discrepancy in Z20E connecting rods...

[Master-O-Turbonics]

So I ordered a set of Z20E rods from a rebuilder, and they sent me L20B rods.... So I look at their catalog and they have two part numbers for Z20E rods, some the same as an L20B rods, and then some from a pickup truck Z20E, which have a different part number.

I got the 200sx Z20E/L20B rods...

Are 80-81 200sx Z20E rods the same as L20B 145.9mm rods? I heard Z22S rods were the same as L20B rods, but not the Z20E.

[datzenmike]

I have removed two sets of '80-'81 200sx rods and they are 152.5mm or about 6". The rods in the Z20S motor in the '84-'86 720 are, I believe, the same. I base this on the fact that the 720 motor has a 9.5 to 1 compression. This is achieved by using the Z20E flat top pistons from the 200sx and they have a specific pin height that will only work on the 152.5mm rod length.

 

There are Z20S pistons that have a dish and a different pin height and although there is no rod length listed, by calculation, they should be in the 148.6mm range length.

 

L20B rods (145.9mm) are NOT the same as any Z20E or S rods. They are, however, the same length as the Z22S and early Z22E rods.

 

If you want the 6" (152.5mm) Z20E rods from an '80-'81 200sx the Nissan pt. # is 12100 N8500

 

 

Hope this helps you out.

[LenRobertson]

I have a Z20 from an '81 SX, with FI and 8-plug head. Also have an L20b block (original bore) and crank. Can I put the Z rods and pistons in the L block? And what is the advantage, just CR increase? I'm going to use a close-chambered head, so will I end up with something that I need premium octane gas for? There is some key thing about the long Z rods I've never quite understood. I went to quite a bit of work pulling the Z20 engine, thinking those rods might be useful. Are they?

 

Len

[datzenmike]

Len, the Z20 E or S engines below the head are almost exactly the same as the L20B. The blocks have slightly different casting webs but are the same 85mm bore and 86mm stroke. Cranks are fully counter weighted and (as near as I can measure) identical. This means that the rod and piston assy from a Z20 E or S will fit the L20B.

 

The more desirable Z20E has the longer 152.5mm (6") rods and shorter piston pin flattops. Popular wisdom has it that the longer the rod the smoother and higher the motor will rev. Longer rods reduce frictional side loading on the big ends.

 

Z20E rods with flattops will give a compression of almost 10.7

[LenRobertson]

Len, the Z20 E or S engines below the head are almost exactly the same as the L20B. The blocks have slightly different casting webs but are the same 85mm bore and 86mm stroke. Cranks are fully counter weighted and (as near as I can measure) identical. This means that the rod and piston assy from a Z20 E or S will fit the L20B.

 

The more desirable Z20E has the longer 152.5mm (6") rods and shorter piston pin flattops. Popular wisdom has it that the longer the rod the smoother and higher the motor will rev. Longer rods reduce frictional side loading on the big ends.

 

Z20E rods with flattops will give a compression of almost 10.7

 

Great information. Thanks! Is the 10.7 CR with an open or close chambered head? Or maybe it doesn't matter so much. Do I recall correctly a closed chamber raises the CR by approx. 0.5, but due to better chamber quench (or one of those tech terms), the closed chamber is actually less prone to detonation? It would be nice if I could remember some of this stuff.

 

Len

[datzenmike]

Sorry Len you mentioned using a closed chamber head so that's the compression for flattops and a p-nut head. An open chamber head would come out to 9.94

 

Open vs. closed chamber head:

 

An open chamber head has a combustion chamber that is round where it meets the bore and there is open space above the piston when it is at TDC. In all gas engines the fuel and air is compressed up into the combustion chamber. When this happens, all the heat in it is super concentrated into a small area. Depending on the compression ratio this can be so high that this heat can cause the fuel and air to ignite by itself before it is supposed to and the expanding gasses try to force the rising piston backwards. This is called ping and it will damage the motor and reduces power. There are other things that can add to this problem. A very hot spark plug tip can be just enough plus compression to cause pinging. A very hot exhaust valve or hot glowing carbon deposits can also add heat to the compression. No fuel air mixture is totally homogeneous, there will be lean and rich areas. Lean areas will run hot as there isn't as much cooling effect from the evaporating gas present. A rich area will be cooler but will build up carbon deposits which can retain heat. So all these factors added to the heat of compression can cause pinging.

