Off Roading Forums banner
1 - 20 of 27 Posts

· Registered
Joined
·
4,722 Posts
Discussion Starter · #1 ·
I have looked around and searched. They both seem like viable upgrades, but the HEI seems simpler,,,, Which do you guys recomend for a 79 cj5 6 cyl??
 

· Registered
Joined
·
2,674 Posts
I think they are both excellant upgrades. I'd base it on what was most readily available to me. If you can find a TFI coil and bracket lying around, the TFI upgrade is probably the cheapest. Then all you need is the adapter, cap and rotor. For the HEI, you will need the distributor, a new drive gear, and to replace at a minimum the cap and rotor. The TFI, you can buy it all off the shelf of your auto parts store, for the HEI, you could buy a distributor, but most likely chose to junkyard scrounge.

Flip a coin. I have the HEI, and like the unitized system and clean hookup of a single wire. If you plan to go fuel injection, I can tell you the HEI system is very compatible with a GM based throttle body system like Howell, or the Megasquirt.

The best argument for Teamrush's TFI system is the wide spacing of the terminals on the distributor cap, and the fact you retain your factory ignition curve (both mechanical and vacuum).
 

· Official Historian
Joined
·
8,275 Posts
In reply to:

For the HEI, you will need the distributor, a new drive gear, and to replace at a minimum the cap and rotor.

[/ QUOTE ]

Actually, there is another write up on just using the HEI module with the duraspark distributor. That would be my choice to do. Then use the ford coil.
 

· Registered
Joined
·
447 Posts
I used the HEI mod with a Motorcraft distributor. Mine is a 75, so I didn't need to remove the resistor wire from the circuit, so it was extremely easy.

If I had a 6cyl, I would go with the HEI distributor. I have a friend that did this and the difference was night and day. I believe the one you need to find is one from a GM 250 6cyl engine. You then remove the GM drive gear and replace it with the AMC drive gear off your existing distributor. This is all from memory and I have never done it myself, so do a search to get the real specifics.
 

· Registered
Joined
·
729 Posts
I ended up doing the TFI upgrade on my 84. It was easy to obtain all of the parts, with the exception of the coil bracket. I found a bracket on an 80's taurus that I used to mount the coil to the fender. I do not like all of the wiring and would like to eliminate/replace/or move my stock ignition module, but just have not gotten that far in the last 2 years. Overall, I have been pleased, and it was easy.

The link that Will posted looks interesting. How would the HEI module compare to the stock module to an MSD module? -- Mike
 

· Registered
Joined
·
1,795 Posts
I did the GM HEI. It does make a night and day difference and is oh so simple to install. I understand the advantages of the TFI system, but I've also read numerous posts from people trying to trouble shoot them. I've got just about $100.00 into my HEI. Just a note.. the caps for them are about 20-25 bucks. Also I noticed someone recently started selling them on e-bay with the AMC gear already installed for about $100.00. I don't think they rebuild or refurbish them in any other way though.
 

· Registered
Joined
·
10,738 Posts
""How would the HEI module compare to the stock module to an MSD module? ""

Both modules are designed to turn on and off, making them the same in that respect.

The difference is the GM coil and the TFI coils have a lower primary resistance, and are built to handle, and use, a full 12 volts instead of having the voltage dropped with an ignition resistor. Without the full 12 volts it acts like a stock coil - no benefit.

The stock Jeep module (a Ford DuraSpark I) cannot handle the increased current of those coils for long. It overheats and frys. Granted, they may work for awhile, but eventually they ---.

The module originally used with the TFI coil (the module's called a Thick Film Ignition module - thus TFI) is not easily adapted to the Jeep engines - you have to swap the entire distributor.

The HEI module, as well as the TFI's module, are designed to handle that extra current.

