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Ignition idle advance
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flc
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PostPosted: Mon Aug 02, 2021 12:40 am    Post subject: Ignition idle advance Reply with quote

Hi folks , so a question on setting up idle advance on a billet pertronics distributor. My fresh built engine spec first
2109cc 5.5 rods
Scat super d heads 9.7:1 compression
44 idfs match ported manifolds
1 5/8 merged
Light flywheel (dpr) and 5lb pulley
Fk8 1.4 aa rockers
So initial static set up of the ign was just to point to number 1 and crank her over , advancing until it fired up and did cam burn, left to cool overnight,oil change valve clearance etc.
Once all that was sorted warmed her up and did initial lean best idle , then checked the timing was at 20 degrees at idle! But runs sweet? I set the distributor up to run 28 @3500 rpm and 8 idle and it will only just start, needing least 15 degrees to to even think about running, it’s currently set at 18 ish as a compromise, no issues cranking or any sign of ping, can this be right? Everything feels good but the number just don’t make sense? I did see this on air cooled.net which does agree with my findings. Anyone found the same thing?
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oprn
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PostPosted: Mon Aug 02, 2021 3:02 am    Post subject: Re: Ignition idle advance Reply with quote

I found the same sort of thing on initial start up of the mostly stock engine I just built but once it ran a bit it accepted a lower initial advance quite readily and is now idling very nicely with very good throttle response at 10* BTDC. I think on initial start up the rings are not sealing good enough to get proper combustion pressures resulting in what you and I discovered. Give it a run or two with a good load and I think you will find it changes.
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UK Luke 72
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PostPosted: Mon Aug 02, 2021 3:44 am    Post subject: Re: Ignition idle advance Reply with quote

I've found with EFI and the ease of tweaking it provides, 17º is about right. For my 2276 that is.
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Ohio Tom
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PostPosted: Mon Aug 02, 2021 4:41 am    Post subject: Re: Ignition idle advance Reply with quote

nothing wrong with 20deg at idle.

I have found you don't have starting problems until more than 24deg.
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flc
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PostPosted: Mon Aug 02, 2021 7:53 am    Post subject: Re: Ignition idle advance Reply with quote

Thanks for the responses everyone,food for thought. I give it a go ,then see if it still wants the same advance after the rings have bedded in a bit.
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mark tucker
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PostPosted: Mon Aug 02, 2021 8:28 am    Post subject: Re: Ignition idle advance Reply with quote

I set idle to 14-16 degrees. clean smooth low rpm idle. I would shit can the 5lb pully and put a light aluminum or oe pully on. heavy pullys are very hard on crankshafts and known to break them. if you need weight add it to the power out put end only( flywheel) or else your just twisting the crank back and forth.
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buguy
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PostPosted: Mon Aug 02, 2021 9:13 am    Post subject: Re: Ignition idle advance Reply with quote

With my efi i think I'm at around 18 degrees and around 850-900 rpm.
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maui
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PostPosted: Thu Aug 05, 2021 3:51 pm    Post subject: Re: Ignition idle advance Reply with quote

My 2500cc engine is at 12 and 34 total and 1000 idle and I have a 5lb pulley for 20yrs now no problem and last rebuild for the crankshaft I got 70000miles and main were really nise so up to you on that.
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Alstrup
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PostPosted: Thu Aug 05, 2021 4:11 pm    Post subject: Re: Ignition idle advance Reply with quote

The poorer your idle mix quality is the more tim ing ity needs at idle.
The weaker the spark/ ignition system the more timing it needs.
The more cam duration the engine has the more timing it needs at idle.

If a dual carbed 2 liter plus engine with an FK8 needs 16-18 degrees idle timing to have a decent idle, somethings wrong.
With an FK89, different story.
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UK Luke 72
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PostPosted: Fri Aug 06, 2021 5:39 am    Post subject: Re: Ignition idle advance Reply with quote

Alstrup wrote:
The poorer your idle mix quality is the more tim ing ity needs at idle.
The weaker the spark/ ignition system the more timing it needs.
The more cam duration the engine has the more timing it needs at idle.

If a dual carbed 2 liter plus engine with an FK8 needs 16-18 degrees idle timing to have a decent idle, somethings wrong.
With an FK89, different story.


Makes sense. My Injectors are poorly placed for low air speed and my idle afr proves it!
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FreeBug
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PostPosted: Mon Aug 09, 2021 1:00 am    Post subject: Re: Ignition idle advance Reply with quote

Again, Black Box: my cranking advance is something like 6°, until you're over 600 rpm, where it jumps to 12°-ish, I don't have the numbers at hand, but that's the gist of it. Seems to work well on the bench
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Lingwendil
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PostPosted: Mon Aug 09, 2021 10:19 am    Post subject: Re: Ignition idle advance Reply with quote

I've mentioned the Dayton TCS-1 timing controller before, but it may be worth looking into. Once my engine is running I plan to play with it a bit.
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King_vw61
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PostPosted: Mon Aug 09, 2021 11:28 am    Post subject: Re: Ignition idle advance Reply with quote

The MSD power grid does all this also. Piggy backs on the older MSD boxes. Not sure if it works with other brands.

I upped my timing to 20 at 1000. Then dropped it to 17 to 31 for the curve. Under 600 is 10 for cranking.

Super smooth.
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flc
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PostPosted: Mon Aug 09, 2021 1:20 pm    Post subject: Re: Ignition idle advance Reply with quote

An update on this, after running it for a while and a few laps of the block , the timing has come down now to around 8-10 degrees, I have followed the advice on the afr thread and set the tick over using the distributor and not the idf idle screws and it’s better and now the Final tuning can start
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