Msd rpm selector switch

[Ian Hill]

I have installed the rpm selctor switch 8670 in my stocker and use it instead of the 2 step individual pills as i have recently been racing at a dtrip that have the first two passes of the night in the day light and the rest at night, so i find myself adjusting the rpm of the launch to compensate for the night time brightness of the tree.

The module (8670) comes with about a 4 inch connector cable, my question is: can i cut these wires and extend them? i'd like to have this module mounted at my shifter where i can make changes as i am about to make my run, rather than sitting in the staging lanes, strapped in and not able to reach it.

Ian

[Ed Wright]

That's what I use. I can't imagine why the wires couldn't be extended.

[KRatcliff]

Originally Posted by Ian Hill

I have installed the rpm selctor switch 8670 in my stocker and use it instead of the 2 step individual pills as i have recently been racing at a dtrip that have the first two passes of the night in the day light and the rest at night, so i find myself adjusting the rpm of the launch to compensate for the night time brightness of the tree.

The module (8670) comes with about a 4 inch connector cable, my question is: can i cut these wires and extend them? i'd like to have this module mounted at my shifter where i can make changes as i am about to make my run, rather than sitting in the staging lanes, strapped in and not able to reach it.

Ian

General Regs 8:2 "Two-steps or other rev limiters that are
adjustable by thumbwheel, replaceable chips, and the like may not
be within the driver’s reach and will preferably be located outside
the driver compartment."

[acme383]

the same cable MSD sells for the ignition box crank/ distributor is the same 2 pin cable. just an option if you don't want to cut it. Dan

[Bill Harris]

The RPM "pills" for the analog MSD boxes are just resistors and are relatively high values compared to the wiring. For example, a 4K pill is 2700 ohms while a 7K pill is 5660 ohms, nominally. Extending the wires won't add enough resistance to vary the set-points unless you use tiny gauge wire and/or make really bad connections.

One thing you should think about, though, is that "pill" is in a pretty high impedance circuit, so it is susceptible to electrical noise which could make the set-point jump around. If you do extend the wires, I would use a shielded cable with two conductors, perhaps an 18 gauge shielded speaker cable (foil shield is best) and ground the shield at the box end only.

[Ian Hill]

Originally Posted by KRatcliff

General Regs 8:2 "Two-steps or other rev limiters that are
adjustable by thumbwheel, replaceable chips, and the like may not
be within the driver’s reach and will preferably be located outside
the driver compartment."

ahhhh, read the rules, seems like as good an answer as any!

Ian

[69Cobra]

Originally Posted by KRatcliff

General Regs 8:2 "Two-steps or other rev limiters that are
adjustable by thumbwheel, replaceable chips, and the like may not
be within the driver’s reach and will preferably be located outside
the driver compartment."

What's the reason for this? Shouldn't the driver have compete control over the car, rev limiters included.

[KRatcliff]

I don't know the reason. I just remembered the rule because I wanted to do exactly the same thing the original poster wants to do, but I had read that you couldn't in the rule book.

[Dave Turner]

MSD #8735 features a shielded cable for that purpose and I have seen it in use in Stockers......planned to use one in mine. It's a 3-step selector featuring burnout & high end chips plus adjustable launch rpm.

[Ian Hill]

hi Dave, is it something you planned on placing within your reach as a driver?