Tom,
here's some comments I can think of. If 1854cc is enough for you then
capacity wise it's definately an improvment. The downsides I see are
dished (9.32cc) pistons that sit too far below deck height (by 0.8mm, I
calc) for any useful squish. You could machine the block about 1mm but
you still have dished pistons. I calculate 8.7:1 CR thats including
gasket using a 39cc head. At this compression ratio and having dished
pistons I see this engine only being suited for street use. Another
possible downside has to do with the head/piston combination. The peanut
chamber head was designed with squish in mind using close piston-to-head
clearances. A better choice for this engine may be the open chamber head
that is designed to induce tumble, but would reduce CR again. Then you
basically have a smaller capacity L20B, lower CR, same rod/stroke, head
design, with a better stroke/bore ratio. Probably a good turbo engine.
I think you'd be better off with what the factory rally cars used,
L18W block and crank an rods using custom 87.8mm pistons for 1889cc. The
ratio's are excellent for a wide powerband performance engine.
rod/stroke of 1.67 and stroke/bore of .89. Using longer rods can
actually sacrifice volumetric efficiency in favor of more rpm. Depending
on application you may be better off with shorter rods.
If you take a look at other engines of the Datsun era before emissions
took over you'll see that BMW, Merc, Saab all used approx the same
ratio's and for good reason.
If your interested download the Mahle piston catalog and have a look at
the piston shapes of the performance cars, you rarely see dished
pistons. Porsche has some interesting turbulence inducing dome designs.
cheers,
Craig.
> Tom Richardson wrote:
>
> Hi List
>
> During one of #ozdat's late night crackpot ideas sessions we came up
> with a frankenstein L which sounds surprisingly good. Its the same as
> the long rod L18 from Jason Gray's frankenstein page, but with a +2mm
> overbore to accomodate Z22S pistons. The long rod big bore L18 was
> born! Capacity is 1854cc, rod:stroke ratio is a favourable 1.705:1.
> The Z22S pistons sit a further 0.06mm under the deck, slightly
> lowering the compression ratio.
>
> L18W block +2mm overbore
> L18 crankshaft
> L16 conrods
> Z22S pistons
>
> With a peanut chambered W53 head (39cc chamber) this would give a
> 9.06:1 compression ratio (super won't be around forever), or with an
> open chambered U67 head it would give 8.2:1- not toooo bad for low
> boost turbocharging. If somebody wants to build this as a race motor,
> find yourself some flattops and shave the deck for 11:1 :)
>
> It almost sounds too good- reasonable capacity, would rev pretty hard
> (to 7 or 8k probably), simple head swap for turbo! Might be expensive
> getting the whole setup balanced well enough for a 7000rpm screamer
> though.
>
> Comments? How hard are Z22S pistons to come by, are they usually okay
> strength wise? Errol, Terry, pick holes guys :)
>
> - Tom
>
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