LZ20 write up

[d510addict]

EDIT

 

First of all I want to thank everyone who had input in this it certainly saved me from disaster.

 

Want I want to try and do now is make a write up that will compile a bit of info on the potential problems with this motor, it won't be terribly technical but will kind of highlight what I went through while trying to get one together.

 

Alright for the basics: LZ20

 

For specs I would refer you to Jason Grey's info

http://community.ratsun.net/topic/996-jason-grey-info/

 

But I will note 1 thing, the pistons for the Z20E are by all that I can tell flat top (and many that I've talked to have only seen them as such) but they have four slight valve reliefs.

Notice the eyebrow type reliefs.

 

Jason Grey's page lists this motor to have large 13cc dish pistons which is more dish than L20B pistons. Some very well could have 13cc dished pistons but those seem rare and I cant seem to find them for sale online anywhere so I am skeptical as to their availability.

 

The pistons also seem to be rather unique in dimensions so there will be no swapping in pistons from another motor without changing other internals (note: VG30 pistons seem to have same height but larger bore and are more available but I've heard there are some differences in wrist pins. Anyone have thoughts on this?)

 

This build is super easy to accomplish assuming you have the proper parts. What you need is a Z20E block and everything inside that block, an L series open chambered head which has had the least amount of material removed from it, from what I understand with an untouched head the compression ratio will be over 9.5:1. You will need the appropriate oil pan and oil pickup (the 521 has a mid sump so the rear sump pickup on the Z20E will not work.). Everything forward the block will need to be replaced with L20b stuff (timing chain/gears/rails/tensioners/cover/appropriate crank pulley and timing plate.). L motor mounts are needed, and you can use the stock points distributor but it would be a good idea to swap to the EI Dizzy. Lastly you will need an oil dipstick and tube from an L motor.

 

This motor goes together just like an L motor would if you were rebuilding it, with the exception of 2 things. You have to drill a hole for the dipstick on the opposite side of the stock location and in the appropriate area and plug the stock hole up. This is done because the exhaust manifold will block the dipstick in the stock location. The other mod is a head gasket mod, you can use a stock L20B head gasket but some of the holes need to me slightly elongated maybe by only a few Millimeters.

 

That is basically it, the motor goes together like an L motor like I said and you will end up with a nice 2.0 litre high compression motor. The compression ratio could be a problem for some, it is rather high and rather difficult to lower. From my understanding you can unshroud the valves but from talking with a machine shop you cannot do much unshrouding with the stock bore. Another option is to use a copper head gasket or a fel pro head saver head gasket, in a perfect world you could use either to help lower compression to something more manageable but I've yet to find convincing reviews of either products so proceed with caution should you go that route.

 

Thats it, I hope this thread can be as helpful to others as it was to me in my process.

[datsunaholic]

That sounds like you've removed about 5cc?

 

About 11:1, give or take.

[d510addict]

no way really? It ran fine on the l16 with regular it was on before I had it surfaced just barely enough to get it flat. I really hope that its not 11:1.

[datzenmike]

Only way to know for for sure how much material was shaved off is to measure the distance from the valve cover surface to the head surface and subtract that from 4.248". The difference is how much has been removed.

 

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

 

Now keep in mind that the actual amount removed isn't verified until you measure the thickness of the head and subtract from 4.248" which is the un-shaved stock thickness.

 

You can also grind away material from around the valves to un-shroud them. This will add volume and reduce the compression.

[DISLEXICDIME]

Have fun tuning that . It took me so long to get that set up right. Amd every time the weather changed I had to retune it . My buddy sold that set up after 2 months of running it.

[Hoosier77]

how can you measure off of the valve cover surface if the valve cover has been surfaced as well, if the head was hot enough to need to remove 25 thousandths to begin with then the valve cover surface was probably warped as well resulting in material loos from the top side. you need to find another reference point to measure from, you also need some cam tower shims.

[datzenmike]

The valve cover side has an 1/8" thick cork or rubber gasket and warpage is not as big a problem. The gasket only has to keep oil spray in.

[d510addict]

Is it possible to use a thicker gasket? Or is there anyone in the Portland area that can do that head work? It's 29 thousandths total removed, either way too much and I don't have another open chamber head unless someone wants to trade me one.

[datzenmike]

Yes, I think Nissan has them. You used to be able to get a solid metal plate that would do the same.

 

A 'new' open chamber head has got to be easier.

[d510addict]

Ya maybe but this head has had lots of recent work done to it, updated valves and valve seats so it wont take a shit on unleaded fuel, it has a nice cam or better than stock cam. I mean a different head would be nice but then I would have to pay for all the stuff to get it together and surfaced again with a valve grind etc. Kind of worries me going that route.

[datzenmike]

All the cam gear will swap. Heads only need resurfacing if they are warped or uneven. Small imperfections are covered by the gasket squish.

[d510addict]

What about the guts of the head (springs rockers valves etc)?

[d510addict]

http://community.ratsun.net/topic/27252-l20b-thicker-headgasket/

 

I read through this no too relevant but its a start.

[datzenmike]

Only way to know for for sure how much material was shaved off is to measure the distance from the valve cover surface to the head surface and subtract that from 4.248". The difference is how much has been removed.

 

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

 

Now keep in mind that the actual amount removed isn't verified until you measure the thickness of the head and subtract from 4.248" which is the un-shaved stock thickness.

 

You can also grind away material from around the valves to un-shroud them. This will add volume and reduce the compression.

 

Neg rep??? wtf...over. Is the math wrong? With a head that has been shaved this much removing material from around the valves is a viable option to reduce compression. An added benefit is un-shrouding the valve and increasing air flow for better breathing.

[d510addict]

What?

[d510addict]

dude I'm so sorry I must have misclicked I by no means meant to do that.

[d510addict]

Np No I didnt mean to click that rep thingy, I dont even fuck with reps at least not purposely.

[d510addict]

I'll try and find a shop that will do it.................then I need to find a different HG as well.

[datzenmike]

Np No I didnt mean to click that rep thingy, I dont even fuck with reps at least not purposely.

 

No worries, it wasn't you. Mods know who, just not why.

[wayno]

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?

[d510addict]

So if a stock head is 4.248 and it being shaved a hair over .029 total the combustion chamber cc is reduced by roughly 6 cc's which bumps it up to 11:1 + CR. I wish I knew the exact cc of the combustion chamber and what it would need to be to give me a 9.5:1 CR.

[BRE_dAtSuN]

just my two cents u can order a copper headgasket at whatever thickness and boresize from hussey performance.. lets say like a 2mm gasket.. i ordered a 1.7mm for my l20 flattops open chamber unshaved... should put me at around 9.79:1

[d510addict]

Well I didn't see pricing on their site but I am going to assume (I know I know assumptions are terrible) that is near $100 for the piece plus S&H. I'm going to check out the shop near my house and try to get a price on his services, from some googling I did it sounds like its a fairly straight forward and quick process for a properly equipped shop so maybe it won't be too much.

[BRE_dAtSuN]

its 79 bucks each plus shipping was like 85 or so

[d510addict]

I just got my A87 open chamber head back from the machine shop. The guy said all was good with it but it had been shaved apparently 25 thousandths already and it needed an additional 3. My worry is that with flat top pistons in my Z20E block that the comp ratio will be too high. Any idea what 28 thousandths off of an A87 head with the Z20e block and flat top pistons would yield C/R wise?

 

Edit: Is there a set number that for example tells me how much my comp ratio will change per 1 cc? If I have the valves unshrouded how many cc will need to be removed to reduce comp ration by 2.