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PostPosted: Fri Mar 12, 2010 9:49 pm 
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3 Deuce Weber

Joined: Sat Feb 13, 2010 8:37 pm
Posts: 78
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hello all

my mom was nice enough to purchace for me a timing light.
its the no frills inductive one from pepboys
[/img]?[/img]http://img.alibaba.com/photo/264640697/Inductive_Timing_Light_Actron_CP7527.summ.jpg[img]

I have never actually used a timing light yet - and have just set it by ear - but I would like to actually be able to do it correctly with the light.

I just hooked up a tachomater yesterday - so I have the ability to determine actual engine rpm to apply the correct advance amount per rpm I guess.

can any one tell me what the initial timing would be - and what rpm is concidered to be for it to properly be set -
and what rpm should the timing advance be "all in" and what full timing curve should be at all in - ( ex = 27 deg. btdc timing all in at 2500 rpm )


my car runs good right now - but is having some erratic idle qualitys in gear vs being in park - and the ocasional skipped beat if you will at idle at times.

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PostPosted: Sat Mar 13, 2010 5:52 am 
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Supercharged
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Joined: Sat Feb 16, 2008 1:25 pm
Posts: 5611
Location: Downeast Maine
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Welcome to the board brian72valiant,

That was nice of your mother to get you a timing-light. Oddly my octogenarian mom wouldn’t have a clue as to what one was, let a lone where to purchase such a device. LAL…

In order to help with your timing queries we will need to know a few facts about your car & engine build such as year, stock or modified & if so what modifications have been made, rear-end ratio, transmission, and intended use of car; daily driver, street & strip, race. You know the old Dragnet line: “just the facts sir, just the facts.

I’m sure SSdan will chime in with his highly recommended reading list of, “must haveâ€￾, books to fully understand, and perform repairs on your “Aâ€￾ Body.

My guess is it is a stock '72

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67' Dart GT Convertible; the old Chrysler Corp.
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07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

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PostPosted: Sat Mar 13, 2010 6:05 am 
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Turbo EFI

Joined: Tue May 17, 2005 4:26 pm
Posts: 1237
Location: CBS Newfoundland Canada
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a stock 225/6 should have 12degs btc with vacum advance disconnected at 750rpms. mark the damper using white-out to give a visible mark. total timing and vac advance is something you will have to work with for you engine, i make the slots in the dist shorter by welding them to get no more than 32degs total mechical, vacum advance i never played with much just to get a fair idle with a bigger cam but some here on this site have more tuning tip on that.


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PostPosted: Sat Mar 13, 2010 9:14 am 
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Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 24500
Location: North America
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Terry, that's not the correct setting for a '72. 12°BTDC types of settings didn't come along until about '76.

Brian, the correct setting for a stock '72 is TDC (0° advance at 750 rpm with the vacuum advance disconnected and the carburetor nipple plugged). There's a little leeway there; you can run a few degrees of advance — try about 3° BTDC — depending on the condition of the engine and the locally available fuel (and what spark plugs are used, etc.). Tune-up parts and technique suggestions are in this thread. The engine will need periodic valve adjustment. Buy the three books in this thread as quickly as you can and start reading!

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PostPosted: Sat Mar 13, 2010 11:58 am 
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Turbo EFI

Joined: Tue May 17, 2005 4:26 pm
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Location: CBS Newfoundland Canada
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i know by the book it`s not but he will find that the engine will peform better with that timing, with low compression more timing is alway better for performance and fuel economy.


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PostPosted: Sat Mar 13, 2010 12:05 pm 
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Joined: Thu Oct 31, 2002 5:39 pm
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Terry, I know you build a very impressive supercharged engine, but the advice you are giving Brian right now is faulty and -- for that reason -- not very helpful.
Quote:
i know by the book it`s not but he will find that the engine will peform better with that timing
Noooo, by reality your advice is wrong. With the '72 distributor he'll find the engine will ping with that excessive amount of base timing advance. That's if he knows what ping sounds like and knows to listen to it and can hear it over whatever other noise the car might make for whatever reason. If not, he'll be doing severe damage to his engine without even knowing it, all because he followed unsound advice.

Remember, the '76+ engines had high-volume EGR and retarded cam timing and other configuration aspects that tended to reduce peak combustion chamber temperature, which is why the extreme base timing advance levels like 12° could be used without pinging. The '72 has no EGR and the cam timing isn't as retarded and peak combustion chamber temps are higher. 12° BTDC is not supportable.
Quote:
with low compression more timing is alway better for performance and fuel economy.
Incorrect. Beyond a certain amount of advance -- much less than you seem to acknowledge -- fuel economy, performance, and driveability all suffer.

