Technical Why Was Factory Ignition Timing So Retarded?

Oem part where probably done in the factory cam grind not always timing chain set ,
By doing little tricks for Tunning the engine , & it runs better and cleaner, The Emissions set up have to be worse , ""OEM specs for carbureted engines ""

400 SBF. ?? Isn't a 400 a FE motor BB,???

Look at BMW Mercedes Volkswagen they just fined in trouble for this ,, when the cars are running around"" engines""" they do one thing,, when they are hooked up to emissions tester , the engine setting / tune is something else !!so there's has to be a reason behind it ,
The engine runs better then the USA Emission standards ???????

 

One wonders if some of that is the ole "the solution to pollution is dilution."

A coworker once bought an "energy star" compliant clothes drier. She was furious, says it took three hours to dry a load of laundry. The old one took an hour. But measured over an hour, the new improved models "use less energy". Maybe even a third as much! Hooray!

 

Is this why the cars back then the motors always need a rebuild after 60 or 80k miles? I heard your lucky if you made it to those many miles.

 

I looked through a 60's Chevy repair manual...Most of the normal performance V8's had about 28-30 degrees of total mechanical built into the distributor...Add the 4-6 usual degrees of static timing and the total is around 34 degrees....That's about right and most performance SBC's with old style heads run 36-38 degrees total timing.. .....Advancing the timing will generally improve mid range response at the risk of detonation and sometime a slight loss in top end power...So to the backyard tuner the engine felt stronger...

 

Most distributors have full advance @ 2000 rpm 36- 38 is OK for high rpm but at 2500 in high gear it's too much . this is why some racers dial back advance in high gear.

 

Fill it up with Ethyl! When did premium gas come on the scene? The only reason I can think of why was to prevent detonation.

 

At $.90 a hour in 1961 working at the Big Donut in Inglewood. I chose a gallon of gas over a pack of cigarettes. Now that I'm 72 it looks like I made the right choice.

 

VERY common tweak back in the muscle car days, almost universal. Take the distributor out and braze up the end of the slots in the advance mechanism. Set up the timing so you had 8 or 10 degrees more initial advance and the same total advance. More pop off the line but you had to have top grade fuel and be aware starting might be harder on cold mornings.

 

Leaded gas was first sold in the mid 1920s. At that time it was only used in premium priced hi test gas and they only put a little bit in. As time went on they used more and more. During WW2 they did a lot of experiments, adding much larger amounts to aircraft fuel in an effort to increase the performance of fighter planes, and building plants to make the tetraethyl lead in large quantities.

After the war they started using more and more lead, even in regular gas. By the mid fifties all gas had lead in it and the highest octane gas was like aircraft fuel of over 100 octane, compared to 75 or so for the best prewar auto fuel.

 

Ah, ethyl=tetra ethyl. Doh! When I came of age all gas had lead in it so I never knew. My best guess was it was named after Ethyl Mertz. Thanks!

 

Yes, that is correct. I suppose the answer as mentioned was manufacturers being conservative and allowing for different altitudes and climate and so on is the answer.

Still the basic stock factory curve though, could easily have been say, 12° to 14° initial without causing starter kickback and they could have maintained the lazy slow ramp to 34° to 36° as always. And anyone who starts tuning notices right away just a few degrees one way or the other can really make a tremendous difference in how a car runs and idles, whether its prone to overheating. Especially too, car with slow timing "feels heavy" and sluggish off the line.. The engineers and marketing types both had to know this.

 

My grampa and all his friends and neighbors hitched their pants WAY up around their armpits like Fred did too.

 

Manifold vacuum drops off when the throttle is open, ported vacuum increases when the throttle is opened. The engineers decided which they preferred, once they had a choice.

Emissions later determined which would remain.


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Are you sure? My understanding is that this is not possible. When the throttle is opened, the engine vacuum goes down, never higher. There is no engine vacuum at idle RPM using a ported source. Once the engine RPM comes back up, under light load conditions the vacuum comes back up.

Connecting two vacuum gauges to either source and taking a cruise proves this. They are identical except at idle.

