gator79

how much timing can you run? my 383 is pinging even at 30 degrees total timing, worse with vacuum advance hooked up. I tried vacuum advance both ways ported and manifold vac. it idles better with it on manifold vac. compression is around 10.5 to 1 and I have iron heads. I use to run the old 350 at 36 total but the compression was a little lower. I hate backing down on timing because that really affects performance. I am running 93 octane with 104 octane booster (does this stuff really work?) I have a mallory distributor with a MSD box. should I possibly run colder spark plugs? the heads are 461 camell humps. thanks

BigBlockk

Are you sure you're getting the correct reading? Damper may have moved. Is the engine running lean? Did you build this engine? The cam may be advanced. When was the last time you had the heads off? There could be carbon buildup in the heads. Are you sure the heat range of the plugs is correct? Are the plugs the correct reach. If the reach is too long there may be exposed threads inside the combustion chamber.

BigBlockk

Later.....

gator79

I just built it, the damper is right I checked it when I had it down, new short block and heads re worked so no carbon, the plugs are the proper reach for the 1964 heads, not sure what heat range I should be running, they are the acell short plugs for header clearance. the cam was not installed advanced, how could you tell if it is running lean?
thanks

lars

If you're running a fairly mild cam with the 10.5 C/R and iron heads, it's quite possible to get detonation problems as you're seeing. You are correct - backing off the total timing has a significant impact on overall performance.

You can play with the advance curve a little to see if you can get out of the detonation zone. Slow the advance curve down a bit so you don't achieve total advance until around 3500 rpm-or-so. You can even slow it down to about 4000 rpm. Check the length of your curve and make sure it's long enough to allow only about 12 initial while still getting around 34 total. Use a vacuum advance control unit that does not pull in any more than 14-16 degrees, and use a unit that is "slow" enough to not pull any vacuum timing in under any load condition. If you give me some manifold vacuum readings under various conditions I can recommend a unit part number for you.

If the thing still pings after playing with the curve like this, you have 3 options left: Retard timing (with the performance loss), install a bigger cam (could be fun), or drop the C/R (real drag).

Good luck tuning!

big_G

I would re-think the compression ratio....some camel-hump heads actually measure 62cc, if surfaced a few times....even less, add to the fact that they are cast iron (hold heat longer)..I would bet your compression is at least 11:1...unless your piston is down below the deck or is dished...IMO....

lars

Good point. If you're running a true C/R of over 10:1, you're not going to get out of detonation by tuning: you'll have to drop the C/R or use more cam overlap to drop the effective compression. Keep in mind that factory advertised comp ratio was almost a full point lower than the actual measured C/R (advertised C/R was based on blueprint minimum specs, and the engines were never built with head volumes at minimum spec). If you have calculated that you're running a true 10.5:1 based on actual head volume, gasket compressed thickness, deck height and piston reliefs, this is equivalent to a factory advertised C/R of almost 11.5:1.

marshrat99

Gator: Sounds like an interesting problem. If it were me, I'd start back at the beginning and re-verify my balancer's timing mark. If it is still where it needs to be, then I'd go thru the trouble of degreeing the cam. Could be that you're timing chain is a tooth or two off. Let us know what you find.

gator79

the cam is a lunati bracket master advertised duration 292/292 and 230/230 at .050, 480/480 lift at 1.5 ratio rocker. 109 lobe seperation.
the block was decked but just to true it not zero decked. pistons are keith black dished with valve reliefs. my compression with 64cc heads and composite head gasket should have been 9.9 to 1, I used a steel shim gasket that should have raised it some so I assume 10.5 to 1 is around where I am. I may be able to get a little more out of the cam with different ratio rockers. I do have a recurve kit for the dist and will work with that. i want to go with aluminum heads but will have to wait for the funds. the difference between 25 and 35 degrees total advance is unbelievable on this motor. thanks for all the advise

Techno

Is your engine running cool and do you have a thermostat in?

Also are you sure your timing light is correct?

comp

i would double check engine temp. and jetting(plug check) does it ping less from a cold start ??

1atti2d

Not to but in, but I am in the same situtation with mine. Just about have it dialed in. A 355 with Trickflow heads/pistons, 10:5.1 cr and the total timing is at 32. Any more she will start to ping. I have a MSD ignition with mechanical advance. Ended up with slowing the advance down and not going with as much. I can stand on it and dont really feel that I lost any performance at all. Plugs are showing the timing is on and look good. Running 92-93 octane fuel. I originaly had this at 36 total with light springs in the distributor. Was alright if you didnt get into the pedal, but if I did , it would ping big time. Now with the Keisler 5 speed, its even more fun! Just how much money can one spend trying to have a good time?

gator79

Techno, it runs 195-200 with thermostat in , the timing light was calibrated not to long ago it is a roll back type.

Comp, the carb is a double pumper 600 cfm should this be enough carb? definitley is better when cold no ping at all

wicked96

This could be fixed with a water/methanol injection system...
You can quench the detonation with pure water or raise your octane rating with up to 25% methanol/75% water mix! You can add timing not take it away!
Very simple to install....

gator79

Wicked96, tell me more about it I have seen metanol injected on a blown motor before but never on a carbed motor, I think on the one I saw it just cooled the mixture down, that could help in my situation who makes this kit???

wicked96

Sent you a PM with the link...

comp

than to me i would go cooler on the T-stat and jet it a little richer

Simmo

Slightly bigger cam with wide lobe separation angle, you want something with intake closing at about 48degrees ABDC

big69

I've been fighting a similar problem after a rebuild and having to set the total timing back to 29 and not use vacuum advance to stop the pinging. I'm going to try cooler plugs next. It now has Champion RC12YC in it (in AFR 305 heads). This is a projected tip plug. Now I'm thinking of trying Autolite #3932. Is it correct in thinking that the projected tips will more likely cause predetonation than standard plugs?

Gator79, what plugs are you using?

Techno

If nothing else a bandaid fix might be to run the engine cooler. I don't think it will give much advance but your saying its pinging already.
I do know an engine running just fine in NY and driving to florida does ping, everytime I went up a hill on the highway.
I retarded timing in georga on the way back and didn't ping with the trailer.

gator79

I recurved the dist and now it may ping once in a while one time. I disconected my kickdown cable so I could load it up in 3rd gear to test.
total timing is 32 with advance starting at 600 and all in by 2800. before it started at 400 and was all in by 1600. I still can't use the vac advance. LARS I will get some vac readings so you can advise on the right advance unit. thanks for the help
big69 my plugs are the acell shorty header plugs not sure on the heat range but I have to use the old style plug in my 1964 heads