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L20B big bore with low end torque


Eriks

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Well you have to bore from 85mm to 89mm first. Getting scary close to the limit.. but doable.

 

If using an L20B/crank and a rod that will work, you basically have a 2139cc engine. Theoretically good for high revving with lots of other add on's, but in reality you have only gained 188cc above the stock engine displacement.

 

If you can find a Z22 crank you can keep and use the L20B rods that you already have and this jumps the displacement to 2288, or a 337cc increase, but the big deal is the longer stroke crankshaft. This will add lots of leverage and low speed torque, which is what you asked for, for every day street use..

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Yep, Z22 crank is the way to go if you want torque, I have a Z22 block/crank bored out to 89mm with Z24 pistons, and basically a 219 head with dual SUs, I have hauled massive amounts of weight, stopping was my issue, I could haul way more weight than I could stop.

One has to have torque to move these types of weight.

DSCN7200.jpg

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Well you have to bore from 85mm to 89mm first. Getting scary close to the limit.. but doable.

 

If you can find a Z22 crank you can keep and use the L20B rods that you already have and this jumps the displacement to 2288, or a 337cc increase, but the big deal is the longer stroke crankshaft. This will add lots of leverage and low speed torque, which is what you asked for, for every day street use..

 

89 bore is close to the limit  ... might this be a head gasket problem in the long run?

 

The Z22 crank suggestion makes sense, thank you. However I read it is not fully counterweight like the L20B crank. Would you say the disadvantage is significant?

 

If no, maybe a healthy solution is to bore no more than 87, using the Z22 pistons as well as the Z22 crank. I suppose the L20B rods would work with this combo as well

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Not a problem with the gasket, it's the thickness left of the cylinder walls. 2mm removed all the way around is a fair amount. Another option is to use a Z22 block and the bore increase is from 87mm to 89mm. A Z22 engine will give you everything you need for an LZ23 using the KA pistons.

 

Fully counter weighted is great for revving smoothly. You won't be revving higher than the Z22 engine it came out of.

 

Yes, Z22 pistons and crank in an 87mm bore will work just fine. You are basically making an L20B into a Z22, well other than the head. I guess L22B would be closer. 2184cc

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You will need a good machinist to know what to look for when boring that large. I generally don't like to bore the L20B blocks to 89mm, but if you had your machinist measure the wall thickness of the bore before hand, that would be ideal. If you can find a Z20 block, they can handle 89mm no problem. Ironically, Z22 blocks aren't my first choice either as they have steam ports in between the 1-2 and 3-4 cylinders. Your machinist will need to offset bore away from those steam ports.

 

Bore flex and ring sealing is the main concern with large bore L motors.

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I have a Z22 block and crank in my work truck, I have revved it to just over 5000rpms once in 5th gear on the freeway when breaking the engine in, in any gear other than 5th the engine sounds over revved but not in 5th under load, I didn't notice any vibration at all, it was smooth but I didn't hold it there either, I let off and let it slow down under compression, as I mentioned I was breaking the rings in, at least I think I was, it doesn't really use oil after at least 5 years now.

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Thank you all, many inspiring feedbacks here. Stoffregen, yes I would leave such a job to a machinist.

Its an L engine that belongs in the car, so I would not consider anything else. Call me sentimental:) Thus nice to know the limits of what to do with an L20B without sacrificing too much reliability.

 

Im a bit confused about the Z22 crank. If fully counter weighted is great for revving smoothly, why would Nissan make the Z22 crank not counter weighted? Would there be any benefit for a crank that is not?

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The L20B has been around for 44 years. Back then Nissan built in a little extra so they could be modified for racing, at least this is what I believe. The Z series are, by design, for very low emission and high mileage. They are great engines just not that good for being modified for high revving. The red line on a 92mm stroke is 6500 RPM and they can safely be revved this high. It just won't get there in a hurry and it won't be making much if it does. 

 

The lack of counterweights makes it lighter weight, but some more harmonic vibrations.

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L20B and a 4.11 or 4.375 differential. It multiplies torque also, but reduces top speed slightly. I have a 4.11 (came with 3.70) in my 710 with a 5 speed. I can cruise around town in 5th gear and roll around in town corners in 3rd. Still goes about 100 although the speedo reads 110. I love 3rd gear the most, it pulls, and pulls, and pulls. Last Canby trip was about 2,500 corrected miles and averaged 34 US MPG.

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  • 2 weeks later...

De shroud the valves where they come closest to the cylinder wall. Going to 89mm means you can take a lot of material out of there and you can gain a lot of airflow due to the fact that the valve isn't right tight to the chamber wall anymore.

