Finally got the new engine in. Took it for a test ride Saturday. The engine seemed to run fine while cruisung under steady throttle. Under a mild acceleration I could here it pinging. Under heavy throttle is seemed OK but I think the noise was not audiable due to the chambered exhaust. I had the timing set to 10*. I backed it off a few degrees while on the road and still had the ping but not quite as bad. I threw the timing light on it at home and I was down to 6*. I just pulled the plugs to get a look at them now that the garage has cooled off a bit. My intention was to pull one plug, but after seeing the first one I decided to pull all of them. 2, 3,5, and 8 were different than 1, 4, 6, and 7. The first mentioned plugs had a dark black mark on the insulator. More of a streak and only maybe 60 degress around and about a 1/8" in length. The rest of the insulator was white as in brand new. The remaining 4 plugs had the insulator being white as brand new. All plugs had a little soot on the ends of the metal by the threads, possibly from idling.
The gas in the tank was about 6 months old and not much in it. Prior to starting the engine I put in a couple of gallons of fresh 93 octane to break in the cam. I was on empty when I took it out on Saturday and put a half a tank of 93 in it. I still had the ping. Later Saturday evening I changed the oil and also added some homemade octane booster which should have taken me to 94 to 94.5 octane. I still had the ping which is why I pulled the plugs.

Here is the run down on the engine. A 388ci (3.75 stroke x 4.060 bore) with 2 relief flat top piston with 64cc Vortech heads. Block was zero decked and I have a standard .038/.041 head gasket. This combination yeilds about 11-1 compression. I know it's not going to run on 87 octane but I was hoping it would run on 92 or 93. Nor is it not running on 94+ octane. The cam is rather small, Lunati 284*, 218* @ .050, 0.458 lift. The carb is a Holley Street Avenger 670 with stock jets.

I am running AC Delco Rapid Fire #3 plugs. The engine seems to be hotter than before, but my temperature gauge never gets above 150*. I used a sending unit recommended by a forum member, but I think I will find an adapter to run my original sending unit which worked fine and I know is accurate, just to be sure.

Since this is not an out of the box engine, my first thought is to go with a little colder spark plugs. Does anyone have a recommendation for a plug? I think getting the right plug is my first step. Perhaps rejetting may help, but I think that would be my second step.

 

Too much compression for cast iron heads, IMO. Maybe a cam with more duration will bleed off some compression. Calculate the Dynamic compression ratio (DCR). I bet it's too high for pump gas.

 

sounds like the compression is a little high. have 2 cars with 11/1 but they have computer control to retard timing with 93 octane fuel. might try to retard timing and see if it helps. i rember in the old days setting up an engine if it pinged slightly at wot in high gear at about 30 mph it was set right. but excessive pinging will destroy an engine.

 

I have the same carb and had to jet up from 65 on the primary side to 70, and from 68 on the secondary side to 73. Plugs read good after that and the car runs great. Prior to the jetting my plugs looked like you described.

On that carb I also had to change the power valve, the squirter, and the accelerator pump cam.

 

Do you nave a vacuum advance ? If you do, disconnect it and see it if still pings

 

I am running the vacuum advance. I was on ported vacumm and pulled over to a rest stop. I plugged the ported vacumm hose and then connected to a ported source to the advance. I really didn't see a difference. I did not try eliminating the vacuum advance. Figured if I was running ported, there wouldn't be much difference.
I don't like the way the spark plugs looked. I never seen a set look like that.

 

Were you completely dry???Any gas over 3 months old is bad. It doesn't matter if you mix good gas with the bad it doesn't fix it the new will not bond with the old. Gas breaks down in 3 months. I don't think adding a stablizer now will help but you can check.

Jim

 

Don't know if this helps at all but my 383 stroker will ping if the timing is set higher than 34 degrees fully advanced. I recently had my distributor out. After putting it back in the engine would ping under load. I reset my timing back to 34 degrees fully advanced and the pinging is gone. I have to run 93 octane also. Just a thought.

 

Hey Madmann This is off the subject a bit but have you ever heard of using 2 diff. plugs--4 of one and 4 of another?Back --way back I used to run a 68 L-88 and I had seen in a tech book a test on big blocks.They ran 4 standard electrode plugs and 4 side electrode plugs for a whopping 31 HP increase !!! We did the same with ours on a dyno and could only come up with a 17 HP increase--we ran like that until we stopped racing the car.The theory they said was "internal" spark timing.Each cyl. can be adjusted somewhat by the depth of the electrode in the cylinder.The big block (they said)was prone to being internally off due to many factors and that its claim to fame was big cubes not precision but it could be made to run more precise.Do you think the small block might respond to this?

 

And before you ask--I'm going back through old race ledgers to see if I can find the artical because I dont remember which cylinders-was it firing order related or manifold related(cyl.runners)Maybe I should start a seperate thread.sorry

 

I have had some success. I swapped to a colder plug which helped a little, but still had the pinging. I drained much of the gas and put in some fresh 93 octane. Really didn't see a difference. I then disconnected the vacuum advance. That has made the biggest difference so far. No ping at 6* and just a tad at 10*. Since there is probably a fair percentage of old gas in the tank which may be causing a problem, I plan on running it below 'E' again and putting a few gallons in it to see how it runs. I pulled the plugs the night before to do a compression check. Compression was between 188 and 202. I did not pull plugs since I ran it with the vacuum advance disconnected.

Edit:
I changed back to my factory temperature sending unit. I am bout 150-160*, running nice and cool. The sending unit that was recommended for by a forum member may have the correct 3/8" thread for the Vortec heads, but it is nowhere accurate. It would barely read above 100*.

 

6-22-06
Change the jets from 65-68, pri-sec, to 68-70 and it made little to no difference. Checked the carb floats and they were on the money. Storms came in and that put the end to any tuning.

6-23-06
I live in an apartment so its a little rude to rev the engine up. Since I am working by myself, it's rather tough (impossible) to hold the timining light and look at the tach. I did rev the engine and it seemed like my timing was coming up rather qiuckly. I have a Mallory distributor and it came with 3 additional sets of springs. I decided to choose the middle set, silver. I also learned that the distributor comes with an adjustable vacuum advance can. I know I should have made two changes at once but I backed off the can fours turns. I set the timing to 10* with the vacuum advance connected figuring I would have to unhook it 2 miles down the road. To my surprise the pinging was gone. Instead of pulling over to unhook the vacuum advance, I pulled over to advance the timing. The only ping I had was for a brief second on a hard punch. I am going to get a look at the plugs and then see where the timing is at after refiring it. I am figuring the initial should be in the 14* range. The Mallory distributor is set up for 24* mechanical, but I'll verify that later with the timing light.
If things work out, it then seems that the distributor was setup from Mallory for low compression engines. At over 11-1 compression on iron heads, it's takes a little more tuning. The cam is small at 218* @.050, but the advertised duration is 284*. The dynamic compression ratio is on the edge for pump fuel but still looked as though it should work. I will get a look at the plugs in the morning. Looking at the ground strap with the colder plugs from the previous driving, they seemed to be in the ball park as far as heat range. The porcelain was nice and white. I am not sure if the jets may be too rich after changing them. I think I am in the ball park now and it needs final tuning.

I realise that this was beyond almost all members knowledge since very, very few even responed. Motorhead started to make me think that perhaps it was a timing problem. With the vacuum advance unhooked it ran OK. With it hooked up it would ping. Although it only takes a small amout of time for the vacuum advance to react, it was enough to cause problems. Backing off how fast the mechanical advance came in, seemed to solve the problem. This seems to opposite of others who have to install lighter springs.