Ignition Timing
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
Ignition Timing
On my BB 454 all the "notes" say to set the initial timing to 4 degrees B. Yet everywhere else I read, most others are set much more advanced like 10-12 degrees.
Why so retarded on this big boy?
Why so retarded on this big boy?
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
That's probably factory spec. Most set it using the following link for better performance.
http://forums.corvetteforum.com/c3-t...long-post.html
http://forums.corvetteforum.com/c3-t...long-post.html
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
To answer your question, GM used a rather conservative curve based on the gas and conditions of the day for the 50 states. Heck, full centrifugal advance did not come in till almost 5K RPM. It allowed for good, but not optimum performance. Good for warranty protection! Bottom line is, you can do better. The stock curve leaves a lot on the table. The upside is improving the curve is a pretty good band-for-the-buck.
Anyways, that's how I learned it.
Anyways, that's how I learned it.
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
So I've been reading-a lot and I still haven't completely understood if its better to advance the initial timing or leave it were it is. I read in a different post where 4 degrees was to little for a good idle. I completely understand the total timing and the curve.
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
I just read Lars paper on how to set the proper timing and I understand a lot more. I realize now it doesn't have to be 4 degrees. I think that may be a lot of my carb tuning issues. I'm going to follow his advice on setting the timing.
Racer
Joined: Oct 2010
Posts: 259
Likes: 3
From: Plano TX
Timing
Well, I suppose it depends on engine specs of course.
My total is 38 with 17 initial. Cam is pretty moderate: http://www.cranecams.com/product/car...detail&p=23804
My total is 38 with 17 initial. Cam is pretty moderate: http://www.cranecams.com/product/car...detail&p=23804
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Well, I suppose it depends on engine specs of course.
My total is 38 with 17 initial. Cam is pretty moderate: http://www.cranecams.com/product/car...detail&p=23804
My total is 38 with 17 initial. Cam is pretty moderate: http://www.cranecams.com/product/car...detail&p=23804
That's about what I'm running too. Factory GM ZL-1 BBC cam. You need to find out what your advance curve is, then adjust the timing for the total (38 or whatever), at 3000 RPM, then go back and see what the initial is.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Before emissions hardware, Chevy recommended setting timing at 8* BTCD; after the EPA got involved, they went to 4* BTDC. Retarded timing causes the combustion chambers to run hotter, which burns off more hydrocarbons. But, even 8* BTDC is retarded as far as the engine is concerned. GM set it in a retarded state to limit the performance of the engine, so that warranty costs would be lessened.
Lars would have you set the engine up for 'performance' by setting timing at elevated RPMS....then just accept what idle timing results. That seems to work well for most engines, when the vacuum advance can is plumbed to a 'manifold' vacuum port.
Lars would have you set the engine up for 'performance' by setting timing at elevated RPMS....then just accept what idle timing results. That seems to work well for most engines, when the vacuum advance can is plumbed to a 'manifold' vacuum port.
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