MGB: MSD 6AL vs. 6AL-2

Are you guys familiar with the newer version of MSD ignition controller, "6AL-2"? If so, would you recommend it?

The "6AL" seems extremely popular with both racers and hot-rodders. One nice feature is its soft-touch rev-limiter. On the 6AL model, you select and plug-in a "chip" (which looks somewhat like a blade fuse) to set the rev-limiter at the RPM you want. The chips are sold separately, and come in 200rpm increments. On the newer "6AL-2" model, the rev-limiter RPM setting is changed via switch settings, in 100rpm increments. Once you figure-in the cost of chips, the price difference between MSD models isn't large. The 6AL-2 is physically smaller, plus MSD claims it's more powerful (535V/135mJ vs. 480V/115mJ). It seems like a no-brainer... which has me wondering why I haven't noticed any 6AL-2 boxes on cars yet.



the familiar MSD 6AL ignition...

Don't pay for those fancy chips or pills. They are just a resistor. I had a friend that used to build an adjustable one with a 5 position rotary switch & 5 resistors.

I think you'll see either folks familair with the electromotive (SCCA) and then just a regular old Distributor - Unilite being the fanciest.

Not in all cases, but mainly what I have seen.

Always ran a 6al on my rotary and it worked great. I never use rev limiter's, just my eyes on the tach. Rev limiters can and will fail and cutting out the spark and loading up your engine with fuel is bad for bearings. I like the MSD's, some people do not. In the MG's we use the Mallory Unilite distributor and a Lucas Sports coil and that's it.

Those are some very helpful comments - thanks!

I was frustrated with my Unilite because its advance springs softened up so much over time. If you run a Unilite for several race seasons, you might want to check it from time to time to verify how much advance you're really getting. I considered having mine re-curved, but Jeff Schlemmer recommended instead rebuilding/re-curving my old Delco-Remy (with Pertronix) since its mechanical advance is more robust.

If you don't need/want a rev limiter, you can save $$$ with the regular MSD "6A". It's ~$170 vs. ~$225, before rebate. Since my application isn't really racing - just occasional autocrosses and club "track days" - the rev limiter isn't a huge deal. (The V8 is all about torque: ~175ftlbs from 2800rpm through 4600rpm. By redline, I'm way off the curve.)

However, I think MSD's multiple-spark feature might be a big help since I spend more time under 3000rpm than a real racer.

I still wonder if it matters much how big a capacitor is used for the "capacitive discharge". 135 vs. 115mJ?

I prefer the Lucas distributor, usually used with a magnetic trigger instead of points, and use the MSD 6AL which gives reliable soft rev limiting. It doesn't particularly wash the cylinder with gas, it just shorts out a few sparks so the engine keeps running but won't pull any higher - maybe firing every other turn. As you always back off immediately and it resumes normal running, I'd think any cylinder washing would be minimal.

I also run an MSD knock sensor and cockpit timing control so I can ensure maximum safe advance without detonation. I expect that more sophisticated systems exist today, but have never bothered checking them out.

I used the Soft Touch rev limiter many years ago on the Huffaker MGB (at the runoffs of course, never, ever try anything new at the runoffs), what a nightmare, we kept having a high rpm miss, around 7500 rpms, we had the famous Dave Tabor in pits with us trying to help us fiquire out what the hell was going on. We didn't suspect the MSD soft touch rev limiter, since we had a 8500 chip in it, but sure as hell, I had them take the MSD rev limiter off and it cured the problem. Later in discussion with many racers about the MSD Soft Touch rev limiter, we were informed that quite a few folks had experienced the same thing we did and fixed the prbem by using higher RPM chips, many like use got rid of the system. It soured my taste so bad about MSD, I never used anyhting made by them again.


I'm with Jesse, watch the gauges, forget the rev limiter, I did use one on the newer Electromotive unit on the 948 Bugeye race car, it seemed to work fine, I wouldn't have opted for the rev limiter, but the car owner insitsted we use it, it worked just like you would expect it to, very accurate.

Here I thought MSD only cut one cylinder at a time - not some fancy program to change the cylinder that's cutting out - ONE single cylinder always being cut, then another if necessary. That WOULD promote cylinder washing, and I really think that's the way they operate. Someone please prove me wrong!

From their website:

"When the engine reaches your selected limit, the Soft Touch circuitry begins dropping the spark to various cylinders. On the next cycle, these plugs are fired again to prevent fuel from loading up in the cylinder. The result is a smooth and accurate limiting action without backfires or roughness."

bills Wrote:

Interesting. I've never had any problems with it - it cuts at the advertised RPM for the chip and it does it so that the RPM just level off andf won't go any higher.

I don't bounce mine off the limiter, it is just there in case I miss a shift or a moment's inattention causes an over-rev.

I have seen people that hit it just about every shift. My suggestion that this wasn't really what they were meant for seems to fall on deaf ears....

bills Wrote:

Anyone running MSD should realize that they will fail sometime and you'd better have a backup. If you check Nascar, they always have two boxes and a selector switch (which MSD sells) and that's so when one of them fails, the other is immediately available to the driver.

I've had a Pertronix fail and it was just like mis-fire. Kind of surprising really, I just assumed those sorts of things either worked or didn't.

Sean

There are all sorts of things that can go wrong with eletrics - so you can get a miriad of symptoms. I was just at a different dyno shop a few weeks back and that's why I questiont he MSD's rev limiting function. The guy had done at least 10,000 dyno pulls on his engine dyno and told me that the MSDs he's had hooked up all cut out a single cylinder (plain as day on the graph) repeatedly, unless you need to cut another and another... He was seeing prolems with single cylinder wash-outs from people using the rev limited HARD.

B-racer Wrote:

Somewhat related. I was in the Carousel at Summit Point two weekends ago and during the Spec Miata race, most of those guys were repeatedly on their rev limiters in the tight area. I guess it was better to wind it to the bitter end than lose the time up shifting and then down shifting.

blackmgb Wrote:

Bill, I didn't say it was right! :D
My point was that the dyno guy realized from ignition patterns that a single cylinder was cutting out, not random cylinders or some algorithmic pattern - that's all.

ggnagy Wrote: