Just reiterating the L20b & L18 Block differences. The "assembled" piston deck height gives the L20B higher compression too so, I guess it's another reason the L20B has been said to have higher comp with same head (L18) It's only a difference of 0.1mm so, hoping it won't be a problem with valves. I've seen an L series (think L20B) that had stock flat tops which had valve depressions in them. May actually be for Z20 engine?datzenmike wrote: ↑12 Mar 2023 16:42 Yup I did post that. I have since corrected it to 9.027.
All my calculations use Jason Gray specs including the crushed gasket thickness of 1.2mm.
can anyone tell me how to identify an L16-L18-L20
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Cracker180B
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Re: can anyone tell me how to identify an L16-L18-L20
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datzenmike
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Re: can anyone tell me how to identify an L16-L18-L20
L20B is 8.4 compression
L18 is 8.436 compression, so slightly more than the L20B.
Deck height on the L20B is 0.45mm below. This deck height volume is 2.55cc and is added to the combustion chamber volume.
Deck height on the L18 is 0.55mm below. This deck height volume is 3.11cc and is added to the combustion chamber volume.
The L18 and L20B have the same bore so it's the longer stroke of the L20B that gives it the increased displacement. As the volume of the open chamber heads are the same it's the 11.36cc volume of the piston dish that lowers the L20B down to about the same compression as the 4.36 piston dish of the L18.
L18 is 8.436 compression, so slightly more than the L20B.
Deck height on the L20B is 0.45mm below. This deck height volume is 2.55cc and is added to the combustion chamber volume.
Deck height on the L18 is 0.55mm below. This deck height volume is 3.11cc and is added to the combustion chamber volume.
The L18 and L20B have the same bore so it's the longer stroke of the L20B that gives it the increased displacement. As the volume of the open chamber heads are the same it's the 11.36cc volume of the piston dish that lowers the L20B down to about the same compression as the 4.36 piston dish of the L18.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs
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Cracker180B
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Re: can anyone tell me how to identify an L16-L18-L20
I was so confused when I read the post here in the Archive section back in 2007 with heading "Compression Ratio Question" https://www.the510realm.com/viewtopic.php?t=7651 - 'hainz' & 'Rehs' were a few of the posters who were commenting that the compression for the L20B with flats & peanut head would be around 11:1 compression. A few agreed but I can't see how? I've worked out the compression to be around 10.2:1 for this set up? Reason it concerns me so much is, this is the exact build I will be doing very soon.datzenmike wrote: ↑13 Mar 2023 12:33 L20B is 8.4 compression
L18 is 8.436 compression, so slightly more than the L20B.
Deck height on the L20B is 0.45mm below. This deck height volume is 2.55cc and is added to the combustion chamber volume.
Deck height on the L18 is 0.55mm below. This deck height volume is 3.11cc and is added to the combustion chamber volume.
The L18 and L20B have the same bore so it's the longer stroke of the L20B that gives it the increased displacement. As the volume of the open chamber heads are the same it's the 11.36cc volume of the piston dish that lowers the L20B down to about the same compression as the 4.36 piston dish of the L18.
These differences in piston dish volume seem to show markedly when fitting flat tops to the L20B block compared with in the L18. That's why when I kept reading that the L20B with flats equated to 10.2:1. Even with open chamber U67 head. I never could work out how the L18 SSS engine only had 9.5:1, using the closed chamber A87 peanut head. I'd work out the L20B with flats & peanut head to be around 10.2:1. Sound right?
I just picked up a complete L20B engine out of a Bluebird here that needs rebuild. May just use stock A87 cam to give it even better low down torque, as I don't want a revver. I want a nice, poky street car...