Old hat...

AJ/FormS said
Now we're talking!
Detonation is just too much heat in the chamber for the anti-knock limit of the fuel you are burning. And/or it can be preceded by pre-ignition, which is just something in the chamber starting the fire before the plug does. So when you eliminate the hot-spot or reduce the heat to below the knock threshold,voila no more detonation.
As to preignition; This can be caused by;hot plugs,hot exhaust valve, carbon, sharp edges in the chamber or on the piston, foreign combustibles in the chamber like oil, or winter gas.
And as to heat; This can be caused by; too much cylinder pressure, improper ignition timing, exhaust back-up/restricted exhaust, hot water temp, hot-spots in the heads, sucking hot underhood air.Electric fans not cycling on soon enough or not staying on long enough, or just not moving enough air.

Yes to all of that.

AJ/FormS said
So, I would start with measuring the cylinder pressure,lets see what pressure you are getting, then we can figure it out.
if it's under 150psi, that would be normal for your combo, and should be fairly easy to tune for pumpgas.
But if over 160, something is wrong and you are in trouble.

I'll either find those numbers...or measure 'em again.

AJ/FormS said
Then I would just cool thechitoutofit,until it she quits detonating, then reintroducing the heat little by little to get the power back.
And that starts with;
Colder plugs, a slower timing curve, perhaps slightly limited total timing,then clean out the chambers with a chemical treatment, and then attack the cooling system. And finally check the exhaust system.
I know you said you did the math and got 9.9 Static compression ratio. With that cam in at 106, the Ica comes to 69*. But with the Hughes people measuring their cams at .008tappet lift, the Ica is actually much later. So IMO,You should have no problem tuning this puppy at 9.9 calculated Scr.
You should be getting about 10/11" of manifold vacuum with a proper Transfer-slot sync,at 750/800rpm, with that cam properly installed and no vacuum leaks. With the transfer slot properly set, your timing might come in around 14 to 16 degrees. Forget about all other timings for now. Just work on the getting the transfer slot right and the idle to 750/800 FIRST, then get the vacuum stable and see if it comes in close to 10/11.

I'll check that. I know my idle vacuum is nowhere near 10/11", but I've never set an idle to 14-16º either.

AJ/FormS said
Make sure you got the right PCV and have it plumbed to the proper port, under the primaries. Disconnect the Vcan and plug the carb-port.Check all vacuum taps. If you have a vacuum booster, clamp off the line. Check the crankcase for vacuum, by flipping out the PCV and sealing the CC, then put a vacuum gauge on the dipstick tube. Check everywhere for a vacuum leak. You can't tune the carb if the engine is pulling in air somewhere, it's not supposed to.

I don't follow that. With the PCV out, why would I see any measurable vacuum on the dipstick tube? There is no cylinder set-up that leaks nada. With no PCV, eight cylinders are going to put some pressure in the crankcase.

AJ/FormS said
You got electric fans on that sweetheart? if yes, then get rid of them. Put a direct-drive 6-blade hi-attack fan on her, and install a proven good hi-flo 180stat.

I do have an electric fan, but it is in addition to a direct drive (no clutch) six-blade aluminum fan, a hi-flow t-stat (don't recall the particulars of that, but I remember having to do some looking to find one advertised to be exactly that). BTW... the fan edges are on the edge of the shroud where they should be. I use the electric fan if I run into a heating problem...slow moving on a hot day.

AJ/FormS said
Now lets look at the D.
Your initial should come in around 14 to 16 with a manual trans, else the very low rpm will get jumpy. And it makes the very low rpm a lil lazier and the rpm easier to control. With 4.56 gears you won't notice a few horsepower down on account of just 14/16* idle timing. But you sure will notice the jumpiness at 20*.
And lets start the power timing off at 32 to 34 but make it come in later at say 3400.

The last notes I have say I used 2-pink. That doesn't sound right, 2-orange does. I know I wanted to get above a 1000rpm 'start' mark. The colors on the springs are less than obvious. I'll check that again, too.

AJ/FormS said
These should get you out of detonation,and prevent pre-ignition.
Now the tuning begins.
First question; when do/did you hear the detonation? as in load and rpm.

Around 3000rpm (50mph) in 4th gear a quick throttle change (not a 'stab', but not a 'roll' either) to just before the secondaries open, I can hear it. That is the general area I've used to determine if it rattles or not because that is the most common place I've heard it before. If it's gone there, I won't hear it anywhere else. Being in 4th, that's the most load I can give it but with 4.56s things change pretty quick. All subjective of course, but that particular spot feels to be where the engine starts breathing the best...where combustion pressures (and load) are ramping up fast.