Distributor wiring 8 plug to 4 plug swap on 720

[Wagmandu]

Hi Everyone! I'm new to this forum so good to meet others who mess with these things also. I Put a z20 in my truck which originally had a z22. I have it in and running on the 8 plug distributor, but only on the outer 4 spark plug wires since the z20 only has 4 plug holes. I have the 4 spark plug distributor and shaft that connects it to the oil pump from the z20. The question is the wires going to the control box on the distributor itself the 8 plug has 3 wires and the 4 plug has 2. Anyone know which ones to plug in by chance? I'll probably have a beer and mess around with it this weekend, but don"t want to fry the electricals!

Thanks

[hang_510]

I'll probably have a beer and mess around with it this weekend, but don"t want to fry the electricals!

Thanks

manual?

should detail which wires are for the primary firing.

 

 

 

lets ask mikey, he hates (knows) everything! :P

[datzenmike]

The '81-'82 720 had a terminal block (probably attached to the rad) that has three wires from the harness joined to the three going to the dizzy. The harness wires are Black/White (power), Red and Blue go to the - side of the two coils.

 

The Black/White stripe wire is the power wire to the dizzy AND the + coil terminal of one of the two coils. Connect the Black/White wire to the B terminal on the Z20 matchbox. The C terminal on the Z20 matchbox dizzy goes to the Red wire which connects to the - of the coil.

 

If you were using the other coil just swap the high voltage wire from it to the coil with the Red wire on it and you are good to go. Leave the unused Blue wire connected to the terminal block and close it up.

 

 

Z20 matchbox should be similar.

 

 

 

 

You could also swap the Z22 head onto the Z20 and run 8 plugs.

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[Wagmandu]

Thanks Guys! That was EXACTLY what i needed to know! I had gotten the motor from a wrecker in mitchigan for 350 shipped! It only has 72000 mi and looks like it had been sitting in their lot for years! It runs but i want the 4 plug distributor since after some research on these blogs i learned the 8 plug only advances 6 degrees during acceleration to due crazy ass EGR setup( correct me please if i am wrong) i've owned the ratsun for 12 yrs+ now and it always accelerated like a tired mule and bogged out when stepping on the gas. So i am hoping the 4 plug, with 12 degrees of advance, the egr eliminated and eventually a weber carb might actually liven up the old truck!

 

http://www.car-part.com/

 

This is the best search engines of wreckers i have found so far found lots of datsun parts i thought i would never find, easy format, supposedly thousands of wreckers are on here and everyone i have called has been Great to deal with. But the shipping fees may get you.

 

http://community.ratsun.net/index.php?app=gallery&module=images&section=viewimage&img=2247

[Wagmandu]

Oh, and not to mention the parts for the 4 plug are about 1/3 the price!

[datzenmike]

It runs but i want the 4 plug distributor since after some research on these blogs i learned the 8 plug only advances 6 degrees during acceleration to due crazy ass EGR setup( correct me please if i am wrong) i've owned the ratsun for 12 yrs+ now and it always accelerated like a tired mule and bogged out when stepping on the gas. So i am hoping the 4 plug, with 12 degrees of advance, the egr eliminated and eventually a weber carb might actually liven up the old truck!

 

 

The vacuum advance should be between 10 and 13 degrees.

 

The static timing on a dual plug Z22 head is about 3 degrees while the older single plug Z20 is at least 8-10 degrees. The reason for the difference? It takes a set amount of time for the fuel and air to burn completely and reach maximum cylinder pressure at a perfect distance after TDC to gain the most push on the down moving piston. This 'sweet spot' is about 17 degrees ATDC and does not change with RPMs. Even at idle the piston is moving so fast that the spark must occur before TDC in order to hit this 'sweet spot' perfectly. On a single plug head this perfect advance is about 10-12 degrees BTDC. Now on a dual plug head, because there are two ignition points, the fuel and air burns sooner. (think of a cigarette lit at both ends) If the fuel and air burns quicker it has to be lit later in order to hit the 'sweet spot'. Dual plug heads can run efficiently at under 5 degrees static timing advance. All thing equal a dual plug head is more efficient. A shorter burn time means there is less time for heat to transfer to the combustion chamber and piston tops so more is available for work pushing the piston. The cylinder runs cooler.

 

 

A Z20 is never going to equal a Z22 motor unless the Z22 was not working properly to begin with.

[Wagmandu]

Thanks for the help! Yeah I originally ordered a z22 but was actually a z20, It was listed wrong at the wreckers. So to keep me from sending it back they knocked $100 off. Being a low mileage engine and it being on hand i installed it. Eventually i'll put a fully rebuilt z22 in it now that i have it out of the truck and can take my time building it.

So as far as i can tell with the 8 plug by actually following which plug the rotor fires when, the exhaust side fires after the intake side. So they are not actually firing at the same time.

My dads friend years ago said the exhaust side fires when the exhaust valve is open, as the burnt fuel moves out of the chamber. But it sounds like they changed up the "frankendizzy" a few times in its short production run. Id prefer it if they both fired at the same time tho!

I guess what i had read, but cant remember where is that the vaccuum advance on the 8 plug only advances 6 degrees since it is trying to burn a lean mixture, and the 4 plug vaccuum advances it 12 deg since its burning a mixture with more "fresh" air and fuel.

I guess I'm just trying to figure out the better part to use in the end.

I appreciate the feedback! Must be time for a microbrew and some wrenching!

[datzenmike]

To clear up some misconceptions:

 

Both plugs on each cylinder fire together. If you look at the dizzy cap the tower terminals are labeled and the rotor has two contacts. If you set the motor near TDC and look down at the dizzy from the driver's fender one of the rotor tips is pointing generally in the 9:00 position, (which is below the #1 Intake plug wire) at the same time the other rotor terminal is at the 4:00 position. (under the #1 Exhaust plug wire)

 

 

Firing order 1-3-4-2 so the next set are the #3 Intake and Exhaust then #4 I and E and finally #2 E and I and back to #1. Always in pairs and the same cylinder.

 

 

 

 

.

[elmerfudpucker]

To clear up some misconceptions:

 

Both plugs on each cylinder fire together. If you look at the dizzy cap the tower terminals are labeled and the rotor has two contacts. If you set the motor near TDC and look down at the dizzy from the driver's fender one of the rotor tips is pointing generally in the 9:00 position, (which is below the #1 Intake plug wire) at the same time the other rotor terminal is at the 4:00 position. (under the #1 Exhaust plug wire)

 

 

Firing order 1-3-4-2 so the next set are the #3 Intake and Exhaust then #4 I and E and finally #2 E and I and back to #1. Always in pairs and the same cylinder.

 

 

 

 

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Just saved this pic and sent it to my phone, Thanks King Rat!!! :w00t: