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Spark advance on steep hills?


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Just curious if anybody knows?  Should you use some spark advance on a steep hill? for extra power?  (given you have a car with a manual spark advance).  I know most of the late 20s cars have mechanical spark advance in the distributer, so if it is free, that should work?

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It would be interesting to see what Ed says.   The 540K Mercedes has an auto advance on the distributor when you kick in the supercharger.  The 500k is manual and you are supposed to advance on your on with the blower.


There are a number of cars that won't turn over without retarding the spark,  Model J Duesenberg being the one that comes to mind first.

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My answer would be.......depends. The year of the car, type of engine, ect. Remember that most cars didn't have a accellerator pump till the late 20's so adjusting the timing may or may not help depending on a bunch of things. My 1917 White has a magneto on it.....and adjusting the advance on the T head four valve makes almost no difference. Since it has a compression relese I just leave the steering quadrant at 2/3 advanced and start the car. By the late 20's most cars had automatic advance on the battery ignition. So, in general my answer would be.....it won't make much if any difference.  

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When did cars have manual spark advance you could control from the driver's seat? Before 1925 I would think. Back then compression ratios were low and gasoline about 50 octane. On a hard uphill pull you would back off the spark advance to prevent knocking, advance it again on flat ground when the engine was running freely.

Gas is so much higher octane now that it should not make any difference in other words, not necessary to prevent knocking.

Edited by Rusty_OToole (see edit history)
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If you would use the advance normally used for starting, the engine, it would be firing after top dead center theoretically giving a better firing angle on the crankshaft yielding more power? Or am I just overthinking it?  Weren't most of the auto advances systems for starting vacuum?  I have noticed the driver controlled spark advance disappeared with the advent of vacuum advance 1930-34?

 

My 1928, 29, and 31 all have manual spark advance for starting, my 33 has mechanical advance in the distributer but no vacuum or manual, all my Graham-Paige cars.

Edited by Graham Man (see edit history)
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Even my 1918 Pierce has "automatic" (i.e., centrifugal) advance in the distributor.  I full-retard the spark on all the pre-war stuff for easier starting, one reason for which is that I usually put an additional 3 degrees or so of initial advance on the distributor.  If I want a smoother idle for display or slow parade travel, I'll retard the spark halfway (parades) or all the way to display a very slow, smooth idle.  Once the engine is running, I go to full manual advance and leave it there -- except for some low-rpm acceleration without shifting after rounding a corner.  The 1934 and 1936 cars have an inconveniently located pull-to-retard spark knob on the dash which I use only for starting.

 

Like Ed says, "it depends..." and part of that is Rusty's information on the octane of today's fuels.

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Ditto on George's technique. I am not the least hesitant to use full retard when starting, and driving/slowly accelerating in a higher gear to avoid needing to shift down in my old Cadillacs. Gasoline in 1920 was just about 40 octane.   -   Carl 

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So assuming the engine is not laboring (being lugged due to being in a high enough gear on a steep enough hill to make it have to run wide open throttle just to maintain rpm and road speed) the best power output is achieved with the most spark advance the engine will tolerate before it begins to spark knock.  The noise from spark knock occurs when the spark is advanced too far ahead of top dead center and the combustion cycle reaches maximum cylinder pressure before the piston starts back down the bore.  It is tantamount to having the piston right at TDC when it gets hit with sledgehammer like force.   It is a clear indication of too much spark advance for the load on the engine.  This is not good for any of the primary rotating mass but is especially hard on rod bearings and pistons.  The vacuum advance came along in the mid thirties to avoid this by retarding the spark just enough to avoid spark knock.  As the road load increases due to the hill and the throttle either gets opened to compensate or the engine slows, manifold vacuum drops and the breaker plate rotates slightly in the direction of distributor rotation retarding the spark.  When the car crests the hill and the engine speed begins to increase and or the throttle begins to close to keep the car from speeding up the manifold vacuum increases and the diaphragm in the vacuum advance working thru the linkage rotates the breaker plate back against the direction of distributor rotation advancing the spark for best power and fuel economy.  You can adjust timing to some degree using a spark advance knob on the dash but the vacuum advance is way more reliable and accurate.  

Edited by Str8-8-Dave
correct spelling (see edit history)
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The answer to the original question is no, you retard the spark under load. As has been pointed out, that was the job of the vacuum advance on later cars. Lower vacuum retarded the spark - made it later.

