Technical Why Was Factory Ignition Timing So Retarded?

Tuneup specs for old school iron typically runs 3° or 4°, but savvy mechanics know the engine will run much better with advancing ignition timing as far as practicable just short of pinging or detonation. The engine will run cooler and get much better fuel economy and power. It's not so much that the total timing numbers is any different but when in the advance curve certainly is. I'm running 17° initial and around 37° total with light springs and pump gas. With vacuum advance it is even more of course.

So what was the rationale though for the slow initial timing? Keep in mind this was long before any thought was given to emissions control or high compression designs as well.

 

Crappy fuel back then?

 

Its a complicated subject but originally timing was retarded to start the engine, manifold vacuum would quickly get it into the 16-18ish range and mechanicals would get it higher. Enter the fed's and they want emissions, vacuum went to ported and the retarded timing at idle burnt the gasses better.

 

Just guesses here, easier to start(crank), lower operating temps and economy.

 

Pollution, simple answer in California anyway.

 

^^^^^^^^^^^^^^^
All the above answers are correct answers.

 

Easier to crank, yes. But operating temps actually go down not up with advanced timing.

Fuel economy goes down with slow timing as well.

 

Ported timing vacuum predates emissions controls by decades. It was around long before anyone worried about smog. It is true that retarded timing keeps certain pollutants at bay, I think that's why they had to introduce catalysts. An efficient (read fuel economy) burn means lots of nitrogen oxides, the component that makes smog. So they retarded the timing at idle, and then burned all the wasted gas in the exhaust? That's stupid, but I think that's what happened?

But none of this mattered in the 1930s, and they had 3° or 4° timing specs for the initial timing then.

6 volt systems maybe didn't crank so well?

 

I thought of that, but the actual total timing doesn't really change with a "hot rod" advance curve. V8 runs about 35 degrees or so not counting vacuum advance. Tuners just change when this advance happens, and how quickly.

 

Exactly... I don't know where the myth about ported vacuum advance not being in use before emission controls came from. But that's what it is; a myth. Ported vacuum was in use on most makes in the late 40's-early 50's. Well before they were worried about emissions...

 

wonder how the really low idle speeds contributed? like 450 rpm was standard

 

Plus, all the time the new car was under guaranty and tune by dealer mechanics, it seems to perform less than what you'd expect!!!!........... around here anyway...........

 

Some good answers. Gas was low in octane, and they had to set up the engine so it would start and run without fail, red hot or stone cold, on top of Pikes Peak or the bottom of Death Valley, and Mrs Peasy Weasy could make every driving mistake in the book and still make it to the Piggly Wiggly with no drama.

Needless to say this meant some pretty conservative decisions. Which is why a hot rodder could get 25% to 50% more HP without hurting drivability or reliability too badly.

 

Maybe we are using the terms differently, I believe 'ported' vacuum is that vacuum sourced from above the throttle blade - like carbs from the 60's on up have. That was an emissions thing, when at idle the distr retarded an draised the exhaust gas temps to burn off the fuel and reduce emissions. You won't find a 'ported' vacuum fitting on any carbs from the 40's or 50's that I'm aware of.
I'm not 100% certain and can be wrong.

 

The MoToRs Repair manual I have from 1950 says that ported vacuum is used (above throttle plates) so as to obtain a steady idle. It was used long before that, I would imagine. Some manufacturers did use manifold vacuum, and ported was used to keep certain NOX emissions lower, but the assertion that ported vacuum is some kind of emissions era atrocity invention foisted on us is not the case. Maybe they had to use it because of technical considerations, but it's been around pretty much forever, probably as long as vacuum advance anyway.

 

Nope, were are not using the terms differently. Let's see here: After Ford lost the lousy Load-a-Matic distributor in '57 they went with ported vaccum (the Load-a-Matics used both ported and manifold vacuum), Early 50's Cads and Olds used ported vacuum (I've had and worked on a few of those) and the Ignition Systems chapter of my 1950 Motor's manual shows both Autolite and Delco-Remy distributors using ported vacuum... The idea that ported vacuum came about because of emission controls is a myth...

 

Truck64... you beat me to it! ;-)

And I just checked my Motor Service's Automotive Encyclopedia from my days at Tech. School long ago. The vacuum advance section of the Engine Ignition chapter makes NO mention of manifold vacuum being used for distributor advance, just ported vacuum. Also, this book is old enough that it has no mention of emission controls.

 

So with all the tweaks Duntov did to obtain one horse per inch with the 283, all you had to do was bump the timing to get more?

 

Use a Vac gauge , @ idle to set initial timing and go from there ,Then check total timing , a good # around 35 degs
But not set in stone , then if timing is like 50 degs or higher
You have to limit total timing , stops on Avance,
Some engines like 35,36,-45 total deg of timing,
You have to experiment and document what you're doing !!
This is part on how to tune a engine,
Ist not just bolt in and go!!!! Work has to go into it,

I uses a 6 inch round vacuum gauge that reads 0 to30 in 1/8 internets , But I am a die hard Motor Head !!

 

Sure, everything you mention is correct. I just wondered why Ford or Chrysler or anyone else didn't use a hopped up curve, especially initial timing. For one thing, fuel mileage improvements. I've seen V8 mileage double with careful tuning.

Some people claim that "back in the day" nobody cared about fuel mileage because gasoline was 20c a gallon. I don't believe that either.

 

20c a gallon was a lot when you earned less than a buck an hour.

 

They didn't burn anything in the exhaust. They just pumped clean air to mix with the exhaust to make cleaner exhaust. Of course that isn't what they told the government but all that was needed was for the exhaust coming out of the tailpipe to meet the specifications.

 

A ll the guys I now that worked a Dealership
In late 50's - 70 where doing this to cars Wright off dealership lot , I guess that's why their cars were kings over other guys they didn't know tunning tricks

 

Truck64 understands a bunch about combustion, and combustion gasses based on what he wrote. He made a good point, which could be restated this way, good hot and clean combustion of fuels makes higher levels of NOx, which is why they cars of the 70's and 80's run like they do. Dig into this if you want to learn more.

https://en.m.wikipedia.org/wiki/NOx

 

Thanks for the kind words, but I really don't understand very much about this. I've read that an engine tuned and timed for maximum fuel efficiency and power will fail certain exhaust emissions measurements. NOX I think, there's HC and CO standards too. It's kind of a balancing act to meet the specs, and probably why some of the 70s era motors were so problematic, they were de-tuning the timing, "lean burn", lowering compression and other things that were kind of a Rube Goldberg approach to the problem at hand.

 

I've heard stories of broken arms from hand cranking an over advanced engine. We had a v-12 in the shop some time ago the timing procedure was to set the timing at top dead center and keep advancing it for best vacuum then back it off if detonation or starter kick ocurred

 

Come on over! Show my Buick to you

Ben

 

The trick when timing is hight at idle is to spin the engine before you turn on the ignition,
No kickback even with a hand start
It would be interesting to know the real reson for 6-8 Degree's at idle ,
Was it poor gas or to keep starter kick back from occurring ???? Or what !!

 

I know of 1 engine in particular, I was doing some research on it.
Thinking I might buy it for use in something else.
1978 ford 400 small block.
They retarded the timing on it by relocating the key way in the timing chain gears.
They did this for emissions. But it is simple to install a older timing chain set from a older engine year.

This just raises the question, How many engines did this, and would there be any practical gain?
Or can you just rotate the distributor and advance it as much?
Would there be any value to a list of the different ford, chevy, dodge etc... engines that did this?

 

You're talking about cam timing. We were talking about ignition timing.