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How much spark advance do I have?

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Old 12-06-2017, 11:27 PM   #1
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How much spark advance do I have?

I really don't know how much advance is being commanded. This is the factory spark map from a 93 Buick TBI L05 5.7 engine. If the Bias is added to the spark table, then the factory commanded around 35degrees at WOT? seems really high no? For an 87octane 350 it seems too high. If I reduce it, it runs worse. Old school thought was 32 degrees all in with 87 octane. Hopefully I'm reading this wrong and I actually have a bunch of headroom for more advance and find more power.


Thanks for looking!
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Old 12-07-2017, 07:42 AM   #2
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Re: How much spark advance do I have?

That bias is subtracted out of the main SA table. The XDF you are using has already done this as noted by the negative SA values shown in the main table.

https://www.thirdgen.org/techbb2/sho...hreadid=317768

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Old 12-07-2017, 02:10 PM   #3
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Re: How much spark advance do I have?

Thanks for the link. I'd seen it but apparently I hadn't read it properly. This stuff is looking less and less like chinese.

That said, the factory was calling for 40 degrees (ish) advance at idle? Seems a bit much but then again, I'm not a GM imagineer.
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Old 12-07-2017, 04:25 PM   #4
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Re: How much spark advance do I have?

Quote:
Originally Posted by Rauldelp View Post
That said, the factory was calling for 40 degrees (ish) advance at idle? Seems a bit much but then again, I'm not a GM imagineer.
No, more in the 17 - 19 BTDC range. Look at the main SA table you posted. Idles at 550 RPM and likely in the 35 - 40 KPa range. Table shows the value(s) for idle.

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Old 12-07-2017, 09:00 PM   #5
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Re: How much spark advance do I have?

Ok, I spent some time, and played with the timing light tonight. I'm still very analog. Poking things helps me learn.

As per usual, you're correct. At idle, engine warmed, 35-38kpa, it was somewhere about 18-19 degrees. This means that from factory this car has at 3600rpm in PE mode we're bumping into 14-15 degrees advance. It would explain why it feels awful to go lower than the factory. It's already so low! Fast burn heads don't need that much advance, but it's gotta want more than that.

Thanks!
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Old 12-08-2017, 07:45 AM   #6
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Re: How much spark advance do I have?

Yep, but recall that a '93 Buick TBI is going to be in one of those big heavy wagons. Combine that with the swirl port heads and 87 octane fuel...

Bump up the octane and put the engine in a lighter vehicle, and more SA will help.

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