MSD Digital 6A and HEI - Lateral-g Forums

61ragtop · #1 04-14-2011, 07:31 PM

I am thinking of going from my HEI with upgraded coil and module to a MSD 6A. What are the main benefits in doing this?

Is there a difference between using my HEI dizzy and switching to a pro billet with vac adv? I was thinking of keeping the HEI till i can afford the new dizzy unless there is no benefit.

Any thoughts and/or info on this would be great.

Incase it is needed I am running a 383ci sbc at about 10.2:1 compression and a 230* .510 lift intake and 236* .520 exh @ .050 hyd roller, AFR 195cc Eliminators and a 2 1/2'' exhaust, and a 750 vac sec speed demon.

61ragtop · #2 04-22-2011, 07:40 PM

**GregWeld** · #3 04-22-2011, 08:37 PM

I can't remember all the details of the different distributors but a good HEI coil and a quality HEI big cap distributor is good for north of 7000 rpms.

What "thinking" is leading you to an MSD box?

61ragtop · #4 04-23-2011, 10:19 AM

Quote:

Originally Posted by GregWeld

I can't remember all the details of the different distributors but a good HEI coil and a quality HEI big cap distributor is good for north of 7000 rpms.

What "thinking" is leading you to an MSD box?

I was just thinking it may help it run cleaner at idle and more efficient in general with the multiple spark. Also the claimed better throttle response and starting can't hurt either.

The HEI I have is a proform I believe with a petronix coil and generic aftermarket performance module from the local speed shop.

**GregWeld** · #5 04-23-2011, 12:12 PM

Quote:

Originally Posted by 61ragtop

I was just thinking it may help it run cleaner at idle and more efficient in general with the multiple spark. Also the claimed better throttle response and starting can't hurt either.

The HEI I have is a proform I believe with a petronix coil and generic aftermarket performance module from the local speed shop.

Here's what I would advise BEFORE you dump $600 into an MSD box and new distributor and coil....

Take the car to a REALLY GOOD dyno... that does carb work. Your description of "idling cleaner" sounds to me as though the carb is not quite right... and needs more than just the idle air screws adjusted.... and that you might also need some timing adjustments to the distributor/set up you already have. Personally - I run as much initial timing as I can.... like 18*.... and use an 18* stop bushing for a total of 36*. My cars start instantly - and idle beautifully... I don't even run an idle air controller on my 8 stack injected Nomad. There's no need for one.

I think you're trying to overcome another symptom with "spark" -- and frankly -- in my book -- once the fuel is lit -- it's lit -- one spark or 70.... Yes I run MSD boxes on my stuff and normal MSD distributors... so I'm not against this combo obviously. I'm just thinking that from your description there might be a better solution and the overall outcome might be a far better performance "in general" with the right timing and curve and carb adjustments all through the entire start to WOT.

61ragtop · #6 04-23-2011, 04:06 PM

Thanks for the advice Greg, The motor was set up on a dyno but I too think there could be some extra tuning on the carbs idle circuit. I do know how to dial it in as far as the idle screws go but that is it.

As for my ignition curve it seems pretty good from the dyno pulls at 35* total and would have to recheck my initial but i think it is at 12* plus 11* vac adv.

Here is what I am trying to clean up at idle.....my emissions test results....

Here are my readings from past tests With fails in red.....

Date & Time -------HC Driving---CO Driving---NOx Driving---HC Idle------CO Idle
2008-06-21 14:13:35 --- 55 ppm--- 2.54 %--------96 ppm-----249 ppm------1.43 % P
2008-06-21 13:11:45 --- 56 ppm--- 2.66 %-------125 ppm-----228 ppm------4.55 % F
2008-06-21 11:24:59 --- 66 ppm--- 3.88 %--------52 ppm-----311 ppm-------3.18 % F
2008-06-21 10:52:31 --- 88 ppm--- 3.59 %-------116 ppm-----457 ppm------4.00 % F
2008-06-21 10:04:13 --- 70 ppm--- 3.47 %-------105 ppm----2000 ppm------0.87 % F
2006-09-08 14:24:01 --- 94 ppm--- 3.80 %--------70 ppm----2000 ppm-------8.12 % F

Passing results for my car as follows

-----------------------HC Driving--CO Driving----NOx driving----HC Idle------CO Idle
------------------------345.00ppm--- 3.49%------- 3415ppm------ 873ppm----- 4.09%

My motor is a SBC 383 that was at 9.7:1 at the time and is mow a 10.2
:1 compression

Cam specs are Hyd roller with 230* int and 236* exh @ .050 and lift is .510 int and .520 exh all on a 110* lobe separation

Carb is a 750 vac secondary Speed Demon, Headers 2 1/2 dual exhaust

The oldest test is were I am at as I have no idea what was done on the other tests other than tweaking timing enough to heat up a bit and I had to jet down the primaries too. The only thing that has changed since then is the compression as noted and I changed the vac advance to manifold vac from the ported vac port.

