Octane vs. spark advance % of reduction

[51caddyman]

Hey, all you masters of EFI,
A little background info here first... My car: 1951 Cadillac Series 62: SBC 355 ci; AFR 190 Votec heads; Lunati Hydro-roller cam: Advertised Duration (Int/Exh): 282/290, Duration @ .050 (Int/Exh): 231/239, Gross Valve Lift (Int/Exh): .535/.550, LSA/ICL: 110/106; 10.97 to 1 CR; Holley Terminator EFI; GM small cap style dist. with full CPU spark control. I'm taking this car on a 3,300 mile road trip from Denver to San Fran and back. I'm going out on US 50 (loneliest Highway in the states) and US6. Here is my worry: IF I can't find super unleaded at some of these stations along the way (200 miles between services for a lot of the trip so I can't get "picky" and just wait 'til the next station, 'cuz I'll be walking with a gas can for 100+ miles). I'm setting up spark maps that pull 1/2* of timing for every 1000 ft of ALT I drop... BUT I have no idea how much I would need to retard the spark if I could only get "regular" gas in lieu of "super". Does anyone know the amount of * of retard required per each full # of R+M/2 octane method drop? I do not have a knock sensor as my cam is so high lift if would send a knock sensor off the deep end if I had one attached (Yes, I have heard of some being able to tune a knock sensor, but I'm leaving tomorrow and will not have time to go that route). So what's the magic formula? Please educate me! Thanks!!!

[Skinny Pedal]

How much timing are you running? Care to share the global file?

[51caddyman]

How much timing are you running? Care to share the global file?

Quite a bit:
26.0 to 49.4

27.2 27.2 27.7 29.2 31.2 32.8 33.8 34.3 35.4 36.9 36.9 36.9 36.9 36.9 36.9 36.9
27.2 27.2 27.7 29.2 31.2 32.8 33.8 34.3 35.4 36.9 36.9 36.9 36.9 36.9 36.9 36.9
27.2 27.2 27.7 29.4 31.4 33.3 34.0 34.8 36.2 37.8 37.8 37.8 37.8 37.8 37.8 37.8
26.6 26.6 27.1 29.6 32.2 35.1 35.9 36.3 37.6 39.4 39.4 39.4 39.4 39.4 39.4 39.4
26.0 26.0 26.5 30.4 34.0 37.0 37.2 37.6 39.1 41.0 41.0 41.0 41.0 41.0 41.0 41.0
26.0 26.0 26.5 31.0 34.5 37.3 38.4 38.3 39.9 41.9 41.9 41.9 41.9 41.9 41.9 41.9
26.0 26.0 26.5 31.4 35.1 37.9 39.5 39.8 40.8 42.9 42.9 42.9 42.9 42.9 42.9 42.9
26.0 26.0 26.0 32.0 36.0 38.9 41.1 41.9 42.9 44.6 44.6 44.6 44.6 44.6 44.6 44.6
26.0 26.0 26.0 32.4 37.4 40.5 42.7 43.0 45.2 46.2 46.2 46.2 46.2 46.2 46.2 46.2
26.0 26.0 26.0 32.8 38.4 43.1 44.7 46.1 47.3 47.7 47.7 47.7 47.7 47.7 47.7 47.7
26.0 26.0 26.0 32.8 39.1 45.3 47.6 48.5 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4
26.0 26.0 26.0 32.8 39.1 46.3 49.1 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4
26.0 26.0 26.0 32.8 39.1 46.3 49.1 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4
26.0 26.0 26.0 32.8 39.1 46.3 49.1 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4
26.0 26.0 26.0 32.8 39.1 46.3 49.1 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4
26.0 26.0 26.0 32.8 39.1 46.3 49.1 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4 49.4

[Skinny Pedal]

Whats the base timing on the dizzy? Gonna guess around 20 - 25......

Whats your cruising RPM and KPA? Whats the AFR table look like? Are you going to modify that based on octane?

[51caddyman]

yep 24* is where the dist is set. As it's the Holley Terminator the CPU auto adjusts up to 200% to keep AFR dialed in at my set AFR requested rate (14.1 on cruise to 12.7 WOT target AFR's) so I had not planned on messing with that table as the CPU will adjust and "learn" by re-setting the fuel table per the input from the WBO2. However if needed I totally can do an adjusted file for fuel. fuel table attached.
Attachment 9351

[51caddyman]

Oh yeah, Cruising RPM 2400-2800 RPM @ 75 MPH 56 KPA on the MAP.

[Skinny Pedal]

I know the holley adjusts but remember that you modifiers like AE are based off commanded not whats being modified. I don't know how far along you are with the tune is the only reason I bring that up. Using the Holley setup I have seen AFR spikes in transitions, just want to make sure you don't lean spike and induce some ping that way.

