Get on down with your PoMoFo self!!!

[Saleen91]

So I've been talking with Fred recently about how lame it is to have to buy MSD pills for everything they make. Shift lights, rev limiters (like what's in our 6AL's), 2 steps, RPM window switches, etc. So Fred pointed me to an article on the Corral (http://www.corral.net/tech/powerplant/arm/) the describes how to make your own variable RPM "pill". The MSD equivalent goes for $45/ea @ Summit, or you can pay $20 for a pill pack that only has pills in an 800rpm range!

Screw that! I'm a PoMoFo! I can't afford that kind of luxury. So today I bought the goodies to make my own. I made a dual Adjustable RPM Modules (ARM) to plug into an MSD 2 Step Rev Limiter. They aren't pretty, but it works! I can plug my volt meter up to these guys and get down to 100rpm increments too!

Total cost, $8/ea!

http://saleen.v8mustang.com/pics/misc/arm1.jpg
http://saleen.v8mustang.com/pics/misc/arm2.jpg

Yes I did get one "backwards" and I didnt catch it until after I had hot glued the internals. So I crossed the wires over internally so it can still be plugged in "straight".

FYI, The #1 module is variable from 1500rpm to 6000rpm. The #2 module is variable from 1500rpm to 11500rpm.

[FE_rex]

Pretty cool. Couldn't you run a battery of resistors, a DIP switch and some boolean logic to have switchable settings?

[Saleen91]

I aint that 'lectronically literate. Hell you should have seen the faces I had to make just to solder these few wires/resistors! :D

[FE_rex]

Should be pretty straight forward. Use two 10 position dip switches. Mount in series. One switch would control 1K, 2K, resistors for 1000 rpm and then the next would have 100, 200, 300 ohm resistors for 100's of rpms. That way you would have positive locks on the rpms setting. If not, an errant brush on that knob may really ruin your day.

[Saleen91]

Originally posted by FE_rex
Should be pretty straight forward. Use two 10 position dip switches. Mount in series. One switch would control 1K, 2K, resistors for 1000 rpm and then the next would have 100, 200, 300 ohm resistors for 100's of rpms. That way you would have positive locks on the rpms setting. If not, an errant brush on that knob may really ruin your day.

That's why I made them recessed. FWIW, I found out, from measuring the ohms of MSD pills, that rated ohms + 1400 = RPM. So for 3k OHMS that would be 4400 RPM.

[HangNail]

damn thats pretty kewl

[Wild Stallion]

All righty then, I was always curious as to how they were setup, never did much dicking with them tho, my last 2 setups I had Crane FireBalls with adjustable rev limiters and a TRC for retarding my retards.
<--- Used to be Avionics tech on F/A18s, know a little about electronics.

[Saleen91]

I was telling a buddy of mine about these little gizmo's the other day and he started drooling on himself. He asked me if I could make a couple of them for him, and I agreed to for a small fee of suds. :)

After cranking out the boxes we started talking about other similar DIY efforts and he asked if I could make something similar to replace the MSD timing pills used to retard timing. I was lost when he mentioned this and explained that I'm an EFI guy and that he must be speaking in "Carb-onese". So after a few links from Summit's web site were sent back and forth, and explaining that he runs nitrous on a carb car I can see a need for such a device.

The problem is that I don't have a list of resistor values for the MSD timing pills like I do for the MSD RPM pills (see below as it's kind of handy to have this information). Does anybody have any MSD timing pills they could OHM out for me, or better yet, know where I might find said information?

Thanks.!

Below are the MSD RPM pill Kohm values in case you ever want to make one of these gizmo's.


RPM Kohms
9800 9.4
9600 9.09
9400 8.77
9200 8.45
9000 8.18
8800 7.91
8600 7.58
8400 7.35
8200 7.09
8000 6.82
7800 6.56
7600 6.29
7400 6.19
7200 5.9
7000 5.62
6800 5.41
6600 5.19
6400 4.97
6200 4.76
6000 4.57
5800 4.35
5600 4.15
5400 3.96
5200 3.74
5000 3.55
4800 3.37
4600 3.19
4400 3.01
4200 2.85
4000 2.68
3800 2.53
3600 2.37
3400 2.21
3200 2.05
3000 1.89
2800 1.74
2600 1.58
2400 1.43

[Blue91]

I have a few timing pills. I'll get em to ya next time I see ya.

[Saleen91]

Thanks Fred.

[TxBandit]

I too have a few timing pills. Let me know which ones Fred doesn't have and I'lll see if I have them.

Troy

[maveRick]

Cool post of the day!

[89LX306]

Yep, that's how I did the window switch on my nitrous. I didn't want to buy all the pills so I did that. Pretty easy and cheap to boot.

For the Diesel guys there is also a mod that is similar to this. It was coined as the 10K mod. I've done a little research on it, but supposedly it works similar to how most chips work. Basically allows you to increase boost. I haven't done it to my truck yet. I'd prefer to have an EGT and boost gauge to see exactly what is going on.

[FE_rex]

Ben,
Where did these values come from? Do you know haow they were measured? There is a jump in the ohm/rpm curve near 7600 rpm when you graph them.

Damn engineers

[89LX306]

Originally posted by FE_rex
Ben,
Where did these values come from? Do you know haow they were measured? There is a jump in the ohm/rpm curve near 7600 rpm when you graph them.

Damn engineers

How big a jump is it? Not that I have to worry about 7600 rpm. If I ever hit 7600 rpm my pot window switch is the least of my worries, lol!