FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: aj on January 20, 2025, 10:22:51 AM
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Engine is stock appearing 69 cj using original points distributor. I’m uncertain what type coil to use while on dyno. 3 ohm vs 1.5 ohm
I have a yellow top (1.5 ohm) coil but those typically work in conjunction with resistor to prevent coil from over heating after initial start up.
Conversely, if i use a 3 ohm coil (during dyno), would there be enough voltage to start the engine. My guess is yes…since on a dyno there’s no starter pulling down voltage to the coil during start up (i think).
Anyhow, looking for suggestion on which type coil to use when dyno-ing with points distributor.
Thanks
Adrian Jacobs
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not sure what to tell you about coil,but if it was my engine,i would replace the points with a pertronix or some other electronic ignition.at least for the dyno that your doing,not cheap to dyno.
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Typically, a dyno uses and MSD and coil it trusts, you just feed the trigger wire from your distributor, it'll ground at a 1/2 V or whatever the MSD uses and will be very gentle on points and dwell isn't an issue
If you do run your ignition completely, you likely have to step it down as you say. I would prefer the MSD option by a long shot, but if for some reason you need to, stepping it down through the coil is no different than stepping it down through the coil and resistor wire.
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Points with a MSD is a good set up and the points become a non wear item with the MSD. Points in a point ignition system the points become an electro magnet from the current flow which is why points always get pits from opening and rubbing block wear while with the MSD its just an on-off switch with no current going through the points , even the rubbing blocks don't wear with the MSD
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Points with a MSD is a good set up and the points become a non wear item with the MSD. Points in a point ignition system the points become an electro magnet from the current flow which is why points always get pits from opening and rubbing block wear while with the MSD its just an on-off switch with no current going through the points , even the rubbing blocks don't wear with the MSD
If that's the case, you wouldn't need a condenser or resister, right?
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That is correct, it's just a switch for low voltage signal coming from the MSD
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Points with a MSD is a good set up and the points become a non wear item with the MSD. Points in a point ignition system the points become an electro magnet from the current flow which is why points always get pits from opening and rubbing block wear while with the MSD its just an on-off switch with no current going through the points , even the rubbing blocks don't wear with the MSD
That is the most reliable system for a non-high performance (under 5k rpm) engine, in my opinion. I ran a MSD Blaster with a stock distributor in my Highboy for 25 years with this set-up. Only had to replace the points one time, and that was due to the rubbing block snapping off. Only time I've ever seen that happen. A good solid system for your typical street car or truck. You don't have the issues that can sometimes plague electronic pickups.
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My dyno's ignition wire provides 12V, so I think I would use the higher resistance coil. The engine may be harder to start without the 12V bypass to the low resistance coil on startup that the car will have, but at room temperature I think you will be OK. Having said that, I've dynoed several engines with bone stock ignition systems and the lower resistance coil, and never seen any problems with the coil or points being damaged. I think you'll be fine with either one.
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You guys are missing an important thing , Todays points are lucky to go to 4800 without point bounce ( regardless of what box they are triggering) yes there are points still out there that will RPM higher ( if the Dist is in good shape ) but the cost in upwards of 35.00 each , Dyno time isnt cheap , I rarely do distributor work with points for this exact reason , a std pertronix will put out twice the spark energy of any dual point setup and will go past 7000 without blinking and will trigger any box put there if you want to use them