Any advantage by switching to a 8 plug head on a Z engine?

[Spiff]

Would there be any advantages of going from 1 to 2 plugs per cylinder? I remember overhearing a guy with a turbocharged corolla gt and he had switched to an 8 plug head because of more powerful combustion if I heard correctly

 

I have a Z20E with a turbo conversion, megasquirt and coil on plug conversion and I have wondered if there was something to gain by going to an 8 plug head. 

[wayno]

Wow, I am going with don't fix it if it's not broke.

I have absolutely no idea if 8 plugs would be better, but I had to say Wow.

[datzenmike]

The dual plugs would fire large amounts of EGR diluted and hard to light lean mixtures.

 

An added plus is the need to reduce your timing advance. With two points of ignition the fuel burns sooner. Shorter burn time means lighting it later is possible and still get maximum cylinder pressures just after TDC . This means less time at maximum temps and pressure when NO_x is formed. (the real reason Nissan went with it)

 

Shorter burn time means less time for heat to be transferred to the combustion chamber walls and piston tops and more available for expansion pressure to push the pistons down. This would reduce hot spots and pinging on an already detonation resistant hemi head anyway.

 

 

 

 In N America the early Z20 single or dual plug head is the same as the Z22 heads which were all dual plug. The Z24 heads are the same as the Z22 with these exceptions.... The opening for the mechanical fuel pump is not machined out so no block off plate and the intake ports are squarish with rounded corners rather than round.

 

All Z20/22/24 combustion chambers are 57cc, all valve the same size and all cams the same.

 

 

 

In '83 when the Z24 came out in the 720 truck a 'Mileage Option' Z20 engine was offered. It has smaller combustion chambers of about 45cc and flat top pistons for 9 to 1 compression (and dual plugs)  Note the small top and bottom quench areas on the W04 casting Mileage Option Z20S head above

 

 

Dual plugs would be more detonation resistant and more efficient. On a stock engine the difference would be small. On a turbo high HP engine this would be magnified..

[Spiff]

I thought the Z24 head was the better of them? The one that flowed best? 

 

Over here I've seen few dual plug Z engines if any. And the few D21's that was sold with Z24 where for the most part carbed with mechanical fuel pump in the head. Not like the one you have a picture of.

 

I found this little study while searching for relevant info, seems there is some advantages to dual plugs, at least with a side mounted spark plug like in a lot of the 2valve heads. http://www.ijsr.net/archive/v2i8/MDIwMTMyNDM=.pdf

 

I don't have any egr stuff on my engines, not as strict emissions here in europe compared to the us at that time. 

I'm more intrigued in the potential for power, and more so reducing the potential for detonation and reducing combustion heat. Better fuel consumption is also welcomed :P

 

If you have a 4 plug head, can you drill and tap on the exhaust side for the other set of plugs or do you need the 8 plug head specifically ?

[datzenmike]

This is my '80 Z20E head, '81s were dual plug. As you can see, and I assume yours is the same, you could with care drill and tap for the extra exhaust side spark plugs.

 

 

Z24 head with dual plugs.

 

 

Again I only have N American, and Canadian in particular, Z heads. Two Z20E single plugs, Two Z22 dual plug heads from the 720 truck and two Z24 dual plug heads from a 720. All valves are the same size, all cams are the same and other than the intake port shaope they are essentially the same. I cc'd all six twice.... same.

 

 

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[Spiff]

I see, but everyone says a Z20 head on the Z24 block gives worse performance than the Z24 head on a Z24 block? Might be drifting slightly off topic here now but.

[wayno]

I see, but everyone says a Z20 head on the Z24 block gives worse performance than the Z24 head on a Z24 block? Might be drifting slightly off topic here now but.

 

Find a Z20 head with 8 plugs, I have one and I have 2 Z22 heads, I cannot tell which one was the Z20 head anymore.

[datzenmike]

Correct. Both Z20/22 have round intake ports with EFI injector notches. The Z24 s do not. (my picture does because I cut them in)

 

 

 

 

I see, but everyone says a Z20 head on the Z24 block gives worse performance than the Z24 head on a Z24 block? Might be drifting slightly off topic here now but.

 

Maybe something is different about the European heads, I can't say. All I know is what I've reported about the three pairs have. The squarish Z24 intake may flow a bit better, but I doubt it's much.

[Spiff]

No this is info i picked up here on ratsun and the Nissan 720 group on Facebook. The square ports might have something to do with it.

 

Hard to find 8 plug heads here in Norway, Z engines in general are pretty hard to come by

[datzenmike]

Maybe the intake as well and the carb. I know the stock carbs are rather small and definitely not for power but more for mileage and anti pollution. Z24 owners say a Weber 32/36 really wakes the engines up.

[G-Duax]

Hard to find 8 plug heads here in Norway

 

Oh, just bite the bullet, and have one shipped in from another part of the world.

I do it all the time.

[datzenmike]

Or have a shop drill out the plug holes. Then you will need a dual coil distributor.

[Spiff]

I'm running coil on plugs on my Z20, so I would need four more coils :-P but they would melt, I checked today and they would come dangerously close to the exhaust manifold and the number 1 would interfere with the compressor housing on the turbo.

If I ran ls coils or some motorsport wastespark coils with spark plug wires it could be done.

There's a machine shop not far from me that could probably drill new holes i guess if I wanted to go that route

[Stoffregen Motorsports]

I was going to suggest a wasted spark coil, but you're already on it.

[distributorguy]

As an ignition guy, I don't think you'll gain anything.  Its such a small cylinder that even if you are boosting it up to an equivalent of 16:1 compression, a single spark will do the trick.  If you want more power, increase the flow of the head.  The square port does have a significantly larger cross-section than a round port, so it will flow better.  Dual plugs have nothing to do with a power increase - unless you get to a point where a single spark doesn't have enough time to burn the volume of fuel/air in your cylinder.  Since the chamber is quite small, and only maybe 88mm across, the flame has plenty of time to travel the entire distance before the exhaust valve opens.  Spend your time and money on head porting, or potentially open your plug gap to increase coil output.  Try .050".