1972 LS5 maximum total timing advance?

[Robert B.]

Can anyone help with the maximum total timing advance for a stock 72 big block? I have read anywhere from 32 to 38. I do not have any detonation with the initial timing at 12-14 degrees. My centrifigul advance is 22. Thanks. Rob

[Tom L.]

Re: 1972 LS5 maximum total timing advance?

I recently went through this myself for my '72 LS-5. I found that 22 degrees centrifigal is correct as stated. this means that at the 8 degree reccomended timing at idle gives you 30 total.

That seemed low to me so I asked my engine builder. He said that "most" big blocks like 36-38 degrees when tested on the dyno but that number is determined by the engine combination. For an application like ours, unmodified and street driven, he said 36 would be tops, to play it safe 34.

I chose 34 total because I'm not racing and don't have any intrest in seeing the inside of my engine any time soon. Have fun!

[Robert B.]

Re: 1972 LS5 maximum total timing advance?

Thanks - Good advice - I'm in the same boat as you. I like the outside of the motor!

[Ken A.]

Re: 1972 LS5 maximum total timing advance?

38 degrees works best on the street, 34 is too low.

[Rich G.]

Re: 1972 LS5 maximum total timing advance?

Are you checking total advance with the vac. connected? Base timing, centrifugal. and vacuum together? They do like to run better with more advance at idle especially with a little better cam. I was just a little worried about to much advance at the higher rpms.

[Robert B.]

Re: 1972 LS5 maximum total timing advance?

I am running a stock cam. I am using base timing plus centrifigul, vac advance disconnected to measure. Car does not have any detonation at 14 degrees base timing, plus 22 degrees centrifigul for a total of 36 at WOT. I was concerned this might be too high. Based on the posts 34 to 38 seems to be what people are running. I want to tweak the most timing I can get without risking my motor.

[Duke W.]

Re: 1972 LS5 maximum total timing advance?

Emission controlled engines of that era typically had less than optimum spark advance for all operating conditions achieved by limiting initial timing and centrifugal advance to less than previous non-emission controlled engines. The centrifugal curves are also typically very lazy.

In some cases excess vacuum advance was used to offset the above at cruise, but the bottom line is that the entire spark advance map was set up to achieve emissions requirements, not performance or fuel economy.

What you basically have is a stroked L-36 with lower compression and open chamber heads, but the same camshaft.

Both the open chamber heads and lower compression can probably use a little more advance under most operating conditons than a '66 L-36, but this is a good place to start. To achieve this you will need to grind out the slot in the autocam to increase total centrifugal advance to about 28-30 degrees, and change springs as required to get it all in by 2500-3000. Change the VAC to a B20 with full time manifold vacuum, and with the initial timing set to 6-10 degrees you will have near optimum total idle advance and near optimum total WOT advance. The maximum will probably be limited by detonation if you are using unleaded regular (which that engine was designed for), so you basically run as much initial as the engine can tolerate without detonation. If you use premium you will be able to run more initial before you get into detonation - perhaps up to 12-14 degrees.

Discussions about tuning and optimizing the entire spark advance map, which may involve changes to the centrifugal and vacuum advance systems in addition to intial timing changes are sprinkled thorughout the archives.

Duke

[Robert B.]

Re: 1972 LS5 maximum total timing advance?

Thanks for the response. Good advice. I will search the archives.