There are some good explanations here, but ideally, the timing should be set up so that the car runs best at light load at cruise speed. Retard fully for starting - usually, and retard a little when pulling hard. You can learn to hear and feel the motor and get an idea where it should be. It also depends on the design - or lack thereof, of the distributor. My 17 McLaughlin ( Buick) 4 cylinder has no mechanical advance or anything. The driver fully controls everything, like a Model T Ford.  By the mid 20's they had mechanical advance, but it was only a few degrees and was an "assist". You still retarded it for starting but you could drive on easy going with the advance at full and it worked well. might have to back it off a little for the hills. Later they added more advance, You didn't have to retard them to start but still had a control. Full automation came with the vacuum advance- which actually is there to retard the spark under load. 

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On 10/28/2020 at 2:51 PM, Graham Man said:

Just curious if anybody knows?  Should you use some spark advance on a steep hill? for extra power?  (given you have a car with a manual spark advance).  I know most of the late 20s cars have mechanical spark advance in the distributer, so if it is free, that should work?

 

No

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My 1912 Maxwell 2 cyl runs best at maximum advance of about 32deg BTDC under all conditions.   Retarding it even slightly when at low RPM on steep hills reduces power.  I only retard it on hand crank starting to stop it breaking my arm .

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Some pretty knowledgeable people weighing in here, so let me ask a basic question. I have heard that timing can be set at low idle by adjusting the distributor to produce the fastest idle. I am assuming this is a compromise, since performance at idle is not what's most important. If the timing was set this way as a compromise starting point on a mid-fifties six cylinder,  should  timing then be slightly advanced or retarded ?  The manual calls for the timing to be set so there is a slight ping on a hard pull, but I'm having difficult hearing that. 

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WPVT: The short answer is no. To time an engine "by ear" the best way is to increase the engine speed to highway rpms where the advance would be "all in"  so lets say 1800 rpm for a 20's car, maybe 2500 for a 50 or 60's v8,  then slowly turn the distributor in the advance direction until you get the faintest indicator of rough running. Then slowly turn in the retard direction ( direction rotor turns) until it just starts to slow down. Right there, or slightly advanced is the sweet spot for that rpm. If you check it at idle you will find that it will run faster with more advance, but that's ok. It needs to be able to "lug" at low speed without kicking back. 

Listening for slight pinging on a pull works on some engines, but some won't ping, at the proper settings,  and it depends what fuel you are running.  Distributor timing is a whole science but assuming proper parts on a stock distributor ( sometimes an incorrect assumption). setting to the specified mark at idle is very close. 

It goes without saying that everything has to be working properly like the mechanical advance free, with proper springs, and no leaks in the vacuum advance. 

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OLDTECH:

This is a little trickier than I had expected. It doesn't help that the vacuum advance line is rigid steel and limits how far you can twist the distributor.

I got the engine up to what seems like typical highway RPM's. I then advanced the timing to what seemed like a little roughness. Then I retarded the timing to find where the speed would decrease. I must have rotated the distributor  a good thirty degrees and the engine speed kept increasing dramatically. I ran out of ability to rotate the distributor in that direction without hearing a real decrease in speed. So that's where the timing is now. We're having snow here today, so no road test until tomorrow. 

It surprised me how much engine speed increased when I was retarding the timing, and how far I actually rotated the distributor from where it had been. 

At idle now it isn't much different than when I started, funny considering how much I retarded the timing.  

If I'm going to retard the spark any more, I'm going to have to change the plug wire positions in the cap. 

 

I will have a timing light next week, so at least I'll be able to say where the spark is in relation to TDC. Still seems like timing by ear is the way to go, though, since a well running engine is what I'm after. 

 

PS In rereading this post, I may have got my description backwards, regarding advance and retard. My apologies.

Edited by WPVT (see edit history)
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Or you could consider timing with a vacuum gauge, once known as "power timing" in my misspent youth:  With vacuum gauge hooked up, advance to highest vacuum, then retard 0.5 to 1.0 inches of mercury on the gauge.  This assumes that you're starting with semi-accurate initial static timing.

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I always did it at warm idle, choke and throttle step-up OFF.  If you get a ping on hard acceleration afterwards, retard the distributor another 0.5 inch Hg and try again.

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4 hours ago, WPVT said:

OLDTECH:

This is a little trickier than I had expected. It doesn't help that the vacuum advance line is rigid steel and limits how far you can twist the distributor.