The extra current is used to create higher voltage and higher current in the coil secondary - thus the term HEI - High Energy Ignition.
The real result is the spark duration across the plug - the spark is there for much longer time - 2.5 milliseconds vs. .75 milliseconds. The longer duration spark ignites more mixture - thus increasing power and lowering emissions - since it burns more.
The HEI also has a side benefit - the rise time of the spark is about 4 times faster - hitting the cylinder better - kinda like an impact wrench hitting a stuck bolt.

The larger cap on either the Ford upgrade distributor or HEI spaces the terminals farther apart, so it has the ability to handle increased secondary voltages.

The MSD - Multiple Spark Discharge - is an entirely different ignition system. It is a true CD ignition rather than a Kettering ignition. It has an even faster rise time, and it fires several times for each firing stroke. But the spark duration is very short, on the order of .2 milliseconds. That makes up for the lack of duration by firing several times. Unfortunately it stops doing it's multiple firing around 3000 RPM.
The end result is the MSD and the GM HEI run about the same in a Jeep. But either are definate improvements over the stock ignition - a very noticable improvement.
 

· Official Historian
Joined
·
8,275 Posts
A couple days ago, I had all the spark plug wires off and drapped over the engine and fenders to do a compression test. Two of the wires that I could see were a little above the driver's side fender. The spark plug connector is about an inch inside the boot and the boot was about a 1/2" above the painted fender. When I cranked the engine, the MSD had no problem bridging that 1-1/2" gap and creating a BIG spark. I promptly unhooked the MSD for the rest of the cylinders but by no means would I want to pull a spark plug wire off while the engine is running to find a missing cylinder.
 

· Registered
Joined
·
297 Posts
[quoteThe MSD - Multiple Spark Discharge - is an entirely different ignition system. It is a true CD ignition rather than a Kettering ignition. It has an even faster rise time, and it fires several times for each firing stroke. But the spark duration is very short, on the order of .2 milliseconds. That makes up for the lack of duration by firing several times. Unfortunately it stops doing it's multiple firing around 3000 RPM.
The end result is the MSD and the GM HEI run about the same in a Jeep. But either are definate improvements over the stock ignition - a very noticable improvement]

[/ QUOTE ]

So does this mean that the GM HEI doesn't run well above 3000 RPM's?
 

· Registered
Joined
·
10,738 Posts
They both - MSD and HEI run very well above 3000! HEI starts to roll off about 6500 in a V8, higher on a 6.
MSD just doesn't multiple fire above about 3000, but it goes up to about the same, maybe a little more with the CD coil. MSD runs very well up there, Jeep engines don't though.
 

· Registered
Joined
·
958 Posts
I ran a TFI with the dura spark and it ran good. I put a new original style back on my jeep to smog and I could tell the difference. the TR style TFI ignition upgrade works. but I will not run that set up anymore. I measured the current through the coil an it is too much. 4.4 amps stock and 8 amps with the TFI. the energy in the coil is di/dt so that extra current means more at the plug, but that is too much current, for the module and the coil.

It is a great setup for some temporary gains but in the long run it is not going to last as long as a stock coil.

I don't know what will fail first, the module or the coil. the coil requires some form of current limiting.

the resistor wire will do that but the TFI has too low a primary resistance. the HEI uses a transistor to limit the current. and it does so actively. but the voltage drop does happen in the HEI module. that is why it gets hot. p=vi.

the TFI coil will burn to a crisp if 12 volts is applied continuously. yes, you do not need to drop the voltage before the coil, but you have to drop that voltage somewhere. and that is what the HEI does. just think of it has having an active resistor built into it so you don't need the resistor wire. but the current limiting has to hapen somwhere.
 

· Registered
Joined
·
13,180 Posts
1. The Juice Box ain't nothing more 'n,
2. A re-packaged set of FOMOCO parts,
3. Used in the TFI upgrade...
4. Parts:
[*] Distributor Cap - Wells F952
[*] Rotor - Wells F953
[*] Base Adapter - F960
[*] Spark Plug Wires - Borg Warner CH857 (V8 wires)
[*]Ignition Coil - Borg Warner E92
[*] Male and Female Wire Terminators
 

· Registered
Joined
·
3,905 Posts
Thanks LEVE, I get it now. Damn Ronco looking site too.

