Hi all, In the midst of trying to trouble shoot the detonation problems I've been having (see thread http://v8buick.com/index.php?threads/350-going-boom-wont-start.300489/) I finally ran a compression test on my motor this weekend. I wanted to post the numbers to get your guy's thoughts, although my results seem fairly clear. I warmed up the engine to 150 degrees prior to the test and then puled all the plugs and disconnected my distributor. Disconnected supply line for fuel pump (gas all over hands and arms . . .) and held the throttle at WOT during cranking. Air cleaner was still on, hope that doesn't make a difference. Test #1 was 3 cranks, Test #2 was 5 cranks. The number (psi) for Test #1 is given first for each cylinder: Cylinder # 1 - 160, 170 Cylinder # 3 - 160, 185 Cylinder # 5 - 160, 182 Cylinder # 7 - 110, 130 (185, 200 after adding oil into cylinder) Cylinder # 2 - 160, 185 Cylinder # 4 - 160, 187 Cylinder # 6 - 163, 182 Cylinder # 8 - 110, 156 (183, 225 after adding oil into cylinder) So if I'm reading this correctly, it looks like cylinders 1 through 6 are doing fine but 7 and 8 have worn rings? Could this also explain my engine consuming a ton of oil? This car is my daily driver at the moment so I'm in no position to pull the engine right now, but my eventual plan is to turbo another 350 that I have on an engine stand, but that's very far away. So I don't mind driving the car as is (I kinda have to) but it'd be nice to know what I'm up against once I do eventually get the engine out.
Seems right that you add oil and they come up means rings but not sure why you get ping. Guess it's loading the other cylinders. Does it still idle some what decent ?
It idles ok, not amazingly, even though I've dropped my timing to about 2 - 4 degrees BTDC idle and about 26 - 28 total (trying to get rid of ping), not running any vac advance. Will have to double check what my timing's at. I know that the one time I hooked up my vac advance it pinged like crazy. Balancer mark verified with piston stop. Interesting. I've noticed that it happens only when I give it a lot of throttle under load, like if I go 3/4 throttle going up a hill. Throttle input doesn't have to be sudden, just "too much" and it'll ping. Also seems to happen more around corners. I've gotten used to driving only on the primaries! I've already changed my jets from .68 to .69 in case it was a lean condition. Tried stepping up secondary rods as well. Changed to a 160 stat in case it was a heating problem. Dialed my timing back as mentioned above. But maybe it's the oil consumption? Burns about a quart every 2 - 3 weeks, sometimes maybe faster. I'd say on average I drive like 80 miles a week. I know that's a lot . . .
Certainly causes detonation, that's a ton of oil consumption. Baby that one until you replace or rebuild...it's worn. They often idle just fine with worn rings and low compression. It doesn't show much until there's some pressure to contain in the cylinder. As you gain experience, you'll see these things quicker...like this problem Now you know what to check first before tuning and WOT your engine for a few months chasing a tuning problem. It's all good. Everyone has done this.
Got it, thanks guys! I do baby it when I drive it, but I still have to drive it. Another interesting thing is that when I swapped plugs to one step colder, I noticed the old ones showed signs of detonation in all cylinders, so perhaps it's not happening in only 7 and 8? For now it doesn't matter, just going to have to drive it nice until it blows up.
