View unanswered posts | View active topics It is currently Wed Jun 28, 2017 11:52 am

Reply to topic  [ 2 posts ] 
 Locked ignition timing 
Author Message

Joined: Wed Jan 29, 2014 12:00 am
Posts: 61
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?

Mon Feb 13, 2017 9:49 pm
Site Admin
User avatar

Joined: Fri Feb 08, 2013 5:50 pm
Posts: 2305
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
Display posts from previous:  Sort by  
Reply to topic   [ 2 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF.