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#1 Apollo77

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Posted 18 November 2017 - 10:02 PM

So from what I have found so far, I am not going to get much more out of the z20 than I am with an L20b. I was planning on a z22 but that block turned out to be a z20. It is what it is and I want to make the best of it, so... What can I do to get the most out of what I have to work with? Z20 block with a A87 head and a 32/36 web

Update:
Pistons are 3.320" or 84.33mm
Cylinders are 3.345" or 84.96mm
Rods are marked N85
exhaust is stock L20b and not cast, however the intake is cast.

#2 datzenmike

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Posted 18 November 2017 - 10:23 PM

What you have is an L20B with long rods, flattop pistons and an L18 head. Compression should be about 9.0 if an open chamber A87. Sounds good to me the way it is.

 

 

Does it have the L16 cast exhaust header? Or the 4 into one L20B? Find the L16 exhaust if you don't.

Myself I would try to find a U67 which definitely has larger intake ports. The A87 may or may not have the larger U67 valves.


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#3 wayno

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Posted 18 November 2017 - 10:43 PM

Does the truck Z20b engine also have long rods?


 

 


#4 flatcat19

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Posted 19 November 2017 - 12:21 AM

I'd be happy to have the Z20.

You can't hang if your nuts haven't dropped...it's physics


#5 datzenmike

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Posted 19 November 2017 - 07:17 AM

Does the truck Z20b engine also have long rods?

 

Yes and a special high compression head for 9.0 compression. It also came with 3.364 diff. ( this thing was designed to ping ) so a knock sensor was added to the block and an ignition retard system. It also came with a 240mm clutch for those full load up hill take offs with a 2.0 liter engine and 3.362 differential. 


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#6 wayno

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Posted 19 November 2017 - 09:51 AM

I have no idea why I put a B in there.

 

So if all Z20 blocks are long rod blocks why does one need to measure anything, the Jason Grey info shows this for the piston height on the Z20s, where did he get this piston height measurement, would this not indicate a shorter rod?

 

Z20s-------------------35.56mm / ? dish / 85mm bore 

 

To me this piston height measurement would indicate a shorter rod, if the Z20 truck blocks are also long rods, did they have dished pistons or do all Z20 blocks have flat tops?

Here is the info for the Z20E.

 

Z20E------------------ 31.75 / approx 13cc dish / 85mm bore (Ive also seen flattop Z20E pistons). 

 

This is all very confusing, if there is no such thing as a 35.56 piston height in a Z20s, maybe this info should be deleted.


 

 


#7 datzenmike

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Posted 19 November 2017 - 10:08 AM

Yes there appears to be two different rod/piston combos... but looked up the piston for the Mileage Option 720 and it was the same as the A10 Z20.

 

Hang on and I'll recheck this. Remember the S110 200sx? It had early and late Z22 with this different length rods?.


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#8 Stoffregen Motorsports

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Posted 19 November 2017 - 10:18 AM

I was always under the impression that the Z20E was the one with the long (N85) rods. And I built a few of those with L heads, but the compression was through the roof. This was all very early on in my career and I learned the hard way that cutting the stock pistons enough to bring the compression down to acceptable levels resulted in cracked pistons.

 

An open chamber L head would be less of a problem, but I think it still would require some massaging of the combustion chamber to get the proper compression volume.

 

Have you done the math, Mike? Is there an L head that works?



#9 datzenmike

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Posted 19 November 2017 - 11:01 AM

OK only one rod part number was used for the 720 Z20 the A10 Z20 and the S110 200sx and it is 12100-N8500. This is the 152.5mm (or 6") rod. Pistons for these rods varied by number... possibly the ring width or maybe there was a small dish but the pin height must have been at or about 31.75.... as Gray listed.

 

He also mentions a Z20 head with 45cc and pistons with 13cc dish.(basically the same as an L20B, well close) compression is 8.35. This has to be from the A10 car.

 

I have two Z20 heads from a 200sx and they were both 57cc which would give a compression of 8.35 only with flattops which they had.

 

I have removed Flattops from two S110 200sx Z20 engines so I know what they have ('80 and an '81) reverse engineered the 9 to 1 compression on the 720 engine and the combustion chamber must be....

 

This is my Z20E piston from a 200sx.

baDrUG8.jpg

 

 

This is alleged to be a Z20 flattop (on left) and a longer pin height Z20 piston on the right. It's dished also

 

V33A7Tn.jpg

 

 

.


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#10 datzenmike

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Posted 19 November 2017 - 12:45 PM

dNyMVVS.jpg

 

This is a Z20 S (carb) from an '81 goon. It has the same pistons as theS110 200sx . Basically an L20B with flattops. The piston is 0.2 below the deck where as an L20B is 0.45mm so slightly more compression. This engine with a 45.2cc open chamber L head is barely 10.08. 10.18 You can't go higher unless domed pistons, closed chamber head or plane the head down.


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#11 Doctor510

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Posted 19 November 2017 - 01:19 PM

Z20 uses a 6.00" rod, compression height (aka "pin height") is .250" SHORTER than the regular L20B pin height, L20B rod length is 5.75".