 

Truck, you said the same thing I posted, .


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But, when you first open the throttle, the timing rises, with ported vacuum. With manifold vacuum, when you first open the throttle timing drops off.
At a steady cruise it's true that it won't change.

 

This is not possible, as far as I know. Throttle opens, vacuum goes down. How could it be otherwise? You canna violate the laws of physics, Captain!

 

You think I read every post? ....Backyard tuners I knew always disconnected the vacuum advance thinking this was necessary to make power since the HP Vettes and race cars had no vacuum advance...Every gas station seemed to have a distributor machine and would recurve your distributor and swap in dual points....And disconnect the vacuum advance...This made the midrange feel stronger, reduced fuel mileage and at the track the car didn't necessarily go faster if the total timing was correct before....

 

I fully understand that you understand but to avoid confusion for others, vacuum will go down when the throttle opens but does not necessarily totally disappear, we will have vacuum at part throttle cruising conditions, which allows us to have vacuum advance for better fuel economy. Any time the throttle plate is partially closed the engine has something to "pull" vacuum against, when it is wide open it will absolutely be zero and slowly go up as the throttle is closed. Not sure if that actually clears anything up!!!


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It goes away momentarily, and then comes back up as the RPM levels off, and the load goes away. There can't be any difference because they are the same thing.

The way to see this, is to connect a vacuum gauge to each - both a ported and manifold source, and go for a drive. I haven't bothered to do this, because other people already have, and I believe them.

"You're probably thinking, "Sure there is no manifold vacuum at WOT but aren't I supposed to use ported vacuum for the vacuum advance." Hold onto your hat, THEY ARE THE SAME THING! Except ported is shut off at idle. There are a lot of misconceptions when it comes to the ported vacuum source. After hearing 20 different theories I decided to hook up two vacuum gauges, one to manifold and one to ported, then drive my car and watch it. I found out they are the same, except the ported is shut off when the throttle is closed. Even then I had a hard time convincing guys so I hooked up a couple MAP sensors and a throttle position sensor to a data logger and recorded them while driving then dumped it into a spreadsheet and made a chart. As you can see, there is a direct relationship between throttle position and vacuum. When the throttle is closed vacuum is high, when the throttle is open vacuum is low, and ported vacuum is the same as manifold except when the throttle is closed. So which one do you want to hook it to? I prefer manifold vacuum. This pulls in more timing at idle which is good since there is virtually no load. Your motor will idle smoother and cooler with the extra timing. One night I was at the drags and my car was running hot in the staging lanes, I swapped the vacuum advance from ported to manifold then it would idle all night at 175°. Believe it or not the purpose of ported vacuum is to raise the temperature at idle, to lower NOx emissions. If you're like most hotrodders that is of no concern to you. If you have a big cam with a choppy idle then a vacuum advance hooked to manifold vacuum can really help. It will idle smoother and requires less throttle to maintain speed. Often a big cam requires you to open the throttle so far that the curb idle adjustment needles won't work. Hooking the vacuum advance to manifold vacuum will allow you to close the throttle some which may be enough for the idle mixture screws to work. Someone told me he noticed less dynamic braking with the vacuum advance hooked to manifold. I didn't notice it on my car but it makes sense. If the motor is running more efficiently with the added advance it will make a less effective brake. So which should you use? Try both and see which you like best."

http://www.gofastforless.com/ignition/advance.htm

 

Just like it is today, this is the biggest thing I change on all chevy's in the pcm when I reflash them. Add timing, 18 deg is not uncommon on todays stuff as it was back then. Basically low timing is safer, and easier to tune.

 

When the engine is idling the only air it receives is through the idle circuit and the tiny crack around the throttle plates that you adjust with the idle speed screw. That means the engine is sucking hard to flow enough air to fill the cylinders allowing it to run. That is when you get the highest manifold vacuum. When the throttle plates are open there is nothing to suck against, so vacuum is very low. Everyone can agree on that I'm sure.

