Hi have a 327 sbc, its got around 11:1 compression, a thumpr cam 279/297 duration .480/.465 lift, an edelbrock 600cfm carb and an hei ignition. basically it pings pretty bad, and surges around 3k rpms. its also hard to get the idle to be steady, theres no vac leaks that i can find, and newer plugs in it. Just curious if anyone has any suggestions, especially on if the carb is correct cfm. Also what timing should i have and where should i set the vacuum advance ? Im at only 8 degrees btdc right now. Wondering if all the pinging its been doing has messed the valves up... Gonna have to run a compression check on it and see.. Motor doesnt have many miles on it either.. Thanks!

 

For starters, you have to run premium gas with your 11:1 c.r., are you? If not, that's problem #1. Either add some octane booster to the tank and/or get gas at a different station next time and see if you get better results. Octane knock (pinging) is caused by an improper air/fuel mix, poor burning cycle, or timing issue. The ping sound is pre-detonation trying to push the pistons back down too soon. Your valves aren't in danger unless they're whacking the pistons, but that would be a physical clearance aspect of the engine build. 600 cfm should be plenty for a 327, but it's possible you may be jetted too lean. Does the surging go away beyond the 3000 rpm range? If so, and the engine isn't falling on it's face, then the carb flow is keeping up. Do you have timing tape on the harmonic dampener to know where your "all in" timing is at? As a rule of thumb, small blocks like total timing to be in the range of 28-32 degrees before tdc. Which vacuum port on the carb is the advance connected to?

 

I run 92 octane non ethanol fuel, ill have to check on which port the advance is plugged into.. And my 28-32 degrees total advance do u mean mechanical advance or with the vacuum advance plugged in also? Its odd with the surging because it comes and goes, and sometimes the motor will rev it 6500 and sometimes it wont go above 5k... The surging does go away after about 3500 but above that it seems there should be more power... Seems like it may be starving, which jets should i be running? And do u have any idea about the metering rods in the edelbrock? What works best with these motors, thanks!