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Running through the L20B options.


kneesamo

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So its time for the old L20b to be gone threw.

 

I have been searching the tubes, forums, and playing around with the OZDAT Engine Design Utility, and have come up with a few combinations.

 

-L20b block (1mm overbore), crank, rods, U67 head (open camber), and late L28 pistons = 10.08/1 C.R. (tad bit high) other than that a relatively normal L20b

 

-L20b block (2mm overbore), U67 head (open chamber) + Z22s crank, rods, and pistons = 9.805/1 C.R. (more like it), 2188cc (nice bump), 0.050mm deck clearance (what i've found to be the minimum), an overall nice sounding motor.

 

-and then there is that option of staying stock, reliable, tried and true, no stress of sailing threw uncharted waters, stock. Bah!!! Where is the fun in all that? Go overboard!

 

So thats why i'm here. To get your actual real world point of view. The point of view of someone who has actually built and ran a motor like i've concocted or similar. Not all that interested in your hypothesis, more like "the rod angle was to steep, so I shaved a lower section of the cylinder bore for clearace. Which was a bad idea since six months later on a hot day, the block developed a nasty little crack between cylinders one and two!", or "the friggin' piston to deck clearance was to tight, and had to source Z22e pistons for a lower pin height, which dropped my compression ration, which sucked ass".

 

I apologize if I didn't probe deep enough into the forums to discover what i'm looking for.......please......indulge me.

 

By the way the motor is for a '73 pl620, with '79 running gear (motor,transmission and rear end), single 45 dcoe, '83 sentra electric distributor, and beebani front disc conversion, basically your "run o' the mill" daily driven bulletside, her name is Butterscotch.

 

Here are some pics My link

 

Thanks for your time,

Ben

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What parts do you have right now? Find the cheapest OEM parts (motor #1) and put it together. Or go find a Z22 out of an early 80s 720 and make an LZZ2... seriously about the best bang for your buck, especially in a truck.

 

Also, after you build it, run an air cleaner on your carb, your motor will thank you.

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-and then there is that option of staying stock, reliable, tried and true, no stress of sailing threw uncharted waters, stock. Bah!!! Where is the fun in all that? Go overboard!

 

When I rebuilt mine I kept it "stock, reliable, tried and true".

 

As you search the forums you'll discover builds where people have great intentions but ultimately the Datsuns stay in their driveway or back yard collecting rust. IMHO ... build a solid reliable motor and drive the piss out of it.

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Ive got an LZ22 in my wagon, Z22 shortblock, U67 head, stock L20 cam, matchbox dizzy, weber 32/36 and thats about it. I portmatched/gasket matched the head and an early L16 intake and it really woke it up from idle to about 5000 RPM... Also the torque curve is in a lower more usable range

When I had the 3:90 gears in it was a little stoplight to stoplight monster, With the 3:70s it is nice on the freeway and I dont have to shift as soon in town. Its still got enough power to pull steep hills/passes in 5th and pick up speed. It knocks down 30 flat for mileage too. Ive talked to people who have raced and daily driven all sorts of L motor combinations and they all have said that for a fun driver, there is no reason not to do the ZL22.

 

The only downfall is that it diesels just about every time I shut it off (higher comp with an open chamber head) Premium gas (if you can call it that) helps a bit but killing it with the clutch is second nature now. If you can find a decent carb with an idle cut solenoid (some webers have them) you probably wont have this problem.

 

As for the other thing I said about assembling a motor out of the available or easiest to obtain parts; a basic rebuilt L20 with a bump in compression, a little bit of headwork and a mild cam will still put a shit eating grin on your face in comparison to a worn out L motor of any displacement, but if youre going to be scraping up hard to find parts with their hard to find prices you can have a pretty good chunk of change tied up in your motor REALLY damn quick, not to mention the time it takes to find the shit... it doesnt quite grow on trees any more. But its your time and your money so spend it as you see fit.

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I tried a few of the engine calculators and they are too confusing and my results don't match. I use some of the Jason Grey and my own piston dish measurements. Using Pi and a calculator I worked out the cylinder volumes, + or - deck volumes, crushed gasket volumes for most L and Z engines plus 1mm and 1mm oversizes and popular piston swaps. I wrote them down and can refer to then and add subtract any variables and quickly re-calculate any compression ratio.

 

 

-L20b block (2mm overbore), U67 head (open chamber) + Z22s crank, rods, and pistons = 9.805/1 C.R. (more like it), 2188cc (nice bump), 0.050mm deck clearance (what i've found to be the minimum), an overall nice sounding motor.

 

 

A -0.05mm deck clearance is way more than you need. The block could actually be decked up to 0.35mm although .3mm would be better. Don't forget the piston can rise slightly out of the block without hitting the head for two reasons.

 

1/ the open chamber head is 'open' above the cylinder. Only a closed or peanut head would have a solid surface overhanging the cylinder.

2/ The crushed gasket thickness is about 1.2mm so the piston can easily rise up into this space.

 

The .3mm limit is for extreme RPM rod stretch not seen in most motors, but better safe than sorry. Now by my figuring a stock Z22 or a 2mm over L20B with Z22 internals and open chamber head would have a compression of 9.87 (very close to yours) and if compression was important in your build, possibly a racing rule that unmodified stock rods and pistons must be used, decking the block 0.35mm would raise the compression to 10.13 with no other changes.

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i was where you are about 3 years ago... :mellow:

original plan was a Z22 crank in the L20b

after 3 cracked L20b blocks, i ended up w/a cracked Z22 block and crank.

 

bored to 88.5mm, to match the nismo HG

forged JE pistons, 1/2 dished for ~9.5:1

U67 ported w/larger IN & EX valves

.480 Isky cam

dual 45 webers

stock ex (header soon)

 

 

its damn fun!!!

