Well, the wider contacts mean there's good rotor/cap terminal alignment through a wider range of spark advance and/or a longer spark duration, which means less arcing under the cap, which is usually counted as a good thing.

Most of a decade ago I spoke with Mitech Ignition (of Welland, Ontario) and they weren't opposed to making wide-contact distributor caps "if the volume is enough to make it worthwhile", which it almost certainly is not. Mitech went out of business in 2010 or so.

A (much) easier workaround to achieve the same goal: "winged" wide rotor tips that could easily be cut out of brass and swapped onto shelf-stock rotors. Previous discussion here and here. Then all we'd have to do is home in on an easy-to-buy, high-quality current-production cap with brass or copper contacts. There are still some candidates that don't look to have been tested yet. If we could find a cap that's consistently ground on-centre even if its contact dimensions aren't optimal for off-the-shelf rotors, that would be fine, because we'd be tailor-making a rotor to suit.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

For that matter, parts could be robbed right off of existing rotors, cut and drilled as necessary, and swapped onto a Chrysler rotor.

Here's a Standard AL178 for old Prestolite applications:


Here's a CH310 for Chrysler/Mitsu 3.0 V6 (this is the fancy version with the toothed and encased contact:


Here's the CH310T budget version with the exposed and non-toothed contact:


Here's DU315 for '80s Renaults with Ducellier distributors:


Here's FD117 for Ford applications....geeze, that contact looks like it might be real close to a direct swap onto the Chrysler rotor!


Here's FD308, another Ford piece with another promising contact:


And…erm…whoah, stop the presses, here's IH318, which is called out for use on International (1964-1980) and Plymouth (1974). Contact tip isn't as wide as some of these others I've posted, but it looks like it could be a drop-in. Is it shorter or longer than a CH303? Donno, but Standard's database calls it out as compatible with distributor caps CH-410 and CH-409, that is the Slant-6 and V8 distributor cap, respectively. ?! Looks like it's got some Chrysler part number equivalents, too: 2875852 and 3620769, neither of which appears in the passenger car FPCs for years relevant to those part numbers' genesis. Truck/van, maybe? Someone buy one of these and check it out:


This isn't an exhaustive list, either.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dammit Dan, you need to stop putting ideas in my head! You are an evil fun-project-pusher! This would be a totally easy thing to fabricate with nothing more than basic tools.

I would love to see some ignition computer scans of the HEI conversion with one of these home-brew rotors.

Update: 2875852 and 3620769 are apparently '74-'75 Dodge medium- and heavy-duty truck rotors. Should be drop-in for the Slant-6. Now all that remains is to buy (Standard IH318) and compare/measure. DonPal…?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'll check the clearances of the wider IH318 rotor but is it extended like the MO3000? Otherwise the decreased .060 will hurt the wide rotor concept test?

Making our own extended wide rotor about .010 longer than a MO 3000 sounds like the real trick. I'll make up one and get the secondary voltage since that has the most promise with a decently machined cap.....of which the test shows occurs once in a dozen times....ugh.

The MO6 cap looks readily obtainable as well as the late 60's chrysler cap for establishing dimensions Chrysler was honed in on.....and the resulting secondary voltages.

So I can see a few more rotor and caps test needed. The weather is a factor here as even though measuring is done inside..... secondary voltages are outside.....I'll post the measurements as I get the caps and the secondary voltages as soon as mother nature gets us back above 40.

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1965 Dart 110k, 225, Carter BBD Super Six, 2 1/4 single exh., sbp manual scarebird front disc, 7 1/4 rear 2.94 sure grip, 14 x 4.5 OEM wheels, 833 OD with hyd. throwout bearing, HEI, electric fan, ram air/heated air, Accusump. http://plymouthcarclub.com/

Don't know -- that's one of the things to be measured about it!
I don't know that, either; it depends on how it interfaces with the cap contacts (which in turn depends on what cap we're testing it against, right?)
There's that one on eBay for $15.
I see one on eBay for $50 (pfft).

Probably ought to get hold of the 2098770 rotor that was meant to be used with that cap, too. Send me a PM if you'd like me to work on tracking one down.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Excellent resource list here.


Dan can you explain why the ch 310 has the teeth?

Thanks!

Greg

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http://www.youtube.com/hyperpack

Sparks jump easier from pointy things.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Makes sense.