I know its debatable but I run engines a little richer than that WOT to help with the ethanol factor. Now that thats brought up it also changes your timing....

So you are cruising at basically 40 degrees. I usually cruise between 35-40 degrees myself. LOL

In reply to a magic formula for timing vs octane..... I have always treated it on case by base, which includes rigs specs & intended use & engine build.

[51caddyman]

I've been working at 5500 Ft tune now for 2 years 24,000 miles. I once a week flash back from the ECU to the HP tuning system, and re-set the base to the learned table via the "easy" button on the fuel learn delta table. For the trip out I re-set my spark table to be smoother and took out my "traction control" reduced S/A where my 3000 stall TC stalls, as I swapped my 245 45 R 20's for some original size tires and 15" rims and hub caps. This set of tunes is just for easy driving and fuel economy - that's safe for my motor. I already have my hot drag race and autocross tunes at my 5500 FT dialed.

[Skinny Pedal]

So why keep the auto correction so high if the fuel is dialed in? Usually with the holley setups I start coarse and then once everything is all good I bring the overall correction way down. That way if I lose a sensor or a wideband, it has happened with our type of environment, that way the ECM cant over correct for a bad sensor.

That's the down fall of the Holley setup, nothing seems to fault out when out of range. Only faults out when dead.

I'm just curious, not saying its right or wrong.

[51caddyman]

Well if I was staying here, at 5420 ft, and knew I had access to all the super unleaded as I do now, I agree. The issue at hand is that I need to know, just in case, if I can't get super along the way, (as I already have spark maps, based off my very dialed daily driver tune plus the road trip "smoothing", set to each 1000 ft of alt change) how much more advance do I need to remove per each full point of octane. I.E. If I get to Ely NV (4000 ft) but can only get regular octane, not super, do I pull 1* per 1 point of octane lost off super (from my 4000 ft tune)? 1/2*? I don't mind trading a little MPG for safety, I don't want to blow my 15K invested in my motor and get stranded just because I didn't get enough spark retard, due to fuel availability, nor do I want to take too much away and go over my $1400 fuel budget for all 3,300 miles. Also I'm taking my wife with me, I don't want to end up murdered and buried in the desert because I talked her into taking this car and I blow it up in the middle of nowhere. ;)

[51caddyman]

Note: I really don't think my wife would murder me; just trying to be funny... That said, I did a lot of smooth talking to make this "bucket list" dream come true... Taking the old stagecoach route in my classic caddy (my all time favorite car), then all the way down the PCH from SF to SD, and then to Las Vegas for a rat pack style evening in sin city. Other than taking the caddy all the way around the world (when I retire, if political reality and $ allow) and down to Jazz Fest in New Orleans (in the next 2 years) is going to be among the greatest times of my life. I'm a total history nut, so this is just about as good as life can offer for me. The wife, on the other hand, respects my craziness, but doesn't have the same level of tolerance that I would, spending time messing with tuning along the way. What I want to do is take all your vast and amazing understanding of EFI (this site is amazing, if it weren't for Gearhead EFI, * Eaglemark, I can't thank you enough for helping me back when I was running the GM TBI setup on this motor, you posts and PM were a game changer for me; I'd be nowhere near as competent). Moral is, I just want to make the best tunes I can for all things that "might" happen, and be as prepared as I can.

[Skinny Pedal]

I know when I tune a rig with dual timing tables, high octane and low octane. I take my best timing and pull 5-7 degrees for the low octane table in the load areas. Thats not for low buck stock stuff either.

Your engine isn't too hot to where it would be super picky, so I couldn't see where more than 1-1.5 * per point would be needed. Plus with that cam size more timing will be needed any way. You also seem to have a good gear ratio to keep you in the correct load range for that engine.

Sorry I can't be of much help for a formula. Every engine is just too different. Hell, I've had a few that didn't care what fuel I put in them and I have had some that wanted fuel from one place only.

[51caddyman]

LOL, so true... Once I was forced to put some mid grade in the caddy, (at that time my fuel gauge was not hooked up yet and ran out of gas as I pulled up to the pump) and drove it 20 miles until I could find a Shell station that had my preferred blend of Super, and never felt a knock. I'll use 5-7 as a base point. That's what I needed to know, a good starting point so, if needed, I can tune fast at an gas pit stop and make it 200 miles to the next station, without dropping too far from 22-24 mpg hwy (like to 6.5 mpg when my TPS died) nor shooting pistons through my hood. As stated above... Gearhead EFI guys, you ROCK! Thanks so much! Keep your fingers crossed from me on this EPIC adventure I'm embarking on! I'll let you all know how it goes. Thanks Again - Paul

[ony]

caddyman have you got an oil temp gauge on your engine?

[51caddyman]

nope, just water temp, but have a 6 qt pan.