 

A closed chamber head or P-nut head does not have a perfectly circular shape the same size as the bore, indeed there are some places where the head surface extends over the bore and is separated from the piston top only by the head gasket thickness at TDC. This area where the piston and head almost touch is called the pinch or quench area. When the piston approaches TDC the air trapped in the quench area is violently pinched out into the combustion chamber and this causes extreme turbulence or swirl. This is beneficial as it further mixes the fuel air for more complete combustion. This turbulence, reduces hot spots and carbon build up two other causes of ping. The cylinder temperature is more evenly distributed and pre ignition reduced. All things equal, a head with a quench area can be run with a higher compression than an open chamber head.

 

For best results:

A head with a quench area should have flattop pistons. Pistons with a dish will leave a larger gap between cylinder head and will not pinch out the air as well.

[LenRobertson]

A head with a quench area should have flattop pistons. Pistons with a dish will leave a larger gap between cylinder head and will not pinch out the air as well.

 

Wow, thanks for taking the time to post such a great explanation. I've read bits and pieces of information on why peanut heads are desirable, but you put it all together so I actually understand it. My knowledge of combustion chamber design dates from the '60s, when the hemispheric camber used by Jaguar and Alfa was still considered to be way cool. I think the art/science of chamber design was moving on at that time, but my thinking stuck with that simple little bowl shaped chamber.

 

It sounds like I need to seriously think about using the Z20e rods and pistons, since I already have them. Of course, they are still in the engine, so I have no idea of condition or whether they are standard or oversize. The "story" I got is this was supposed to be a "good" engine before it was parked, but that usually tends to be the "story". If I end up having to use premium gas, it wouldn't be too much of a problem.

 

Is there anything regarding valve/piston clearance I need to know about if I use the Z20 rods and pistons?

 

Finally, you made the mysteries of combustion chambers so understandable, how about explaining String Theory in physics to me? I worry a lot that I don't understand this. Maybe you can help!

 

Len

[hang_510]

they gave you the wrong rods. <_<

 

Popular wisdom has it that the longer the rod the smoother and higher the motor will rev. Longer rods reduce frictional side loading on the big ends.

isnt it a *rod/stoke* ratio more than that, optimal being ~1.7?

i got close...

[hang_510]

Is there anything regarding valve/piston clearance I need to know about if I use the Z20 rods and pistons?

yes, after you select a cam...

 

String Theory in physics to me?

gravity sucks!

just ask the one on the right

 

[LenRobertson]

gravity sucks!

just ask the one on the right

 

hang - Fantastic, you gave me just the hint I needed to figure this out for myself. Okay, Gravity is the force that pulls a wrench or bolt down when you let go of it. It falls until it hits the garage floor. What is usually thought of as "bounce" is actually an invisible force similar to Gravity that pulls the dropped item under the car, just like it was tied to a string and pulled. Hence, the force must be String Force. How often does a dropped whatzit come out from under the car and land between your feet? Virtually never, right? It normally goes back under the trans, if you are working on the engine. I suspect the String Force is somehow similar to the poles on a magnet, where like poles of two magnets push away from each other. String Force pushes dropped objects away from people, or mechanics anyway. So thanks for helping me with my problem. My next problem is, I'm getting so smart my wife is about to throw me out of the house. Although maybe "You are nuts!" is her way of complimenting me.

 

The more I study the pics of the young ladies, the more sure I am the one on the right is actually lifting all the rest, sort of like cracking a whip. The camera just caught it when it looked as though the rest were jumping.

 

Len

[datzenmike]

Actually, the string force always pulls a dropped object to a point equidistant form all four sides of the vehicle. Therefore it is a speed bump on the road to free will. We observe and determine that it is closer on one side because we cling to the belief that we are in control we have options, we choose..... but in reality it never really mattered what side we reach under from as it is always just out of reach.

 

In some cases space time closes in around the dropped/dropping object and on the Planck level, the mass of atoms is forced into a singularity of infinitely small size and effectively 'drops out' of our universe that we share with eleven others. It falls and falls and will continue falling 'till the end of time' or the heat death of the universe, whichever comes first. Everyone, or at least many of us (the others are in denial) have experienced this phenomenon. Who hasn't dropped a part that never hit the floor? I mean a clean concrete floor with no hiding place. A most exhaustive search of the vehicle fails to turn it up. It's still falling. I once found a dropping part that had returned to our universe months later and several blocks from home. How it accomplished this I have no idea, usually once dropping it is never seen again. It was distorted and bent as if exposed to titanic forces.This universe is a mysterious place.

 

 

 

Is there anything regarding valve/piston clearance I need to know about if I use the Z20 rods and pistons?

Len

 

 

A good question Len. I assumed because the L16/18 can survive flattop pistons then so would an L20B.

