Stock timing curve/advance

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Gregs672000
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Stock timing curve/advance

Post by Gregs672000 »

OK, another question... does anyone have the stock ignition curve for a U20? I've reviewed the manual and it's clear as mud. From what I can tell it adds 14-16 degrees at 1900rpm (!) starting from 16 degrees at 600rpm. That is waaaaaay different from what a typical curve would be I believe. I've been trying to get on the dyno here for weeks, and there's no open slots at ANY of the shops I've called. Several months out at where I've been going before (Turbo Technology) and I wanted to stay with the same dyno, but now I'd take it anywhere. To that end, I've been working on my timing map it bit due to some knock under high load on a hill in 4th gear between 2500-3500rpm, and I want to optimize it everywhere, and more importantly make it fully safe. Cranking compression is now down to 210lbs from 220lbs after I had the pistons machined to lower compression (maybe not enough). With data logging I've figured out what is "cruise" load and what is higher demand loads, and pull out several degrees under high loads. I also backed my initial timing down from the "Solex recommended" 20 degrees initial to 17. I reviewed an advance curve by Dave Andrews for "modified" engines (I think most of his work was with 2liter Ford Pinto motors, also used in Formal Ford race cars) and based it off of this and my previous experiences. I have no idea what his compression ratio was however. This is what I came up with...

Current curve
"cruise" load: higher load
1000rpm: 17 17
1500: 19 19
2000: 23 21
2500: 27.5 22.5
3000: 32.5 24
3500: 37 26.5
4000: 37 30
5000: 37 31
The controller progressively pulls timing the more load increases, with specific target points per each identified load/rpm set by me.

I currently pull a fair amount out under load, especially with the hotter weather we have had. I plan to run it on 92 octane with this curve, and adding a bit of Boostaine to bump it to 95-96 in temps above 80 degrees (only takes 2 ounces in 10-11 gallons, Love this stuff). You typically want to run more advance under light loads for fuel economy. I currently have the controller targeting 14.7 at light/cruise loads (13.3 at high loads), and have improved fuel economy from 24mpg with carbs to 27mpg with EFI consistently (with more power no less!), and saw 29mpg last trip (anomaly?).

Anyway, if someone has actually mapped the stock curve and can post, that would be greatly appreciated.
:smt006
Greg Burrows
'67 2000 #588
Tacoma, WA
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theunz
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Re: Stock timing curve/advance

Post by theunz »

Greg, have you tried listening with a stethoscope? They really amplify sounds.

Oops, wrong thread😱
Last edited by theunz on Thu Sep 01, 2022 10:17 pm, edited 1 time in total.
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Re: Stock timing curve/advance

Post by Bwk2000 »

Maybe go back to a previous tune that you know worked well for you before (link below, page 2) and use that as the new baseline to work from 🤔
At any rate, there is an ‘almost’ stock B-Cam U20 curve listed on page 1 as well.

viewtopic.php?t=29035
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Gregs672000
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Re: Stock timing curve/advance

Post by Gregs672000 »

Bwk2000 wrote: Thu Sep 01, 2022 7:34 pm Maybe go back to a previous tune that you know worked well for you before (link below, page 2) and use that as the new baseline to work from 🤔
At any rate, there is an ‘almost’ stock B-Cam U20 curve listed on page 1 as well.

viewtopic.php?t=29035
Wow, embarrassed to say that I've clearly forgotten so many posts... thanks for digging that one Up! I compared the map that was posted to what I'm running now, and other than max timing at 40 under light loads and high rpm, it's pretty close. As noted, my engine is much higher compression, which is problematic. The previous map I posted back then knocked heavily on the dyno before I was EFI.
Greg Burrows
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Tacoma, WA
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Gregs672000
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Re: Stock timing curve/advance

Post by Gregs672000 »

I'm just wondering what a stock curve would look like if it were profiled on a distributor machine.
Greg Burrows
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Tacoma, WA
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Re: Stock timing curve/advance

Post by unklpat »

Greg, it's fairly easy, but not precisely accurate to map your timing curve with a dial back timing light. I can do my "b" cam profile once my motor runs. Stock distributor. Hopefully within the next few days. Pat
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Gregs672000
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Re: Stock timing curve/advance

Post by Gregs672000 »

Well, let's hope this engine gets fired up soon Pat! I know you have been waiting a very long time.
Greg Burrows
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Tacoma, WA