280ZX Distributor Advance Curve Reference

[George_Zed]

Thank you so much Blue for making things more simple for me

But I haven't finished (please be nice to me hahaha )

So, can I do something for the starter issue? May be a bigger one or it doesn't make a difference?

The most important and final question... Can I do something else and keep the VA? Is there another solution? Or this is the only way and I have to live with the fuel efficiency issue on cruising?

[240260280z]

The starter should be fine. No worries there.  It is just a consequence of high initial (static) timing.

 

You could also swap the advance canister to one with less advance.

 

 

You could also modify the vaccum advance to have less excursion.  In fact if you carefully chip away at the plastic seal in the centre of the canister, you will find an adjuster.  It is usually difficult to do however.  Have a look at the bottom of this page for what lucks under that blob:

http://newprotest.org/projects/510/jasonGrayDistributor.pl

 

Another modification would be to try to extend the grove in the canister that pulls the advance pin inside the distributor.

 

You could even put a small hole in the vaccuum advance line so there is less vacuum to pull it.

[George_Zed]

I asked for advice and solution and you gave me!!!

Thank you so much Blue for your help and patience

[240260280z]

Hey George!  You ask great questions.  It is clear you want to learn.... that is what makes helping fun.

 

You will find this forum to be filled with helpful, friendly and knowledgeable people .

 

BTW I just noticed where you are located so I now understand... Greeks are great thinkers, students and teachers it is in your genes! Embrace it!

 

Photos of your car are always welcome on this site.

[George_Zed]

Thanks for your kind words Blue

I think that the best way and more reliable to me from the choices you gave me, is swap the advance canister to another canister...

I looked at the distributor advance curve attached in this topic and found that the ideal I need is the distributors D6K9-09 and D6K8-06 from 1980 and 1979 automatic 280zx models...

The advance canister I found for them has the part number 22301-P8106 for the D6K9-09 and 22301-N7705 for the D6K8-06 distributor...

I found these part numbers in http://www.nissanpartszone.com/parts-list/1979-nissan-280zx/distributor.html

May be I am right, but may be I am wrong... If someone has knowledge of this, he is more than welcome to share with us

I will continue the research though till I am sure about it yet

[Zed Head]

I think that many of the vacuum advance canisters that come with rebuilt distributors don't have as much advance as the factory units.  They seem to have settled on a mid-range advance so that they can use one part for many applications.  If you get on to a parts store site you'll see that they use the same distributor and canister for the whole range of 280ZX years.  Probably worthwhile to check first.  The vacuum advance canister may not match the distributor part number. 

 

If the distributor is on the engine and you have a timing light, you can check the full vacuum advance by setting initial timing to a low number (so that the mark will still be on the scale), like 0 or 5, then attaching the vacuum advance hose directly to the intake manifold (not ported vacuum).  Timing will jump to the maximum vacuum advance.  Do the math and you'll know what you have.  If you have a dial-back light, you don't need to reset initial/static timing.  Or if you want to know even more, you can connect a gauged vacuum source to determine when the advance starts and when it is full.  You might need to adjust the idle speed down if you try this to make sure you're not getting some mechanical also, when the idle speed increases.

 

I've also found that several of my 280Z distributors have more mechanical advance than they are supposed to.  It's common to see 10.5 and 11 degree weights in a 280Z distributor.  21 and 22 degrees.  Just something to be aware of.

[George_Zed]

Thanks Zed Head but the distributor is not on the engine now, I am just gathering information to proceed. Thanks for the info though, I will have this in mind when I install my distributor

Now the big question is if the advance canisters I found above match the distributor I have... If I can't find someone who already done this, I will go for Blue's other suggestion and modify the canister...

[Walter Moore]

First check the "breaker plate" in your ZX distributor to make certain that it actually moves. (Many of the older ones are stuck) You have to remove the advance canister to check this. If it is stuck, there is no reason to pursue the vacuum advance. (At least with that distributor.)

 

I actually modified the breaker plate to limit the maximum advance by adding a hard stop in the slot.

 

I have my initial timing set to 10 deg. BTDC. Using my dial-back timing light I have verified 17 deg of centrifugal advance (for a total of 27 deg at 2800 rpm) and 17 deg of vacuum advance. However, if I run anything less than 92 octane the car pings when the vacuum advance comes on at highway speeds. It works best at 93 octane.