 

As for cranks, the z22 is good. Don't worry about it only being half balanced I have spun mine to 7500 lots and so has others in race motors. I have not seen any pictures of broken z22 cranks only ld28 cranks.

 

I do have one of those fancy ATI balancers though as I was concerned about it shaking to death myself. Rebello is using a BHJ balancer on their race engines

 

I've had a 75-100 shot of nitrous on the car as well and hasn't shown signs of distress.

 

The more cc's you have, the more torque, hp you can potentially have. If you can get your hands on a z22 crank, run it!

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In this case U60 marking is certainly not a steel grade.  It is a marking system Nissan used for the engine family.  U6X markings are used on the L20B (and apparently Z2X) engine parts.  I will have to check my Z22 crank for this.  I didn't notice it earlier.

 

BTW, pertinent to this thread, I am considering doing an L20B block/Z22 crank/custom pistons of some sort.  Reasons being I don't want to bore to 89mm, would like to use the crank, and don't know of any regular stock pistons that fit with the proper piston height, etc.  Anyone done this with custom pistons care to reveal specs they used?  I would probably be game to go to 87mm bore.

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BTW, pertinent to this thread, I am considering doing an L20B block/Z22 crank/custom pistons of some sort.  Reasons being I don't want to bore to 89mm, would like to use the crank, and don't know of any regular stock pistons that fit with the proper piston height, etc.  Anyone done this with custom pistons care to reveal specs they used?  I would probably be game to go to 87mm bore.

That's one of the reasons people started boring to 89mm, so they could use an off the shelf piston.

 

There aren't many choices in smaller bores, though I do remember hearing about a modern Chevy piston that would work and also maybe one from a Mitsubishi. Don't have any other details.

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U60 is not a part number.  Its a steel grade.  High quality.

 

It may also be a steel grade but here it's an identifier for the L20B.

 

L20B crank part number 12210-U6000SV. There is also U60 in the flywheel part number, bolts, timing chain, guides,.

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I have custom 89mm pistons.... you could just use z22 pistons if you wanted to.

 

or if u went custom pistons, there is a Mitsubishi rod that's really close to useable for a datto in 156 length if you want to turn your crank down to Honda/Mitsubishi journal size

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  • 4 years later...

The L20B and the Z22 rods from the 720 truck and the early S110 200sx are the same, however the distance from the piston pin center line to the tops of the pistons are different. The Z22 pistons are shorter by about 3.5mm so if on an L20B crankshaft they will not reach all the way to the top of the bore by this amount. This 3.5mm X 87mm bore above the piston adds up to 20cc of extra combustion chamber and this will lower the compression ratio to around 7.6.

 

There are two ways to go here, three if you order custom pistons but I doubt this is the case. There are 2 other pistons with the same pin height as the L20B and they are from the L28 engines. The first is the '75-'78 280x with an 11cc dish very similar to the L20B but 86mm bore, just 1mm larger than the L20B. The compression would be about 8.55 just barely above the stock L20B compression of 8.4. The other is a piston from the '79-'83 280zx which has no dish and is also just 1mm larger bore. This makes the combustion chamber smaller and raises the compression to about 10.1 I have no idea if these pistons are available still.

 

Advantages? of the L20B crankshaft...

1/ The theoretical rev limit or 'red line' for stock reciprocating parts is about 4,000 feet per minute. This is the speed above which the metal parts begin to stretch towards their failure point from the extreme g forces. Below this point the engine can run all day without harm providing it has proper clearances, lots of oil and is not over heated. 4,000 feet per minute is the average speed of the piston and rod going up and down. Obviously a long stroke will move the piston farther on one turn than a short stroke or a shorter stroke will have to turn more than one turn to go the same distance. The 'red line' on a Z22 crank is about 6,500 RPM. the red line on the shorter stroke L20B is higher at 7,000 RPM. Under ideal conditions (certainly not stock engines) a gas engine doubles it's power output with each doubling of it's RPM so revving it higher makes more power. Special after market fasteners, exotic titanium rods and lighter pistons can increase the red line but for average use not a factor.  

 

2/ The L200B crankshaft is fully counter weighted to reduce harmonic vibrations where the Z22 and Z24 crankshafts are not. It spins smoother at higher RPMs than the Z22 crankshaft. At highway speeds this is not really a factor. Obviously the extra counterweights add weight.

 

L20B top and Z22 below

xdtIW9O.jpg

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If you have $1000 spend, a custom forged set is really the best way to go.

 

You can build a custom long rod "2200" with all stock Nissan/Datsun parts, but the 89mm bore will have to be done by somebody who knows Datsuns (they are tricky to get done right).

 

EDIT - the parts needed for a 2200 are not rare, and easy enough to source.

Edited by Stoffregen Motorsports
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