I got the engine up to what seems like typical highway RPM's. I then advanced the timing to what seemed like a little roughness. Then I retarded the timing to find where the speed would decrease. I must have rotated the distributor  a good thirty degrees and the engine speed kept increasing dramatically. I ran out of ability to rotate the distributor in that direction without hearing a real decrease in speed. So that's where the timing is now. We're having snow here today, so no road test until tomorrow. 

It surprised me how much engine speed increased when I was retarding the timing, and how far I actually rotated the distributor from where it had been. 

At idle now it isn't much different than when I started, funny considering how much I retarded the timing.  

If I'm going to retard the spark any more, I'm going to have to change the plug wire positions in the cap. 

 

I will have a timing light next week, so at least I'll be able to say where the spark is in relation to TDC. Still seems like timing by ear is the way to go, though, since a well running engine is what I'm after. 

 I assume this is a 50's car we're talking about with vacuum advance. It sounds like the spark was way too advanced, be sure the mechanical advance is working properly. if it's stuck you will get strange results.  Turning one wire position is likely too much. One tooth on the drive gear may solve it.  Make sure the throttle is constant- like use the idle screw to get the speed, choke off. 

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5 hours ago, Oldtech said:

 I assume this is a 50's car we're talking about with vacuum advance. It sounds like the spark was way too advanced, be sure the mechanical advance is working properly. if it's stuck you will get strange results.  Turning one wire position is likely too much. One tooth on the drive gear may solve it.  Make sure the throttle is constant- like use the idle screw to get the speed, choke off. 

Thanks. Maybe it was off that far. I had been setting it to get the fastest idle and it seemed OK on the road.

Hard to imagine it was off by that much. (30 degrees would be 15 degrees on the crankshaft, I believe. ) 

I can't tell if the centrifugal advance is working properly until I check it with a timing light. The vacuum advance is new and I assume working properly.

 

The engine is a 1954 Dodge flathead.

 

 

 

 

Edited by WPVT (see edit history)
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20 hours ago, WPVT said:

The engine is a 1954 Dodge flathead.

 

This explains alot about running fairly well when way out of spec.

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15 hours ago, WPVT said:

Just checked the timing. It's about 4-6 degrees advanced at idle.

 

Just keep in mind if you're using the crank pulley timing marks, that the pulley has an inner rubber component (harmonic balancer), which goes soft with age resulting often with displaced timing marks, hence relying on timing marks can be problematic, additionally today's fuels are far removed from 1954, again the timing marks may not be as relevant as they were back then. 

 

I much prefer Grimys' method of vacuum timing if you can find a suitable source for vacuum. As Grimy says, start at warm idle and move the distributor until you reach the highest reading (usually 18 - 20 inches ) then move back about 2 nches and lock down the distributor. Go for a drive and listen for any pinging, if it doesn't ping you're good.

 

One thing I'm curious about is that you say that as you retarded the distributor the revs kept rising, usually this is what happens as you advance the distributor,  just wondering if you're turning the right direction  ?

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Thanks. Mine doesn't have the harmonic balancer, just a pulley. Correct according to my parts book.

As to your question of whether I was advancing or retarding the spark, as I recall, I turned the distributor counterclockwise quite a bit, and the rpm's kept rising. So I was advancing the spark. My apologies. Usually I check my posts more carefully, but in this instance I got my description backwards.

Thanks for reading my post carefully. 

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18 hours ago, WPVT said:

Thanks. Mine doesn't have the harmonic balancer, just a pulley. Correct according to my parts book.

As to your question of whether I was advancing or retarding the spark, as I recall, I turned the distributor counterclockwise quite a bit, and the rpm's kept rising. So I was advancing the spark. My apologies. Usually I check my posts more carefully, but in this instance I got my description backwards.

Thanks for reading my post carefully. 

 

Yeah the danger with too much advance is getting into the pinging zone. 

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On flathead Chrysler products there is a small pipe plug above the #6 piston. Remove the plug and you can drop a screwdriver down the hole on top of the piston. This allows you to find TDC. Since #1 and #6 rise and fall together it gives you TDC of #1, allowing you to check the timing or timing marks.

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Thanks. I've had the plug out, checked,  and the timing marks are right on.

I believe I have the timing about right at this point.

Now, using the timing light and tach, I'll find out where "about right" is. 

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