Rev limiter recommendations???

obrut · 03-06-2005, 12:52 PM

Well I didn't have much luck on the main board, so I thought I'd try here

http://forums.pelicanparts.com/showthread.php?threadid=209488&highlight=limiter

I have a 964 distributor I'm modifiying to fit to the 2.7 MFI engine in my RS replica. I'm currently using the stock rotor button rev limiter in my 6 plug distributor - but that type of button will not fit the 964 dizzy.

Can anyone recommend a stand alond rev limiter for this application?

The class rules I race under do not allow an overall engine management system.

911pcars · 03-06-2005, 08:46 PM

Ryan,
A rev limiter only prevents over-revs due to introducing large amounts of air (and thus fuel) into the engine, as in too much throttle. The engine needs 3 things for combustion: air, fuel and spark. Eliminate any one of these, e.g. spark and there's no combustion. You're safe.

However, none of the spark-based devices (rotors and electronic boxes) will prevent over-revs caused by an inadvertant mechanical coupling between engine and gearbox as would happen, for example, if one completes the dreaded downshift from 5th to 2nd. If you think about it, this could happen even with the throttle closed, ignition OFF and/or with an empty tank.

For those occasions, you need another product.

Sherwood

obrut · 03-06-2005, 09:28 PM

Sherwood - I know when a rev limiter will and will not limit engine revs.

My question is what is a good stand alone replacement for the rotor button system I am removing.

911pcars · 03-06-2005, 09:39 PM

Ryan,
Okay. Just wanted to be sure you realized what is and what is not.

Not aware of any standalone system other than the aftermarket spark boxes from Crane, MSD, etc. Anything wrong with them? Track rules won't allow them?

I don't think these are considered engine management systems.

Sherwood

obrut · 03-06-2005, 09:41 PM

I was hoping for something easier that didn't require me to throw out my current CDI's. Oh well - guess not.

911pcars · 03-06-2005, 10:06 PM

A quick glance through the Summit Racing catalog shows the following:

MSD Soft Touch Rev Control. This version for OEM electronic and points system. Comes with 6, 7 and 8K plug-in modules. MSD 8728, $115

Pertronix Digital Rev Limiter; no details. PNX-600. $130

Hope this helps. Let us know what you find out.

Sherwood

obrut · 03-06-2005, 10:44 PM

thanks for that - this seems to be the ticket

Elombard · 03-07-2005, 09:19 AM

How much is that? Let us know if it wires in and works

obrut · 03-07-2005, 12:52 PM

US$120 - will do

obrut · 03-07-2005, 08:14 PM

update - not compatible with the CDI box.

back to the drawing board...

Elombard · 03-08-2005, 05:12 AM

Thats what I was afraid of. I have called about several of these and they always say they will work but something in the back of my mind is telling me they are all not compatible with CDI boxes. Thats one reason why people go full MSD. Good luck in your search

rallye911 · 03-08-2005, 12:27 PM

Most stand-alone rev-limiters state that they are not compatible with CDI systems, however after some research I have concluded that this is because they are intended to be installed with the switching wire connecting the CB(-) terminal on the coil to ground, and that doesn't work for CDI. But they are mostly just a speed-(or more accurately time-interval) dependent switch, which you can connect across the trigger circuit of many CDI installations. I am using a Pertronix Ignitor to trigger the Bosch CDI in my 1973 2.4T, with an Armtech Panel-mounted Rev Limiter (about £95 here in the UK) in parallel with the Ignitor.

Hope this helps

Angus

obrut · 03-08-2005, 12:50 PM

Angus

Thanks for the info - neat little unit.

Do you have this system installed now? Any chance I could get a rough wiring diagram?

Also, how do you set the rev limit on the armtech unit?

TimT · 03-08-2005, 04:57 PM

Ryan,

scroll through the Lumenition
catalog, they have a number of different rev limiters. Im not sure of the availability down under though.

rallye911 · 03-09-2005, 10:23 AM

Ryan,
Very simple wiring, the rev-limiter has 3 wires, red, green, black. The red is +12V, same connection as the red wire on the Ignitor. The green is ground. Black is the switching wire, and connects to the trigger terminal of the CDI (= the black wire of the Ignitor in my installation). In other words, black and green are the two connections of a switch which parallels the points or the Ignitor, and only when both switches are open will the ignition fire.

To set the desired rev limit, press the push-button for 3+ seconds until the LED indicator flashes, rev the engine to half of the desired limit speed, and release the button.

There are other versions of the limiter available with another wire to connect to a clutch switch for full-throttle gearshift, or to a steering-wheel push-button for start-line rev-limit prior to the starters flag.

I'll try to scan the installation drawing for you tomorrow, but it is as simple as I have described here.

obrut · 03-09-2005, 12:48 PM

thanks angus

jpnovak · 03-09-2005, 01:05 PM

Out of curiousity, what are you using for the advance curve? Are you installing the 2.7 internals in a 964 dist? The 3.2 and 3.6 distributors do not have an internal advance. It was all done electronically.

obrut · 03-09-2005, 02:21 PM

jamie,

the 964 distr does have an internal advance mechanism of sorts - but from what i understand it was not originally set up to provide the range required for an early engine. my mech gave it to a distr specialist who changed the springs to mirror the curve of my original distr. it is still with the dist guy at present - i will post results after we have fitted/tested it.