Setting ignition timing on a 472

[mikanystrom]

Apologies if what I am about to do breaches Forum etiquette...  I actually am going to repeat a question I asked in another thread, but I think it deserves its own thread because it MUST be an issue lots of Cadillac owners have and I have been singularly unable to find a good source of information for it.  Surely I'm not the only one?

I am going to ask a simple question: what is a good procedure for setting ignition timing on a 472?

I know the standard answer is, well duh, follow the tune-up sticker!

Here's the thing, though: I have three high-compression 472s (two 68s and one 70) and only one of them has all the emission control equipment installed (a '68 Eldorado with 50k miles on it).  And I have never seen people go out of their way to keep the emissions equipment in good working order (if they don't have to).  I am sure some people even, ahem, defeat the emission controls... sometimes...

So my question is not pertaining to totally stock engines but to "simplified" engines.  For example, neither one of the two incomplete 472s has the thermal vacuum valve (this is a key issue for me, see below).  The '70 doesn't have the Transmission Controlled Spark, and the other '68 doesn't have the A.I.R. pump.  Yes I know if you were going to car shows you might want those things, but nobody else does.

So let's say I just take a "bare" 472 engine and want to give it a tune-up. 

My first observation is that studying the shop manuals from 1968 and 1970 suggests that the difference in tune-up procedure is entirely because the '68 had A.I.R. and the '70 did not---that's why the 68 runs less advanced timing and richer idle mixture (it's set to run rich to give the AIR something to combine with in the exhaust pipe).  (In detail: no lean drop on the 68, a lower RPM, and 5 BTDC (1968) instead of 7.5 BTDC (1970) base timing, with the vacuum and mechanical advances speced exactly the same in the shop manuals.)   If you don't care about A.I.R. I don't see why you couldn't advance the timing on a '68 to 7.5 and get a bit more power, a bit less heat, and a bit better gas mileage.  All the other specs are the same in the books.

I tried to get my 70 running well (see my other thread for more detail) and I am pretty close.

First of all, I figured out that the distributors you get from parts stores today have Cadillac shafts but Chevy internals (way too much mechanical advance).  So I drilled and tapped a hole in the cam plate to use as a stop for the advance weights.  Book says 14 degrees of mech. advance is right---the Chevy (or whatever it was) distributor had 36.  My hack gets me down to 18, and then I can put some bushings on the screw to adjust further.

After lots of test driving my setup is as follows:

-- first of all, I have a Comp Camps 260H camshaft (not too far off from stock, a "bit" more I think, close to an MTS #5) and Pertronix "solid-state breaker points"

-- vacuum advance set basically by the book (using a Crane adjustable can): comes in around 8 inches and gives ~12 degrees advance max(using a Crane adjustable advance stop).  Book says 12.25 degrees starting at 8-11 inHg and maxing out at 13 inches.

-- mechanical advance slightly LESS aggressive than book, coming in around 800 rpm and maxing out around 2000 rpm at about 10-11 degrees (book values are : start at 400, max at 2000, total of 12-14 degrees)

-- base timing of 10 BTDC (book says 7.5)

-- set mixture to where the lean drop begins (book says 20 rpm lean of that)

-- connected vacuum advance to MANIFOLD vacuum

-- readjusted idle as low as it would go ~750 rpm

I drove the car around with base timing of 11 (marginally OK).  12 (definitely pinging).  So I adjusted it to 10 and I know that the engine is basically on the verge of pinging both under part-throttle vacuum and full-throttle RPM---so it ought to be really close to optimal.  The performance is really very good.  The car starts like a new car too, a tiny flick of the key and it's running.  It's amazing, never drove an old car that drove so well.

This is my remaining problem: the car won't idle slower than 750-800.  That is with the throttle plates dead shut.  This gives me a bit of an unsteady idle (maybe the vacuum advance signal is pulsating and causing the advance to be a bit erratic, I'm not sure).  In any case it's not idling like a Cadillac should.  On ported or no vacuum, I can get the engine idling smoothly at 600 rpm.  Maybe my mixture is off because I set the mixture with no vacuum advance and now I'm idling with 10 or 12 degrees of vacuum advance?