(That is U.S. octane rating methods, your country may be different.)

 

After driving the car this way for 5 years, I am not sure that VA really accomplishes very much. It mostly makes the engine "feel bigger" when you accelerate gently in too high of a gear. At wide open throttle the VA does nothing at all. That is why the racing guys (who are always either full throttle or no throttle anyway) just disconnect the thing.

[Chickenman]

Just to further comment on Blue's link to Jason Gray's page. All Nissan Electronic distributors have a vacuum advance that is FULLY adjustable for both travel amount and for the spring pre-load tension. Understanding how this works can really open your eyes to tuning possibilities.

 

http://newprotest.org/projects/510/jasonGrayDistributor.pl

 

Vacuum advance pays huge benefits on any street driven car. It is particularly important at cruising speeds where a Vacuum advance will increase engine efficiency and MPG. If you're not running a Vacuum advance on the street you are just throwing money away from wasted fuel mileage. That is a proven fact. On Race Cars a vacuum advance doesn't matter because you are nearly always at WOT.

 

It does matter on a DD though. At cruise speed and RPM's,  the engine is at very light loads and with very little throttle opening. The low throttle opening  reduces the Volumetric Efficiency of the engine and the air/fuel mixture density is very low.  The low mixture density with a VE of 60% ( example )  takes much longer to burn than when the cylinder is filled at maximum density ( VE 100% ) . This requires lighting off the mixture much earlier in the combustion cycle so that Peak cylinder pressures occur at the proper time ATDC. This maximizes torque and fuel efficiency.

 

It is important to note that the reduction of VE at cruise RPM's and low throttle opening also reduces what is called " Dynamic Compression " ratio.   Static compression ratio is the mathematical calculated compression ratio of cylinder volume. It is calculated using 100% VE.   Dynamic Compression ratio is what the engine actually sees in a running condition and VE is a variable.  This is why when you do a standard compression test, the instructions always tell you to  jam the throttle wide open. If the throttle is closed when taking a compression test, very little air can enter the combustion chamber and you get a false reading.

 

It is also why engines with big cams require more ignition timing advance at low rpm's and mid-range than a stock cammed engine. The big cams overlap period reduces the Dynamic Compression ratio at idle and low rpms' ( below approx 2,500 rpm )  and you also get exhaust dilution at idle from the over lap. Additional advance at idle is required by bigger cammed motors.

 

Getting back to stock engines. At cruise RPM and light loads, it is not uncommon for Petrol engines to require a total ignition advance of 50 degrees BTDC. Even engines with high static compression ratios ( IE: 10 to 1  ) require this to operate at Peak efficiency.

 

Continued....

[Chickenman]

Going back to Jason Gray's excellent distributor article, many people skip over the part on Vacuum advance. Don't do that. Read it carefully and then read it again.

 

http://newprotest.org/projects/510/jasonGrayDistributor.pl

 

Here is a very important part pertaining to the Datsun Electronic Distributors, as others have mentioned:

 

 

The vacuum advance canisters can also be re-curved. All the EI dizzys use the same canister that is adjusted at the factory for desired advance characteristics. To re-adjust, remove the putty blob on the end of the canister with a high speed grinder to expose the adjustment screws. Inner coaxial pin limits vacuum advance travel, outer grub screw adjust the spring pre-load on the diaphragm. Turning the outer screw counter-clockwise reduces the amount of vacuum necessary to initiate advance.

 

So what does that tell us? Well lets say you want a total mechanical advance of 32 degrees ( Depends on fuel quality and other factors ) at 3,500 to 4,000 rpm. Full mechanical advance is usually all in by 3,500 rpm. Some people prefer it coming in faster, some later. It all depends on the engine, fuel quality and drive-train setup.

 

You should check the distributor plate and calculate the numbers. IE:  a 10 stamp on the  dizzy plate = 20 crank degrees. Add 12 degrees initial timing and you're bang on at 32 degrees total.

 

Now lets look at the D6K82-01. This has an 8.5 dizzy plate = 17 degrees crank advance. A fairly common number. Add 15 degrees initial timing and you have you 32 degrees total mechanical advance. Always double check the figures with a Dial-back timing light.

 

Notice that we have not discussed vacuum advance at all. That's because when setting total mechanical advance, you musty always have the vacuum hose disconnected from the distributor ( and open end plugged of course ).

