{Chrysler 300} H vs. J distributor

Hi Kurt,

The distributor differences are in the internal mechanical (also called centrifugal) advance curve. The vacuum advance is about the same on both, assuming the vacuum advance was working correctly on the J distributor. The reason for the mechanical advance difference is because the H cam profile/in-line intake is different from the J cam profile/short ram setup. The J also has a more advanced initial timing setting (12.5 to 15 degrees BTDC) than the H (10 degrees BTDC). The J advance curve curve tops out at 13 degrees (plus initial of 15 for a total of 28 degrees) at only 910 rpm, and so it is "all in" just above idle (J idle is 750-800 rpm). The H advance curve is fast at low speed (13 degrees at only 640 rpm, plus initial 10 degrees for 23 degrees total just above idle) but then has additional ramp up to 22 degrees (plus initial 10 degrees for a total of 32 degrees) by 2400 rpm, where it is "all in" (no further advance with increase in rpm).

So, what this means, is that the J distributor, assuming everything was set and working properly, was probably limiting your high speed/full throttle performance as it was only advancing to 13 degrees (+ 10 initial) for a total of 23 degrees. Whereas, your proper H distributor will advance 22 degrees (+10 initial) for a total of 32 degrees. At heavy or full throttle, vacuum advance goes to zero. Vacuum advance gives you better fuel economy at light throttle/cruising. You should experience livelier acceleration now.

One risk with more advance is that you may hearing detonation (pinging), and so you'll want to check for that in the spring. Fuel and spark plugs can affect that as well.

Hope this helps.

Carl

Thank you Bob. Carl Bilter kindly replied but I see it went to me only, I’ll ask Carl to post for other members.

Kurt

On Sunday, February 16, 2025 at 5:25:33 AM UTC-6 Bob Merritt wrote:

Here is a chart of distributors

http://www.chrysler300club.com/rcmstuff/lettercardistributors.html

It has the curve data.

I don't think you will see much

performance difference J vs H distributor.

On 2/15/2025 9:25 AM, Kurt Brueske wrote:

Interesting video:

https://youtu.be/bzEZPiQ4GKQ?si=T-rd0TIkTWG0W0nF

Starting to get cabin fever here in Omaha although it allows garage time for winter projects. Just finished installing a freshly restored and correct distributor in our 300H…very happy with work that Joe White performed (check out his Facebook page). For some reason, my 300H had a 300J distributor…pretty similar minus differences in the part number, or so I suspect. Are there any other differences? Should i expect improved performance and what would this be? I appreciate feedback on this.

Thanks in advance!

Kurt

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