Turn your carb upside down and with the throttles closed you will see a small hole just to the engine side of the throttle plates that is where your idle mixture of air and fuel enter the engine. As you open the throttle slightly you will see another hole or sometimes 2 or 3 in a vertical row in only one throttle bore. That is the distributor vacuum port. At an idle the point of highest vacuum in your carb will be where the throttle plate is close to the bore and there will be no measurable vacuum above it. As you open the throttle slightly the point of highest vacuum moves up in the bore along with the edge of the plate uncovering the distributor vacuum port(s) and pulling a high vacuum through that port thus advancing the distributor. There is still very low vacuum in the rest of the bore above the plate. As you continue to open the plates the point of highest vacuum continues to rise and in only a few degrees of throttle opening the point of highest vacuum has risen far enough up in the bore for the vacuum in the distributor advance port to fall off to the same as manifold vacuum which is also going down. As the throttles open wider the point of highest vacuum moves to the venturi which usually contains an even smaller venturi called a boost venturi that draws the fuel through the main jets to feed the engine as the speed and demand increase, but that's getting off of this topic.

That is why the vacuum gauge rises and falls off again just above idle. It all happens in the first 10 degrees or so of throttle opening. As it turns out, most driving around town and in parking lots etc. is done with the first few degrees of throttle opening and at fairly low RPM so the centrifugal advance is not yet making any changes to timing. The vacuum advance is there strictly for low speed driving and provides drastically improved low speed performance. Any more than just a few degrees throttle opening and the vacuum advance circuit is out of the program and dormant.

An engine with a wild cam and low manifold vacuum at idle usually does not have enough vacuum to efficiently operate this system and no use for it anyway. Stock engines need it for ease of drivability. As to the original question, I have no idea why the factories called for slow initial timing.... I always ignored their number and added 6 or 8 degrees to initial timing. Most mom's and pop's almost never used enough throttle to bring in the total advance anyway, ha,ha.

 

Actually no. My question was initially why the ah, initial timing was so slow.

But since this has sort of migrated to vacuum advance, it should be pointed out that vacuum is very much present anytime the load has leveled off including and especially at highway cruise speeds of 50 or 60 or 70 miles per hour. The engine is very lightly loaded at steady cruise on level ground and the engine vacuum will be very high. The fuel charge is quite lean and needs more, not less, ignition advance. Consequently under these conditions the maximum possible advance will be found, on a V8 50° BTDC is not unusual. This is why vacuum advance is so ingenious, it is a totally separate and parallel system that works independently of mechanical advance.

Careful carburetor selection, setup, and tuning - mixture adjustment, jetting, and power valve, coupled with first getting the optimum distributor timing curve makes for the best over all driving and performance and economy. Easy starts cold and hot, good part throttle and full throttle acceleration, best fuel mileage (and range) + performance, and minimized pollution. What's not to like?

 

Actually yes, ha,ha. I did state that I was not answering the original question, but so many people seem to not have any idea how the vacuum advance port works that I figured I'd do a little 'splainin'. Also I didn't say there is no vacuum at highway speeds, just that the vacuum is very low when the throttle plates are open. Sorry if I stepped on your toes.

At 60-70 MPH the throttles will likely be open too far for the vacuum advance port to be operational except in a very light car with a big engine, probably a hot rod (factory or otherwise). A factory engine with a slow initial timing specification (such as mom's station wagon) would generally not fit in that category.

I agree with you, ported vacuum advance is ingenious and should be left operational on a stock street engine. Have fun.

 

I feel like it is necessary to toss out a translation for our Boston Area readers:

Dats wikked retaaded timing.

I home that helps.

 

funny...wanted to ask the question my self.....advanced my sbc crate motor just the other day until it started good....ran good....and turned off good..........

 

Advance it until it pings climbing your biggest hill, then back off a few degrees.

 

This provoked me to get the timing light on my anemic 305 sbc with stock HEI. The compression is low enough that it can be advanced to where it's hard to start and it still won't ping. Through trial and error I have it about where it runs best, and with the dial back timing light I'm getting about 14 at idle and 36 total (plus ported vacuum advance). I read that all HEIs had 20 degrees of centrifugal advance, so that about jives. Might try some lighter springs.