I'm about to go MEVI. (YAY.)

For the RPM switch, I've narrowed it down to 2 -- the first of which is used by almost everyone here, but I noticed a problem.

First, SUM-830449.
- The problem: (and I quote)- What's this 8-cylinder nonsense? Is there a way to recalibrate it for 6cyl?

Second, SUM-830450
- Digital readout, and works "with 4, 6, 8, 10, and 12-cylinder engines."

I like #2 better, but is there a difference as far as useability, performance, and/or ease of install?

Thanks for your help! (and for not flaming me for YET ANOTHER MEVI question)

tyler

 

The way the first one works is it counts the number of pulses it receives from a coil wire and then multiplies it by 8 to calculate RPM, because it's set up for 8cyl cars and 6 cylinder cars have less spark events per engine revolution. So if you set it to 5000rpm it would activate at 5000rpm on an 8 cyl, but on a 6 cyl car it would activate at 6666 rpm (5000/6cyls = 833. 833x8cyls = 6666). In order to activate it at 5000rpm on a 6 cyl you just need to set it to like 3750rpm. Just takes a little math to figure out what RPM activation point you need to set. That is the switch I had and it worked perfectly fine, just had to figure out proper RPM point to set it to - took about 20 seconds of math and then 2 minutes testing on the car. It has two sets of switches, one sets the thousdands of rpm, one sets the hundreds of RPM.

That other switch must be changeable between different numbers of cylinders, and apparently has a readout rather than just the little switches themselves.

 

I was using the Summit until it burned out on me, for some reason. I have no idea why, but its no longer hooked up, and when it was, it sent no signal to the tach, and didnt activate. I did buy it used, however.

 

QFT. Nice explanation Neal.


OP, you could always go the Harlan RPM switch route.