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post #21 of (permalink) Old 09-09-2005, 06:49 PM
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Re: TFI and HEI what\'s the difference?

Here's a comparison that John Strenk made between his "Stealth HEI" module and a Dura Spark module:

<font color="red">The DuraSpark at idle:</font>


<font color="red">And the HEI Module at idle.</font>


Click either picture (same link) to read the thread on JU.

And then if you want to read more of John's adventures, this is a very good one (click it):



A few weeks ago for kicks I fired up an old o-scope, nothing nearly as nice as John's. After more fiddling with trigger inputs and crude pickups than I would care to go into.... I saw the same type results just not as pretty or easy to read due to the very old and uncalibrated scope.

[img]/ubbthreads/images/graemlins/applause.gif[/img] John Strenk [img]/ubbthreads/images/graemlins/applause.gif[/img]

While I still have some work to complete the project I intend to standardize the four Jeeps that end up in my driveway when broken to the "Stealth HEI" module with a few spares to carry.

[img]/ubbthreads/images/graemlins/40BEER.gif[/img]
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post #22 of (permalink) Old 09-09-2005, 06:52 PM
 
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Re: TFI and HEI what\'s the difference?




For the little Jeep first...
I have a switch on the dash (have the HEI module there too.)
Flip the switch, go from HEI to DuraSpark without missing a fire sometimes...
(Watching on the laptop if I got a mag trigger and no coil fire)
DuraSpark factory resistor wire on the DuraSpark module,
No resistor wire on the HEI.
Diodes on both to keep from back feeding current either way.
I figure with resistor wire in place, and a stock canister coil, I'll get a better idea of what most of the readers are dealing with.
When I start collecting data with an E-core coil, I'll drop the resistor wire, or maybe test with it in place, then drop it...
Don't know yet, just have to see....

I have been doing silly stuff, like getting into a good pull on a hill and switching ignitions, or during a highway pass and switching.
Interesting results, somewhat confusing, but interesting.
-------------

The coil spark energy breakdown on the little jeep is probably the ignition coil, and the current reaching it. Small wires, resistors, age, Dumb****astan construction all lead to problems, and DuraSpark module (also discount store cheepie) breaks down about 1,500 RPM with total failure about 3,700 RPM.

The HEI isn't much better, spark energy breakdown using it to fire the same everything else is about 1,700 RPM with total failure about 5,700 RPM, but that's with no load.
I wouldn't be a bit surprised if either of them couldn't get the fire lit reliably beyond 3,000 RPM.
-------------

As for the MSD, you pretty much made all my points...

Multi fire in the RPM ranges most of us drive in, so full benefits...
Mine have been working fine for over ten years (probably more like 15) and I trust MSD.

With at least 600 volts going to the ignition coil, saturation times are at least 50+ times faster.
12 volts Vs. 600 volts is no contest in saturation times.

Standard 12 volt inductive ignitions are limited by saturation times, PERIOD.
They simply can't sustain reliable spark energies past a point that is about 1,500 on the standard V-8, a little longer (more saturation time for less cylinders) for 4 bangers or 6 cylinders, but around 1,500 RPM is normally when spark energies start to suffer.

MSD removes that obstacle, saturation times are faster than discharge times, so the little CD module has removed that problem.
Now the problem becomes how fast can you discharge the standard ignition coil...
It has to discharge before you can fire it again... And that is the limiting factor now instead of saturation times.
It really isn't a problem, when you can fire the plug 6 times in the span of time factory ignitions fire once, if at all...

Also, with 600 volts hitting the coil, you get MONDO more amperage!
The spark energy is so much fuller and richer (to borrow cooking terms! I am a fat guy after all...)

What you may want to watch is the time between MSD firings.
With the basic laws of thermodynamics, if you can fire the plug a SECOND time, or a THIRD time fast enough, you can take advantage of the heat 'Trail' left by the firing before.
(I can't think of the proper term for the residual heat...)

The first fire gets the area up to (and beyond) flash point, and if the second firing is fast enough (and MSD is) the second can take up where the first one let off,
IE: much shorter time to flash point than the first firing...
Not to mention MSD throws enough amperage at the gap to knock you off your feet, and it will fire a plug in a cup of oil.
(I've tried it, you can!)