#12 datzenmike

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Posted 19 November 2017 - 01:48 PM

Yes 6" or 152.5mm

 

The L20B and Z20 block is 227.45mm tall

 

L20B/ .... 1/2 stroke is 34mm plus 145.9mm rod plus 38.1`mm piston pin height is.... 227mm or 0.45mm below the deck

Z20/ ....... 1/2 stroke is 43mm plus 152,5mm rod plus 31.75mm piston pin height is..  227.25mm or  0.2 below the deck


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#13 wayno

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Posted 19 November 2017 - 05:27 PM

You guys have me worried now when you start talking about having to cut pistons down and such.
 

I have a 1981 Z20 block that I put a W53 closed chamber head on, the block has flat top pistons that were pretty close to being flush with the deck as I used a feeler gauge and a strait edge to check clearance and it wasn't much(I forgot what it was now).

How worried should I be, I was planning on using non-ethanol premium(92) to fire it up, now I wonder if I should even try too.

What is the compression ratio going to be again? 10 to 1?


 

 


#14 datzenmike

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Posted 19 November 2017 - 07:15 PM

Z20 with flattops and 41cc closed chamber head would be

 


L20B/ .... 1/2 stroke is 34mm plus 145.9mm rod plus 38.1`mm piston pin height is.... 227mm or 0.45mm below the deck

Z20/ ....... 1/2 stroke is 43mm plus 152,5mm rod plus 31.75mm piston pin height is..  227.25mm or  0.2 below the deck

 

L20B 

0.45mm below the deck is 2.55cc plus

the crushed head gasket (1.2mm) for 6.8cc plus

piston dish 11.36 plus

the combustion chamber 45.2cc for

Compression of..................... 8.422 (this is the stock compression)

A closed chamber head is..... 8.90

 

Z20

0.2mm below deck is 1.13cc

gasket volume is 6.8

dish is zero (you are loosing 11.36cc of combustion chamber here)

open chamber head is 45.2cc for

Compression of..... 10.18 (sorry wayno)

Closed chamber.... 10.968

 

The Z20 uses a 57cc Z series combustion chamber so the compression would be a lot lower.

 

Find a U67 head and hog out around the valves to relieve them. You can also scribe the gasket circle and dremel away the cylinder wall near the valves for un-shrouding and better breathing, but don't go down into the ring land. Adding just 2cc of extra volume drops the compression to 9.84....4cc drops to 9.53


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#15 wayno

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Posted 19 November 2017 - 07:29 PM

So will it run on premium(92)? race fuel(103/110)?

 

I had a Chevy Nova with a built 350 with very high compression when I was a kid and it ran on regular, it was so high compression that I had to give it the same amount of pedal to go up or down hill, as I have mentioned in the past if I let off the pedal to fast the rear wheels would just quit turning when the street was wet, it was dangerous to drive unless one knew how to drive it.


 

 


#16 Stoffregen Motorsports

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Posted 20 November 2017 - 09:20 AM

Anything 10:1 or under can run quite well on pump gas.

 

With 10:1 you should be able to run 32 degrees total ignition timing and 91 octane.



#17 wayno

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Posted 20 November 2017 - 09:39 AM

I have never successfully done a compression test where I believed the results I got(diesel engines), but I have doubts this engine will show close to 11 to 1 CR, it is a used block(I seen it run), and a slightly used head(less than 5000 miles on rebuild), I have a couple hand held compression testers but would need to connect a transmission case and starter, I have a napZ case I could use to do the starter, but it would be stone cold, this engine has never been started the way it is.

Do I do the test dry?


 

 


#18 Stoffregen Motorsports

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Posted 20 November 2017 - 10:18 AM

I would buy a burette and measure the volume instead of relying on any compression tester. It is possible to measure the compression volume on an assembled engine, then you use basic engine math to figure out the CR.

 

Here's a simple burette - https://www.amazon.c...eywords=burette

 

Here's a basic how to - https://www.yourmech...mpression-ratio



#19 Crashtd420

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Posted 20 November 2017 - 12:03 PM

I would buy a burette and measure the volume instead of relying on any compression tester. It is possible to measure the compression volume on an assembled engine, then you use basic engine math to figure out the CR.

Here's a simple burette - https://www.amazon.c...eywords=burette

Here's a basic how to - https://www.yourmech...mpression-ratio


I found while working on my L series head that I couldn't read the burette accurately.... it was good to see what cc your chamber is for that calculation....

But I was hand grinding clearance into my head so I wanted to be more accurate..

What I figured out was 1cc of head volume was equal to 1 gram of water weight ...
To me I couldn't see the slight variations as i was removing material, using weight was easier ....
I would fill a syringe weight it, fill the chamber, weigh what was left over... subtract 1 from 2 and that gave me the cc of the head....

What I did notice was temp varied the weight slightly....
So I had to check all 4 chambers in a row for an accurate reading between all 4 ... i was able to get them within .01/.02 grams/cc of each other....

#20 datzenmike

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Posted 20 November 2017 - 12:19 PM

Go to google and type... "cc your head for free. ratsun" .... You don't need any special equipment. I told the pharmacist what I was trying to do and he gave me what I needed, the rest was just lying about. Good to 1/10th cc.

 

 

A compression tester only manages PSI and does not take into account the intake valve does not close at BDC but almost 50 degrees past this. On a half circle starting at BDC and ending at TDC this is over 1/4 of the way. At cranking speeds the air is being pushed out of the cylinder till then as the piston rises. Only about 130 of the 180 degrees is being compressed.

 

At high engine speeds you can actually cram more than 100% of the cylinder volume


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