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 Locked ignition timing 
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Joined: Wed Jan 29, 2014 12:00 am
Posts: 64
Hello Everyone,
Lately, I've been contemplating going back to mechanical advance in my ignition system (drag car). For the past several years I have gone along
with the majority and locked out my ignition timing (36 degrees total). It has not been an issue really, I have never had the engine kick back hard,
requiring a start retard. But after reading some posts by Shrinker on Motorsports village, where he explains how he does not recommend locked timing, and
seeing some videos on youtube, I am now thinking about going back to an advance curve.

Shrinker stated that an engine with locked timing, always wanted a leaner fuel mixture (slower burn) at idle.
He also mentioned that if your engine ran better with locked timing, the engine must have had low vacuum at idle and therefore poorly vaporized fuel in the cylinders (large droplet).
Idle horsepower would go up, and rpm drop when placed in gear would be less with less timing at idle.

What I found interesting was the video stated that too much timing at idle, would promote a large amount of HC's in the exhaust, because the
charge is not compressed enough to completely burn (flame goes out).
Perhaps this could help reduce fuel in the oil (especially methanol).

To me everything points to reduce ignition timing at idle as a win/win. Unfortunately, it is still cold and won't be able to test this for a least another month.

I am curious to see how the idle vacuum is affected..
Has anyone here performed a back to back test on this and compared idle quality?


https://www.youtube.com/watch?v=SAApLek5hQo


Mon Feb 13, 2017 9:49 pm
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It really depends on the engine and car combination. Engines with low vacuum at idle and low RPM's, big cams, can benefit from more timing at idle and low RPM light loads. Low vacuum at idle and low speeds will not vaporize fuel as well, takes longer to burn as a result, needs more timing to make it up. How much more depends on the combination and the volatility of the fuel With real large cams and converters with high stall you typically need all the timing you can get at idle, I even add timing with a digital ignition, take it out about 4000 RPM before the engine sees any significant load. Works like a vacuum advance in a way. And speaking of vacuum advance, it adds timing at idle and low load conditions, even on engines that have high vacuum at idle. the only reason to reduce timing over what it needs for optimum power in the RPM range you race it at is if you run it at heavy load at lower RPM. A stick car may see some benefit, or an engine with insufficient octane, but will still need a load controlled timing, vacuum or MAP controlled advance to have sufficient idle and low RPM light load timing.


Tue Feb 14, 2017 1:50 am
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Joined: Sat Feb 09, 2013 10:46 pm
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The newest HOT ROD magazine had a good article on timing advance. In it they described the effects of vacuum advance under low load, lead mixture conditions.

Until I began to run the car I have now I always ran a mechanical advance. My previous ride had an 817HP R&M 502 in it with 14:1 compression. I did this digitally with an MSD 7AL and an MSD 8979 Multi-Function Ignition Controller (no longer available). It was a simple curve really. Eighteen degrees on the crank and the Ignition Controller returning 2 degrees, starting at 1000 RPM, every 100 RPM until 3000 RPM for full advance. Please note this car had no crank trigger and used a Mallory distributer. Also, I wasn't a carb junkie then. Something the carb on that 502 helped change.

My current car didn't have the capability to do this, it just had a 7 AL3 and a crank trigger. I installed a Dig 7 Programmable a couple of years ago. Now, I'm considering adding a curve of some sort when we run Super Street. When I can use the MSD to program a curve based on RPM I need to investigate if I can do it based on time.

So, given that I want to use an ignition curve in Super Street, can the all knowing hermit Yeti come out of his cave to answer the questions of this mere mortal? When the engine is in cruise phase on a Super Street run do we add timing or reduce timing? The RacePac tells me that @ 3400 RPM we run a relatively high HG and rich mixture. Will additional timing on cruise lean the mixture out?

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Mon Jul 10, 2017 4:32 pm
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Image

Yeti says, "Mortals are too tedious to trifle with."


Mon Jul 10, 2017 10:53 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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Use a MAP sensor and add some timing when the vacuum is high at part throttle.


Tue Jul 11, 2017 10:40 am
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Joined: Sat Feb 09, 2013 10:46 pm
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yeti wrote:
Image

Yeti says, "Mortals are too tedious to trifle with."


That's cute.

Add timing at cruise is what I thought but, wasn't sure. Thanks for clearing that up. The fact that the OP is a racer too is what made me wonder about all of this. After all, drag racing for the most part has two throttle positions. Idle or wide open. We Super class racers, on the other hand throttle down and then throttle up. There may be a positive result from adding timing during the cruise phase.

I'll report back on the results.

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Tue Jul 11, 2017 2:46 pm
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Vacuum advance on circle track and road race cars lets them cool down on yellows instead of heat up. They loose cooling air because of going so slow just rolling around behind the pace car and usually get hotter than when they were running at speed. This is usually why you see an engine pop shortly after a restart, it got hot when it was going slow.

The added timing at part throttle will improve throttle response during the transient when going back to WOT.


Tue Jul 11, 2017 3:30 pm
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Worked out a timing curve I think will work. Normally we run 37* locked. We will continue to do that but, will add 8* during the cruise phase. The ignition will allow me to reduce timing at cruise if testing warrants it.

Just had this thought. I was planning to run a straight locked out curve for full throttle bracket racing and change curves as the type of racing changes. I think I'll go back over some old RacePak files and see how fast the engine accelerates through the cruise RPM when at full throttle. Maybe that will happen fast enough the engine won't notice.

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Mon Jul 17, 2017 4:41 pm
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Do you have a MAP sensor? I think the Digital 7 Programmable can use one. That's what you need to compensate for reduced load.


Thu Jul 20, 2017 10:14 pm
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