400 timing

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May 3, 2014 | 10:08 PM

XTfx4

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Joined: Mar 2007

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400 timing

Trying to figure out total timing on my truck.79 350 4wd with a. 400. Edelbrock carb intake , no emissions at all stock duraspark dizzy. I've read 6, 10, 12 intial 34 to 36 total ? Which is it. If I go with any of these initials plus the mechanical of 36 from my stock dizzy, using the 18l slot, I'm well over the 34 to 36 total. Also upon researching, the 400 has 4 degrees retarded built into the cam. Does this 4 get subtracted from your total ? Exp. 12 intial 20 mech. - 4 for a total of 28? Thanks for any info. Bought this truck not knowing anything that was done to the motor ? Tried the timing with a vaccum gauge method seems to like the 12 intial the best ? But what about the mecahical of 36? Sorry just confused. Thanks again

May 3, 2014 | 10:55 PM

Tedster9

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Joined: Apr 2002

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From: Waterloo, Iowa

Not an expert, but remember the total is total - initial plus mechanical, so you have to disconnect the vacuum and use a timing light and see at what RPM the max advance is. So it's not just your total, but when it's all in max?

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May 4, 2014 | 09:46 PM

Blue and White

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Joined: Nov 2011

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Factory specs for the 400 seem to have varied from 8 to 12 initial. The timing curve varied based on emissions setting including egr/no egr. EGR suppresses ping and allows leaner AF and more advance. If your setup is all stock, a 350 with higher GVW may have had EGR and no catalyst and wants 12 initial/34-36 total (vacuum advance line disconnected and plugged as posted above). If EGR is inop, less timing and/or richer AF may be needed... or refurbish the EGR and put it back to stock.