Simple 8973 question...

I have been running my 8973 with a transbrake and delay box and it has been working great. I have been using the step 1, launch curve, and run curve. Now I am going to experiment with foot braking it instead of the transbrake. Since I won't be on the button anymore I need a way to trigger the blue wire to set my stuff to 1st gear and load the launch curve. Is there any reason I can't just plumb a hydraulic brake light switch into my brake line, so when I go into the lights and hit the brakes it charges the blue wire? Then when I switch feet it would kill the circuit, starting the timed curve if I decide to use it?

In my mind it seems to accomplish the same thing as the transbrake button.

Input?

-Brian

 

switch

Just put a switch under the throttle pedal You can adjust it to whatever you want. Call Leahey if you need one. Saves time rather than looking thing up. You can wire it open or closed. Oh, by the way, be a driver + get rid of that crutch as in delay box. Never used one + never will!!!!! Don

 

The title of this thread made me laugh.....we had three or four but we already gave them all away Your best bet....as in the one that's not going to RUIN your investments is to use the Leahy box and a six shooter, we have two six shooters stacked on our car.

Brandon Booher
NHRA TAD #35

 

8973

common sense tells you that all those boxes couldn't be bad. We've run 1 for over 4 years.

Glenn

 

8973

We have run the MSD 8973 with great success for 3 years now, and never had any trouble and run a blown alcohol hemi-THANKS! Jim

 

8973 is the best !

 

make it simple..unhook all the bells lock the timing at what ever you wanna run foot brake it and get the car from point A to point B then start using a 6 shooter or the stuff you have...I know the car and motor you have I have watched this car run and run very fast..call Malcom and see what he used..Dave

 

I talked to Malcom for quite a while last winter. He seemed like a strait shooter, and told me everything I asked about. I'm pretty sure the car came to me with his setup still in it for the most part. I'm gonna launch it off the foot brake at my next outing. Timing will be a very simple curve. I think it's gonna go this time.

-Brian

 

I second secondwinds! comment. As i was scrolling down reading all the posts i kept saying to myself just disconnect it all. Use the bare minimum to start and work up from there, just like the advise on leaving from idle on the brake. Keep it simple. No offense scouder but i get the impression you are not trying to run mid 5's so you just don't need it. A points fired mag 3 and coil fix timed at 28 degs got me mid 6's with ease. Best of luck and let us all know how it goes on the next pass..

 

I've got to go back out to the shop to verify my timing on the last run, but I believe I had 23 degrees in it at the hit. With the transbrake leaving at 3000 on our little airport track it wadded up the tire and then just drove through it into spin. A little less timing and leaving on the footbrake should get it through first gear. Second gear hooked and went, so I know I have a baseline to work with there. And you are right, I can't afford to run 5's! I'm just shootin' for the top half of the 6's for now.

-Brian

 

done 5 things 1 worked!!!!!!!!which one worked out of the 5???..take small steps also remember if them are fuel heads they like some timing..fat heads is a hole different ball game..Dave

 

All MSD controls use various combinations of their technology, the 8973 doesn't contain anything that is not being used in other "boxes".

 

I know, I know! But it's really only 2 things! My crew is me, my wife and a friend. My friend says the same as you. He thinks its close enough that if I leave the timing where it is and just foot brake it she'll stick. I think it's close enough that it might not. I'm gonna pull just a little more timing to make sure. I have got to get a baseline to tune from, then I'll start putting timing back.

Hope you had a good time on the island!

-Brian

 

we had a blast...didnt want to come home next year we will stay for 3 weeks..Dave

 

In my opinion the 8973 (like any solid state electronic device) needs to be protected from transients to the inputs (needs a solid, preferably separate 12v-16v power source a tool battery works great) the main reason for the separate battery is that we use the battery in our race cars to supply a number of solenoids ( shift, transbrake, air throttle control, fuel system contol, etc) and all of these coils will cause a spike, when power is interupted, if not protected correctly. In addition to this box's also need to be shielded from EMI, from magnetos etc.

In my opinion MSD as well as many others could do a much better job of protecting thier box's from voltage transients as well as EMI, by investing a little time and maybe $40.00 they could improve the power supply section of the box so that it would filter anything but the most extreme spikes, as well as encapsule the box's in a EMI resistant enclosure.

MSD for whatever reason does not do this on thier box's ( they should not have to but thats another story) so since race cars are notorious for problems with voltage supply as well as EMI, I think its well worth the time to build a small box to protect the solid state components of a car as well as using a separate battery for the power supply.

While many get away without running an enclosure and a separate battery, for me I think its well worth the trouble.

 

Protecting electronic stuff

Hi all, you can also put a zener diode across the 12v input to the device, I would suggest a 1watt 30volt zener as this will eliminate any spike greater than 30v. They are cheap and readily available from most electronic stores. These do NOT go in series with the supply, they go across it as a capacitor would. Its cheaper and easier than seperate batteries and boxes etc. Cheers

 

All MSD timing controls, six shooters, etc. should be installed with an 8830 capacitor, as shown in the directions.