OK, this is a subject that I have only mulled over in the back of my head, never given any focus or research effort.

Since I prefer bowties to blue ovals the HEI always seemed like the way to go when I get around to going there. Well likely way past time now but it's still a project for some day in the future. But after looking at this thread and much of the mountain of information linked it seems to me that someone has tried about everything. Here's what I am thinking so far.

1. Everyone likes the simplicity of the HEI one wire, just add +12V.
2. The FOMOCO distributor parts are easy to find and solve the crossfire issues when used to retrofit the AMC stock distributor.
3. At this point I assume that the TFI (Thin Film) technology is integrated with the coil it's self.
4. There are some small issues with either upgrade path be that advance curve, distributor drive gear fitting or simply mounting the components.
5. Both HEI and TFI are children of the 80's but AMC didn't update their technology to that level. Many other things are now on the market including MSD, Jacobs etc etc.
6. For the sake of using off the shelf parts that can be found in the average auto parts store why get into anything that wasn't originally GM or Ford.

Since your basic "pre Chrysler" Jeep is a mutt crossbreed of Ford, GM and other designed parts and pieces assembled into the ultimate platform for cross cultural exchange (bowtie / blue oval). Please don't go off into some NASCAR rant based on this statement. What if someone tried this:

1. Use the Ford distributor adapter, cap and rotor from the TFI vintage parts to eliminate crossfire, adapt to plug wires that can handle the higher spark voltages and keep the stock advance curve.
2. Use the HEI module and external HEI coil to eliminate the Dura Spark module and simplify the wiring (eliminate the stock ECM from the ignition), boiling everything down to four or five wires that could be developed into a harness and heat sink assembly.

Would that be the best of both worlds, and use the best/cheapest parts to accomplish a very simple yet effective ignition upgrade???

It may well be that I have over looked something basic here that needs to be addressed. I'm still trying to think this thru without putting it on the front burner (so to speak). So many people have done so many things and it simply boggles my mind to try and sort it all out.

Still thinking! (but only on the back burner)

 

· Registered
Joined
·
10,738 Posts
Already done - Go to:

http://www.geocities.com/jeeperaz/hei.htm

It uses the Ford big distributor cap etc, and a remote HEI module - With the TFI or DuraSpark II coil.

The problen using the HEI coil remote is the output - normally a spring loaded button. It's hard to connect the coil wire to it.
The Dura Spark II coil, or the TFI coil has essentially the same parameters and output as the HEI coil. Works fine.

As far as the advance curves go - aftermarket kits use lighter springs, causing a faster advance. That's good for a street racer or race car where you launch at high R's and the only time the engine runs at 1000-1500 RPM is stopped.
But in a Jeep you need a slow curve for low end torque. You want pulling power, not horsepower.

You don't need or want full advance at 1200 RPM like aftermarket kits will give. Slowing it down even more than stock helps grunt power.

The kits have springs that "look" heavier, but test them on a distributor machine - they aren't near as strong as stock ones. The weights may "look" lighter, but the cam grind advances quicker.
The only usable thing in the HEI kits is the tiny brass bushing that goes on the limiter pin underneath the weights. The stock rubber one falls off. Use it! -- Well woth the $5 for the kit. Toss the rest.

Hest way unless you have a distributor machine and a dyno to curve it slow is to leave the stock weights in. That's whether HEI or Ford distributors.

The vacuum advance is the other thing - adjustable advance diaphrams are available for both GM and Ford - see your local speed shops. Most are Crane's, even though rebranded. You might even find a stock adjustable one for the Ford - circa about '76?

But you can't just throw it in. To start with, tighten the Allen adjustment screw all the way counterclockwise - that makes it the least sensitive - else it'll be too fast - wrong way.

Install - be sure to install the tiny limiter cam - it limits the amount of travel. Without it it will advance waaaaaay too far - ping, overheat, holes in pistons etc.