So why not connect to ported vacuum, if that "fixes" the idle?  Because I started this whole journey to fix overheating problems, and if I connect to ported vacuum I will risk overheating since there's then no advance at all at idle.  It was 111 degrees in So Cal today, and traffic was bad, so there would be lots of idling...  and that gets back to the emission controls: if I had the thermal vacuum switch I could use that to switch between ported and manifold, but without it, what to do?  I guess I could whip up a thermoelectric vacuum switch using modern components somehow.. and use that to switch between ported and manifold vacuum.  But maybe there's another way...?  Surely someone else has had to solve this problem before!  What to do?

[Scot Minesinger]

My 1970 Cadillac runs really well, and it is has the Pertronix electronic ignition without the timing advance solenoid - just routed from port vacuum on carb to timing advance actuator on distributor.  The distributor is a replacement, but since car runs well did not bother modifying it.  Also have worked on cars with air pump under alternator and with ones removed (1969, 1969, 1971, 1972, 1973 and 1973 all had them (1970 only year without)), seemed no difference in setting timing.

By running well I mean never pings, starts nice, idles smooth, runs cool (temp gauge reads 208'F when it is 100'F outside even in prolonged stop and go traffic), and has good power - all just set according to factory specs.   

To set timing all vacuum leaks must be cured.  The most common vacuum leak (that is major) I notice is that if the intake manifold was off the car and a new valley pan gasket was installed with the rubber side seals it was not sealed properly with RTV.  CONTRARY to directions on gasket set, the entire bead on aluminum gasket must be caulked, not just the 8 intake ports, and the sides (ESPECIALLY THE CORNERS) at 4 ends of rubber seals must receive generous RTV sealing. 

On to setting the timing, remove vacuum hose from distributor vacuum actuator and plug it.  Obviously test vacuum actuator on distributor and replace if bad.  Car is in drive with helper foot on brake and idle is set to factory test procedure (about 600 rpm for a 1970), and then set idle to factory spec.  This is all per shop manual.  You can tell there is a vacuum leak if the timing reading fluctuates during reading/setting, should be steady.

Often timing set ups can be troublesome if other problems exist.  Best of luck.

[TJ Hopland]

Go over the part again about the ways you have tried to get it to idle.   Something isn't making sense there but it could just be the way you wrote it or I'm reading it.

It will idle at 600 on manifold vac but won't on no or ported?  Do the idle mixture screws seem to be responsive both directions in both modes?

["Cadillac Kid" Greg Surfas 15364]

Mika,
If you read the Comp cams literature, this cam is advertised with a "slightly noticeable idle"

http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=94-302-5&Category_Code=94-CAMHE

That said, and looking at the cam profile, AND ASSUMING THE CAM IS INSTALLED STRAIGHT UP the idle will never be as smooth as a stock Cadillac.  I am a bit confused.  You say you can't get the motor to idle below 750 RPM and then you say it idles at 6700. Confused..
I also think you are mixing distributor degrees with engine degrees in your post.  Lets stick with engine degrees.
The total advance for your motor is just about 33 degrees (engine) that includes the initial and the mechanical, and the mechanical should be top out at about 3000 RPM, not 2000.
At 111 degrees you car will be running somewhere around 230 degrees, so that would be a benchmark.
Vacuum advance for you motor, nbot a stock motor, should be for idle/low speed high traffic operation to aid in cooling.
What is your idle vacuum?
In my "cammed" car I run an initial advance of 13 degrees and a mechanical advance in the distributor of 21 degrees all in at 3000 RPM .  Total 34 degrees.  For vacuum I have a can that gives me full advance at 8 inches which is shut off when the car is "off idle".
I think that among your issues is that the mechanical advance comes in too soon (if you are talking in engine degrees) and the vacuum advance is also in way too soon.
Should come in at idle vacuum and not be at full advance under cruise.
Hope that helps.
Greg Surfas

[mikanystrom]

All right to clarify the issue that's remaining (it's a minor issue, really, unless I'm missing something, which is always a possibility):

The car idles well on ported vacuum.  OK, it is not quite as smooth as stock, but as noted, that's expected with the cam I have--it's installed 1 or 2 degrees advanced BTW (closest to straight up that was possible with the parts I had).  I can get a nasty idle at 400 or relatively reasonable at 600-650 (close to specs, which are 600 in drive for the '70 and I think 550 for the '68).

