Chevy Big Block Pinging
Thread Starter
1st Gear
Joined: Nov 2018
Posts: 1
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Chevy Big Block Pinging
I've got a 71 chevy 396 in my truck, and it runs pretty well and seems to been pretty well timed. Except, when I accelerate under load (up a hill most often) it begins to "ping," which is a case of detonation I guess. Does this mean that it's a combination of low octane and slightly too advanced timing? Thanks for the help!
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Actually, Ethanol has a higher octane value than the former gasolines. But, yes, it is awful stuff.
What's your advertised compression ratio now? Where is your total timing set at?
You may have to kick it up a notch on your octane purchase choice and / or reduce overall timing a smidge.
What's your advertised compression ratio now? Where is your total timing set at?
You may have to kick it up a notch on your octane purchase choice and / or reduce overall timing a smidge.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
There were no low compression 396's. The 1 year only 2 bbl sta wagon engine was 9 to 1. And they used a 122cc head to get it that low. You need to retard the advance til it stops. You. Are probably around 34-36 at 3000 right now. Good for performance car. A lil high for a truck under load.
Last edited by derekderek; Nov 2, 2018 at 09:17 PM.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
If it’s pinging, you simply have too much timing for your fuel. Couldn’t say which needs to change without knowing everything about your engine. If you have lower compression (which you probably do) you should just set the timing for regular unleaded. Check your numbers. If you don’t ping at WOT and only at light throttle/light load in higher gears, it may be your Vacuum advance is putting a little to much in. May need to fix your vacuum can degrees. Check that you are plugged into manifold vacuum.
-Stroke
-Stroke
Last edited by Strokemyaxe; Nov 3, 2018 at 10:37 AM.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,091
Likes: 4,016
From: New Braunfels Texas
A proper curve would probably fix it if you knew where you are at right now........
A proper curve is the #1 tuning trick there is.....and dirt cheap if done right......like $10
Once a proper curve is realized....you can set the total and initial.
Then work on the vacuum curve.......does your distributor have an adjustable vac can? This could help eliminate pinging under load as well. But you need to get the mechanical part right first and lock it in....then play with this.
Jebby
A proper curve is the #1 tuning trick there is.....and dirt cheap if done right......like $10
Once a proper curve is realized....you can set the total and initial.
Then work on the vacuum curve.......does your distributor have an adjustable vac can? This could help eliminate pinging under load as well. But you need to get the mechanical part right first and lock it in....then play with this.
Jebby
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
When you stab the throttle, engine vacuum goes way low and the distributor advance can should retard the timing sufficiently. If it does not, your advance can might be faulty. Connect a timing light to see how timing reacts when you 'pop' the throttle (timing should retard). If that is working OK, perhaps the transmission didn't downshift as it should have...or YOU didn't downshift as needed.
If advance can is working OK and the same thing happens on FLAT ground, you need higher octane fuel and/or need to retard the ignition timing somewhat.
If advance can is working OK and the same thing happens on FLAT ground, you need higher octane fuel and/or need to retard the ignition timing somewhat.