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Timing questions

 
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SCEADU
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PostPosted: Thu Jul 01, 2010 3:18 am    Post subject: Timing questions Reply with quote

I have a SB 327 with the Edelbrock EFI (1st gen). I can add degrees or take them out at different RPMS and loads from the module.

1) What should be the most advance I want to run? (36 is where I have it set to)

2) Is there a rule of thumb for setting the timing at different RPM and load?


Example : Cruising down the Hiway at 2500 RPMS 75 mph, I have 6-9 vacuum and at about 25 degrees advance. Sound right?
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squeeezer
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PostPosted: Thu Jul 01, 2010 3:20 am    Post subject: Reply with quote

NO!!!!!!!!!

if this is your "cruise speed" then ALL your timing should be in by this rpm also makes for a cooler engine

i assume you are not using vacuum advance, just mech. advance right?

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squeeezer
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PostPosted: Thu Jul 01, 2010 3:25 am    Post subject: Reply with quote

fwiw ....i have a sbc that takes only 34 degrees and 1 that takes 40 degrees total advance

need to test at the track or dyno to find what that motor wants
yeah most sbc's are between 36 to 38 degrees but that is just guessing

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SCEADU
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PostPosted: Thu Jul 01, 2010 3:25 am    Post subject: Reply with quote

HMMMM!!!


I thought more advance meant higher temps
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SCEADU
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PostPosted: Thu Jul 01, 2010 3:34 am    Post subject: Reply with quote

The computer handles all the advance, but i can adjust it however from the module in the cab.
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SMOKEmUP
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PostPosted: Thu Jul 01, 2010 11:40 am    Post subject: Reply with quote

General rule of thumb is to run as much timing as you can before pre-detonation then back off a couple degrees.

For different load points it's hard to figure out how much the engine needs unless you have an engine dyno, knock sensors, and you hit each load point on the timing map.

One of the main factors of timing is fuel air density. The more fuel and air in cylinder the closer they are together so the flame spreads much faster resulting in less timing required for higher fuel air density.

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Big Dave
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PostPosted: Thu Jul 01, 2010 2:44 pm    Post subject: Reply with quote

Might add that the bigger the bore the more timing you have to add as the flame has further to go to get from one side to the other in time to contribute to doing any work (while the piston is still in the neighborhood to push on).

You can have too much timing without getting into detonation as if all of the fuel air charge was fully combusted before TDC your engine would be beating the bearings to death and wasting energy trying to compress a very hot gas that is trying to expand. In this situation you are also leaking more than the usual 1/3 of your BTU load into the coolant so the car will run hotter than normal; not cooler.

I agree all of your timing should be in by your cruise RPM. You can adjust both the weights and springs and if you have a vacuum can as I read from your post you can swap it out for an adjustable one that allows you to dial in more vacuum advance at a lower vacuum setting so that the vacuum contribution to total timing is already all in.

Big Dave
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af2
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PostPosted: Thu Jul 01, 2010 6:38 pm    Post subject: Reply with quote

You should have all advance in by 2500.
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squeeezer
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PostPosted: Thu Jul 01, 2010 7:19 pm    Post subject: Reply with quote

af2 wrote:
You should have all advance in by 2500.








or earlier if speed limits are in the 60mph zones
i have mine all in by 2200-2300 rpm

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af2
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1933 Willys Coupe

PostPosted: Fri Jul 02, 2010 12:05 am    Post subject: Reply with quote

squeeezer wrote:
af2 wrote:
You should have all advance in by 2500.








or earlier if speed limits are in the 60mph zones
i have mine all in by 2200-2300 rpm


Very true. I just gave an example.
the OP has 25* at 2500??? Not good. You can watch the fuel gauge lower.
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