Engine Knock - Too Lean or Too Much Timing?
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Joined: Jun 2002
Posts: 544
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From: La Jolla California
Engine Knock - Too Lean or Too Much Timing?
I've been trying to adjust the timing to get rid of all my engine knock on my 383 carbed LT1. What I am doing to test this is I get going about 30 in 3rd gear (TH-350) and then just floor it. If I'm too advanced I hear it knock and I just retard the timing until the knock stops. Currently I have 29* of mechanical advance (vacuum disconnected) all in by 3200 RPM (stiffest springs) and no knock. If I advance the total or go w/ a quicker advance I get knock.
What I'm wondering is if the carb (Holley 750 DP) is just going too lean when the secondaries just dump open causing the engine to knock. It seems when I ease into the pedal, or downshift and then floor it, I don't hear this knock even with the timing advanced more.
My engine specs are as follows:
383 LT1 (modern) running 11.7:1 compression
Holley 750 DP (stock jets)
GM Carbed Dual Plane Intake
Comp Cams CC306 w/ 1.6 RR (duration @50 230i/244e w/ lift .544i/.576e)
Aluminum Heads "Stage II" ported (flows 265i/190e @.50 w/ 2.02/1.6 valves Hooker LT Headers
Dual Flowmaster Exhaust
3.55 rear end
2500 stall
TH-350 trans
160 deg thermostat
MSD 6AL
Meziere electric water pump
It seems I can run around 34* timing w/ a quicker advance if I'm not flooring it while cruising in 3rd gear. Is it possible that I'm getting knock still but just can't hear it over the engine?
Does this sound like too much timing or too lean a fuel mixture?
Thanks!
What I'm wondering is if the carb (Holley 750 DP) is just going too lean when the secondaries just dump open causing the engine to knock. It seems when I ease into the pedal, or downshift and then floor it, I don't hear this knock even with the timing advanced more.
My engine specs are as follows:
383 LT1 (modern) running 11.7:1 compression
Holley 750 DP (stock jets)
GM Carbed Dual Plane Intake
Comp Cams CC306 w/ 1.6 RR (duration @50 230i/244e w/ lift .544i/.576e)
Aluminum Heads "Stage II" ported (flows 265i/190e @.50 w/ 2.02/1.6 valves Hooker LT Headers
Dual Flowmaster Exhaust
3.55 rear end
2500 stall
TH-350 trans
160 deg thermostat
MSD 6AL
Meziere electric water pump
It seems I can run around 34* timing w/ a quicker advance if I'm not flooring it while cruising in 3rd gear. Is it possible that I'm getting knock still but just can't hear it over the engine?
Does this sound like too much timing or too lean a fuel mixture?
Thanks!
Burning Brakes
Joined: Oct 2002
Posts: 835
Likes: 3
From: Water Winter Wonderland
Re: Engine Knock - Too Lean or Too Much Timing? (Langadorf)
31-32 is about all I can go w/ 11:1CR on 93 octane
Car likes 34 deg. if I run 50:50 103 octane/93 octane.
11.7:1 on pump gas seems like an awful lot of compression without a computer.
Just my $0.02
Car likes 34 deg. if I run 50:50 103 octane/93 octane.
11.7:1 on pump gas seems like an awful lot of compression without a computer.
Just my $0.02
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
Re: Engine Knock - Too Lean or Too Much Timing? (Langadorf)
jason, from my dyno experience, i will say most people don't realize their cars are detonating.
that said, i also think you should use a wideband to see what the a/f ratio is. that tool alone will make things a lot easier.
dyno it if you get a chance, i've always wondered what sort of power curve that dual-plane intake provides...
that said, i also think you should use a wideband to see what the a/f ratio is. that tool alone will make things a lot easier.
dyno it if you get a chance, i've always wondered what sort of power curve that dual-plane intake provides...
