This is something that has puzzled many people. My 1970 2bbl Buick 350 ran great when I got it, and honestly it still does. Unfortunately, I've run into an issue with detonation. I run 93 octane gas with lead additive and 104+ Black bottle octane boost, and any combonation of the three with our without each one. I've replaced the distributor (it needed replacing anyway... desperately.), all the plug wires, tried cooler plugs, and retarded the timing to 4 degrees initial. I've tried running the carb a little rich, and right on the money, I've checked out everything in the cooling system, and there doesn't appear to be a blown head gasket (no milky oil, the coolant doesn't foam when I run the car with no cap, no white/discolered smoke), I've changed the thermostat from the winter-friendly 195 that was in it to a 165... and it still detonates slightly at part throttle. The condition doesn't seem to be there at upper RPM's or even while climbing a mountain, just in around-town driving. It runs fine, idles fine, and though it is quite lacking in the power department since the timing is so detuned... it seems to be ok other than the VERY slight "ting ting ting" of detonation. If I brign the timing back up to 6-8 degrees initial the car detonates so bad, and so deep within the engine under even normal acceleration that I have to pull over and tune it back down for fear that I won't make it home otherwise! I know the next step is pulling the heads, but I really wanted to check everything external before I yank apart my never-opened engine. Any suggestions? What else is there to do?? Should I stop worrying about it until I can afford to tear into it? The detonation isn't loud and can't be heard outside the car... only when you're sitting in it. Am I being paranoid? I'd really like to get the tire smoking torque it once had back by advancing the timing at least back to stock specs, but I can't due to the extreme detonation that happens then! Thanks in advance for any help.
Eric, Check to see what your total advance is as you rev the engine. You can do this with a dial back timing light. If you dont have one, make a second timing mark exactly 1 3/4" clockwise around the damper(facing the engine). This corresponds to 30* Rev the motor, with a regular timing light, until the new mark stops moving up and read the total timing off the timing tab. Example if your new mark stops at 2* on the timing tab, your total is 32* Also look to see if the advance stop bushing is in place. This is a picture of the distributor upside down. The advance stop bushing is at the end of the red pen. If this bushing is missing, it will allow too much advance as you rev the motor. Hope that helps.
Thanks both of you, I will try to get my hands on a dialback timing light or try the alternative method, and I will check my distributor to see if the bushing is missing. If neither of those work then I will have to wait a while; brakes come first, and I have a hole in one of the hardlines
Pinging problems I've had- The engine was running at over 200deg. I didn't realize it until I put in a temp gauge. Ended up being the radiator. Power brake booster taps of off cylinder #7, my booster was leaking, so #7 was running lean, and pinging. Also caused a burnt #7 exhuast valve. just some other things to look into... Good Luck -Nick
I've got manual brakes, but the temperature thing is something I am investigating. The radiator looks brand new, but it could just be a cheap coat of paint which would effectively lower the radiators ability to cool... I will have to get a temp guage just to be positive that it isn't running too hot. I have a low CR engine (2bbl so its 9-9.5:1) so it doesn't make sense for it to detonate... Something leaking into the cylinder is another concern of mine, but I've no idea what it might be. One person suggested a slightly cracked head gasket, but I think by now I would see the tell tale signs of it as I drove it most of last summer and have had no (serious) issues, and it doesn't smoke. The oil is also clean as I stated before. Thanks for the advice, I will do more investigation into the cooling system.
