Locking a Distributor?

[510six]

http://www.msdignition.com/pdf_catalog/Ignition_accessories_102-117.pdf

 

For a street driven motor an MSD unit like the one above, can be used to set the timing curve via PC on a locked out distributor. A friend of mine is using one of these units with a MSD Digital 6 with a locked out distributor on a 71 Nova with really good results.

[Phlebmaster]

Here is my latest work...... :D

 

Hail to the Ratsun Salute!! :lol:

 

 

 

I love this one... :lol:

 

 

This is a work in progress, so I will try it soon and let you know.

 

I still have to set up the actuator to the cab. Almost done though. :) I plan on using a threaded dial for fine tuning.

Edited April 12, 2009 by Phlebmaster

[slodat]

Aaron, be careful with on the fly timing adjustments. If you run more than 37 or so degrees advanced, you are likely going to have detonation. Detonation = no more engine real, real fast. Be careful.

[kgrantkey]

Have to agree. Some track tricks don't translate over to street very well.

 

At full throttle, gas and air always takes the same time to burn fully and expand to push the piston down. The point of maximum expansion should fall at about 17 degrees after TDC. The whole idea of timing advance is to offset the shorter time allowed for the fuel to burn as the motor speeds up. Higher speed (RPMs), shorter time available to burn, so start the burn sooner. (advance) Mechanical advance is fixed and is dependent on RPMs only and maxes out at 30-35 degrees on or before 3,000 RPMs. This includes the 10 degrees static timing at idle. The distributor doesn't spin fast enough below 1,200-1,500 RPM to cause the advance weights to move and advance the timing nor is it needed. The static 10 degrees will cover that at low speed. All of the above is for heavy throttle

 

 

Notice I said 'at full throttle'. Funny thing is, is that at part throttle, it takes even longer to burn as the molecules are less densely packed and the flame doesn't travel at it's maximum speed compared to a full throttle/fully packed cylinder. So at low speed, light throttle, (or load) it would be advantageous to advance the timing so that every ounce of hot expanding air in the cylinder is pushing down on the pistons at just the right time after TDC. The mechanical advance can't do it because it only varies timing due directly to RPMs.

 

The best method yet is to use the manifold vacuum. At lower speeds it varies directly with throttle position and load. Light throttle, high vacuum, high advance. Heavy throttle, low vacuum, low advance. The perfect solution.

 

Say you are driving around town, accelerating slowly in traffic at low speeds and part throttle. The partially filled cylinder needs more time to burn completely so the manifold vacuum advances the dizzy about 15 to 20 degrees (plus the initial static timing of 10 degrees plus any small mechanical advance, say 5-7 degrees depending on RPMs) to around 30-37 total degrees, often higher. This give the optimal time for complete combustion and you get ALL the energy from your fuel.

 

Now say you are accelerating up to highway speed. Full throttle, over 2,500 RPMs, full mechanical and static advance of 30-35 degrees is reached and you have maximum power. You reach cruise speed, let up on the throttle. Now there is less fuel and air in the cylinders which need way more time to burn but the mechanical advance is locked in at 30-35 degrees. But when you let up on the throttle it closes, and manifold vacuum rises and so does the vacuum advance to the tune of another 10-15 degrees which added to the 30-35 mechanical degrees becomes up to 50 total degrees.

 

Without the vacuum advance at cruise speed the mechanical advance would allow your fuel to burn too late and the maximum expansion would occur well after that 17 degree after TDC 'sweet spot' and your economy would suffer.

 

If there is any advantage to 'welding the dizzy' it is only at extreme throttle and RPMs where there is no need of any variable advance, mechanical or vacuum.

 

Good assessment. I want my advance to work properly.

 

http://www.msdignition.com/pdf_catalog/Ignition_accessories_102-117.pdf

 

For a street driven motor an MSD unit like the one above, can be used to set the timing curve via PC on a locked out distributor. A friend of mine is using one of these units with a MSD Digital 6 with a locked out distributor on a 71 Nova with really good results.

 

This would be the only reason to lock the advance in place for a street car...but then he still gets the full effect of advance curve with this set up. I'm limited on some things $$$$$$.

[Wharf Rat]

Looks cool to me I aways wanted to do that on my gas hog V8s

 

Don't be scared Doc :eek:

[datzenmike]

No one has asked why there is no vacuum advance at idle?? This is a perfect time for advance: low RPMs, no throttle, high vacuum very little fuel/air in the cylinder.

 

All cars after around '70 use a port inside the carb that is just above the throttle plate. When you come off idle, the plate lifts above this port and manifold vacuum is applied to the distributor, advancing it. But at idle only, there is no advance, effectively you motor is running retarded or below it's preferred efficient position. This is merely a very poor attempt to control exhaust emissions back then. Running the idle timing at the static setting, 10-12 degrees, when the engine would prefer 30-40 degrees, in effect burning the fuel as it leaves the cylinder instead of making full use of it to push down on the piston, increases exhaust temp in order to burn off hydrocarbons in the manifold and reduce oxides of nitrogen formation in the cylinder. What it did was also transfer huge amounts of heat to the head through the exhaust port causing a hot and crappy idle.