Initially set it so it limits the travel to about 1/3, yes, only 1/3. (It's capable of about 45 degrees without the limiter cam.)

Test run it with a light. Slowly tighten the adjustment so it goes to full advance at about 2500 RPM - freeway speed.

Set the limiter cam so the total advance does NOT EXCEED 35 degrees.
You'll have to fiddle back and forth to get it right, but it's well worth it.

Initial 8
Mechanical - 12-15
Vacuum - 12-15
Absolute total - do not exceed - 35

Be sure you are using the correct vacuum too - ported - near 0 at idle, as speed increases gets stronger proportionatly. -- No matter what carb you use.

You'll love the results.

How do I know? 2 of my shops specialized in performance dyno tuning - curving carbs and distributors. $400-600!
The biggest reward - the big grin on the driver's face!
 
G

·
Speed buggy, I got a few Q's. You wrote:

I ran a TFI with the dura spark and it ran good. I put a new original style back on my jeep to smog and I could tell the difference. the TR style TFI ignition upgrade works. but I will not run that set up anymore. I measured the current through the coil an it is too much. 4.4 amps stock and 8 amps with the TFI. the energy in the coil is di/dt so that extra current means more at the plug, but that is too much current, for the module and the coil.

the coil requires some form of current limiting


My questions are:

1. Duraspark I or II?

2. Were you running the resistor wire at the time of your current test? I have to take issue with your statement of longevity, otherwise.
.
.
.
.
.
BTW, I am using a ford distributor and pickup with locked out advance to trigger an 8 pin HEI module on my TBI system on the 258HO. I'll update on how it runs over time. I've had it going now for a few weeks with no problems.
 

· Registered
Joined
·
958 Posts
In reply to:

My questions are:

1. Duraspark I or II?

2. Were you running the resistor wire at the time of your current test? I have to take issue with your statement of longevity, otherwise.
.

[/ QUOTE ]

1. duraspark 1. ( I did the TR updrgade, execpt for the spring kit)
2. yes, running the resistor wire. 1.35 ohms of it. just like the FSM says too.

take issue with my concerns with longevity? I'm a electrical engineer and deal with statistical predictions of longevity of parts like this all the time, all day long. and although I didn't set up a bank of these coils and run them to termination, the first things I would do to accelerate the testing would be to double the current, and increase the number of ignitions. all I said was that it would not last as long as the stock coil. That is a really weak statement. and given the amount of current going through these parts, it is a safe bet that they will fail to TE.
 
G

·
I reread your post, and I can't argue with your statement that they wont last as long as a stock coil, as I've only put about 40K miles on mine.

By 'take issue', I'm not saying you are wrong, just that my experience with this setup has not led to the failure of any parts. Maybe we'll soon start to see your concerns realized as more and more miles are put onto TR setups around the country.

I am well aware of your background, which is exactly why I posed these questions of you. I've been trying to get some hard facts on the resistor issue for some time now, and I thought I got some from RRich when this came up last time, but you seem to be refuting that when you say:

"the TFI coil will burn to a crisp if 12 volts is applied continuously. yes, you do not need to drop the voltage before the coil, but you have to drop that voltage somewhere"

You seem to be contradicting your self in your post. You say that you don't have to limit the voltage at the coil, but if you are regulating the voltage after the coil, aren't you still applying 12V to the coil? Your concern is really the current flow through the coil, right, not the voltage applied?

The resistor drops the voltage to 8-9V at the coil. My understanding was that the voltage at the TFI coil could be 12V, but that the duarspark I module couldn't handle the switching duty of 12V. The point of installing the resistor wire is, in part, if not entirely, to limit the heat in the module.

If you are limiting the voltage to 8-9V at the coil, and the coil was, in fact, meant to be supplied with 12V than what is going to cause premature failure of the coil is too much current flow through the coil.

You contend that the stock Jeep resistor wire doesn't adequately limit the current through the coil, correct?

 
1 - 20 of 27 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top