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Discussion Starter · #1 ·
i have a 421 sbc with a big shot plate and am wondering how much total timing you guys are using on your big tune up

i have 325 in now and was wondering if pulling 15 degrees is too much

i know every combo is diff but i wanted a ballpark figure on similar combos

oh i have a 23 degree head

thx
 

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27,956 Posts
Me

i have a 421 sbc with a big shot plate and am wondering how much total timing you guys are using on your big tune up

i have 325 in now and was wondering if pulling 15 degrees is too much

i know every combo is diff but i wanted a ballpark figure on similar combos

oh i have a 23 degree head

thx

I run a 415 with a 23 degree head and a big shot. When I had it set at 325 it seemed to like 11.5 the best. Every motor is different though so start high and pull back after each plug reading. Till you get it right.

Sbc seem to get away with pulling less than the Sbf from what I've seen.
 

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SOFA KING WHAT?
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I use the 2 degrees for every 50 hp.

I would pull 12 - 13 degrees and check the plugs.

I am assuming you use 36-38 degrees for your initial?
 

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SOFA KING WHAT?
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43,675 Posts
Pull 12 degrees and check the plugs.
 

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EFI/N2O JUNKIE
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18,065 Posts
How much does the timing line get affected by running colder plugs? If he is running 36 total now and pulls 15 as a very safe starting point, what range plug would he then use? I would think he has something like a -9 NGK in there now. Go down to a -10? What if he went to a -11 with the same timing as the -10, does the line move back towards the end of the strap (away from the base?).

Just trying to figure-out this heat range / timing line stuff myself.....
 

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EFI/N2O JUNKIE
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The way I do this I want as W I D E of a window as possible!!!
What is the disadvantage of running too cold of a plug? Can't clean-off the deposits from idling around, driving through the pits, etc...... Can those deposits cause a problem? I've read that those deposits can get so hot that they can short-out a plug, but I think that's an old wives-tale........ What does anyone think of that? Any truth to it or BS?
 

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EFI/N2O JUNKIE
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18,065 Posts
I decided to make one nitrous pass first thing this morning just to move things around on a qualified ladder on one of the classes I race in. My plugs were nasty! Should have put in fresh plugs first, but I wasn't looking at setting a record or anything, just wanted to qualify in a different spot on the ladder. Anyway......... these plugs looked shot before the pass, gap was, who knows, it was pretty huge! Digital 7's eat non-resistor plugs like a kid eating candy! Had maybe 25 passes on them. Gap was probably .050 on them. Looked like they had 100 passes on them too. Car picked-up .9 and 10 mph and ran flawlessly on a .055 jet (big shot plate).

I was expecting less and not a clean pass knowing what the plugs looked like before the run. After the run, they were still nasty-looking! They did not clean-up at all with the extra heat. Ran the rest of the day on motor and car was perfect, until the storm came by! We ran for cover. Our tower got hit by lightning!

I'll be buying some sets of -10's and do a little testing next weekend and see what I can do.
 
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