Dart is recommending Autolite AR3933 or AR3910.

I typically run either AC Delco or NGK plugs. Would an MR43LTS plug work? I usually use either MR43T or MR43LTS depending on the reach. The 308s require a .75 inch tip.

This is a NA 454 turning 5600rpms

You know I've always run the mr43 including in my pro 1's. So evidently the 308 casting is thicker. Even in the old oval port Darts I used mr43's. Hopefilly someone will back up darts reasoning and explain. 308 is the only head of darts I think I haven't used or installed. Excellent head though.

I will measure to be sure, but they say .75 inch reach plug on their site.

How about the heat range, 43 good?

I ran NGK in a pair of 540's with ported 308's. I've sold the boat and still have the spare set of (16) NIB plugs sitting on a shelf in the garage. I'll see what model they are and make you a great deal if they work for you.

Those Autolite plugs are a much better plug than the others you have listed.

Which one of the 2 autolites? It looks like one of them crossreferences to a r41t, which is a colder plug than a mr43t right?

What makes them better in your opinion?

I agree with Black Baja on the autolites. I would run an Autolite 3934 or 3935 to start with. The 3933 is too cold for what you have imo. They do take a .750 reach gasketed style plug. I buy them from Rockauto.com , good prices. You can install a .460 reach tapered seat plug in them like an MR43, as long as you don't mind the the plug tip being way up inside the threaded hole. I've seen where someone installed them in a Dart Iron eagle, the engine ran, but fouled plugs, and was down on power, and hard to start.

The 3910 is a projected tip plug, the 3933, 3934, 3935, etc, are not projected tip.

Ok, thanks.

We use the Autolite AR 3911 with 9.3 to 1 CR.....Perfect tan color