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Engine rebuild, L18 pistons in an L16?


DATSUNgeo

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Greetings fellow Rats…

 

I have a question, could I bore an L16 block to an L18 piston?  That would be the only change.  If pistons are comparable in price and the machining cost the same, my thoughts are why not?  Would there be any disadvantages or is it even possible?

 

I don’t want to get a different engine just yet. I an doing a full restoration and will take the time later to decide what engine swap I would like to do.  Thanks guys.

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L series pistons are all identical but for the bore and dish volume. Boring the L16's 83mm out to the L18's 85mm will produce a 1672cc displacement with 8.76 compression if you retain the L16s 210 head which has a smaller combustion chamber, valves and ports. If you use an open chamber L18 or L20B head the compression is 8.5, almost identical to the stock L16's. The displacement is increased by 78cc. HP would increase by roughly 10 perhaps a little less. HP back then was measures in gross output without accessories such as water pump, alternator even an exhaust system. Later in the '70 this was changed to include them and called net hp, a smaller but more realistic number. My L20B says 110 hp but net is about 93. The L16 net is guesstimated at about 70 the L18 at 80. 

 

 

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The U67 has the same combustion chamber as the open A87 head and the later W58.

 

Look for the engine displacement. It's stamped behind the dip stick handle on the block just below the head. You may need a wire brush. You may have an L16 but they only came on the '73 620. Odd that it would have a U67, maybe it's an L20B?????

 

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It's only an L16 if you check. I hate to be a stickler but you might have mistakenly been told it was. L16s only came with a 210 head. True a vehicle this age may have had an engine transplant or a head replaced. I've seen some weird things. 

 

Put the year of your 620 in your profile. It will save repeated asking of simple questions. The 620 ran for 7 years with many changes and knowing the year will save many questions.

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10 hours ago, DATSUNgeo said:

My apologies… I’ve posted the year of my 620 in my profile, it’s a 1973.  The head must have been changed. Pictured below the marking on the head and the marking on the engine block. Thanks for the help.

 

 

No worries, I'm learned to make sure of as many assumptions as possible. Not the first time has someone had a problem that went down the wrong path for a couple of pages that turned out to be an assumption made early on. So... L16 with later '75-'77 L20B U67 head.

 

At the present your compression with the U67 head is a sad 7.7. So increasing your displacement with L18 pistons will raise the compression to 8.36 with the U67 head. 

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I'll have to go back through my engine combo list. I remember building a 1750 or something like that. It ran great, but it wasn't a power house.

 

Favorite short block L motor is the 1900. L18 with long rods and Z22 pistons. I've built a few of those and owned one myself. Great little motor.

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5 hours ago, DATSUNgeo said:

Wow, so even with L18 pistons and the U67 head I won’t even get compression to the factory 8.5! I have an A87 head, will that help? What heads will get me higher compression? Thanks.

 

Milling the U67 head by 0.5mm or 0.020" gives an 8.44 compression

 

Flattop pistons were used in the Japanese 510 Coupe L16SSS and L18SSS. You won't find them here but maybe in Japan??? L18 flattops would give 9.12 compression.

 

Don't get all wet over compression numbers. On a really, really, really good day, going from 8.5 to 9.5 (one point of compression) might get you an extra 4-6% HP at power peak. You might have to run more expensive octane gas too. 

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Thanks Datzenmike for the valuable information.  Now I have some useful information.  I’ll think about what direction to go.  If I can’t find L18 pistons I may just have the machine shop mill 0.5mm off the head and have the block bored to L16 0.75 pistons.  

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18 hours ago, datzenmike said:

 

Milling the U67 head by 0.5mm or 0.020" gives an 8.44 compression

 

Flattop pistons were used in the Japanese 510 Coupe L16SSS and L18SSS. You won't find them here but maybe in Japan??? L18 flattops would give 9.12 compression.

 

Don't get all wet over compression numbers. On a really, really, really good day, going from 8.5 to 9.5 (one point of compression) might get you an extra 4-6% HP at power peak. You might have to run more expensive octane gas too. 

With the right cam and distributor curve, 9:1 is fine. I've mentioned this before, when I was building L motors for a living, we aimed for 10:1 on street motors that ran on pump gas. The last 2200 I built for my street 510 had almost 12:1 and ran on pump gas.

 

Other than the HP gains, I love hearing the crisp firing of a motor with a higher CR.

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On 12/5/2021 at 10:59 AM, john510 said:

Beware if you do find L-18 pistons. They might be 11cc dish instead of 4cc dish.

 

These would be stock L20B pistons, which as John mentions have 11cc dish.  Often sold as the same because the bore and pin heights interchange.

 

2 hours ago, Stoffregen Motorsports said:

With the right cam and distributor curve, 9:1 is fine. I've mentioned this before, when I was building L motors for a living, we aimed for 10:1 on street motors that ran on pump gas. The last 2200 I built for my street 510 had almost 12:1 and ran on pump gas.

 

Other than the HP gains, I love hearing the crisp firing of a motor with a higher CR.

 

Domed pistons?  What head?  I am planning to put together a 2.2 in the future.  Thanks.

 

On 12/4/2021 at 11:58 PM, banzai510(hainz) said:

my 510is a l16 with L18 pistons STD size which is a .040 over bore in a L16 and same pin height.

 

Actually 0.080 overbore (2mm) as stock bore is 85mm in the L18 and 83mm in 16.

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54 minutes ago, iceman510 said:

 

Domed pistons?  What head?  I am planning to put together a 2.2 in the future.  Thanks.

The 12:1 2200 used a closed chamber A87 head (with big valves) and a machined flat top KA24E piston, hence the high CR.

 

After that, I started using KA24DE pistons and machining them to the proper deck height. The DE pistons have a dish in them, which brings the CR down to around 10:1.

 

If you're going to build a custom motor from scratch, don't rely on available information (cc's and pin heights, etc). Buy yourself a burette and a couple cc plates to cc your own head, piston, etc. Then do the engine math and a thorough mock up to see how the combination fits together. The most complete mock up includes top rings with grease on them, a head gasket and valves in the head, then cc through the spark plug hole to get your actual compression volume.

 

You can buy a cheap plastic burette on Amazon for about $20, and make your own plates. Usually two are required. A flat one and one with a ring (like an upside down shallow cup) molded to it.

 

Engine math is universal - https://www.enginebuildermag.com/2018/05/engine-math-for-engine-builders/

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If you only build the odd engine you can cc the heads for basically... free. The swept cylinder volume, deck height volume + or -, crushed gasket thickness volume and dish volumes are just measurements and math

 

 

 

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One thing I learned about trying to cc a head was buy a quality burrette. Figuring I was only using it once why spend extra money, well I know why.. I couldn't read or determine anything...

What I did figure out is 1cc of water is equal to 1 gram of weight....

I would just weight the syringe I was using before and after to get the cc used .... 

I did notice a slight variation day to day so to be accurate make sure you check all 4 at once if your doing any grinding or descrouding in the combustion chamber..

 

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37 minutes ago, Stoffregen Motorsports said:

Good to know. I have a glass burette so I've never experienced that issue.

 

Ya I think I got the summit racing special.... it was good to just see what the cc was in general but I was grinding piston clearance into the head and needed to be alot more accurate to keep all 4 chambers the same volume....

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19 hours ago, Crashtd420 said:

 

I did notice a slight variation day to day so to be accurate make sure you check all 4 at once if your doing any grinding or descrouding in the combustion chamber..

 

 

It's very small but liquids expand and contract with heat. So does the aluminum head.

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