Timing curve mild sbc 355

[Nick_nl]

SBC 355.
With a Lunati 60102 @0.050 219 int./227 exh.
The heads are the same Trickflow super 23 175cc head, resulting is 10.8:1 compression.
The distributor is a MSD 8360 locked out with a MSD 6530 doing the timing
The induction is a holley 1850-3 with a edelbrock 2703 intake.
No headers are used but 2.5inch rams horn manifold that should provide good flow.
The current timing curve is

During cranking 20⁰
idle 30⁰ from 400-800rpm
from 800 till 3000rpm it does increase to 34⁰

This way provides 15inch vacuum at idle.
There is also 10⁰ vacuum advance available.

This looks like a lot of timing at idle but the car runs good. Would this be normal for this combination?

[rgalajda]

15 inches vacuum in gear ( automatic ) or in neutral and what rpm?

[Nick_nl]

In gear its about 14" @550RPM. In neutral its 15" @ 650 but not super steady.
The Torque converter is 1800 rpm stall speed with ath2004R and 3.70 gearing with 26.1" tire height.
No knocking.
I have revised this timing already to
During cranking 20⁰
idle 24⁰ from 400-800rpm
from 800 till 3000rpm it does increase to 34⁰

Turns out i had the idle screw so far down it closed the transfer slots. That might explain the lean spot just above idle.

[rgalajda]

Timing Advance

Example 1: 9:1 compression RV cam 200@.050
5 degrees initial 32 total
mechanical advance comes in slowly
Vacuum advance : starts 10" --- total 18 degrees , giving 45 degrees ( to slow mechanical advance) at 2,000 -- 2500 cruise

Example 2: 9.5 - 10.5 compression larger cam 230@.050
mechanical advance comes on faster at first
10-14 degrees initial - slope to 30 degrees at 3000 rpm
34 to 36 total 4000 to 5000
Vacuum advance : starts 3-5 inches ---- total 14-18 degrees , giving 45 to 50 degrees ( to mechanical advance ) cruise
Total advance affects top speed more than anything.
Fast burn chambers require less total advance.
Sometimes manifold vacuum applied to distributor ( or to much advance at idle ) can cause the carb throttle plates to be closed too much.

I assume something like the above can be programmed to your MSD
Anyone have thoughts?

[Nick_nl]

Yes, this is possible. Except it works in reverse.
You first decide what the maximum total combined advance will be. => 44 deg in my case.
This is where you set the locked out distributor at.
The MSD box can only retard 30degr total.
Large image
You can just drag the dots to the correct value and ad extra dots as needed.

[rgalajda]

So you can't use the vacuum advance. You could use a map sensor (vacuum curve) comes in and retards timing as vacuum drops ?

[Nick_nl]

Yes that's exactly how its done. A GM map sensor can be used for boost retard and vacuum advance.
I have used a 1 bar map sensor to provide 10 deg advance.