Is a lot of initial advance a crutch for low compression?

[Mebsuta]

For 68 RR with 383 4 spd, factory pattern cam, pistons with original HP compression height, 902 open chamber heads, no cutting or milling, blue Fel Pro head gasket, I get around 150 psi cranking compression cold with the throttle open. I always just tuned it by the book and set the initial at 8-10 degrees BTDC. Got to reading and tinkering and think it runs better with 16-18 initial. It's more responsive down low. However, if you do that the total is about 40 BTDC, which is supposed to be too much. It's real easy to start like that and I don't hear any pinging or detonation (how could I over the ancient and leaky headers). If I leave it at 18 BTDC initial I will go in and limit the total to 35 or so.

Question is why would it seem to run better with all that initial advance if the books and manuals were telling you something else? Is all the advance a crutch for low compression? Why wouldn't they just set it up like that to begin with from the factory?

PS - You know what? Years ago when I used an Isky 270 Mega cam (108 LSA) and 906 heads, car would rattle and diesel unless you used 91 or 93 octane. Now with the 902 heads, 115 LSA cam, and all the ethanol in the gas, it will run on 89 and even 87, although I don't like to do it. Cranking compression was about 160 psi with the Isky and 906 heads.

 

[mattsmopars]

You have to think the manuals were written when leaded 100 plus octane gas was common. The last 383 I built was 9 to 1 compression ratio with standard flat tops and 915 heads with felpro gaskets. It liked 16-18 initial timing and about 36-38 total. Had a small Hyd. Cam in.
Seems most factory 383 have the piston .050-.060 in the hole so that and the open chamber heads drop the compression down so I would say that the reason it likes more timing.
Matt

 

[Kern Dog]

I think that the tuning specs stated in the factory manuals were conservative. The settings were meant to provide a balance of emissions compliance, fuel economy and power.
Regarding your first question, My experience is the opposite. An engine with a more aggressive cam needs more initial timing to run right. It isn't uncommon to see 17*-20* in a performance engine. I run 17 degrees and could use more, but cranking it up puts me into detonation when all the mechanical advance comes in.

 

[eric383]

Don't be afraid to advance the timing. See how it runs and if it starts to rattle back it off.