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 Post subject: Only if...
PostPosted: Sat Mar 13, 2010 8:33 pm 
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9714
Location: Salem, OR
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Quote:
low compression more timing is alway better for performance and fuel economy.
Yes, but as Dan says only up to certain point... I had a stock 1972 points distributor that I was able to pull the curve off with my Sun machine and
The vacc advance was a 9- so 18 degrees between 20-10"Hg applied vacc.
13 governor meant 26 degrees achieved at 3300 distirbutor RPM (not like he's going to get 6600 crank rpm out of it...) It was 16 degrees at 2800 rpm (assume 3 spd and 2.94's with short tires...)

16 at cruise + 26 Vacc. = 42... If I wanted the perfect cruising for this distributor I'd use Dan's original advice of setting for 5BTDC and work up to 8BTDC initial and thus have 50 degrees highway cruise for good mileage (maybe 48 if the regular is crap, or it pings)....at 8 initial + 4 off idle +26 vacc..=38...that's about all I might want out of a good running slant and a distributor in good shape...

A stocker lo-po with a 9R 1976+ governor and a 10x or 11x can...you bet I'd say start at 8 and work up to 12 if possible/not pinging under part throttle/cruise...

-D.Idiot


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PostPosted: Sun Mar 14, 2010 7:09 am 
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Turbo EFI

Joined: Tue May 17, 2005 4:26 pm
Posts: 1237
Location: CBS Newfoundland Canada
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i started off like everybody else with a stock 1bbl engine in a 4door 69 valiant, that was 32yrs ago and learning from my father who was a mechanic for local chrylser dealer,i know what worked for me by what i was shown and all i can do is share my experience, if that`s not what the books say is right then it must be the sea side fresh air that make the difference. :roll:


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PostPosted: Sun Mar 14, 2010 7:36 am 
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Turbo Slant 6
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Joined: Sat Oct 25, 2003 12:41 am
Posts: 844
Location: wichita ks
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edit-- read the links to Dan's post-- & experiment with your ride-- do a search on here for timing numbers-- they have been posted-- if they are not in Dan's link.
Have fun

Lawrence


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PostPosted: Sun Mar 14, 2010 8:26 am 
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Supercharged
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Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
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I probably got the most aggressive timing, but I choose to experiment allot.
I have my good engine out at the moment for a few updates, double roller chain, Doc's heavy duty oil pump, crank scraper, etc. getting it ready to race this year.

I have a stock 1980 SL6 barn find under the hood right now and am able to run 10 degrees initial timing with a 15r governor and a 11r vacuum can with out any pinging. So that is 10 + 20 + 22 for 52 degrees at 2500 rpm with out pinging. The distributor has been recurved to limit mechanical advance to 20 degrees at 2500 and 23 degrees at 3000. The vacuum can has been adjusted 3 turns out from full on so it doesn't not engage right away. It doesn't ping at all on regular gas and feels much peppier than at 0 degrees or even 6 degrees. In fact this old engine averages 22 mpg running around locally up to 23 mpg so far. I installed it the week after Christmas.

To read the total timing with your timing light just file extra notches in the damper every 10 degrees or use some white pin stripping.

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG


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PostPosted: Sun Mar 14, 2010 9:11 am 
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TBI Slant 6
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Joined: Tue Jun 05, 2007 5:27 pm
Posts: 187
Location: northern NJ, USA
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Quote:
with low compression more timing is alway better for performance and fuel economy.
Quote:
Incorrect. Beyond a certain amount of advance -- much less than you seem to acknowledge -- fuel economy, performance, and driveability all suffer.
Optimal ignition timing will result in peak cylinder pressure occurring at 20-25 degrees ATDC. Engine speed and load (the amount of air/fuel in the cylinder) determine how fast the fuel will burn, and the timing advance curve has to conform to these parameters. Retarding the timing from optimal results in more heat going into the engine and out the exhaust, and less being converted into work. Advancing the timing from optimal results in excessively high cylinder pressure, overheating the cylinder head, valves and spark plug, increasing loading on crankshaft bearings, and increasing the piston side and top loads. The overheated cylinder head components lead to preignition and knocking. The "knock" noise is the piston slapping against the opposite side of the cylinder as the connecting rod passes TDC. Tremendous forces are involved, so damage can easily occur.

btw boat engines don't use vacuum advance because the engine is always at full load at whatever speed it is turning.

Ken
:-)


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PostPosted: Sun Mar 14, 2010 9:22 am 
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Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
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Location: North America
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Quote:
it must be the sea side fresh air that make the difference. :roll:
Yup, a lot of things work "differently" in Newfoundland. :lol:

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Too many people who were born on third base actually believe they've hit a triple.

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