Ignition Timing
#1
I phoned Ford Racing tech the other day with questions about cam selection for the 351W in my 69 Mach 1.  I currently use their X303 hydraulic roller cam (I think made by Crane).  It is a little lazier than I prefer below about 2500 RPM.  Ford racing tech told me that is a great cam choice for a 351W and suggested my ignition timing is not set right for that cam.  I have it set at 10 degree BTDC initial and all in at 3000 RPM with 35 degree's total.  I was told that cam needs 16-18 BTDC initial and 32-34 degrees total.  I am not use to that much initial timing.  My motor has 10.7:1 CR and at 12 degrees BTDC initial it will ping once right at start up when hot, at 10 degrees BTDC initial it's okay.

X303 cam specs:  Adv duration at 0.004" tappet lift is 286/286 degrees.  Duration at 0.050" tappet lift is 224/224 degrees.  Valve lift is 0.542"/0.542".  LSA is 112 degrees and intake centerline is 107 degrees.


Anybody else here use a lot of initial timing on their motor?  I don't like that initial single ping right at start up.  Most late model cars will do that on a hot day.  Is that something to be concerned with.  I use premium pump gas which is 91 in California and mix Torco Accelerator with it to raise the octane.  I use to mix 110 octane race gas with premium pump gas but I can no longer find the race gas near me.  Wow! It ran good with the race gas.


Also, would a colder spark plug help stop that single ping at start up when hot? I use the stock heat range now. 


Mike
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#2
Man did you open up a can of worms. To put it mildly, no a little ping on start up when hot, won't hurt a thing. Now with that said 10.7 to one, is a good solid compression ratio. Probably near the top of the range, of what is streetable on todays gas, even the premium. Try bumping your timing up about 2 degrees, at a time, till you get to where it doesn't want to start, then back it down about 2 degrees, and you should be safe. Make sure it doesn't ping on acceleration, and you'll be good.  As long as it doesn't ping you're good. There is a ton of reasons for pre ignition. Chamber shape, volume, piston crown, if domed, etc. Now the big thing is sharp edges, inside the combustion chamber. Just like when using a cutting torch, you always start at an edge cause it will turn cherry red quicker. so everyone started rounding, and smoothing, all the edges in the combustion area, to eliminate the hot spots, which contribute highly to pre ignition. There are other reasons, but this is the majority of them. Hope it helps.

JTS

Ps a colder plug could also help things.
"We built these cars to drive the "HELL" out of them, not to be museum pieces!"  Carroll Shelby

2008 Mustang V6 5 speed "Diablo Sport Predator" tuner, 87 octane tune. WOW!
1994 Ford F150 Shortbed
1986 Honda 450 Rebel
1995 Honda Pacific Coast
1989 Jacobra / Jag xjs
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#3
Thanks.  I haven't tinkered much with timing and advance curves to tune a motor.  In the past I always had stock distributors and adjustments were not easy.  But with an MSD distributor it's simple without having to remove the distributor.  I'll try it at 12 degree BTDC.  It has a permanent magnet gear reduction starter so it should crank just fine.  At 12 degrees initial the mechanical advance is curved so it will have 33 degrees total at 3000 RPM.  The next step quicker would be 33 degrees total at 2500 RPM.  That might be too quick for this compression ratio.

Stock compression ratio for a 1969 4-barrel 351W was 10.7:1 with a flat top piston.  Plus I'm kind of old school and stuck in a time when it was normal to build a street motor with 10.5:1 to 11:1 compression ratios.  More cylinder pressure = more power.  I get the impression younger people today typically build about 9:1 CR motors, advance the ignition timing a lot to get some power, and not experience pinging or hard cranking conditions. 


Unfortunately the 1969 and 1970 351W blocks have a 0.020" shorter deck than all the other years so there are very few off-the-shelf pistons available.  Most off-the-shelf 351W pistons have taller compression heights for the later year blocks.  I wanted a forged piston and at the time Ross Racing was the only mfg. making one for the 1969-1970 blocks.  It's a flat top with valve reliefs like they originally had.  Most mfgs don't specify what year 351W their pistons fit and it's very easy to get into a situation where the top of the piston is above the deck.  I know first hand with some KB Hypereutectic pistons.
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#4
Lots of technical information flowing in this post.   Have you ever thought about getting your car dyno-tuned?  I have heard this is best way to achieve maximum performance.  I have considered having my car done.
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#5
After a lot of research I found a heat range colder spark plug, Autolite 124.  It is one heat range colder than the Autolite 45 spark plug.  Apparently the last number indicates the heat range for Autolite spark plugs.  Lower numbers are colder and visa-versa.  Not many spark plug options for the older large diameter spark plugs.  Funny thing is the Autolite 124 is for 1668-1970 302 motors when used in pick-ups and Bronco's.  Passenger cars got the hotter 45 spark plug.  Any idea why?

NGK has a short article on when to use colder spark plugs.  https://www.ngk.com/learning-center/arti...-do-i-need
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#6
Good Post, very good article on plugs, how and why. Explains a lot 

JTS
"We built these cars to drive the "HELL" out of them, not to be museum pieces!"  Carroll Shelby

2008 Mustang V6 5 speed "Diablo Sport Predator" tuner, 87 octane tune. WOW!
1994 Ford F150 Shortbed
1986 Honda 450 Rebel
1995 Honda Pacific Coast
1989 Jacobra / Jag xjs
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#7
Short update.  I recurved my distributor and set the timing to 12 deg BTDC.  So I now have 12 deg initial and 35 deg total at 3200 RPM.  I have colder plugs to install, Autolite 124.  Now just waiting for a day with lower temps to drive it.  We've been stuck in a heat wave for several days, 100 deg temps.  I hope this works.  My original plan was to install a slightly less aggressive cam.  Then Ford Racing tech mentioned my ignition timing wasn't right.

I found an article with general ignition timing information for small block Fords.  It had initial timing and total timing guidelines based on static compression ratios and camshaft advertised durations.  I'll search for it again and post a link.  It's helpful for those of us new to tuning the ignition timing curve.
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#8
Good deal, a little tuning is a lot cheaper, and easier then a cam swap. Hope it works.

JTS
"We built these cars to drive the "HELL" out of them, not to be museum pieces!"  Carroll Shelby

2008 Mustang V6 5 speed "Diablo Sport Predator" tuner, 87 octane tune. WOW!
1994 Ford F150 Shortbed
1986 Honda 450 Rebel
1995 Honda Pacific Coast
1989 Jacobra / Jag xjs
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#9
Update.  I have it running again with the new timing curve.  Base timing set at 14 deg BTDC and total of 35 degrees BTDC at 3000 RPM.  Still waiting for the weather to cool off some.  Every day is still a little over 100 degrees.  Since Holley now sells most of their carb main bodies for fairly reasonable prices I also installed an HP style 650 CFM main body.  I've been wanting a 650 CFM HP carb for quite some time but could never afford one.  New carb prices are ridiculously high.  In the garage the motor runs much better, crisp throttle response.  If it drives as good as it runs in the garage it will be a huge improvement.
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#10
Here's Hoping Thumbup
"We built these cars to drive the "HELL" out of them, not to be museum pieces!"  Carroll Shelby

2008 Mustang V6 5 speed "Diablo Sport Predator" tuner, 87 octane tune. WOW!
1994 Ford F150 Shortbed
1986 Honda 450 Rebel
1995 Honda Pacific Coast
1989 Jacobra / Jag xjs
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