[catalina_dream]

Does anyone have any dyno data or other real world experience that shows when an MSD style box truly becomes effective? I don't really need a fancy rev limiter.

Would a low compression 455 with a RA 4 cam see any benefit? Just wondering when does it start to show results? Always does? High compression? Big cam? High RPM? It seems like there are a lot of people running these with all different types of combinations but when does it really show some type of benefit?

Do we just put them on by default because everyone else has one so it must do something? I know that the high end boxes have additional features that benefit racers in a bunch of ways like timing control, etc. But for the 350 to 550 HP crowd is there any improvements to be had with the simpler bolt on boxes?

Thanks - Kevin

[Tom Vaught]

Personal Opinion, but based on info from our Research Ignition Expert:

A)

1) Benefits with Multi-strike pulses. Apparently more so with emissions + F.E. vs performance.

2) Benefits with higher amp ignitions.

3) Benefits with short Pigtail (plug wire) "coil on plug" ignition systems.

So the multi-strike pulse deal in #1 would be available on a MSD obviously.

Higher amp ignitions could apply to several ignitions including factory stuff.

Coil on Plug mostly on factory stuff.

B) REV LIMIT / OVER-REV PROTECTION.

1) Worth its weight in any discussion. Chit does happen and if a rev limiter will protect the engine, it is a good thing, even if you feel you do not need it.

2) If the spark fires when it is supposed to then 99.99999% of the time a second spark does nothing on a normal mild street car that an enthusiast would own.

3) Boosted Engine much more likely not to have the plug fire so higher energy and milti-strike is a big advantage on a street car.

JMO

Tom Vaught

[catalina_dream]

Tom,

Thanks for posting. Great info and insight. But just to clarify my comment, it is not that I wish not to have a Rev controlling device, simply that if the MSD box would have no other benefit then there are other means to control RPM. The MSD #121-8728 Soft Touch Rev Control can be had for about $125, or about half the price of a MSD 6AL-2. It would also be easier to mount (hide) since it has a much smaller footprint. Even more economical is the MSD #83647 Digital GM High Energy Modules with Rev Limiter. Both are options that I have been considering.

Again, I appreciate the technical info that you include in your posts.


Thanks - Kevin

[mgarblik]

Agree with Tom on all items. I would add that the MSD on a nearly stock engine would possibly have a slight benefit if the carb. was not tuned perfectly at all RPM ranges it will be run at. The key is one good spark at the exact time it is needed. At lower RPM's where an MSD provides the multi-strike, there is a better chance one of the strikes will ignite the mixture, where a stock ignition will just deliver a mis-fire. The MSD as Tom mentioned, does have the advantage of higher amperage also. Bottom line, if your engine is perfectly tuned, there is no advantage to an MSD in your application. The benefits of a rev limiter should also be considered.

[cgeise]

On the digital box's you have the ability to tune your timing curve to suit your needs -- along with multiple rev limiters

[66bonne]

You don't need one for your application. I have an MSD box in my Catalina and it helps smooth out the idle.

Jim

[Tom Vaught]

I personally run a "potted" Factory Looking Ford SVO Performance replacement ignition box. Because it is "potted" the chances of a failure due to vibration are ZERO.

It does have a rev chip slot (which I use) but for general info, the typical MSD module triggers about 300 rpm below the number on the module. Would that make a difference on my street car. probably not.

Tom V.

[Blued and Painted]

Originally Posted by catalina_dream

Would a low compression 455 with a RA 4 cam see any benefit?

How low compression? Those cams need 10 to 1 and some stall speed. Sounds like you may be looking for a band aid. IMO.

[catalina_dream]

Not looking for a band-aid. Car runs great for what it is. Just wanted to have a discussion about whether or not an MSD would bring anything to the party at this point.

[Skip Fix]

I can tell you using an MSD distributor and 7A box my pump gas motor dynoed the identical numbers as a DUI HEI. No noticeable idle improvement either.

[72pontiac]

when I went from stock points to msd distributer, box and coil, start up, and idle were vastly improved. as well as improved throttle response.

[Sun Tuned]

Agree with T. Vaught except for the rev limiter deal, I could fill the next 3 pages with info about that deal.

That "potting" deal is the cats arse. just remember I told you guys that. Tom knows why....

What have you got now on your combo and how fresh is it??

[ponjohn]

I ran a Digital 6 for the flexibility and features.

[KO]

MSD box only multi sparks at low RPM (under 2 or 3K I believe) They help keep the plugs from fouling at low RPM. The spark at higher RPM is single but more amperage and helps spark under high cylinder pressure.

[catalina_dream]

Current combo is 455 .030 over, TRW flat tops, stock rods w/ARP bolts, stock nodular crank, Crower 60919 cam, degreed per Cliff's suggestion, 1.65 roller rockers, 6X heads that flow 244 @ .500, '72 cast iron intake gasket matched, Cliff's Q-Jet, 1-7/8 Hooker Super Comps, Flowmaster full exhaust with H pipe, 2500 stall, turbo 350, 3.73 posi, 275/60 drag radials, stock fuel pump, repop RA air cleaner with paper element, hood scoops are open, car was 3925 with me going down the track. Car went 12.94 @ 103.5. Best 60' was 1.65. See my other post about fuel system. Upgrades are coming. I realize the obvious shortcomings of this combo. I did not set out to build a racecar, but I made a few passes and now I am hooked.

[gman005]

Save the money you don't need it. Buy new tires.

[Motor Daddy]

A quote from the Innovate Motorsports SSI-4 manual:

"A capacitive discharge ignition system (CDI) uses a capacitor to store the spark energy. The capacitor is charged to about 400V and then rapidly discharged over the ignition coil's primary winding. The coil thus only acts as transformer and does not store energy (and can therefore be smaller). The advantage of a CDI system is a very high and fast rising spark voltage (less susceptible to spark fouling). The weakness of the CDI system is the very short duration spark, which might not be long enough to ignite the mixture. Multispark ignition systems try to overcome the inherent weakness by creating multiple spark pulses over some degrees of crank rotation to increase the likelihood of igniting the mixture. The distributor switches the spark voltage to the appropriate spark plug."

[Tom Vaught]

Coil NEVER stores Energy. It is always a transformer (with the flux lines in the expanded position) and waiting for the circuit to open so that the flux lines collapse around the higher winding portion of the coil windings creating the high energy necessary to bridge the gap on the plug electrode to ground strap.

Tom Vaught

[grandville455]

Originally Posted by catalina_dream

I did not set out to build a racecar, but I made a few passes and now I am hooked.

And that's How the fight started ,lol

[Airic1]

Originally Posted by gman005

Save the money you don't need it. Buy new tires.

YOU NEED MORE GEAR!!!! Tell him about more gear Gman...