Now if I start with the car idling well on ported vacuum and switch to manifold vacuum, the idle rises immediately to about 1050.  If I then back off the idle screw, the screw falls out of the carburetor when the idle is 750 or so.  (The limiter on the low end of the idle is the throttle plates, in other words.)  This is how I have the engine set now, idle at 750 with advance from manifold.  The idle is also fairly lumpy (worse than on ported vacuum at 600 or so).  Under these conditions I think I see 16-17 inHg or so of vacuum.  I'm at a bit less than 1000 ft elevation (Pasadena, California), expect ambient air pressure of 29 inches.

I *don't* think it's right to have the distributor permanently on ported vacuum.  It might be OK under most conditions but I would think you would not want that if you are stuck in traffic with the a/c running and it's over 100 degrees outside.  That's why it had a thermal vacuum switch from the factory, isn't it?  Under hot operation you want manifold vacuum at idle, to keep from overheating.

But there are other questions having to do with the timing specs that don't seem to be entirely answered either...

Greg, I don't have my shop manual handy but are you saying that the shop manuals mix distributor degrees and crank degrees (if so, without warning, as far as I can tell!)?  I got all my numbers from there.  I will double-check these #s this evening and update.

[TJ Hopland]

The crank vs distributor degrees has always confused and annoyed me too.   If they are talking about the timing mark it should always be crank.   Its when they are talking about only the distributor they MAY be talking about distributor degrees.   I think the distributor test machines often work in distributor degrees.  The one I saw one time had both so you could select or read which ever scale you were interested in.

This is all with a conventional stock style points distributor?  No fancy modules or boxes?  Have you been keeping an eye on the dwell using a meter?  Last time I tangled with one for an extended period over the time I was messing with it the dwell had drifted pretty far out of the optimum range and I ended up trying to compensate for it by screwing up other stuff.    Also make sure you are keeping an eye on your spark plugs too.  My tinkering has sometimes messed up the plugs so when I tried to go back to stock or previously working settings it still didn't run right. 

Does higher compression and more aggressive cam usually want more or less advance?    I just got my timing running electronically so I have been tinkering with it and having surging issues in the mid 30's (at the crank) so now I am pushing 40 and everything is getting better and no audible signs of detonation.   After I finish this tank of gas I plan to do a plug read to see what things are looking like there before I try and go further.   Mine is a low comp build with an only slightly better than stock cam so the rules could be quite different for me. 

["Cadillac Kid" Greg Surfas 15364]

Mika,
You have something going on.  First of all, "ported" vacuum gives you no signal at idle with the throttle blades closed unless there is something amiss in the carb circuitry. The switch to manifold vacuum and the resultant increase of speed indicates that with the vacuum signal to the vacuum advance you are getting advance, and the fact that even with the throttle blades closed you are getting a 1000+ RPM "idle" I would suspect a pretty decent vacuum leak.
Greg Surfas

[TJ Hopland]

Do you have an AC compressor still?   I remember when I first removed one I didn't notice that one of the rear bracket bolts runs into an intake runner.   That was a big leak.    You could also have leaks in the HVAC, parking brake, crusie, or brake booster that may not be obvious.    Try disconnecting everything and see if anything changes.   None of those things should constantly be 'using' vacuum.   PCV is about the only constant 'leak' you should have.    Level ride compressor would be another possibly constant use if its still hooked up.   

[mikanystrom]

When I say I switch to manifold vacuum I mean I take the hose that runs to the vacuum can and connect it to the manifold vacuum (with my hand).  So to some expect to see the rpms jump.  And yes I see the timing advance by the approximately 12 degrees that I have dialed in.  From 10 to 22 BTDC, in other words.