With the heat and ion trail established, and so much more amperage going to the plug, the second and third, and fourth and fifth....
Firings are almost completely sustainable flash point burns, where the first one (and the ONLY one in a 12 volt inductive ignition) is almost entirely consumed just heating the flame channel up to flash point...
----------------

Let me ask you this...
Why do Supercharger manufacturers, CNG, LPG & other gas kit manufacturers, Alcohol conversion kit manufacturers all recommend CDI modules if not MSD ignition modules by name?

The fact of the matter is, Gasoline is the only fuel you can fire with a standard 12 inductive ignition even remotely reliably...
You can't even fire kerosine unless the engine is above 200 degrees (water temp), and that's gasoline's closest cousin!

Remember the old tractors and Ford cars and Trucks that has a gallon tank for gas to start the vehicle on, and a main tank for kerosine?
They usually had louvers in front of the radiator to block air flow so you could heat the engine up to kerosine temperature faster...

Ever worked on a mulit-Fuel engine?
Why do you think that when you switch over to kerosine the ignition switches off?
It's worthless, it isn't firing squat, that's why...

With MSD on the new military scout vehicles, they can reliably burn gasoline, kerosine (jet fuel), diesel, bio-diesel, alcohol and just about anything else you can pour in the tank!
(I've heard they can actually get sugar water to fire, the holy grail for multi-fuel engines...)
It's not your basic 6 series module, but the internals are pretty darn close!
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post #23 of (permalink) Old 09-09-2005, 08:08 PM
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Re: TFI and HEI what\'s the difference?

Good points on the CD. Remember the old tube type CD's used on Porsche?

Wondering - when you flip the switch from HEI to Dura, does the timing remain the same? There may be a variation due to the voltage threshhold levels needed to fire the HEI vs the Dura. The HEI triggers at a higher voltage, not as sensitive as Dura, good, and bad.

How are you handling the coil wire into the distributor? A "Y" configuration would tie the two coil's secondaries together, putting an undue load on whichever is running at the moment. One would absorb the energy from the other.

You said you are still using the round coil - no E coil yet with the Dura. If you are driving the round coil (to avoid the "Y" problem above) with the HEI that may be the reason the HEI's crapping out early. I don't know how the HEI likes the different internal resistance of the round coil - never tried it. With the internal current limiter and variable dwell it may not give the round coil enough charge.
And - you must have a pretty elaborate switch to switch in the resistor for the Dura, and none for the HEI.

Of all the HEI's I've tested and run on my or customers cars, the HEI did not even start to roll off at less than 6K. Something's bad wrong if it does.

Way to test roll-off - scope, unplug a plug wire - voltage should go up to about 40-42 KV, called Available Voltage. Of course if insulation is bad, or a bad rotor, it won't.
Rev it up, watching the Available Voltage, rev till it begins to drop significantly. Usually when it drops 10% is called the roll-off point. So if it was 40KV, then 36KV is the roll-off point. It still works above that, but does not have as much power.
I've found stock HEI's are effective to about 8K+. Beyond that they turn to mush.
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post #24 of (permalink) Old 09-10-2005, 02:44 PM
 
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Re: TFI and HEI what\'s the difference?

[ QUOTE ]

Good points on the CD. Remember the old tube type CD's used on Porsche?


[/ QUOTE ]

Yes I do, but they took HUGE amounts of current to operate.
The only thing I liked off that ignition system was the ignition coils.
No Iron core, just wrapped around a foil tube. Discharge build times were nearly instantaneous, but duration wasn't that great.
Really helped with total discharge times though.
Still only one discharge per firing window...
----------------

[ QUOTE ]

Wondering - when you flip the switch from HEI to Dura, does the timing remain the same? There may be a variation due to the voltage threshhold levels needed to fire the HEI vs the Dura. The HEI triggers at a higher voltage, not as sensitive as Dura, good, and bad.


[/ QUOTE ]

That's one thing I'm wondering about...
I'm using a single distributor mag trigger (Chrysler), and switching it over.
I'll have to use a crank trigger for base line comparison if I really want to know how much delay is inhearant in the different systems... I just haven't fabricated a crank trigger yet.
(not a hard job, just a lazy man! And I've had other 'Irons' in the fire lately.)
I do know the trigger to actual firing time is increased when using the HEI (equivlent of taking advance timing out), but not enough to get bent about.

