Big chief Ignition timing

Old 04-27-2007, 01:34 PM
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demented
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Default Big chief Ignition timing

I was wondering if someone can help. This year I changed from a conventional headed BBC to a 14 degree big chief setup. I know that these heads require less ign. timing but I'm not sure were to start. It's a 622ci alcohol injected motor. I use a crank trigger that was set at 38 degrees with the conventional head. Where should I start with this combo?
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Old 04-27-2007, 04:48 PM
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obsessedtruck
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Being that these have smaller domes I would start at 32-34. From Jeffs motors in the past none went more than 36. Got a ? for ya though? did you buy these new or used?? And if used may I ask from who you got them from? If you don't wanna say on here you can PM me if you wish..
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Old 04-27-2007, 05:46 PM
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bjuice
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i have a 622ci..big chief pontiac 14 degree heads...i run on gas a pair of 1200 dominaters....this motor was dynoed and made it max hp at 34 degrees..i have the dyno sheets in hand...1186hp at 7600..it also made 950 ft lbs of TQ..

Hope this helps...if you want to pm me a fax number i can send over the dyno sheets if you feel this will help you finger what your motor will make at what rpm etc......

just for the record..i tinkered around with the idea or placing this motor on alcohol and i was advised by several well known engine builders that this motor would make more hp on gas..i run c-16 vp fuel.
i do know that majority of the injected systems run on alcohol.
i woulsd still think your timing would be closed to where mine is ..if anything with the alochol you may get away taking 1 or 2 degree's out of it..

IF I WERE YOU...i would start out at 31/32 and go from there..this way you cannot go wrong..i would not think it woulf like no more than 34 or 35 tops..i get this idea from my 622ci.

Good luck

Brian
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Old 04-28-2007, 03:28 AM
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demented
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Thanks for the info guys. You've both give me a good starting point. As for switching back to gas I thought about it in the past but the new big chief heads I bought are solid so i can't run coolant through them.
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Old 05-06-2007, 05:55 AM
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After checking the comp ratio on my motor, I have a little more compression than I thought I did. The comp ratio is 16.4:1 What should I start with as far as timing goes with this new bit of info. I'm thinking now starting at around 28-30 degrees with alcohol. Is this a good start or to low.
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Old 05-06-2007, 06:19 AM
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mine runs at 30 degrees total,as per Steve Schmidt set it on the dyno
600+ inch 18 degree BigChiefs and 13:1 nitrous motor,single 4bbl

I just assume whatever he says is the bible
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