How do people that run their cars with manifold vacuum to the distributor do tuneups?  I mean, you set the base timing without any vacuum.  You do this at some RPM.  Then you add the vacuum, and of course your rpms jump, or?  Then you have to lower the RPMs again.  With ported vacuum to the advance unit it's not such a big deal, because you have close to no vacuum signal at idle so not such a big jump in RPM, you can just leave it at whatever idle setting you used to set the timing.

The A/C is there (it even blows respectably cold!)  No ride compressor on the De Ville.  Vacuum hoses in generally good condition but of course I could have missed something.  I'm sure there are vacuum leaks SOMEWHERE.

I have a completely conventional distributor except for the Pertronix "electronic points".  So there's no dwell setting but otherwise it's the same as a points distributor.

But yes I will go looking for vacuum leaks.  I'll spray starter fluid here and there and see what happens.

Anybody have an idea how low an idle you can get on a 472 with the spark coming at ~23 BTDC (initial + vacuum)?  You should be able to stall it by closing the throttle completely? 

Hmm my total timing (total=mech + initial) is only about 21 degrees.  The high compression definitely limits the amount of advance you can have without pinging but I'm surprised it's such a big difference.  35-40 seems totally out of the question on my engine.  With the distributor only slightly advanced over where it is now (from say 10 to 12 initial) there's noticeable pinging both under medium load at lower RPM (vacuum advance) and at higher RPM (mechanical advance).  That's from 21 to just 23 degrees of total timing.

[TJ Hopland]

78 was a year where at least the federal emissions Cads ran direct manifold vac for the distributor.  It was direct, just a short hose to a nipple on the intake.    I don't remember the details or have a manual handy but that car did have a way different procedure to set the timing.    I want to say part of it was done at like 1800 rpm?   Like I said I don't remember the details.    What I do remember is we had the dizzy out to look at the timing chain and we didn't bother to check with a timing light before we did it so we just kinda winged it and tried to time it like any other car from that era but it just didn't run or respond the way we expected.   It was at that point that we looked at the sticker (or maybe the manual) and found and followed what seemed like a wacky procedure that actually worked.

Maybe if someone remembers or can post that bit from a 78 manual that will give some insight to what the theory may have been. 

[mikanystrom]

So indeed it does appear the book mixes distributor and crank degrees.  And doesn't label them very well.

Hmm..  I don't see how I could run with that much advance and not have an issue.

It does seem, then, that the one distributor I had that was marked "728 CCW" was right for the car..

[wbdeford]

Is "as far advanced as possible without pinging" a reasonable target?

[Scot Minesinger]

What year 472 are you working on?  They were manufactured from 1968 thru 1974.  Of course the 500 (1970-76), 425 (1977-79), and 368's (1980-81) were all similar.

[mikanystrom]

Is "as far advanced as possible without pinging" a reasonable target?

Yes but there are a lot of variables here... in particular the centrifugal advance is causing headaches.  See my next post...

[mikanystrom]

What year 472 are you working on?  They were manufactured from 1968 thru 1974.  Of course the 500 (1970-76), 425 (1977-79), and 368's (1980-81) were all similar.

I have a '70 to start with, was going to use the learnings on my '68 after that.  They are almost identical in terms of ignition specs, only difference is 2.5 degrees of base timing.  See my attachments above.  The one that says 5 BTDC is 1968, the other one is 7.5 BTDC.

[mikanystrom]

Just want to summarize where I am and to thank everyone that weighed in for their help!

This business with distributor degrees vs. crank degrees is a real trap.

I understand now that on the specs page of the manual, the ONLY number that is crank degrees is the base timing.  ALL others are distributor degrees.

So actually the factory setting is 24.5 degrees of vacuum advance, coming in starting at 8-10 inches and maxing out at "at least 13 inches".

The factory setting for centrifugal is 28 degrees (so a "728 CCW" distributor is correct) at --4000-- RPM.

So what I needed was a lot more advance but a lot later. 

Now the fact is that 28 at 4000 isn't all that different from 14 at 2000!  (If the advance is linear, it's the same up to 2000..)  But of course it implies much more total advance.  Can't tell much of a difference at lower RPMs.  Hopefully it helps a bit with fuel economy to get it right.