Like I said, I'm trying to collect data on what every configuration someone on the BBS might be running after the initial cap, rotor & plugwire upgrade, so I'm open minded...
I'll let the data tell me what's going on, instead of me trying to manipulate the data to fit a preconsived notion of what supposed to be going on...
------------

[ QUOTE ]

And - you must have a pretty elaborate switch to switch in the resistor for the Dura, and none for the HEI.


[/ QUOTE ]

Switch, 4 pole, double throw.
Default on both modules when NOT powered is coil ground OPEN. This helps.
2 for mag trigger switching, one for coil ground, one for module/coil power.
Modules are in the drivers compartment, so that helps with the wiring spegatti bomb.
Diodes keep power from back feeding on coil/module power legs at the coil.
Only ONE ignition coil and coil wire.

I do run seprate coils, and will run dual triggers and coils later, but right now I'm trying to keep it as close to stock as possible so I can figure out what is going on.
-----------------

[ QUOTE ]

You said you are still using the round coil - no E coil yet with the Dura. If you are driving the round coil (to avoid the "Y" problem above) with the HEI that may be the reason the HEI's crapping out early. I don't know how the HEI likes the different internal resistance of the round coil - never tried it. With the internal current limiter and variable dwell it may not give the round coil enough charge.


[/ QUOTE ]

I do expect the HEI is suffering with the factory round coil, but like I said, I'm trying all of the posibilities that readers might have, and that is certianly one of them.
I'll let the data tell me *IF* and *HOW MUCH* when the tests are done...
Pre-concieved expectations are not productive right now...

No where in any HEI conversion writeup did I see where it was MANDIATORY to change to an E-core coil...
(Oversight on someone's part,) So there is a VERY REAL POSSIBILITY there are several out there that followed the HEI articles, and still have the round coil.

And, there is the crowd like Dale writes about, that just WON'T spend the money...
And the crowd like the wrecked crew, that just won't follow directions no matter how well written or explained...

BTW, I don't have a real problem with one coil absorbing much spark energy...
the second coil isn't grounded unless it's ignition system is activated, so energy loss is minimal.
------------------

[ QUOTE ]

I've found stock HEI's are effective to about 8K+. Beyond that they turn to mush.


[/ QUOTE ]

If they were reliable to 8K, wouldn't all of the GM guys be using them in racing, instead of MSD?
8K would put them in NASCAR racers. I've never seen a HEI in a NASCAR...

What I've been trying to tell you, and illistrate to you, is there is a WORLD OF DIFFERANCE between winging the throttle in the driveway or garage bay, and actually running down the road or track or trail...

Setting in the drive way, you don't have all the lights, 105 accessories on, and water in the alternator... Or brushes in the alternator momentarily loosing contact with the sliprings when you hit a bump or rock, or the slip rings loosing contact when the engine rotates when the clutch is poped or the there is a big throttle movement...
That's why a battery elminator capicator won't work for a HEI distributor.
All of this affects input voltage for the HEI, not to mention the factory undersize power wire they use.

How about 70 throttle changes every operating minute.
That's what Bosch came up with for the average driver when working on fuel injection.
And I'm sure it's much more than 70 with a older vehicle on a rough trail or rough road...
That relates to 70+ different fuel ratio mixtures every minute that the ignition has to overcome.

How about moisture content in the intake charge?
Ever hit a puddle and have steam come out from under the hood?
Ever drive on a rainy day? How do you think moisture affects charge or just the spark in the chamber, not to mention every inch of the conductors & connections under the hood?

How about the residual exhaust gasses left in the combustion chamber with 70 throttle changes a minute?
When you are in the dirve way, with constant and smooth throttle changes, that exhaust flow isn't impeaded, and draft gets to play a big part in things...
You get pretty consistant fuel ratio numbers... Get off the shop floor, and things change!!!

They change so much that we need larger alternators, dual batteries, bigger tires, deeper gear ratios, ect...

I'm not knocking you for what you do/did in life, we all need diagnostic tools, but diagnostic tools in the driveway/garage bay and the real world don't often 'Play Nice'...
Just ask the current alternator that served my little '73 CJ-5 for 33 years...
Like Tim Allen says, 'Time for MORE POWER!'
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post #25 of (permalink) Old 09-10-2005, 03:46 PM
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Re: TFI and HEI what\'s the difference?