Could that mod be applied to other rotors if done with decent tooling?


Thanks again for the info.

Greg

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http://www.youtube.com/hyperpack

Don't see why not!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

In the best Adam Sandler Waterboy voice I can muster:

"Mama says, that the rotor has teeth, because it's smiling that some slixer is going to install it in a 225 and whup on some poor V-8..."


Sorry couldn't resist...

United CC-611X data added---close/almost hit rotor
Std IH-318 does not fit on slant distributor shaft (too small ID)
MO 6 and 2642986 data added to 60's info (note avg. gap at .020)

Below table has all the original & latest data plus provisions for the 60's caps.

Also started table for Secondary Voltage Tests of significant data cases and places to add upcoming significant data cases.

Slant Six Distributor Cap Terminal To Rotor Tip Gaps
Table shows results with Exchlin MO3000 Rotor (uln)
CAP MODEL CAP# MAX MIN ECC
Echlin MO 40 1 .030 .013 .008
Echlin MO 40 2 .038 .010 .014
Echlin MO 40 3 .041 .012 .014
Echlin MO 40 4 .022 .017 .002
Echlin MO 40 5 .034 .014 .010
Echlin MO 40 6 .038 .008 .015
Echlin MO 40 7 .040 .015 .012
Echlin MO 40 8 .032 .015 .008
Echlin MO 40 9 .041 .009 .016
Echlin MO 40 10 .030 .025 .003
STND CH-410 1 .030 .008 .011
STND CH-403X 1 .040 .015 .012
AIRTX 5D1022A 1 .030 .005 .012
REMANUF Echlin 9 .018 .012 .001
UNITED CC611X 1 .040 .006 .017

1960's & Early 70's Typical Gaps

ECH MO 6/1838516 1 .028 .013 .007
2642986/1838516 1 .027 .010 .008

For Different Rotors measured:
Echlin MO 13 add .057 to all gaps
CARQUEST D147P add .056 to all gaps
MOPAR 1838516 subtract .008 to all gaps (interference fit on Echlin #6 & Standard #1)

All dimensions in inches

Secondary Voltages

THE DATA CASE GAP SEC VOLT

The Worst Gap .114 22,000
IH-318 rotor
Medium Gap .025 9,000
60's Dbl. Width .028 2,200
Machined Gap .018 5,000
Mod IH318

Will put IH-318 rotor tip on different rotor and adjust for .015 avg gaps
Will also test 60's caps with other period rotor.

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1965 Dart 110k, 225, Carter BBD Super Six, 2 1/4 single exh., sbp manual scarebird front disc, 7 1/4 rear 2.94 sure grip, 14 x 4.5 OEM wheels, 833 OD with hyd. throwout bearing, HEI, electric fan, ram air/heated air, Accusump. http://plymouthcarclub.com/

What are you measuring with the ECC(entric) measurement?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

"What are you measuring with the ECC(entric) measurement?"


Indirectly measuring offset of the center of the cap versus the center of the distributor shaft
Said another way if we cut the distributor and distributor cap in half we could measure a difference between the center of the distributor cap at rotor position and the center of the distributor shaft at that same position (or elevation)

Detailed Proceedure:
1) Rotor is the gauge of a fixed length rotating about the distributor shaft centerline.
2) Record all gaps between rotor and each terminal and record on the cap
3)Scan the cap for the highest and lowest value
4)Note that in every case so far they are diametrically opposite ie terminals 2 and 5 or 1 and 6 etc.
5)The center line of the distributor is furthest away from the biggest gap terminal
6)Take the last case where the biggest gap was .040 and the least gap was .006 then if the distributor shaft center was .017 further away from the .040 gap terminal it would be .017 closer to the .006 terminal
7) the eccentricity direction is defined by the two most opposing gap differences

Take the cap off the jig and turn it 180 deg and all the extreme gaps change opposite to what they were as the cap "lean" put the center of the cap to the other side.

Not measured directly but inferred from the gaps determined by our measuring tools (the rotor and feeler gauge).

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1965 Dart 110k, 225, Carter BBD Super Six, 2 1/4 single exh., sbp manual scarebird front disc, 7 1/4 rear 2.94 sure grip, 14 x 4.5 OEM wheels, 833 OD with hyd. throwout bearing, HEI, electric fan, ram air/heated air, Accusump. http://plymouthcarclub.com/