:hmm: hopefully bigger numbers than Ztrain

 

i have a .510 cam i may try after header...

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Z train

 

those are real impressive and with just a weber DGV??????

 

I need to know the Cam grind or is this Top secret. or is it a cam from another grinder and they slap there name on it?

Don Potter used to hide his cam specs for some reason also.

Just a Weber.And if i can find the numbers,i'd be happy to share.I called Rebello and he couldn't find them.I'll see.

 

 

Getting numbers bigger than mine shouldn't be an issue as this was a specifically built low RPM truck motor.

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Just wonder if you could get a little more with a 38/38 DGES on there. The double opener weber?

 

Rebello can only have so many grinds How can the guy forget. Maybe its stock cam?

Is this a rebello Dyno or another? as I dont trust the Rebello ones as they might have 25hp just at idle.

 

 

met a guy longtime ago how had a LZ hybrid with coil packs and Throttle bodies ect.

was a 5k $ Rebello built motor. he put it on a local Dyno andgot 142 to the rear wheels. So the LZ with a Weber down draft is pretty impressive

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Wow...thank you all for them specs, and I will keep you informed my own build.

 

Suppose I should let you know what parts I have at hand

2-L20b blocks, one is still intacted, the other has been torn down (all parts indexed), hot tanked, primered and oiled.

1-U67 head, open chamber, square port, torn down (all parts indexed). Awaiting hot tanking with all other internal parts. The plan is for a simple port match job, and radiusing any edges in the combustion chambers.

1-W58 head, open chamber, round port exhaust (blah) with a burnt exhaust valve number one cylinder (the reason for the motor rebuild).

1-set late L28 pistons and rods. haven't measured the skirts yet, but a visual inspection shows minimal wear, very little if any score marks

-looking at them last night brought to mind something I read in Jason Grey's thread,

VG30E pistons and have the tops milled by 2.7mm

Has anyone done this or had it done? Instead having them milled how about turning them down on a lathe, possibly mimicking the

dish you find on most pistons. Just a little dish is what I thinking, otherwise what's the point.

1-Norris reground "street cam" #327, duration 280, lift 480. The Norris shop is still up and running, figure that if I end up using this cam I will go threw them for the proper lash pads and (if need be) set-up springs to

reattain proper rocker geometry.

1-A local, capable machine shop ran by four brothers who are good friends.

 

Stuff I thinking of, or need to obtain.

1-Square port exhaust manifold. I'm looking for the 4-2-1 design. I don't want a header, for a simple reason, the cast iron will last forever, and it's actually a nice design.

1-Z22s short block. Local junkyard sells them for $118.67. Every time i've time I go to that junkyard I see a few 720 pick-ups. So not to unobtainable.

1-Sugar Momma! Don't we all! Ok...now back to reality.

 

after 3 cracked L20b blocks, i ended up w/a cracked Z22 block and crank.

 

What was causing the cracks? The overbore, or something else?

 

So i'm on the teetering point, of which way I will go. The more I think on it the more good ol' stock sounds appealing. I do have two motors to mess with here though, so maybe going stock at first (get the old truck running again), then taking my time and properly building a monster of one sort or another, is the best plan. If I have a wheels again I wont feel so rushed, yah know?

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the L20 and taller blocks crack for some reason between the center water port and by the threaded holes.It seems the bolt pulls on the block and these are strteing to get 30years old.

this is now a common site if u can find a non cracked block.

Up here in washington there are still plentiful since all the KA swaps.

 

i have 2 exhause manifolds and they are hard to sell at 20$ Most are too lazy to pick them up.

Im to lazy to ship and box a heavey part just to get 20$

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i have 2 exhause manifolds and they are hard to sell at 20$ Most are too lazy to pick them up.

Im to lazy to ship and box a heavey part just to get 20$

 

Im gonna keep my eyes out at the local junkyards, but if I have no luck, maybe I could make it worth your while to ship?

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  • 2 months later...

So the motor is finished, it stayed essentially stock.

IMG_0011.jpg

 

Ran threw the first two break-in procedures last night, was surprised at how well it ran, right off the bat.

 

The motor didn't need much work, bore was good, valves, guides, springs, cam, crank, and rods were all good. Had to fly cut .007 from the head surface, which had been shaved before, so there was an unknown amount of material removed from stock on the head. Instead of shimming cam towers, and finding rocker arm geometry again, I just moved the cam sprocket to its next locating hole. In doing so I advanced the cam a little, the notch on the backside of the sprocket and the timing mark on the front side of the camshaft thrust plate, now split each other, with the cams mark to the right. I don't know how much it is advanced, but I don't think its much. A nice hone to the cylinders, and a valve job, were all the other machine work needed.

 

I still have an extra L20b laying about, and now that I have my truck back, I wont feel so pressured to do a quick tidy job, so I think i might take my time on a nice frankenstein motor build, but not until the Corvair's turbo spools once again.

 

Thanks for the info,

Ben

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For an L20b I like staying with stock components if I can, but, mix and match a couple of things to help it out a bit. Staying with a stock L20b bottom end I like a stock A87 head, either open or closed chamber, whatever you've got. This'll bump the compression up a bit to say the 8 and 3/4 range. Stock A87 cam is fine or at most a real mild cam street cam.

 

I like using a pair of dual 38mm SU's with this, port match the intake and manifold by narrowing up the runners on the SU intake and widening and radiusing the ports on the head so that you can keep a better bottom end ... As you can see I'm not into revving out the motor, just want the bottom end grunt better. You can run a 32/36 weber with what I do fine, just reject it to take advantage of the higher compression.

 

Nice and reliable, cheap, decent gas milage and a bit more grunt than a stock L20b ....

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