So what is the bottom line. All this technical info is really cool but would you notice a difference when driving with a HEI vs MSD vs Duraspark?
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post #26 of (permalink) Old 09-10-2005, 05:02 PM
 
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Re: TFI and HEI what\'s the difference?

If you have an '83 or newer Jeep with BBD carb, you *shouldn't * do the HEI module or you will defeat the on board emissions crap.

With my '73, you have to upgrade to an magnetic trigger to use either the DuraSpark or HEI.
The '73 was originally breaker points.
http://www.junkyardgenius.com/jeep/cj502.html

The '78 to '82 are the most likely candidates for the HEI module.
---------------

[ QUOTE ]

So what is the bottom line. All this technical info is really cool but would you notice a difference when driving with a HEI vs MSD vs Duraspark?


[/ QUOTE ]

Clearly MSD rules the day.
---------------

The facts in my mind are clear, MSD kicks ass on all common factory ignitions.
It's so much stronger that the test isn't fair...
When we compare DuraSpark to HEI, we are comparing Apples to Apples...
MSD is a CD or Capacitive Discharge ignition, so it's like comparing Apples to Beer, Steaks & Horny Prom Queens.

It's 50 state emissions legal, it will help your emissions.
Although it's not cheap, it's reasonably priced.

It works with all common ignition triggers, even points.
(Unfortunately, Jeep used an UNCOMMON ignition in the Prestolite ignition for about 4 years, depending on engine, from '74 to '78)
Replacement FACTORY distributors grow on trees, so this isn't a huge problem...

MSD works with all common factory ignition coils, internally resisted or not.
This makes it a GREAT item for us 'Mix & Match' types.
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post #27 of (permalink) Old 09-10-2005, 06:15 PM
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Re: TFI and HEI what\'s the difference?

Properly upgrading to either MSD or HEI you'll never notice the difference in performance between the two. With the HEI you'll have money left over for other things you need. Plus HEI parts are readily available and cheap.

Either will make a big difference in performance and mileage over any version of the Ford Duracrap, or Prestojunk.
If you are in a state where modifying the ignition is illegal, suggest you hide the HEI module in the old Ford box - Stealth HEI. Or use the CARB approved MSD.
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post #28 of (permalink) Old 09-10-2005, 06:16 PM
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Re: TFI and HEI what\'s the difference?

I have a hard time beleiving that a Jeep engine that rarely sees over 3500 RPM needs anything other than a stock or HEI ignition. I see the need for the biger distributer cap and rotor but it is not a race car. The HEI is easy and you don't have to mount the MSD box somewhere.
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post #29 of (permalink) Old 09-10-2005, 09:14 PM
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Re: TFI and HEI what\'s the difference?

[ QUOTE ]
I have a hard time beleiving that a Jeep engine that rarely sees over 3500 RPM needs anything other than a stock or HEI ignition. I see the need for the biger distributer cap and rotor but it is not a race car. The HEI is easy and you don't have to mount the MSD box somewhere.

[/ QUOTE ]

[img]/ubbthreads/images/graemlins/applause.gif[/img]

Thanks for saying exactly what I've been trying to put across. [img]/ubbthreads/images/graemlins/blush.gif[/img]

[img]/ubbthreads/images/graemlins/40BEER.gif[/img]
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post #30 of (permalink) Old 09-10-2005, 10:32 PM
 
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Re: TFI and HEI what\'s the difference?



Well, I have a hard time believing that no one here can get that the biggest gains you can achieve with your ignition work is the MSD module...

I just can't seem to stress the point enough, MSD delivers it's greatest assets at the RPM you all are talking about...
Namely, 400 to 3,500 RPM.
My experience has been different than RRich, I routinely see MSD firing multiple times past 3,000 RPM.
Even if it fires one single time past 2,500 it's still a much hotter and sustained spark.

HEI if you want to, DuraSpark if you want to...
The Question was which one delivered the good best, and that would be MSD hands down.
DuraSpark and HEI aren't even LITERALLY in the same class as MSD.
----------------

If you are a cheep guy, use the factory DuraSpark...
If you are adventuresome or experimental type, use the HEI,
If you want the best in your given RPM range, use MSD.

I personally don't care what anyone uses... but I don't want to hear the sob stories and complaints later...
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