Curiousity Question For Discussion

[Jon S]

At what Timing Setting will a carburated Cadillac cold start easiest?  Top Dead Center, Advanced to Specification, Advanced slightly more than Specification, Retarded from Specification?  I don't know the answer, but am leaning toward Advanced to specification.  I know they run quicker and cooler slightly advanced beyond Specification and more sluggish/hotter retarded but was curious about cold starting differences.  Thoughts???

[Coupe Deville]

You know I was asking myself this same question the other day. On my 472ci in my 72 CDV, the stock base timing setting is 8 degrees BTDC. I advanced it to 10 degrees and it starts better and seems to run happier there. I would try advancing a little, take a drive and go from there.

-Gavin

[Jon S]

Gavin -

My 1958 calls for 6 degrees advanced - it has been at 10 degrees advanced for some time and also seems to run best there.  I was just curious about starting effects especially after sitting for several weeks with this Ethanol mixture of gasoline.

[Coupe Deville]

Oh. I see now. Not sure about starting so much. I have set my fathers 390 to the factory timing mark for premium fuel. The 'A' mark on the pulley. His car runs fine. And when it sits for a month or two not run, all I do is pump gas once to put choke on, and one more time just to shoot gas down the carb. It cranks for maybe 3-5 seconds then fires right up. I know that some engines are different but this is just from my experience. We did have a problem with the fuel pump years ago when the car would always be hard to start hot or cold sitting or not, but once it got started it ran beautifully even at high speeds. Are you experiencing starting problems?

Yes, every time I fill up I say yeah, ethanol...... Not sure what gasoline you have where you live but here in California we have oxygenated gasoline. Their selling air!     

["Cadillac Kid" Greg Surfas 15364]

Jon,
The original timing specs were for a new car using what was the then (110 octane +) gasoline formulation.  If your car runs "best" set at 10 degrees initial and there is no pinging during acceleration than that is the setting your engine "likes". FWIW that magic 10 degrees seems to be what most of my cars seemed to like.
Greg Surfas

[Jon S]

Gregg -

The original octane was 101 back in the 1950's/1960's for high test, but that may have been calculated differently than today's method.  I add real TetraEthyLead to boost the 93 pump gasoline. 

Anyway, getting back to my original question, does it imply the best running Ignition Timing e.g. 10 degrees advanced is also the optimal Timing setting for best starts?  I think so, but was not sure.

["Cadillac Kid" Greg Surfas 15364]

Jon,
On the west coast (at least) we had the "octane wars". I don't remember the specifi brands but 115 and 116 were the numbers.  Octane rating is still calculated the same way. R + M/2.
What I was really trying to refer to was the chemical composition of the gasoline when these motors were developed, and the timing curves designed for new motors with those fuels.  Each motor with its stacked tolerances and clearances, as well as drivers driving characteristics determine the "perfect" numbers.  If the particular batch of fuel has slower burning characteristics then a little more initial advance might be beneficial. The opposite is true for a highly volatile mixture.  No single number is valid for all cases.
Greg Surfas

[Scot Minesinger]

Have had 1970 Cadillac RWD timing set advanced and retarded and at any setting it never pre-detonated or knocked.  It seemed to start nicer when advanced and idle better.  I read that advancing timing beyond factory setting I not good for the engine.  Further advanced timing is less efficient (from combustion perspective) so the engine runs hotter at highway speeds.  You would think that that the factory got this relatively simple adjustment specified optimally when the cars were new.  It seems wrong to advance it, although I agree it starts and idles nicer.   

I think we can all agree retarded timing is to be avoided.

On the gas and timing, the gas was more resistive to pre-detonation in 1970 than today, so it would seem that high octane gas that generally prevented pre-detonation not being available today would mean the opposite and the timing should be retarded some to avoid this.  I was working on a 68 with a 472, 10.5 to 1 compression ratio and after curing all vacuum leaks, had to set timing at one degree retarded from factory setting to keep it from pinging when accelerator is floored (owner instruction - set timing so it does not ping when floored - wanted to keep as close as possible).  Surprised that one degree fixed it, but it did.

My timing is set to spec on the 1970 Cadillac 472 RWD, will that get some more authenticity points at GN?   

[Scot Minesinger]

George,

Yes joking. 

Always trying to win at GN, but driving a car 4k miles per year makes it difficult.  Plus I have the Diamond back dual stripe radials and dual exhaust. 

The exhaust system is so well done, I just do not have the heart to remove it and replace with authentic single pipe system.  The dual system also makes the flywheel cover and oil pan easier to remove.  I did replace all the hangers with authentic type used in 1970 - bought two used sets, removed rubber, media blasted, powder coated with hi-temp, replaced rubber and installed - looks real nice.

