Rally Pac with HEI Distributor - Ford Mustang Forum
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post #1 of 17 (permalink) Old 06-22-2018 Thread Starter
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Rally Pac with HEI Distributor HELP

Hello. I recently purchased the Scott Drake Rally Pac (V8 6000 RPM) for my Mustang. I have a rebuilt 302 powering my baby with a HEI style distributor. The Rally Pac instructions have the signal wire connecting to the - side of the coil, however with a HEI there is no external coil. The distributor does have a blade style TACH output that I assume would work if I change the wire connection from a loop to a blade, but I am hesitant as I can't really find anything online where people have covered this. And I promise I did a search here before posting this question. ;-)

I'm hoping someone has experience with this setup and can give me some advice on whether or not it will work. I'm concerned about frying the Pac, so I'm looking for thoughts on the topic. I did talk to the folks at CJ Pony Parts and they were 50/50 on the topic.

Thank you in advance for the help. I am a long time lurker on this forum, but this is my first real post, so I am thankful there is a community out there that can assist a novice like myself.

John


Last edited by John3020; 06-22-2018 at 11:34 PM.
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post #2 of 17 (permalink) Old 06-23-2018
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John, I am not going to troll you with my suggestion to get another dizzy just because I hate HEI distributors. *grin*

Unfortunately, I really *don't* know the answer to this! I can see why it'd be a problem, but I'm not sure how you can work around it either.

Best wishes, and let us know how this turns out!


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post #3 of 17 (permalink) Old 06-23-2018
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I have a HEI MSD dizzy and it does have an external coil.
My rally pac runs through the MSD Tach adapter box.
What brand dizzy do you have?

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post #4 of 17 (permalink) Old 06-23-2018
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FWIW, MSD does not make an HEI distributor. HEI is the name GM gave to it's electronic ignitions in the 70s and it's distinguishing feature was the coil is built into the cap. Davis Unified Ignition (DUI) took this concept and makes distributors for other manufactuers engines. A tach adapter is needed wihen using a multi spark capacitive discharge ignition because many tachs can't deal with the multiple sparks.

To the OP, I have installed tachs on GM products that did not come with one by connecting the trigger wire on the tach to the tach connection on the cap and it has worked fine every time.

Dave
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post #5 of 17 (permalink) Old 06-23-2018 Thread Starter
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Thanks for the responses. I had considered switching to a "traditional" distributor and coil, but I'm not sure it's worth the effort or the money just to get the Rally Pac hooked up. I have no issues with the HEI style and the engine is not original to the car. I can think of no logical reason why it wouldn't work with the setup I have. I'm just surprised to see that my situation isn't more common as I can't find anything online discussing it.
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post #6 of 17 (permalink) Old 06-25-2018
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I suspect the adapter at the link below is what you need, although, like most MSD products, it isn't cheap. I'd just ask Summit if it will work with the Rally Pac; they are really good about responding.

https://www.summitracing.com/parts/msd-8920
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post #7 of 17 (permalink) Old 06-25-2018
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Quote:
Originally Posted by Charles Reeves View Post
I suspect the adapter at the link below is what you need, although, like most MSD products, it isn't cheap. I'd just ask Summit if it will work with the Rally Pac; they are really good about responding.

https://www.summitracing.com/parts/msd-8920
The OP does not have an MSD ignition, his question is will his tach trigger off the tach output on his GM based HEI distributor. The tach connection on the cap should be the (-) side of the coil since it has worked just find with the tachs I have hooked up to GM cars in my past.

Dave
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post #8 of 17 (permalink) Old 06-25-2018 Thread Starter
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dgc333 is correct. I do not have a MSD ignition and I honestly do not know who made the distributor. There is nothing on the cap with a makers mark. It could be on the inside, but I haven't taken it off yet. On the cap it has LATCH LATCH C- CRD B+ and TACH and BAT molded in. The TACH side aligns with the C-, so I am very confident this is the negative side of the coil, which to my knowledge, should be fine for the Rally Pac hookup. Electrically, I can't think of any logical reason why the pulse coming off the HEI would not be registered by the Rally Pac to drive the needle.

I'm thinking about tackling it this weekend, but am using the time to ask around as much as possible. I truly appreciate all that have voiced their thoughts in trying to help me.

Last edited by John3020; 06-25-2018 at 03:44 PM. Reason: spelling error
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post #9 of 17 (permalink) Old 06-27-2018
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Like the word Thermos being applied to all vacuum bottles. HEI is usually referring to a NON TRADITIONAL coil and cap set up. Ford did have a HIGH OUTPUT ignition system where the coil was hidden under a plastic shroud on the fender apron and a Hall effect magnetic pick up and reluctor replace the traditional rotor and points. Even this system had a tap at the coil labeled TACH because many models included an in dash tach. So depending on your particular set up I'm sure there is a negative side of the coil some where!

