The Ford Barn

37fatfender · 03-04-2016, 07:26 PM

Here's my setup in my 40 Coupe, 8ba block bored 3 5/16, Merc 4" crank, 276ci, Schneider cam. Edlebrock 1125 early heads, the block is not relieved. I guessing a CR of 8 to 8.5 according to the Jim Lies/Joe Ablin spread sheets. Induction is a Holley 390 cfm carb with "50" main jets. I run 91 octane in it all the time. The engine has a steady 15-17 inches of vacuum at idle.

The ignition is a 49-53 Bubba Chevy dizzy WITH a vacuum advance can, it has 18 degrees mechanical advance.

I can set the timing to give or take 4 degrees initial without vacuum to the dizzy. Giving me a total of about 22 degrees. No problem. Drivability is good until under load pulling a hill then the engine will ping. Experimenting I pulled the vacuum from the dizzy and alas no ping?? No Vacuum advance, I must be missing something, I thought under load the vacuum advance would be very low or none. So why is it pinging? For now I am running it without Vacuum advance, as "Old Ron" would say its a race engine.

Should I increase the size of the main jets in the Carb?

03-04-2016, 07:26 PM	#1
37fatfender Senior Member Join Date: May 2010 Location: Mesquite, NV / Gurnee, IL Posts: 314	ignition ping when vacuum added Here's my setup in my 40 Coupe, 8ba block bored 3 5/16, Merc 4" crank, 276ci, Schneider cam. Edlebrock 1125 early heads, the block is not relieved. I guessing a CR of 8 to 8.5 according to the Jim Lies/Joe Ablin spread sheets. Induction is a Holley 390 cfm carb with "50" main jets. I run 91 octane in it all the time. The engine has a steady 15-17 inches of vacuum at idle. The ignition is a 49-53 Bubba Chevy dizzy WITH a vacuum advance can, it has 18 degrees mechanical advance. I can set the timing to give or take 4 degrees initial without vacuum to the dizzy. Giving me a total of about 22 degrees. No problem. Drivability is good until under load pulling a hill then the engine will ping. Experimenting I pulled the vacuum from the dizzy and alas no ping?? No Vacuum advance, I must be missing something, I thought under load the vacuum advance would be very low or none. So why is it pinging? For now I am running it without Vacuum advance, as "Old Ron" would say its a race engine. Should I increase the size of the main jets in the Carb?