[LenRobertson]

I have long suspected, although can't prove, there is at least one, if not several, parallel universes and things (maybe people?) can pass on to them and may or may not return. Actually I can prove this, at least to my own satisfaction, by watching my wife in action. She has the ability to pass most smaller objects to "somewhere" - usually her keys, but many things and papers can "go away" when she needs them. She generally can bring them back from "wherever", or they return on their own, after minutes or hours of searching. She never finds lost things in the last place she looks as normal people do. Things generally appear in the first or second place she had originally looked. It is spooky to watch.

If I lose something, it is usually gone for good, although the explanation is rather boring - I likely threw it away by mistake. So it went to the landfill, and wont be back. But I do have to deal with String Theory every time I'm near anything mechanical.

 

I think my valve clearance question came from the phrase "long rods". My mind pictured those poor little flat tops being poked way high in the cylinder. I'm going to have to pull the head on the Z20 and take a look at what is there. I have the head off an L16 to compare it to.

 

Len

[hang_510]

I'm getting so smart my wife is about to throw me out of the house. Although maybe "You are nuts!" is her way of complimenting me.

 

The more I study the pics of the young ladies, the more sure I am the one on the right is actually lifting all the rest, sort of like cracking a whip.

she will NEVER let you get there! she will however throw you out w/o hesiattion, compliments or not ;)

 

 

re the pic: actually, only the 1 on the right jumped up, gravity then returned her to the original poistion and the others responded, observing newton 3rd law, and were launched into the air (OK... whip like)

... and somewhere a butterflys wings were crushed :(

[datzenmike]

Len has your wife ever lost you? Presumably you must have been recovered. I'd stay on her good side.

[LenRobertson]

Len has your wife ever lost you?

 

Yeah, she loses me every time we get in Fred Meyer or any other large store. I don't where she goes, but I can walk the aisles for 15-20 minutes and not see her. Osama bin Laden isn't even in the game compared to her. When she finally reemerges from Wherever, I'm so exhausted I hand her grocery money and go wait in the car. I think she senses when I am just about to drop in my tracks, and appears in time to get the money.

 

Len

[Master-O-Turbonics]

I have a Z20 from an '81 SX, with FI and 8-plug head. Also have an L20b block (original bore) and crank. Can I put the Z rods and pistons in the L block? And what is the advantage, just CR increase? I'm going to use a close-chambered head, so will I end up with something that I need premium octane gas for? There is some key thing about the long Z rods I've never quite understood. I went to quite a bit of work pulling the Z20 engine, thinking those rods might be useful. Are they?

 

Len

 

The combo you listed of an L20B with stock Z20E rods/pistons (13cc dish) will give you:

max rod angle: 16.378 degrees

deck clearance: .2mm

Rod/stroke ratio: 1.773

Bore/stroke ratio: 1.012

Static compression ratio: 9.076:1 with a V91 L20B head with 41cc chambers, and a 1.25mm head gasket height. 9.3:1 with a 37cc chamber.

 

Calculated using: http://www.ozdat.com...e/enginedesign/

 

 

In my L26, I had flat top 83mm pistons and open 44.7mm chambers bringing me to ~9.236:1 compression ratio and it ran pretty good on 89 octane, better on 93.

[datzenmike]

Only problem is that all the Z20E rod/pistons I've seen are flattop with small valve reliefs.

 

 

Z24 Z22S Z20E L20B

 

 

 

 

.

[hang_510]

Only problem is that all the Z20E rod/pistons I've seen are flattop with small valve reliefs.

why are the reliefs a problem?

 

i used 1/2 dished pistons w/the U67 to have a little squish, and they still needed releifs for the IN

[hang_510]

bringing me to ~9.236:1 compression ratio and it ran pretty good on 89 octane, better on 93.

@ ~9.5:1 i can run 87 in cruise mode, 91 is much better though :)

93... i wish! :angry:

[datzenmike]

The combo you listed of an L20B with stock Z20E rods/pistons (13cc dish) will give you......:

 

I'm saying none of the Z20E pistons I have are 13cc dish. As far as I am concerned they were flattops with reliefs for the valves. If you have 13cc dished Z20 pistons you likely them from a Z20S? Here's a picture of the Z20S piston:

To tell the difference the Z20E has a pin height of 31.75mm and has to be this height to work on the 6" rods. Z20E piston rings are also thinner top to bottom than the Z20S. I think 1.5mm vs. 2mm on the Z20S

 

why are the reliefs a problem?

 

i used 1/2 dished pistons w/the U67 to have a little squish, and they still needed releifs for the IN

 

Hey Brian, not saying the valve reliefs are a problem just pointing out that they are flattops but have them.