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Discussion Starter · #1 ·
So I'm about to finally get to cranking my motor up and setting timing here soon. I've got a Holley 4160 carburetor at 650CFM and I adjusted my transfer slots (which were way off) as suggested on this forum and plan to get my mixture screws adjusted to max vacuum once timing is set. Anyway, My question is how to determine what my motor likes in regards to ignition timing? How do you get to this assumption? Is there a specific tool and/or way to test and see what the motor likes (initial timing, curve, and total timing)? Y'all suggested 18-22 initial for how my motor is set up, but how did y'all come to this conclusion?
350 w/ 9.64:1 CR static, 232 duration at .050" mechanical flat tappet cam, .528 lift int/exh.
 

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Anyway, My question is how to determine what my motor likes in regards to ignition timing? How do you get to this assumption? Is there a specific tool and/or way to test and se lie what the motor likes (initial timing, curve, and total timing)?
I like to refer to the Demon selection guide.
Demon Fuel Systems
The chart that comes up is for Mild Cam profiles. Ignition advance needs are shown at the far right of the page.

In the middle of the page are 3 tabs. Click on the other tabs, Performance Cam Profile and Radical Cam Profile to see ignition timing for other cams on the far right side of the page.....

As far as total timing, that would be determined by the combustion chamber design and use of the motor, supercharged?, Nitrous?, gears?, car weight?, street only?, street and strip? Generally you will not get into trouble on a naturally-aspirated street motor with total timing if you limit initial + centrifugal to 34 degrees with current combustion chamber designs. Older chamber designs will require more advance.

These are guidelines, your motor may need more or less advance to operate properly. Back to back drag strip passes will make the job of finding the "sweet spot" easier.

Purchase a spark plug reading magnifier and light and learn how to read plugs. You will be worlds ahead of your buddies if you can intelligently read spark plugs....
https://www.google.com/search?q=rea...Fspark-plug-reading-light-2441.html;1200;1200
http://www.dragstuff.com/techarticles/reading-spark-plugs.html
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp
http://members.uia.net/pkelley2/sparkplugreading.html
http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm

In order to read plugs effectively, make a full, hard pass and click the ignition, coasting to a stop. DO NOT RUN THE MOTOR UNTIL YOU HAVE READ THE PLUGS. Idling back to the pits will ruin the plugs for reading the full power pass.

.
 

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Discussion Starter · #3 ·
Hmm. Thats a helpful tool. It's recommending for my set up 16* initial. Which is definitely a helpful too, but I just can't understand how or why that number is determined. Idk maybe I'm just getting technical, but I like understanding how things work. Is this just one of those things that are experienced over the years through trial and error and thats how these numbers were determined?
 

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Discussion Starter · #4 ·
0h sorry about that techinspector. Im looking at this thread on my phone and it didn't load the rest of your reply. I appreciate the info! That is good stuff.
 

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The engine will not start at 16* initial advance even with compression ratio as low as 9.64:1.

Start the engine with the initial advance at 10* degrees BTDC withg the distributor vacuum disconnected and the vaduum source plugged. Advance the initial timing two degrees, and restart the engine. Do that until the engine is difficult to start and then back the initial advance down two degrees. After that procedure, you will find that 12* degrees initial advance is best with stock distributors and the factory recommended heat range spark plugs. When adjusting the initial advance, adjust the idle speed screw until the engine idle RPM is as low as possible or at least less than 800 RPM. After the initial advance is set, reconnect the distributor vacuum cannister and readjust the idle.

Long duration racing camshafts with low vacuum may not idle below 1000 RPM (throttle plates closed). If that kind of camshaft is what you have, disregard all of the above. Then ask yourself "Why am I asking how to set the initial advance if I have a racing engine."
 

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Discussion Starter · #6 ·
Hahahaha no no, not race cam... it's a nice street cam (with too much duration for my build). I don't have a stock distributor though, it's based off an AC delco, but with all new MSD internals (springs, weights, coil, cap and rotor).. even with that you still don't think I'll be able to get it started with 16 initial?
 

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The engine will not start at 16* initial advance even with compression ratio as low as 9.64:1.

Start the engine with the initial advance at 10* degrees BTDC withg the distributor vacuum disconnected and the vaduum source plugged. Advance the initial timing two degrees, and restart the engine. Do that until the engine is difficult to start and then back the initial advance down two degrees. After that procedure, you will find that 12* degrees initial advance is best with stock distributors and the factory recommended heat range spark plugs. When adjusting the initial advance, adjust the idle speed screw until the engine idle RPM is as low as possible or at least less than 800 RPM. After the initial advance is set, reconnect the distributor vacuum cannister and readjust the idle.

