Rebuilding L20B

[73DATSON]

I'm new at this. I'm just buying the parts and I have a shop doing the work. But I just what some insight from u guys. I'm about to buy a new head U67 with a bigass cam,new lifters, springs. Port&polish. And I just order flattop piston from a 280zx(86mm). So what u think? I'm looking for a good street racer!!

[73DATSON]

Is the L20B a long block? What is the size of the piston?85or86? If some L20B are long block how can you tell?

[DanielC]

These are general definitions. This is for Datsun engines, and if I bought, what I would expect.

 

Short block. The engine block. Includes the block, crankshaft, pistons, and rings. These parts assembled together. You supply the head, front cover, oil pump, manifolds, camshaft, rockers, cam timing chain, oil pick up, oil pan, and other small stuff, and have to time the camshaft to the crankshaft.

 

Long block. Short block, plus head, attached. Probably includes timing chain, camshaft, rocker arms, front cover. May include an oil pump. Manifolds, oil pan, oil pick up not included.

 

If you are buying either partial assembly, ask what is included. Different suppliers may have different ideas on what exactly a short, or a long block is.

[banzai510(hainz)]

280xz piston are 86mm and that wuld be 1mm over bore in a l20 as l20s came with 85mm

 

I would NOT use flattops on a daily driver motor.whats the gas octane where you live?????? Flattops and open chamber is going to lead to detonation unless you got HIgh octane gas.

 

But its your car do with it what you want.

I would not get the biggest cam. Give some specs!!!!!!!!!!! Types of carbs you runinng ect....

 

 

oldddatsuns.com read it about 1000 times

[73DATSON]

Oh...lol:-)) got you.. I feel like a lil teenage girl:-)))

[screamer510]

from my very similar L20b rebuild thread coming to a final conclusion...

 

Yes, however....

 

Standard factory pistons range in size from 3.3459" to 3.3478"

Standard factory bores range in size from 3.3465" to 3.3484"

 

This means that if you get a 'largest' piston (3.3478") even if within spec, it won't even fit in the 'smallest' bore, (3.3465") even though it is within spec. On top of this you need from 1 to 1.8 thousandths of clearance piston to cylinder wall.

 

I believe Nissan grades and stamps (1 to 4) their pistons according to size so that a 'small' bore can be quickly fitted with an appropriate 'small' piston

 

and yeah, long block or short block describes the pieces and parts you get with the engine, not a length or measurment at all. That term is good to know :thumbup:

[banzai510(hainz)]

http://www.kb-silvolite.com/silv-o-lite/spistons.php?action=Mfg4l&mfg=Nissan&Div=Nissan&l=1952

 

I would recommned stock L20 pistons in stock or whatever oversize the machine shop needs. and a closed chamber head.

 

maybe L18 pistons if you can find them with a closed chamber head and have 93 octane avsail minimum

 

anything other your risking a not 100% motor. Maybe if you have 100octane.

[EricJB]

Block terminoligy can get a liitle mixed up sometimes. As others have said, the difference between longblock and shortblock is the state of assembly. They often get confused with smallblock/ big block in the V8 world.

 

In Datsunland we have short (L 16/L18) medium (L20 Z22) and tall (Z/KA24). That is the distance between the oil pan surface and the deck. Over the years it increased with the stroke of the crank

 

Which piston you choose will determine your compression ratio. Something that will be influenced by your camshaft selection . More duration will need more compression. But if you dont have the intake/ exhaust to support the camshafts needs, it will be miserable to drive and not be up to its potential. Your cam must match your externals.

 

The Kieth Black Silvolites that Hainz suggested are available thru Summit. Not in their catalog, on the website. Good choice as long as the duration of your cam is below 290(advertised)

[HRH]

You need to buy the Datsun bible and read it. Thoroughly. "How to Modify Your Nissan/Datsun OHC Engine" by Frank Honsowetz. Available from Amazon and many others I'm sure. It's a wealth of information and answers a lot of your questions, plus has bore/stroke combinations, etc.

[EricJB]

X2 ^^^^^^^^^

[datzenmike]

I'm new at this. I'm just buying the parts and I have a shop doing the work. But I just what some insight from u guys. I'm about to buy a new head U67 with a bigass cam,new lifters, springs. Port&polish. And I just order flattop piston from a 280zx(86mm). So what u think? I'm looking for a good street racer!!

 

That would be just under 10.1 assuming the U-67 has never been milled.

 

What HRH said. This is quickly becoming a build by committee. Ordering 86mm flattops without knowing the L20B bore is asking for future problems.

 

Is the L20B a long block? What is the size of the piston?85or86? If some L20B are long block how can you tell?

 

 

Research, research, research. You could just as well bore your L20B to 87mm and fit Z22crank and pistons to your rods. Fitted with a U-67 head your now 2.2 liter motor would have a reasonable compression of 9.84. You might find a wrecker Z22 motor for the parts for $50 or even free. Displacement always trumps cam and compression.

[HRH]

Boring an L20 block to 87 mm isn't the greatest idea either. It's 85 stock, 86 is doable (I'll be doing that) but beyond that you're going to have problems with water jacket issues. Z22 has water ports cut off one one side to account for the extra width.

[datzenmike]

Lets just say it's is do-able but the risk goes up above 1mm. BTW 1mm is the total amount removed around the cylinder wall to get 2mm increase overall width. 1mm is only 0.040".