 

 

Back before the 70s, distributors were supplied with direct manifold vacuum, usually from a port on the carb receiving venturi vacuum at all times. If you look at the procedure for setting the static timing on cars made back before then, you'll see that you have to disconnect the vacuum advance so it doesn't inter fear. A motor with vacuum advance at idle will idle cooler and smoother because it is running more efficient with the reduced fuel supplied. To test this simply connect your dizzy vacuum line directly to the manifold vacuum. Did you notice that the idle speed shot up 250 or more RPMs with no other change? Now you can reset the idle speed and mixture and it will run cooler. I don't advise doing this yet as the vacuum advance canister on your dizzy is set for the (smog) zero advance at idle and may not be optimal. Also the mechanical advance may need to be tinkered with and lets not forget the static timing of 12 degrees. It may need to be lowered with the stronger earlier vacuum signal. Change one thing and it affects all.

 

Remember, ALL of this talk of vacuum advance is for any throttle position between idle and full. Anyone that drives at ANY part throttle position, needs a variable vacuum advance to optimize engine performance and efficiency. This has no effect on full throttle high RPM performance and isn't really needed for strictly drag racing or where the RPMs don't drop below 3,000-4,000. In other words, full race. Anything else will benefit by having better cooler idle, better part throttle response and much increased fuel economy.

Edited April 12, 2009 by datzenmike

[Buzzbomb]

No one has asked why there is no vacuum advance at idle?? This is a perfect time for advance: low RPMs, no throttle, high vacuum very little fuel/air in the cylinder.

 

All cars after around '70 use a port inside the carb that is just above the throttle plate. When you come off idle, the plate lifts above this port and manifold vacuum is applied to the distributor, advancing it. But at idle only, there is no advance, effectively you motor is running retarded or below it's preferred efficient position. This is merely a very poor attempt to control exhaust emissions back then. Running the idle timing at the static setting, 10-12 degrees, when the engine would prefer 30-40 degrees, in effect burning the fuel as it leaves the cylinder instead of making full use of it to push down on the piston, increases exhaust temp in order to burn off hydrocarbons in the manifold and reduce oxides of nitrogen formation in the cylinder. What it did was also transfer huge amounts of heat to the head through the exhaust port causing a hot and crappy idle.

 

 

Back before the 70s, distributors were supplied with direct manifold vacuum, usually from a port on the carb receiving venturi vacuum at all times. If you look at the procedure for setting the static timing on cars made back before then, you'll see that you have to disconnect the vacuum advance so it doesn't inter fear. A motor with vacuum advance at idle will idle cooler and smoother because it is running more efficient with the reduced fuel supplied. To test this simply connect your dizzy vacuum line directly to the manifold vacuum. Did you notice that the idle speed shot up 250 or more RPMs with no other change? Now you can reset the idle speed and mixture and it will run cooler. I don't advise doing this yet as the vacuum advance canister on your dizzy is set for the (smog) zero advance at idle and may not be optimal. Also the mechanical advance may need to be tinkered with and lets not forget the static timing of 12 degrees. It may need to be lowered with the stronger earlier vacuum signal. Change one thing and it affects all.

 

Remember, ALL of this talk of vacuum advance is for any throttle position between idle and full. Anyone that drives at ANY part throttle position, needs a variable vacuum advance to optimize engine performance and efficiency. This has no effect on full throttle high RPM performance and isn't really needed for strictly drag racing or where the RPMs don't drop below 3,000-4,000. In other words, full race. Anything else will benefit by having better cooler idle, better part throttle response and much increased fuel economy.

 

There are TONS of people that will argue through pages and pages with near religious views about ported vs. manifold vacuum on many different websites...That is one of the most concise and sensible descriptions I've read about WHY manifold vacuum is actually better for older cars...GREAT! :)

[datzenmike]

You know a couple of years ago I was that person, and erroneously advised someone with side drafts that they couldn't run on intake vacuum. :o That and the fact that my first car, a '64 Dodge, needed the vacuum advance disconnected to set the timing but later cars did not. At the time I shrugged, but it got me thinking and I started to look things up and did some research and read some fine articles by even older guys than me. They remember how the idle quality tanked in late '60 early '70 cars as a result of poor advance. This was the easy/cheap way to get the new cars to pass the new idle emissions goals.

[Phlebmaster]

This is all good info...thanks Mike and others who have contributed. :D

[mnementh666]

Thanks Mike for that explanation of the manifold vs. ported timing.

Helps me understand why my engine ran so much better with mani vac, rather than the ported advised.

That should be in the random tech tips :D