[ieatdrt]

10 deg. initial, 10 vacuum, 31 total, without vacuum, all in at 3400 rpm. With vacuum, no load, the total is 41. The tranny is a manual. I've trimmed the ground back on the plugs and rounded off the edges to prevent hot spots. I know the 3922 is the coldest Autolite offers. I'll have to do some digging for another brand. I think I'm going to swap out the 800 for the 750 and tune around that. The carb is giving me a lean condition under light acceleration that won't go away until you give more throttle. Sounds like the stepup springs, but it's not responding to spring changes. This carb may have some ghosts, so I may be trying chasing my tail here. I'll do the carb swap tomorrow, and test further. I've also just filled it up and added some octane booster. No help there. It's a light ping, not a continuous condition. It's just annoying and shouldn't be there. I should be able to get that to stop. It's most notable as the clutch if fully released lasting only for 1/2 sec. Then intermittent very light pinging while accelerating lightly. I'm thinking that might be from my lean condition during transition from cruise to power mode. Either that or the ping is causing a false lean reading on the A/F meter. Wish I could quiet the exhaust to hear things better.

[The Greek]

I think that there is confusion between the vacuum advance and centrifical advance. The base timing and centrifical should total between 36* to 38* BTC all in by 3200 RPM. This is with the vacuum advance disconnected. With the vacuum advance connected at 3200 RPM, no more than 52* BTC.

From what I can tell, you aren't advancing enough.

[ieatdrt]

You're correct, I have the timing backed down to try and counter the detonation. I have 10 initial, and with the vacuum disconnected I'm getting 31* total. I'm running on the conservative side to try and prevent the detonation. I'm definitely not running the amount of timing I should be. What I'm going to do today is pick up some NGK racing plugs with a recessed tip and a bit colder than the Autolite 3922's I'm running now. It responds much better with 14* initial and 35* total, but I was turning it back to try and eliminate the pinging. I'm now thinking that it's not due to timing, as it pings the same with 10*/31* and 14*/35*. I'm going to set it with 14* initial, 35* total w/o vacuum and the new colder plugs. See how it feels there. It's supposed to rain all day today, so I don't think I'll get a road test in.

[429ragtop]

sounds to me like your compression is to high.

[Ivy66GT]

Originally Posted by 429ragtop

sounds to me like your compression is to high.

Or the octane is too low.

A 10.8:1 compression nominally requires a 98 pump octane gas. It will always ping on 93. You can fudge the octane a little with timing, etc., but not 5 octane numbers. If you could, then no one would really need premium in a new car.

Adding about 40% ethanol to 93 octane gas might be about right. Ethanol by itself is about 115 octane.

[429ragtop]

Originally Posted by Ivy66GT

Or the octane is too low.

A 10.8:1 compression nominally requires a 98 pump octane gas. It will always ping on 93. You can fudge the octane a little with timing, etc., but not 5 octane numbers. If you could, then no one would really need premium in a new car.

Adding about 40% ethanol to 93 octane gas might be about right. Ethanol by itself is about 115 octane.

I disagree. My 429 has 10.8:1 compression and runs through the rpm range on 93 octane with no additive and no ping whatsoever. There are many variables in different engines that can and do cause this condition. It would be incorrect to make a sweeping statement that just because an engine has a certain compression ratio, it will always ping with 93 octane.

[Ivy66GT]

429ragtop,

I agree, there are a lot of variables. What is your altitude? That makes a big difference. Eastern Washington could make that a lot easier than in Boston. The first 1000' reduces the octane needed by about 1.5. At our 6150' altitude its reduced 9 octane numbers so 93 would be overkill which is why they don't even sell 93 around here.

[STERLING351]

Originally Posted by 429ragtop

I disagree. My 429 has 10.8:1 compression and runs through the rpm range on 93 octane with no additive and no ping whatsoever. There are many variables in different engines that can and do cause this condition. It would be incorrect to make a sweeping statement that just because an engine has a certain compression ratio, it will always ping with 93 octane.

I agree, my 351w is 10.6:1 and i run on 93 pump gas, every now and then i will add a little something, but not everytime.

[ieatdrt]

Actually I need to make a correction. My static compression ratio is 10.4:1. I'm thinking it's related to the high cylinder pressure do to the stroke and the 236* intake duration not bleeding off enough. I installed a set of NGK 5820 racing plugs, colder than the Autolites and have a recessed tip. No difference, so I'm ruling out ignition at this time and leaning towards an excessively high cylinder pressure. I'm going to get a new compression tester, mine only reads to 150psi, and test the pressure this week. Maybe I can find a shop around that sells race fuel and see if it helps. The octane booster, Lucas Oil, didn't help at all.