Simon- It had an external balancer and flexplate on it when I bought it. I was able to watch it run, on a stand, before I bought it. Only thing I changed from it running on the stand was an external balance flywheel. I've since installed a new external balancer during my troubleshooting as well.

This is the best picture I have of the crank flange. The crank flange is cast with a counterweight on it.

Here is my cam:
https://www.summitracing.com/parts/lun-60105

Here are the #3 and #4 cylinder plugs from last week. BUT, this was just after having the engine warm up at idle. I haven't done a proper shut down after WOT plug reading.

Daniel

Daniel, just throwing out all possibilities. If you're able to check with the guys you bought the engine from, try to see if you can find out the specific crank they used. I realize it had external components but just in case the wrong parts went on.
You purchased a new flywheel, is it the one with the weight pad that's bolted on? I realize this is a alot of bs but maybe take the weight off and see what happens.

The plugs look okay, the cam specs seem to be a bit high for the compression you're running. I'm wondering if that has an effect on the run cause Lunati says it requires a minimum of 10.5 compression.

Simon- I appreciate ANY ideas, really. At this point, I've resigned myself to pulling the engine this winter. So, I don't mind chasing any possibilities up until that point.

After I bought the engine, I removed the oil pan to verify it was a 383 stroker and see what the cylinders looked like, etc. I've attached the photos I took while the pan was off (sorry for the low quality). The number cast into the crank counterweight is hard to read. After a lot of research time online, I *believe* the crank is made by CAT (Cal Auto Transpeed). A lower quality, chinese import, that subsequently is out of business from what I can tell.

The guy I bought it from said PAR Racing in Spartanburg, SC assembled the engine for him. I'm waiting for a return phone call from them.

Yes, the flywheel I bought has removable weights. I've tried running without a weight and it was clearly not happy. I've also tried different amounts of weight trying to "sneak up" on the correct balance, but no luck.

As to the compression ratio, I used online calculators and the specs I was told to calculate the ratio. With that cam's overlap, the dynamic ratio estimate was about 9.5:1, with the static ratio about 10.5:1.

The calcs I used indicated 10.51:1 static/8.67:1 dynamic @ .020 deck height (or 10.89:1/8.98 w/a .005 deck) using typical generic 383 numbers & that Lunati cam. Seeing your cranking compression >200psi would suggest your in the ball park. I've been advised exceeding the 200# number on pump gas is pushing things & for worry free operation things needed to be optimized for every different combo.

Have you tried just backing off the timing to see what happens w/the 'run-on' scenario?

that plug does not look happy. have you verified which advance springs are installed? Are you using a non-digital timing light to time it?

ScotI- No, I haven’t had the timing lower than 36* total. I’ll decrease it 1 or 2 degrees and see what i get.

Mike- the 21* bushing is in it. I’m using a basic, non-digital, Craftsman timing light.

Daniel

I backed the timing down to 13*/34* and went for a short drive this weekend. The vibration did not change at all, still there.

Interestingly, the engine run-on still occurred as well. It *may* have been a bit less run-on then previously, but not a significant change.

Daniel

Try 32° total. This would be strictly for the run-on issue as I think there is something different causing your vibration.

If still experiencing run-on @ 32°, I would seek out some higher octane rated gas & utilize it to eliminate octane as a possible cause.

Daniel......which spark plug part number are u using?
Do you know if they are the right heat range?
Do you know how far they protrude into the combustion chamber?
Plugs are available in regular reach as well as long-reach.....maybe u have the long version. Look up plug manufacturer charts and cross-reference charts.
Call up the head manufacturer to get plug recommendation.
Try side-gapped plugs to minimize protrusion into chamber. Too much protrusion will create a hot spot because the ground electrode stays too hot and promotes "dieselling" which is also pinging. Auminum heads would draw enough heat from the plugs as not to be an issue if heat range is correct but not if protrusion is too much.
Colder heat range plugs are fatter in the center electrode thereby conducting heat back into coolant more quickly.

http://www.ngk-sparkplugs.jp/english...q13/index.html

As ScottI says, octane rating is critical. Octane booster is available as a concentrated additive. Try a half tank full.

13* static sounds way high to me. 10*_32* should take you out of the twilight zone......again ask the head manufacturer.

I'll reduce the timing to 32* and see what happens. Then try octane booster if needed.

The plugs are NGK BKR5E, per NGK's tech support that I spoke with.

I've also tried NGK BKR7E and Autolite 3922 plugs.

Not sure if I'll be able to wait until winter to pull the engine for a new rotating assembly...I'm getting antsy.

Daniel