**GregWeld** · #7 04-23-2011, 08:37 PM

I wouldn't run ported vac to the distributor.... you're probably pulling in too much timing at idle. Non ported vacuum will all the distributor to just sit at it's mechanical setting (base timing) until the vacuum is needed. Vacuum advance is just a fuel economy issue anyway. It pulls in timing when you're cruising - light throttle - and adds some advance when the motor has little load. The minute you get into the throttle - the advance drops out (vacuum drops) and the mechanical advance kicks in. People confuse vacuum advance as a "power" issue all the time... and it's a common mistake.

There are several items that can cause a high CO at idle...

Missing - so fouled plugs - or incorrectly gapped - or a bad plug wire

Rich idle adjustment

Over advanced ignition timing

It can also be caused by a "lean miss" -- to a too lean idle can act like a too rich idle. Go figure - but it's true.

It can also be caused by a vacuum leak.

I would check your plugs - check the gap - really pay attention to your plug wires...

Then I'd be checking for any vacuum leaks

I'd switch the ported vac back to unported and re-set the timing

Adjust the carb idle circuit using a tach - AND a vacuum gauge... you want to adjust this for highest rpms and highest vacuum reading.

Of course a guy could write a book about all these little issues and there cause and affect -- but I'd start with just the simple stuff and see if things improve before throwing a bunch of dough at it and winding up without a cure.

61ragtop · #8 04-25-2011, 06:31 AM

Thanks again for the reply Greg,

That is exactly how I do check and adjust the idle mixture screws (tach and vac gauge). By unported do you mean Manifold vac for the vac adv? That is where I have it now and she runs much better than when I had it hooked up to the "ported' vac port on the carb. The canister is restricted to only pull an extra 10* as well.

For the $179 it will cost me for the MSD Digital 6A box with all the parts to adapt it to my HEI, Is it a worth while addition to my ignition? Even if I have other issues and this doesnt fix my emissions for testing (I plan to deal with those issues as well), is it worth it to add the box?

I have the top end apart right now and thought why not add it now while the distributor is out.....

I apreciate all the advice as I am a backyard hotrodder jsut trying to learn as I go with no buddies that are into all this stuff.

**GregWeld** · #9 04-25-2011, 06:52 AM

Well.... I'm trying to help...

It's so hard to do this via emails - or in this case posts... so I'm just thinking and posting as I can come up with somewhere else to look.

RE: Ported / unported manifold vac

Timing is typically "set" (the initial timing or "static" timing as it's sometimes called) with the vaccum line to the distributor disconnected and plugged (so it doesn't cause a vacuum leak). So let's say that is set at 10*

If you then reconnect the line to ported (manifold) vacuum... you are going to be adding vacuum thus also adding "advance" and changing the initial timing.

If the car runs better with MORE initial timing --- then what should be done is to set the distributor up (stop bushings etc) so that it is timed at the proper initial timing (let's say 14*)... without the aid of the vacuum advance. Not sure what distributor you're running but a quick check on the internet to the manufacturers website should give you info on what (if anything) you have to do to set the proper stop bushing and adjust your timing CURVE. THESE settings are CRITICAL to the performance and overall operation of the motor.

You want to have the initial advance be set... at whatever the motor WANTS... there is no 'book' on this - so it's a "where it likes it" kind of setting... BUT --- then whatever that number is -- needs to be SUBTRACTED from the TOTAL TIMING number (let's say 36*).... so if you set initial at 14* and want a total of 36* -- you need to LIMIT the mechanical advance to 22*. You do this via stop bushings in an MSD.

The vacuum advance would then be connected to the PORTED vacuum (NO vacuum at idle) and would only pull vacuum when driving... and even that needs to be checked to see how much advance it's adding while cruising. That's another discussion.

There should be springs etc -- or some way to adjust the timing CURVE on your distributor. The rate of mechanical advance is important -- too much causes problems and too little will rob you of power and give you different problems. Sometimes this requires a good educated guess... and seat of the pants testing --- or a dyno is the best place -- because timing is everything.

RE: MSD BOX --- Yes by all means I'd add this. They work great and certainly would be worth the small cost.

**GregWeld** · #10 04-25-2011, 08:37 AM

The reason you want a ported vacuum on the distributor is so you can eliminate any pulsing the vacuum adds to the timing --- so if you're vacuum is bouncing around a bit at idle -- then so is your timing...

Having said that - that's not 100% pure -- because it "depends" -- depends on how much pulsing your vacuum is doing etc... but basically that's the reasoning behind it.

The other thing is -- that if you time your initial - without vacuum advance -- and you've adjusted your idle screws etc -- and THEN plug in vacuum and advance the timing -- all your other adjustments are now worthless. Timing changes with RPMS -- idle changes - and on down the line.