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502 timing

Old 11-06-2021, 09:16 PM
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Default 502 timing

Best timing for a 502,single motor 30 Velocity cmi headers 850,bravo drive mild hydraulic cam looking for total use 93 not high compression basicly stock motor
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Old 11-06-2021, 09:34 PM
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Carb or EFI? N/A or forced?
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Old 11-06-2021, 09:35 PM
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What heads?
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Old 11-06-2021, 11:16 PM
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If its basically stock and compression is below 9.0, set it to 34* and you should be able to run 87 octane
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Old 11-08-2021, 08:46 AM
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You need to watch the latest Engine Masters episode, Does more octane make more power. They ran everything from 87 to 116 in an LS crate motor and even E85. They found that with all octane levels the engine wanted the same timing. AFR only changed minimally between the blends. E85 was the only fuel that made more power and wanted more timing. Timing is determined more by combustion chamber design and bore size than fuel. They determined that the engine wants what the engine wants regardless of octane. Combustion chamber efficiency is the biggest determiner of timing requirements. That's why an LS or the vortec head small block head require less timing.
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Old 11-08-2021, 08:52 AM
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What about if it's a 556cu NA motor with ali heads? I'm currently running (what I think is) a conservative 30, but I've been meaning to start dialling a little more advance in.
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Old 11-08-2021, 09:43 AM
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Originally Posted by MadMat View Post
What about if it's a 556cu NA motor with ali heads? I'm currently running (what I think is) a conservative 30, but I've been meaning to start dialling a little more advance in.
I have AFR heads with CNC'd chambers and a 4.565" bore and 10,1:1 compression and I am running 35 degrees on 93 octane. Your killing your power at 30 degrees, BBC's need at least 34 degrees with stockish valve angles and the large chamber. Once you get into the small chamber heads all bets are off on that.
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Old 11-08-2021, 10:10 AM
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Me too - I have the AFR 315cc CNC heads, 9.35 compression on a 4.5" bore & 4.375" stroke.
30 was intentionally conservative - but I'll be winding a bit more in in the spring. So is 34 a safe "next run" setting, and then try 1 more degree at a time from there, would you say?

ETA - I think can answer this with a "yes", but I'd forgotten I set up my ign timing based on the "stock" thunderbolt IV timing curve to get started - which maxxes out at 30 - and then I forgot that at least 34 should be safe with potentially even 36 on the table subject to testing based on the notes I made when I was designing/building it all.

Last edited by MadMat; 11-08-2021 at 10:43 AM.
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