427 FE Cobra Street: MSD 6AL or AL2 ?

[AC Ventura]

Hi guys. Apologies of this has been done to death, but I'm a little confused regarding which of these two units to install, one has plug in rev limiter modules and one a dial... I think. I'm not sure I understand the 2 stage thing on the AL2 either.....
My main reason for the rev limiter (for me) is that if ever my my grown boys want to ever drive the car, I could unbeknownst to them, limit it to 3000 rpm for example. To save too many questions, whose running what and why?

[Large Arbor]

I am running the 6AL with the rev limiter set at 6,000 rpms. It had a version of that which died so I replaced it with the newer version. Mine has the dial version which is easy to set. You might have to hide that from the boys if they get curious (:

Phil

[Gaz64]

Early analogue 6AL only had high speed limiter with a plug-in limiter module.

Simple, reliable, and easy enough to fit a 3000, or any other rpm up from there, since you can buy them in sets of 10.

The later digital 6AL has high speed limiter, and a user selectable low speed limiter used as launch control from a brake or clutch pedal switch input.

But the limits are set on the unit, and so anybody can change them at will.

If the unit is hidden, and your second drivers don't know about it, go for digital 6AL2.

There is also a programmable 6AL2, but then crossfire within the cap becomes a concern if you don't get rotor phasing correct.

Gary

[patrickt]

Old style 6AL, with a hidden adjustable rev limiter in the glove box. And since all the kids are now off at school, we dress Ellie up for Halloween.

[Bearwolf]

The 2 stage is designed for launching in the straight line variety of racing with an automatic trans. What you could try is setting the lower limiter to 3500 or 4000 rpm and the higher limit to 6500 or 7000 rpm and hiding the toggle switch, turn the toggle on when your sons drive so they are stuck with the lower rpm range and when you drive turn it off and have fun.

I've debated running an al2 on a small block car and limiting myself to 6000 rpm on the street and 7500 rpm on track days.

[AC Ventura]

Okay guys, got it. The 6AL used to have a plug in module to control the upper rev limiter, but the newer 6 AL Digital has dials instead. The smaller packaged 6 AL2 has the latter but additionally a low rev limit, for launch control.
So with the AL2 for launch control, you engage this via an external switch, right?
So you set at 3000 for example, to control wheelspin and no matter how hard you press the throttle, it revs only to 3000, right?
So during this time, all your excess, possibly unburnt fuel is going into the exhaust....
Is this a possible fire risk?
How does the unit remove the rev limit control, once you are rolling? Surely you don’t have to flick the switch while you are trying to keep the car straight?

[Gaz64]

Originally Posted by AC Ventura

Okay guys, got it. The 6AL used to have a plug in module to control the upper rev limiter, but the newer 6 AL Digital has dials instead. The smaller packaged 6 AL2 has the latter but additionally a low rev limit, for launch control.
So with the AL2 for launch control, you engage this via an external switch, right?
So you set at 3000 for example, to control wheelspin and no matter how hard you press the throttle, it revs only to 3000, right?
So during this time, all your excess, possibly unburnt fuel is going into the exhaust....
Is this a possible fire risk?
How does the unit remove the rev limit control, once you are rolling? Surely you don’t have to flick the switch while you are trying to keep the car straight?

With a clutch car (manual trans), you fit a switch to the clutch pedal, and a relay circuit, we'll go into that later, that allows the desired rpm limit with the clutch pedal depressed.
So while staged at the lights, the rpm will hold at the desired limit.
It is a soft limiter, not a hard limiter like the high end.
It drops cylinders as necessary, but fires them on the next cycle, so each plug doesn't foul. It gives crackling exhaust etc, but that's part of the fun.
Others will know what is happening when it does occur.

Gary

[AC Ventura]

Thanks Gary.

I kinda thought exactly that, but as somebody new to this (I'm UK based) I could find no reference to it anywhere. Not on the u tube videos, nothing. Anyhow thanks !

[cycleguy55]

I bought a Summit-branded box, apparently made by MSD. You can set the upper rev limit by dials, but only single stage. The Q&A indicates you can use MSD add-ons, but I see nothing in the instructions - presumably those would come with the add-ons.

https://www.summitracing.com/int/par...0610/overview/

https://www.summitracing.com/int/par...a/instructions

[AC Ventura]

Hmmm.....if Bearwolf is correct and on the Al 2 I can set the 1st step, not as a launcher, but as a switchable lower limit, that sounds just what I need. My kids drive powerful cars, but they have all the protection of modern fail safes. I don't want them trying out the Cobra and it ends badly. That's my reason for the limiter.

