Total advance with 91 oct.

[allrightmike]

 The question is, with zero ethanol 91 oct. fuel, what range of total spark advance is advisable? I will provide background. 427 low riser engine & heads. Oversize valves, 10.7 comp. ratio, flat top pistons, minimal squish. Comp. #282S. 336 @ .050. Streetmaster intake, Holley EFI. 3900 lb. car, Wide ratio C6, 4.11 with Gearvenders OD. Street use occasional foot on the floor.

[My427stang]

Total WOT, likely 36-38 for best power, if computer controlled I would add another 8 at low load (cruise).  Also if computer controlled, having it crank at 10 and idle at 20 really helps vacuum and off idle response.  If standard distributor, I'd likely go 16 initial, 38 total, all in by 2800 with another 6-8 ported.

Iron heads usually like a bit more than most, but if quench is tight and compression is high-ish, you should be good at 38

I am not in a place I can run DCR, but you will be right on the edge if you have an accurately measured 10.7:1.

[allrightmike]

  Yes standard dist. I'll need to take some advance out as 12 initial nets 38 at this time. Will I have cooler running with some vacuum advance added? None vacuum at this time.

[cleandan]

A properly adjusted vacuum advance will net you better efficiency and cooler running.

Keep track of your spark plugs because the porcelain will tell you if you are detonating.

Get your total right first, then work with the initial so things start nice when fully hot.
After those are proven good then move onto adjusting the vacuum advance based on load and what your engine will like.

I like to find a long, steepish hill, where I can run with about 3/4 throttle (if an auto trans be sure you don't induce downshift) and I drive up the hill listening carefully for detonation and adjust accordingly until I am at max advance without detonation.

This usually happens by finding where detonation just starts to show itself then backing off 2* advance and testing again.

If you really want to test things put about 500 lbs weight in the vehicle for the uphill load test.

[Falcon67]

My 351C is 10.5:1, pretty good size hydro roller cam.  Best power/MPH is at 37.  There is no "non-ethanol" fuel around here.  It will pepper the plugs on straight pump fuel 91 at the strip.  I run no less than 50% VP110/91 pump.  So yea- runs to about $10.40/gallon right now.  Thats feeding from a wholesale 55 gallon drum of 110. 

[My427stang]

I ran the numbers and you are going to be where you don't want to be

DCR comes in at 8.35, although it's not a bad number with a real good tune and tight quench, it's on the ragged edge for an iron headed street car on a hot day or a bad tank of gas.

The good thing is you aren't far off.  If the engine is apart, you could retard the cam 4 degrees, which gets you to 8.07, and then I'd probably tighten up the valve lash a little.  I wouldn't go tighter than about .014, but take the specs they give you and go .004-.006 less.  It won't do a lot, but it's good for the valvetrain in general, and may add a 1/2 degree or so  to advertised duration, which the 427 will like.  Then, I'd set that at 36 total, let the initial fall where it is now, and see how it runs. I think in the end, you'd like 14-16 initial and 36-38 total, but feel it out

If you don't want to pull the timing cover, or if you didn't measure everything, (degree the cam, deck height, chamber size) and you used web numbers).  You are probably fine because chambers are generally bigger and pistons aren't usually zero deck, etc