Long duration racing camshafts with low vacuum may not idle below 1000 RPM (throttle plates closed). If that kind of camshaft is what you have, disregard all of the above. Then ask yourself "Why am I asking how to set the initial advance if I have a racing engine."
Sorry, I have to disagree on this......a good battery, clean and tight connections and a good starter will have no issue with 16* initial. And a cam with 220-240 duration isn't a "racing cam" by any stretch. I spent most of the summer with a 234/244 cam with 20* initial and a factory GM mini starter with zero starting issues. That saw the track a few times and the commute to work daily. Idled at 1000 in park and 800 in gear happily.
In reality I have never had an issue starting anything with 14-20* initial timing other then my Vette which was a wiring disaster. Once that was fixed it worked best at 16* and again no starting issues.
 

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Discussion Starter · #9 ·
Well I guess the only way for me to know is to try and start the damn thing haha. I do like those links on reading plugs though... that's good stuff. That's getting bookmarked and used for sure.
 

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It depends on what you are calling "initial" advance. Do not include the centrifugal advance with the initiial advance setting. The centrifugal advance starts advancing the initial setting at 950 - 1000 RPM by the spinning counterweights in the distributor. There are three settings you should be concerned with ....initial without any vacuum or centrifugal advance and total with full centrifugal advance added to the initial advance.

Defination of Initial ... "Occurring at the beginning".
Synonyms: starting, commencing, first, early, primary
 

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It depends on what you are calling "initial" advance. Do not include the centrifugal advance with the initiial advance setting. The centrifugal advance starts advancing the initial setting at 950 - 1000 RPM by the spinning counterweights in the distributor. There are three settings you should be concerned with ....initial without any vacuum or centrifugal advance and total with full centrifugal advance added to the initial advance.

Defination of Initial ... "Occurring at the beginning".
Synonyms: starting, commencing, first, early, primary
What I'm referring to is initial, at 850rpm, before the centrifugal begins to come in. I'm aware how the advance works and when, and without starting an argument, im simply saying that your inncorect in your statement that the engine won't start with 16* initial. There's dump trucks full of things I don't know, but this isn't one of them.
 

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This is my experience and how I set up my stuff for basic timing. Before I even setup anything I always go over to make sure before I put my distributor in that its indeed on 0 TDC then I put the balancer on 10 BTDC and then put the distributor to point the towards the terminal I want for the number one cylinder. Then after getting it down all the way I put the cap on and hand turn it back to make sure it lines up correctly with the cap.

Then I hook all the spark plug wires up and double check they are all correct in firing order then I just snug the distributor down. Now on the carburetor I completely back off the primary idle screw to where no transfer slot is showing and the idle screw is not contacting the butterfly linkage then I slowly turn it to where it just makes contact then I look to see how many turns it takes to get to where .020 of the transfer slot is open and mark that down on paper. Then I set the secondaries in similar way but it depends on how big your cam is etc on how much of the rear will be shown and if its a double pumper or vacuum secondary as the transfer slot on the vacuum secondary carbs sit up higher then the front.

Its a trial and error thing for that depending on your engine etc. I usually set it at a half turn past contact on the secondaries for a holley vacuum secondary. Then I put the idle mixture screws at 1 and a half turns out from seated position and also dry set my floats according to holley specs. Then after checking everything over and making sure the carb is primed with fuel I proceed to get the engine running and if it turns over a little slow then it needs more advance so just advance the distributor a little till you get it running and to stay running you might have to give it a few shots of gas and if your choke is hooked up that will help some too.

After it gets warmed up and the choke is off then if you need to adjust the primary idle make sure you note how many turns you opened it up or how many turns less so you know where your throttle blades are in relation with the transfer slot. It varies but most say no more then .040 at the most for transfer slot exposure and some books say less but nothing more then that or other issues will happen. After getting running to a steady idle below 1000 if your cam is not too big then make sure the vacuum advance is disconnected and aim your timing light at your timing tab and if your balancer does not have timing marks then you can make your own but I don't know the link but Techinspector1 does.

I then get the timing pretty close as possible to where it sounds good and revs good and has a steady idle then proceed to do minor carb adjustments such as the primary idle and the idle mixture screws and that is where carb tuning comes into play and making sure you note where your primary idle speed screw is in relation to the transfer slots and that is why I mark down how many turns either way I go as I try to get the idle mixture screws set as best as possible along with the primary idle screw to stay in relation with the transfer slot and then crack open the secondaries a little more if needed or close them but always try to keep the primaries correct. Then there is hooking your vacuum advance back up to either ported aka timed port which is on the primary metering block or full manifold which is at the base and that in itself depends on what your engine needs and that is a whole other topic there. I use about 12 degrees for vacuum advance setting with an adjustable canister that you can get from summit or jets unless your distributor already has one. I use full manifold for my builds but its a trial and test deal.

As far as how much is enough and what you engine needs it all differs on what your setup is such as compression cam etc. The link from demon carburetors is a general starting area but you will have to fine tune it your self to what it wants and needs. And a great deal of great info has already been posted to get you started in the right direction.
 
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