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Don't agree HEI has always been a GM thing. Ford called their first electronic ignition Duraspark and Mopar just referred to it as electronic ignition but had different control modules for different performance levels; Blue - stock, Orange - to 6500 rpm, Gold - to 7000+ rpm.

What made the HEI unique is the coil and ignition module we're under the cap while everyone else they were separate.

The aftermarket D.U.I. took the GM concept and makes distributors using the HEI design for Ford and Mopar.

Dave
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FYI, the SD rally pacs are known to run slowwwwww. Mine was slow 75 rpm at idle. Not bad you say ? But it got progressively worse as the rpm increased. Not good. When the tach showed 4700-4800 rpm the motor was really at 6,000 rpm !!! A replacement was identical.

Check the tach with a good brand of timing light. Even the $80 Craftsman digital timing light works really well and is dead on accurate.

I ended up getting a small 52mm AutoMeter tach and used it more than the RP tach. The truth is, Scott Drake parts have a very spotty quality track record since he sold the company several years ago. Their R-P is just one chapter in this sad story.

Z


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post #12 of 17 (permalink) Old 07-01-2018 Thread Starter
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Well I can confidently report back that my Rally Pac is installed and hooking up to the TACH side of the HEI/DUI distributor does send the signal to the gauge. Install was relatively easy although user error is causing me to replace a couple of minor parts. Note to self: Don't try closing the door with the courtesy light plunger pulled out!

Zray-Interesting that you mentioned it was running slow for you. I don't have the equipment you do for testing, but I was thinking the same thing, though I did not notice it even close to the measurements you were getting. Idle was at about 800 RPM and 70 MPH was at 3500 RPM. In my mind I always thought it was faster, however that is likely due to my internal bias saying a 3 speed has got to be going faster. Couple that with the sound of the headers/exhaust and it seems like it's working harder than the gauge is telling me. I'm not using the Pac for any technical readings, but I would like it to be reasonably close.

Again-My thanks to all that chimed in on this topic and advice that was given. It was much appreciated.

John
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Quote:
Originally Posted by John3020 View Post
Well I can confidently report back that my Rally Pac is installed and hooking up to the TACH side of the HEI/DUI distributor does send the signal to the gauge. Install was relatively easy although user error is causing me to replace a couple of minor parts. Note to self: Don't try closing the door with the courtesy light plunger pulled out!

Zray-Interesting that you mentioned it was running slow for you. I don't have the equipment you do for testing, but I was thinking the same thing, though I did not notice it even close to the measurements you were getting. Idle was at about 800 RPM and 70 MPH was at 3500 RPM. In my mind I always thought it was faster, however that is likely due to my internal bias saying a 3 speed has got to be going faster. Couple that with the sound of the headers/exhaust and it seems like it's working harder than the gauge is telling me. I'm not using the Pac for any technical readings, but I would like it to be reasonably close.

Again-My thanks to all that chimed in on this topic and advice that was given. It was much appreciated.

John
3500 Rs is a bit high at 70. That is, if you're running a 2.8 or even 3.00.
What rear ratio are you running?

Ken
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Quote:
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3500 Rs is a bit high at 70. That is, if you're running a 2.8 or even 3.00.
What rear ratio are you running?

^^^^^^^^ I agree.

With a modest 24.7" diameter tire, 1:1 transmission, and a 3.50:1 rear gearing you can hit 75 mph and still not reach 3.500 rpm (@ 75 mph rpm is 3,493)

Interactive RPM Range Computator Program

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post #15 of 17 (permalink) Old 07-04-2018 Thread Starter
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To be completely honest, I'm not sure what the rear end is. I bought it with this set up. I know it's a 9 inch, but am unsure of the gear ratio. It shifts into second around 25 mph. Second gear must be pretty tall because I don't feel it shift into third and that's getting up to 70+ mph.

I was rounding a little bit when I was mentioning the RPM's in my earlier post. I was glancing up and down while driving, so it's not exact by any means. Couple that with the fact that I know the speedo is 10 MPH too slow (checked with my phone) so my measurements were not precise. Cruising today at 60 mph I was just under 3,000 RPM's.

I do appreciate the feedback though. The car will be in the shop this week to get the power steering adjusted, so I'll ask if they can put a light on it to see how close it comes to the reading on the Rally Pac.

John

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