LZ20 write up

[BRE_dAtSuN]

2 points of compression is alot to try to remove.. like someone else said ur best off starting with a new head.. im running retarded timing colder spark plugs copper head gasket and unshrouding the valves in order to make my 10.29:1 to 9.7 or so

[datzenmike]

Are the A87 and the U67 open chamber heads the same, what I mean is, side by side do they yeild the same compression ratio, assuming they are stock?

 

If both are open chamber they should.

[datzenmike]

 

Z20E with flattops and stock open chamber is 9.941

 

28 thousandths off of an A87 (open) head removes 5.67 cc of space from the total combustion chamber volume and will increase the compression to 10.978

 

 

If the stock compression is 9.94,1and removing 5.67cc gets 10.9 then you need to remove 5.67 from the head to bring it back down again.

[banzai510(hainz)]

L20s and Z series blocks w flatops is just bad news in my opinion on a street car

 

L16/18 its fine.

[d510addict]

It's what I have though. What is so bad about them?

[d510addict]

Are the A87 and the U67 open chamber heads the same, what I mean is, side by side do they yeild the same compression ratio, assuming they are stock?

 

Doesn't the U67 have larger intakes than the A87?

[banzai510(hainz)]

What is so bad about them?

 

Youll find out.

[d510addict]

Well I'd rather not find out the hard way but unless there are dished pistons for this I'm stuck.

[datzenmike]

For dished pistons you will need to change the rods also. Way too much work and rings needed too. Head swap is best.

 

I think the U67 valves are the same but the A87 intake ports may be slightly smaller. I would still remove some metal and try to drop the compression down some.

[d510addict]

I guess me being confused is causing an issue here. In a earlier thread when I was trying to find pistons it was mentions that the Z20E block with a open chamber l head would yeild 8.9:1 C/R. The head is apparently 10cc smaller than theZ head and with hte Z head the C/R was 8.4:1. Now the Pistons I have are stock Z20E pistons they have Valve reliefs in the top (4 to be exact) the rest of the piston is flat with the top of hte block. I though these were considered flat top pistons but I'm not sure. Anywho I guess this would be easier if I sopmeone could point me to the equation for calculating Compression ratio, as well as the cc those reliefs add to hte combustion chamber as Jason grey info doesn't point out what he consideres flat top or dished let alone the cc of the dish.

[datsunaholic]

The ratio for determining STATIC compression ratio is this:

 

(Head Chamber Volume + Head gasket (crushed) volume + Piston Dish Volume + Piston understroke Volume + Cylinder Swept Volume)

 

Divided by

 

(Head Chamber Volume + Head gasket (crushed) volume + Piston Dish Volume + Piston understroke Volume)

 

 

The difference between the top and bottom is only the swept volume, but you need to know ALL those numbers to get an accurate estimate.

 

 

IF you have piston overstroke (both L16 and late Z22Es do, everything else has understroke) you subtract that instead of add it on both sides.

 

IF you have domed pistons, you subtract that instead of add it on both sides.

 

 

The big thing is you need volumes for all those. To get the volumes you need information. Like actual head gasket crush (most assume 1mm, but it's never that exact). And a lot of the "compression ratio tables" make assumptions on piston dish- Z20 pistons were "measured" to have 13cc of dish, vs 11.36cc for an L20B, but every Z20 block I've had apart had essentially flat pistons with eyebrows. However the Z20 had a lot less understroke than a L20B due to the different rod length and piston pin location even though the swept volume was exactly the same.

 

Hell, even changing to a longer or shorter nosed spark plug will change the compression ratio.

[d510addict]

Ok then I need to make a decision then. I know many of you guys know a lot about Datsun motors and many of you have different opinions on these things. I have an l20b block that needs new pistons and more than likely needs to be bored, on top of that the block needs to be surfaced which worries me. Would it be safe to say that if I can find an unmolested U67 head and maybe open the combustion chamber a bit that this LZ motor will run on premium or lower gas?

 

If I won't realistically be able to keep the motor at or under a C/R that will keep the motor running well on premium or lower, what is a easier way to go. Source and rebuild the napz20e injection stuff (I have all hte parts just don;t know how good the injection parts are) or rebuild the bottom end of an l20b.

 

The l16 in my truck is knocking me and it's a bit worrisome so I need something to put together to drive soon.

[wayno]

I am starting to feel bad here guys, I am the one the got d510addict to focus on this block, I mentioned that he had a Z20E block he was selling, and asked what was wrong with that block, I said that the only thing I didn't know was how high the C/R would jump, it was posted that the stock Z20E had 8.4 to 1, and if he used a stock L head it would jump to 8.9, now you guys are talking about 10.+ to 1 What happened to the 8.9 to 1 with a stock head? This block was supposed to be a win/win with the L head.

[datzenmike]

8.9 to 1 is an L20B with a closed chamber head.

 

An L20B/Z22E with flattops and open chamber head is 9.94 BUT his head has been milled down.

 

If you had an un-shaved open chamber head and ground away some of the combustion chamber. Removing just 5cc would drop the combustion to 9.1.

[d510addict]

Lol no worries wayno all I've lost is a bit of hope a few hours, I am actually pleased regardless as I've found that the block and internals are primo can even see the hatch marks on the cylinder walls.

 

I'm going with the l20b though, the head that I know is good with good internals can bolt right up to the l20b, I have to get pistons though as the ones in the block were cracked.

 

Also I'm glad and thankful for the input on this as now others will know a bit more about this type of conversion. When I'm not high on hydrocodone and benedryle (itch fit from hell due to soap getting in the pours of my sunburned back, was thinking of dropping the Z20E off the engine off the stand and onto foot to get me thinking of something else) I will try and edit my first post with the accumulation of info from responses. Now at least I have a decent chance of selling some L stuff to pay for pistons rings bearings and machine work.

[Guest kamakazi620]

I know where a virgin u67 head is

[DISLEXICDIME]

I know where a virgin u67 head is

 

Not if you have touched it! ;)

[d510addict]

Are headsaver shims and those copper head gaskets the same? Roy Paolo mentioned using one instead of opening up the combustion chamber and I was wondering if anyone has tried using them.

[datsunaholic]

No. Head saver shims go under the cam towers. Need them when they've been milled over .010 or so (maybe its .025) and using a standard thickness head gasket. Otherwise the chain is too slack and you'll never get it timed right, adding to the fun of having too much compression since now you have 2 issues that both cause pinging and run-on. It behaves like a very stretched chain.

[d510addict]

Oh thank you.

[banzai510(hainz)]

Felpro make a copper head saver shim that is a headgasket spacer. Thhis was their cheaper version of the cam tower shims. to restore overall head height. persoanlly I dont think it will be a big difference.

 

The felpro one I just think is more likely to leak but I cant verify this. I tore a motor apart that had one and previos owner sai it was OK.