/experience with the 8981 timing computer. My questions are this: Does that work with a 6AL box or right off the distributor? Also, must one lock out the mechanical advance in the dist to use one of these? And, what about the vacuum advance? Thanx much!

[SSedan64]

Check with Bubbahotep, his post in the TunnelRam thread said he uses one.

[Greg T]

I sent him a PM. Thanx for the tip. It sounds like just the thing I need but even the MSD site doesn't answer my questions. And the tech support wanted me to hold for 20 minutes.

[bubbahotep]

I've had that thing in my ride for nearly 20 years and have messed with it hundreds of times

you can use vac advance for better mileage but NOT to correct for a better idle timing. Meaning, some guys use the manifold vacuum to increase their idle timing. The 8981 screws up if you do that so just use vacuum advance on manifold but have it only come in off idle under load as intended

It will work with weights but it's not the best way. Locking out the advance at total (36-38 etc) will give perfect results always. I used it with weights fir a few years and had mixed timing because the computer is limited by what the weights allow it to do

works like this: you have 3 dials, idle timing, rpm to begin advancing, slope

the computer dials use your locked out timing as a maximum setting. 36' locked means it knows it can only give you 36' advance. If you adjust the idle dial to say 16'.....the computer drops 20' from 36 total.

If you use weights and the computer together: let's say the weights are partially out to 30' advance. The computer still wants to deduct 20' from whatever the total is so you now only have 10' idle timing. Only when you are at WOT will the computer give you precise timing

I have it locked 38' for my 383 stroker with aluminum heads. 28' idle setting gives me a nice rpm in gear. The computer gives 20' starting retard so starts are easy.

My only F-up was that my rotor phasing was way way off and I had hard starts when hot. People on this board pointed me in the right direction

it works with all msd boxes I think. It basically goes in series with existing msd wiring like a switch. Easy hookup, a few wires not including the high speed rpm retard option for boost

[Greg T]

Okay. Think I got ya. Lockout the mech on my pro billet and use the computer to manage it. I did not quite understand about the vac. Should I run full manifold advance at idle? Or does it want ported?

[bubbahotep]

Ported would be better because it's not advanced at idle and you'd have an easier time picking an advance canister. It'll advance under load giving you over 36' (50' for example).

If you use manifold vac you'd be good with an adjustable vac canister. Turn in the adjusting rod to tighten the spring so it Doesnt advance at idle.

Either way you might get some pinging under load which means the vac advance is too much. That's always trial and error

[Greg T]

Okay, great. Thanx much. I do have an adjustable can on my pro billet and a limiter plate set to 12*

[Overdriv]

Go here for the manual for the 8981.

[Greg T]

Originally Posted by Overdriv

Go here for the manual for the 8981.

Thanx. I couldn't find that. All I could find on the site was the 8980.