I was able to adjust basically to the factory specs using the gadgets I have on my car (Crane adjustable cam, Crane adjustable stop, kit with distributor springs), except for one thing, the Crane springs aren't strong enough to give a centrifugal advance that tops out at 4000.  They claim 3200 is the highest RPM you can get the weights to bottom out at.

So now the car runs well with the factory settings, except a bit of pinging on the top end at full throttle.  (I reset the base timing to 7.5 BTDC.)  Compared to misreading the specs the main thing is I probably get a bit more top-end power, but I can't really tell the difference (the pinging doesn't help).

I have some vacuum leaks, for sure.  I'm going to replace the brake booster, it's hissing audibly, as it turns out.  For now I can mask this by using ported vacuum for the advance, and I get a decent idle.  Will fix the vacuum leaks and revisit the idea of manifold vacuum at a later date.  But the car runs great even as is..

[Scot Minesinger]

Not much point in setting timing until that vacuum leak on brake booster that hisses (and any other vacuum leaks) are fixed. 

On a 1970 Cadillac that did not have any noticeable vacuum leaks, I replaced every vacuum hose and found a few bad actuators (vacuum break on carb for one) and replaced all those.  After that had to reduce idle and set timing (both significant adjustments).

[mikanystrom]

Not much point in setting timing until that vacuum leak on brake booster that hisses (and any other vacuum leaks) are fixed. 

On a 1970 Cadillac that did not have any noticeable vacuum leaks, I replaced every vacuum hose and found a few bad actuators (vacuum break on carb for one) and replaced all those.  After that had to reduce idle and set timing (both significant adjustments).

Hmm, how do you mean?  The mixture and idle speed I can see would definitely change, and sure the vacuum leak can explain why I can't get a reasonable RPM with my distributor advance on manifold vacuum (even with the throttle closed, the engine is running on air from the brake booster)... but it shouldn't affect the way the ignition timing is set, should it?  Base timing is set with the vacuum advance disconnected...

In any case my timing issues (pinging) have mostly been at full throttle, high RPM, and I can't imagine even a very bad vacuum leak could be significant then.

But this opens up ANOTHER can of worms in my mind.  Surely the engines are designed with some amount of allowance for vacuum leaks?  (Isn't that part of the reason why there's an idle mixture adjustment in the first place?)  I know on my Eldorado the headlight-door actuators are pretty leaky in the... open position, they leak down in a few seconds (not so bad in the closed, they will hold vacuum for ~5 minutes).  There would be no way to get the leaks to "zero" without replacing the actuators (or disconnecting them and propping the doors open).  Hmm... and I recall there are some "calibrated leaks" designed into the climate control, but we're probably talking about very small leaks there.   Hmm hmm.. next time I drive the Eldorado I'm going to listen carefully to hear if the idle changes when you turn on the headlights!  Ah these are complicated machines...

[Scot Minesinger]

Vacuum leaks contribute to pinging at full throttle too.  A few years ago was working on a 1975 Fleetwood that had never had the vacuum hoses replaced, and they were the consistency of burnt toast (Southern car).  The car always pinged horribly, then after vacuum hoses were all replaced, no more pinging.

The shop manual states that the vacuum line on distributor needs to removed and plugged.  If the shop manual is worried about that little vacuum leak, then the engine is not tolerant of vacuum leaks. 

It is a lot easier to repair vacuum leaks than it is to change or adjust engine internals.  You have to fix these vacuum leaks anyway.  Repair all vacuum leaks (you should pull like 20 psig negative in park at idle, as negative as 24 psig coasting down a hill at 50 mph).  I have a vacuum gauge on my car.  Also vacuum should be steady, not fluctuating.

You may just suffer a vacuum leak problem.  I would resolve all vacuum leaks and set timing.  Then see how she drives.

[76eldo]

What is the best way to determine if your centrifugal advance and vacuum advance are working correctly?

With a timing light connected and the vacuum disconnected from the distributor and capped off you can set the base timing at idle. When you fan the throttle you can see the timing advance with the timing light.  When you add back the vacuum you should see much more advance I assume?

I'm betting that a lot of our cars have advance that is not working and due to the way most get driven it is not noticed.

Brian