 

So lets address that. You have your D6K82-01 dizzy dialed in to 32 degrees total advance so lets see what your total mechanical and vacuum advance will be under cruise ( light load with maximum vacuum ) . Lets see... the D6K 82-01 is a low compression emissions engine, so Nissan equipped it with a 30 degree vacuum can and low static timing ( 6 degree BTDC ). Then you came along and  bumped the initial timing from 6 degrees to 15 degrees because = HP!! . Your mechanical advance curve is now good for maximizing fuel efficiency and HP, but lets see what happens when we add in the Vacuum advance. 15 initial + 17 mechanical + 30 vacuum  = 62 degrees!!!    Houston we have a problem!! What vacuum canister am I going to use? Simple...the original one the dizzy came with. No need to buy a different canister, just reset the limit stop on the present one.

 

Edit: Remember that you want the total mechanical and vacuum advance at cruise RPM to equal approx 50 degrees BTDC . You can adjust that down a bit if you get pinging under light throttle application at cruise.  

 

Remove the Epoxy blob with a thin flat plate screwdriver. Just chip it away. After 35+ years I've found that the epoxy has usually gone all brittle and flaky. Re-seal with an RTV blob. Then adjust the inner limiting screw to limit the maximum travel to achieve 18 degrees vacuum advance. 15 initial + 17 mechanical + 18 Vacuum = 50 . There should be enough adjustment to handle all situations.  I make a rough estimate and then do a final check with my Dial-back timing light and a Mighty-Vac. Jason Gray's article even tells you how much each mm of adjustment affects timing advance.

 

 

For each 1mm of travel of the vacuum canister actuating rod, the timing is changed by 4.24 crankshaft degrees.

 

 

You can also adjust how quickly the vacuum advance comes in by adjusting the outer threaded sleeve. This can come in very handy on motors with big cams. I'll post some info o that later.

 

These vacuum canister adjustments can be made on any Datsun EFI dizzy.  If it has a putty/epoxy blob on the end of the vacuum can, that's a fully adjustable vacuum canister. Lucky us.

Edited December 5, 2014 by Chickenman

[George_Zed]

Nice... 

 

I haven't tried to remove the advance canister yet, didn't have time to work with my distributor, but I will let you know when I do it if the breaker plate moves in order to continue with the vacuum advance adjustment...

[Chickenman]

^ I made a couple of edits to my original post as I made an addition error. The important thing to remember is that you can fine tune the Vacuum canister to reflect your particular engine specifications and fuel requirements. To maximize fuel economy you want the engine just on the verge of light pinging. BTW, modern engines with Wide Band fuel control and Knock sensors can be much more aggressive in the ignition Timing maps than the ECU's and limited sensors that they had to work with in the late 70's,1980's and early 90's. Partly the reason why you have seen such advances in Fuel economy since OBD-II standards came into play in the Mid 1990's.

 

With good fuel ( 91 to 93 Octane ) , 10 to 1 CR and a good combustion chamber design, any carburated or EFI aluminum head engine should be in the 50 degree total advance range under cruise condition. If you encounter a slight ping when applying light throttle at cruise, then reduce the amount of Vacuum advance by a couple of degrees with the limit stop.  This assumes that you have adjusted your mechanical advance to be perfect. A chassis Dyno really helps there.

 

For example. My 1986 Chevy Camaro that I used to Autocross/Hillclimb put out 420BHP and ran quite happily on the street with 91 Octane gas. ( It also easily passed Provincial emission specs with a HF Catalytic Convertor ) Ignition Timing was 12 initial + 22 mechanical = 34 Total mechanical . All in by 3,000 rpm.  When I went racing ( Hillclimbs ) I would use 94 Octane as I needed every single BHP I could squeeze out of the engine.  On 94 Octane fuel I could run 16 initial + 22 mechanical = 38 Total mechanical. This was set to give maximum HP and Torque on the Dyno. Vacuum advance ( Crane fully adjustable vacuum can... just like our Nissan's ) was adjusted to give 15 degrees extra under Cruise conditions.  With my street tune of 91 Octane that gave me a total Mechanical and Ignition advance of 49 degrees. With 94 Octane total mechanical advance and vacuum advance = 53 degrees. Never any pinging.  I would pull 22 to 24 mpg out of this 420 hp Holley 780 carbed car consistently, which was amazing. That is because of a sharply tuned car that ran a properly adjusted Vacuum advance.