[twobjshelbys]

Originally Posted by AC Ventura

Hmmm.....if Bearwolf is correct and on the Al 2 I can set the 1st step, not as a launcher, but as a switchable lower limit, that sounds just what I need. My kids drive powerful cars, but they have all the protection of modern fail safes. I don't want them trying out the Cobra and it ends badly. That's my reason for the limiter.

I guess you're faced with a Ferris Bueller's Day Off scenario. I think if I had a Cobra, where every time I sat in the front seat the car whispered "I'm going to kill you" and I instructed the kids that they were NOT to ever touch it, and I didn't feel I could trust them to heed that order, then maybe I've got a bigger problem than a rev limiter should be expected to fix. I'd be certain that anyone that can figure out how to get the car out of the garage will figure out how to turn the switch for the limiter. It might be useful for a valet (and that is precisely what some valet keys do) but not much value otherwise.

[AC Ventura]

Originally Posted by twobjshelbys

I guess you're faced with a Ferris Bueller's Day Off scenario. I think if I had a Cobra, where every time I sat in the front seat the car whispered "I'm going to kill you" and I instructed the kids that they were NOT to ever touch it, and I didn't feel I could trust them to heed that order, then maybe I've got a bigger problem than a rev limiter should be expected to fix. I'd be certain that anyone that can figure out how to get the car out of the garage will figure out how to turn the switch for the limiter. It might be useful for a valet (and that is precisely what some valet keys do) but not much value otherwise.

The problem is you never know where the actual limit of accerator pedal travel is in a 500hp Cobra in 2nd gear. As Brian Angliss of Autokraft said “The 427 allows you to think that you’ve tamed it, but in reality you never can”
In a split second one can lose all control and by the time you realise it, your future is a matter of good or bad luck. 4 people in Germany died recently in two separate Cobra accidents, doing exactly that. I’m just trying to prevent that possibility. There’s a whole generation of kids that have never had to regain control of an out of shape and the Cobra sure isn’t the car to learn that on. It’s nothing to do with not trusting my kids, it’s to help protect them as we can’t tell them at what point the fun will stop.

[Gaz64]

Originally Posted by AC Ventura

Hmmm.....if Bearwolf is correct and on the Al 2 I can set the 1st step, not as a launcher, but as a switchable lower limit, that sounds just what I need. My kids drive powerful cars, but they have all the protection of modern fail safes. I don't want them trying out the Cobra and it ends badly. That's my reason for the limiter.

The lower limit can be used for either a launch limit, or an engine power limiter while driving, depends on how you wire it to whatever switch you like.
The engine won't pull past the limit, since it will continue to misfire randomly at the cut rpm.
The randomly misfiring starts before the chosen rpm by dropping one or two, then however many it needs to keep the rpm stable.

Wide open throttle on the dragstrip while the cut is occurring, then only needs the clutch or brake pedal released timed correctly.
Once you get to know how hard your car can launch, then reaction and 60ft times improve.

Of course for a street car, there are limits as to how high you would set the low rpm limiter.

Gary

[cycleguy55]

Originally Posted by AC Ventura

The problem is you never know where the actual limit of accerator pedal travel is in a 500hp Cobra in 2nd gear. As Brian Angliss of Autokraft said “The 427 allows you to think that you’ve tamed it, but in reality you never can”
In a split second one can lose all control and by the time you realise it, your future is a matter of good or bad luck. 4 people in Germany died recently in two separate Cobra accidents, doing exactly that. I’m just trying to prevent that possibility. There’s a whole generation of kids that have never had to regain control of an out of shape and the Cobra sure isn’t the car to learn that on. It’s nothing to do with not trusting my kids, it’s to help protect them as we can’t tell them at what point the fun will stop.

I used to drive a Ford van with a 138" wheelbase. Not much power, but it had a limited slip rear end and I loved seeing the looks on people's faces when I drifted that thing in the winter. Long wheelbase and easy to control when sideways.

A Cobra with more way power and a short wheelbase is a totally different beast. You have to be on your 'A' game all the time and, as you noted, not the car to learn on.