[marauder]

The compression might be a little high as we measured the cylinder head pressure at 155psi. Ported #62 heads, dished pistons,

Here's the scenario:

Right now initial timing is set to 20 at idle, 38 total, all in by 2300rpm however I'm taking 5 deg out of it at full throttle position with the MSB retard function (Digital 6)

It only pings at part throttle.

Kicking around a looser converter, I have a 2400 now, might need to go up to a 2800.

For now maybe if I back initial timing down to 17 at idle, that would give me 35 at top and I could turn the retard down to take two out and be back at 33 total which it seems to like.

It is a A/C convertible so it is on the heavy side with a 3:42 posi rear and 7004R. I think all of the timing is coming in before I get in the power band. The looser converter and a 3.73 rear may help.

455 roller cam car with 230/236 duration at .05, 110 LSA, 510/520 lift

Any suggestions?

[Billy177]

You may need an adjustable vaccum advance. My car had pinging problems until I switched to a 160 degree thermostat and put stiffer springs in the distributor and an adjustable vaccum advance, after that all was well.

[Stuckinda60s]

What size engine?

Rich

[Tim Corcoran]

You might try backing the total timing to 32 and doing away with the top end retard, and what Billy said.

Tim C

[marauder]

Originally Posted by Stuckinda60s

What size engine?

Rich

Original 400ci, .025 over and stroked to 455

[mchell]

Was the motor zero decked ? What cc dish ? Were the heads cc'd ? Just wondering because 155 psi static does not seem to high at all.....you didn't mention what kind of gas you are running?

I wouldn't think at that static pressure you should have any pinging......but then again it seems that some engines run easily at 10 to 1 on pump gas and others ping at 8.5 to 1.......interesting to know all the particulars

[marauder]

Originally Posted by mchell

Was the motor zero decked ? What cc dish ? Were the heads cc'd ? Just wondering because 155 psi static does not seem to high at all.....you didn't mention what kind of gas you are running?

I wouldn't think at that static pressure you should have any pinging......but then again it seems that some engines run easily at 10 to 1 on pump gas and others ping at 8.5 to 1.......interesting to know all the particulars

Yes, it was zero decked, I'll have to check to find out the dish and head cc.

Running 93 octane Sunoco.

[PITTSBURGH 64]

Shorten the vacuum advance by 1/3 is normal travel and connect it to manifold vacuum, 160 T-Stat, and a cool air pick up to the air cleaner from the front grill.

110 LSA............

[marauder]

Using MSD pro-billet mechanical advance distributor and ram air now.

[b-man]

I'm guessing the heads have the exhaust crossover passages filled with aluminum since they're ported. No heat to the intake manifold, correct?

I would have a GM distributor with vacuum advance recalibrated by one of the PY board experts, I recently had Rocky Rotella do up a points distibutor for me since I'm still living in the '60s. Haven't had a chance to run it yet, but he knows his stuff and he may be able to help you. Good chance he could optimize the timing curve on the distributor you have now to help with your proplem.

[chiphead]

A street 455 at 9.5 compression with open chamber heads should like 13-16* initial, and 33-36* by 2800 RPM. Put the two blue springs and the 18* bushing in there and see if the problem goes away. Then sneak back up on max advance and advance rate. My SWAG would be too much timing, too soon. Assuming the fuel mixture was correct......

[Geoff]

I can think of many reasons that can cause your problem, & I'll still forget some because there are so many!!

Engine runs too hot: poor circulation, rust in water jackets, pump impeller clearance, etc.
Pistons too far in the hole [ poor quench raises octane requirement ].
Lean mixture.
Too much advance.
Poor ring seal allows oil into chamber, which reduces octane rating of fuel.

[smagnotti]

since you have D-port heads, Install long reach BB chevy spark plugs one heat range colder than what you run now, and drop your total timing back to 32 or 34 maCheck your valve to plug, and plug to piston clearance with some clay on the nose of the long reach plug, and add another washer if needed. .060" of clearance is plenty!

[Cliff R]

Why are you using so much initial timing, which provides too much total timing, then pulling a bunch of it out with the MSD?

Set the initial timing at 10 degrees, total around 30 degrees, medium weight springs, and see what happens.

A 455, zero decked, 230/236/110 cam, 155psi cranking pressure, should easily manage pump fuel with the settings provided above. This assumes the static compression ration is in the 9.5-10 to 1 range.....Cliff

[PITTSBURGH 64]

Wow I need to read these post better. I didn't see that 20 degree part.
My 455 likes 11 on 89 gas when its cool outside and 91 gas when hot.

Isn't it hard to start at 20?

[Cliff R]

Agreed, 20 degrees of initial timing with a mechanical advance distributor is HUGE. I can't believe is doesn't "buck" the starter on hot restarts, unless the MSD is used to dial back the timing to start the engine......Cliff

[marauder]

OK, guys, I'll back out some initial timing this weekend. I've now heard reccomended intial timing ranges from 10 to 14 and finals of 30 to 36. This seems rather broad although I'm sure it is dependent on engine combination.

[PONTIAC DUDE]

Check and see what springs are in the advance under the rotor. I forget what was dne at this point in time. It might be advancing to quickly and remember it's a conv and heavy with more load then most other cars.

I do know the block was zero decked and the compression in the 9.5-1 range with dished pistons on paper. 155psi should be in the proper range for 93 octane. It feel it's in the timing and advance.

DO NOT INSTALL BBC LONG REACH PLUGS AS STATED ABOVE!!!!!!!!!!!!

[marauder]

Originally Posted by PONTIAC DUDE

Check and see what springs are in the advance under the rotor. I forget what was dne at this point in time. It might be advancing to quickly and remember it's a conv and heavy with more load then most other cars.

I do know the block was zero decked and the compression in the 9.5-1 range with dished pistons on paper. 155psi should be in the proper range for 93 octane. It feel it's in the timing and advance.

DO NOT INSTALL BBC LONG REACH PLUGS AS STATED ABOVE!!!!!!!!!!!!

I recently paid someone to recalibrate and adjust the advance in the distributor and to go through the carburetror again since I wasn't happy with the way it idled, the large cloud of unburnt fumes when I got on it (the people behind me really hated this), the bog and the pinging.

He was highly reccomended and seems to know his stuff and was formally a R&D guy for Federal Mogul among other places.

It idles great now and starts up right away without the bog when I punch it. We also eliminated the unburnt fumes that used to make my eyes water at long stop lights and when I got on it. It doesn't hit quite as hard as I would like from a stoplight though and sometimes has trouble getting the tires spinning until the rpms increase and they break loose.

I agree that the timing is just not quite right yet. The pinging is almost gone at night if I don't use the A/C and overdrive which is why I was thinking about a 2800 stall converter and eventually switching to 3.73 gears so that the motor wouldn't be loaded down as much and be up in it's power band.

All the timing was coming in by 2800rpm before but now it's coming in earlier, by 2300rpm.

The next step seems to be to take some more timing out of it but we were hesitant as we are trying to maximize the performance.

[marauder]

Had to back it down to 15 initial and 33 deg final to get rid of it. I thought that most guys were running a final of 36 deg. Some engines just like a little timing??