The AUJP Bin has an inital spark advance of 6°. Is this to match the base timing of the engine or should I set the base timing to 0°?

If I set the base to 6° and leave the initial timing in the Prom at 6° would the real timing at idle be 12°?

Also the maximum spark advance is 41.8°, this seems a little high compared to the old school way of thinking with 36-38° total timing. What gives?

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My Camaro Project

 

Used to match the base timing that you set at the distributor. As an example ... my distributor is set to have initial base timing at 10º BTDC. I have the constant for the intial timing also set to 10º. This is so the computer KNOWS where you set the timing. The ECM has no way to detect WHERE you set the base timing. Thus, it uses a preset constant.

No. As mentioned above

You are thinking in terms of WOT only. However, that value is used for more than just WOT. Think part throttle too.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
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Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
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Moderator: PROM board at thirdgen.org

 

Thanks for the quick response. It makes much more sense now.

 

Well, I think I disagree. If you look at the stock timing for a 305, its 0*, but if you look in the chip, its set at 6*. So the computer will use a base timing of 6* ASSUMING that the dist is set at TDC (0*). Now if you crank your distributer to 6*, and the computer thinks it is advancing it to 6*, 6+6=12.

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According to my 1991 GM Shop Manual, the TBI is 0* and the TPI (305 & 350) is 6*BTDC. But as Tim said it is really irrelevant as long as the base timing in the eprom matches what you set your distributor is set to. If it does not match, the Total Spark Advance will be off by the difference between the two.

 

You can disagree but its true! What Glenn said also backs up what I have explained.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Various manuals manuals have all sorts of errors in them. some on purpose, some out of a writter not knowing any engineering (ie magazine writters are classic examples of this.
Timing on the engine should match the chip period.

 

Thanks for all the educated responses. I tried both. First I set base to 0° and told the prom the initial was 9.8°. It did not run very well, noticable even without going to the track. I then set base and prom initial to 9.8° and the response was great, engine ran smoother and better response.

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86 Camaro Sport
383 Speed-O-Motive Crate Engine, Raptor 700R4 Tranmission, Trick Flow Twisted Wedge G2's, 58mm Accel TB, 3.73 Auburn Pro, SLP Cold Air Induction and Headers, Hooker Cat-back, Serpentine Belt Setup, Dual IROC Fans, Jamex springs, 16" IROC Rims, 36mm/24mm Sway Bars, Global West Steering Brace. Hotchkis Rear LCA's,Panhard Bar and SFC's.
My Camaro Project