MSD Digital 6A and HEI

[61ragtop]

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]

[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?

[61ragtop]

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]

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]

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.