3.0 rev-limiter

[beamonk]

hello all, I have a 83 Euro 3.0 motor in my 76. I have never hit the rev limiter although I have reved it to what the tach said is 7000-7200 on many occasions. I have heard that the limiter is in the cd box on the SC cars, I am using the CD which came with the motor, but I have never hit it. I am about to track it soon and don't want to overrev it. Does the limiting rotor of the earlier cars fit on an sc based car? May this be a problem with the tach being off and I just have never hit it? I dont want to run it to 7500 to find out!
Thanks,

[Joe Bob]

Mine was adjustable by using different rotors. The rev limit is printed on the side. Pull the dist cap and look at the rotor....should have a number on it....if it does not, go buy one. Get a limit that you feel comfortable with.

[dd74]

In that event, what's a safe rev limit (beyond factory) for a stock SC motor? I've heard 7,000.

Does it vary between "the kinds" of 3-liters, i.e. years '78-'79 might have a higher or lower rev limit than '80-'83?

[1980SC]

As mikez stated, your rev limiting must be done by the special rev limiting rotors. In my search for them, I was only able to locate the 6800 rpms rotor to fit a 3.0L. The 2.7 limiting rotor came in several different rpm values, but didn't fit my 3.0's distributor (I tried).

Oh, and my tach must be buried at an indicated 7,000 rpms before the limiter will cut the spark. Tachs tend to read a few hundred higher than actual.

The CD box never controlled the rev limit. The USA SC's have a rev limiting relay up in the front, behind the oil pressure/temp gauge. It cuts power to the fuel pump.

Rob
1980sc euro

[kstylianos]

The USA SC's have a rev limiting relay up in the front, behind the oil pressure/temp gauge. It cuts power to the fuel pump.

I knew I hit some type of rev. limiting device when I over cooked first gear, but it wasnt the usual buzz-buzz-buzz you'd expect from an ignition type of limiter. I had total loss of power, like the fuel cut out.

Now I know

BTW: What is the cut off limit for US SC's (80-83)?

[dd74]

Originally posted by kstylianos
BTW: What is the cut off limit for US SC's (80-83)?

Yeah? What is the cut off?

[Bill Verburg]

The early cars thru '77 used the distributor rotors for rev limiting. The later cars used a fuel pump cut off which was kinder to cats.

[jmz]

I use an MSD ignition box with a chip for rev-limiting.

[dd74]

My question is how safely can a stock 1983 SC motor be reved to? I've heard they can rev upward to 7000 RPM, though after 5500 RPMs, then seems like a waste of time.

[Superman]

I think that redline for my engine is stated as 6300 rpm, and that the rev limiter kicks in at 6500 +/- 200 (or something like that). In reality, my rev limiter kicks in just as an indicated 7000 rpms are achieved on the tack (which probably lies).

[kstylianos]

I'll check the manual at home for the cutoff value. But just for kicks, it it possible to disconnect the fuel cutoff and add a rotor limiter, say for someone building a high reving engine?

[dd74]

Originally posted by Superman
I think that redline for my engine is stated as 6300 rpm, and that the rev limiter kicks in at 6500 +/- 200 (or something like that). In reality, my rev limiter kicks in just as an indicated 7000 rpms are achieved on the tack (which probably lies).

Jim: but wouldn't your rev limit have something to do with your 20/21s?

Oh, and another question for you: remember when you had your stock SC cams, and the power came on suddenly when you hit, say, 4,500? Is that "burst" negated now that you have the 20/21s (read: a better or more even spread of the torque/power curve), or do you still get that nice shot of power after 4,500?

[Early_S_Man]

'Euro' SC engines use a 7000 rpm rev limiter rotor ... and other than their use of forged Mahle pistons, vs USA Alusil's, I can't think of a good reason to use anything lower for a rev limit on USA cars. Earlier year's model of 911E used a 7100 rpm rev limit with cast KS or Mahle pistons ...

[dd74]

Why doesn't power just simply cut off at the end of the powerband? In other words, if 5800 is the end of power in a stock SC engine, why is it allowed to rev farther, potentially putting a needless strain on the engine?

They really can't make more power after 5800 - 6000, in stock form, can they?

[Superman]

David, I think my rev limit circuit takes its cues from the CD box, so I don't think the cams had any effect on the rev limiter. As far as the power band goes, it has moved around a little with the various changes I have made. The two biggest changes were the 20/21 cams and the day John Walker set my timing and mixture. Both of those changes had the effect of smoothing the power band and providing more bottom end torque. Oh, and one other change...when I timed the cams I set them up all the way toward one end of the scale (don't remember whether I had them advanced or retarded), which supposedly improved bottom end torque. So, as a consequence of this (especially the cams!), I have good power starting at 1500 rpms...very good power from about 2300-3500 rpm, great power from 3500 to 5000 rpms and terrific power from 5000 on. The great power increases according to my butt-dyno happen at about 3500-4000 rpm, and again at 5000 rpm. Those power increases are very easy to detect on the butt-dyno. The real difference is that before, there was NO power below about 400 rpm, whereas now there is very good power at engine speeds below 4000 rpm, and even below 3000 rpm. It used to be on/off. Now there is a smoother transition.

[dd74]

Excuse my ignorance, but what is a CD box? Is that something you changed because of the 20/21 cam change, Jim?

[kstylianos]

when I timed the cams I set them up all the way toward one end of the scale (don't remember whether I had them advanced or retarded),

Superman, you probably timed the cams toward their advanced limits if you were going for more torque. This is a good thing, I was told as the new (or old) chains wear, your initial cam timing will migrate back down a little. This little trick only moves the power band around 200-300 rpm either up or down, dosent improve or degrade total performance. Timing it towards the advance moved the power band down, and vice-versa. I just recieved a set of cams from Elgin and when I called asking about the timing specs, this is what I was told.

[MotoSook]

My fuel cut of (78SC motor) is well past 7000 (maybe at 7300-7500..only hit it once and it spook the doodoo out of me). I have power from 3500 up to maybe 6500, but my engine breaths a bit easier than stock.

I have considered buying the turbo ign rotor (or centrigual rotor) for 7K ig cutoff (no worries about the cat..it's gutted)

[Gunter]

dd74: CDI is Capacitance Discharge Ignition and the "Box" is the module located on the left side engine comp.

[beamonk]

Great answers all, but where can I find a 7k euro rotor?