Although, I wish they took the cars for a drive at GN, that would really help me, as car drives so damn nice - understand that is completely impractical.

Back to the topic at hand, cannot imagine Cadillac got this timing setting wrong.  Advancing the timing means the park plug fires late and you do not get the efficiency needed, and it cannot be good for engine either long term - valves.

[cadillacmike68]

Advancing the timing means More degrees before TDC, so it fires earlier. 

That's what the vacuum and mechanical advances do - they increase the amount BTDC. The engine is spinning faster & the chambers are opening up faster so the spark needs to be sooner relative to TDC to burn.

Too much advance though and you end up with ping / knock city.

[n2caddies]

Chiming in here from California.  My 59 and 60 seem to like the timing advanced about 10 degrees on premium pump gas.
Randy George

[cadillacmike68]

Is that base timing, at idle with NO vacuum or mechanical advance?  Different years had different specs.

[TJ Hopland]

Too much advance hurts starting.  At the extremely low speeds of cranking you can 'get the fire going' too soon.    Think about it, if you start 'pushing' down before the piston reaches TDC you will be trying to turn the engine backwards.   At higher speeds the advance works because things are moving fast enough that 'lighting the fire' before TDC just happens to time out so that by the time the real explosion / pressure happens you are past TDC so the power is used to keep things turning in the direction you want.     

[Scot Minesinger]

Mike, yes sorry meant early not late on firing.

TJ, my car definitely started way nicer with timing further advanced than factory spec, which I agree trying to push engine backward a little bit seems contrary to logic.

[cadillacmike68]

What I've found with this generation is to read and follow that wide sticker that is on top of the radiator shroud. It is a condensed version of the language in the shop manual. 

An adjustment might need to be made for modern fuels, but timing is only one part of the equation. Proper setting of the carb's idle circuits is also important.

[TJ Hopland]

TJ, my car definitely started way nicer with timing further advanced than factory spec, which I agree trying to push engine backward a little bit seems contrary to logic.

There is definitely a 'sweet spot' for a given engine and rpm.   If you get too much advance during cranking you will know it, the engine tends to kick pretty hard.  Hopefully you notice it before you break the starter off the block.   Its usually not a big problem for stock engines.  People with 'race' engines know these issues well.

Biggest issue I have seen lately is stock original vacuum advances are now often dead from old age and the replacements tend to pull way more advance than the originals and what is needed.   Common result is detonation.   Most people deal with detonation by retarding the base timing.   If you have a stock setup the factory manuals give the specs for the vac advance.  Some of the 'performance' vacuum cans have an adjustable cam stop to limit the travel, this is what you want to buy because you can adjust it to get the factory curve.   

[cadillacmike68]

^^^
Crane Cams makes a good one. It also comes with several spring sets to adjust mechanical advance as well.

[Jeff Rosansky CLC #28373]

Speaking from a starting perspective, Retarded is best.

Think about it.  It is designed to fire so the combustion event will be at its optimum when the piston is ready to be blown down.  If it is too far advanced, and just spinning at starter speeds, the combustion event will be complete well before the piston is ready to come back down.  You also risk the risk of it kicking back if it fires too early. 

The airplane has an impulse coupling on the magneto.  It is designed to deliver a hot retarded spark during starting. Flywheel weights bring the coupling pins in when it is spinning faster than what the starter will do.  The plane does not have an advance. 

I would think the car will run better more advanced--which they do. They have to be dummied down to run at idle.  The 7/8 degree point is probably as advanced as they could have gone to have a decent idle and a reasonable start.
Jeff

[Glen]

Biggest issue I have seen lately is stock original vacuum advances are now often dead from old age and the replacements tend to pull way more advance than the originals and what is needed.   Common result is detonation.   Most people deal with detonation by retarding the base timing.   If you have a stock setup the factory manuals give the specs for the vac advance. 

I had the same problem with my 68 ELDO until I read the Distributor Test Information in the shop manual.  Then I tested the vacuum advance and found it followed the specs exactly except it would go well beyond the specified 12 degrees of advance, going to 22 degrees.  So I installed a stop to prevent it from going that far and I no longer have pinging. 

[Steve W]

I had the same problem with my 68 ELDO until I read the Distributor Test Information in the shop manual.  Then I tested the vacuum advance and found it followed the specs exactly except it would go well beyond the specified 12 degrees of advance, going to 22 degrees.  So I installed a stop to prevent it from going that far and I no longer have pinging.

I know its an ancient post...but if anyone is reading this...how did you install a "stop"?