Nick,
Do the PRC rules state a maximum cubic capacity?
If your running a 1600 then the maximum capacity allowable is probably
1899cc.
And the 180B I have been told can run L20B (is this true?) which would
allow 2099cc. There is no set weight for the stock 1600 or 180B but
Wheels Magazine Oz weighs 1600=910kg, 180B=1000Kg, and I have been told
a 180BSSS=1080Kg. The 180B or SSS may increase in weight a little with
the taller/heavier L20B in it too.
Nearly every datsun book I've read recommends a maximum of 2mm oversize,
that's from 85 to 87mm for both L18 & L20B. Any further and the block
would need to be sonic tested first.
An L18 at 87mm bore and 78mm stroke is 1855cc.
An L20B at 87mm bore and 86mm stroke is 2045cc
The L18W and Japanese made L20B with Japan cast into the side of the
block seem to be the go for large bore L's.
You haven't stated what size the valves are in your (U67?) open
chambered head. I'll Assume its a stock L20B U67 head & valves. Your
limited with a stock L20B/SSS cam (11.02mm/248deg) as to where max rpm
power is generated. I've just started writing my own engine simulation
program, and according to it, the stock L20B U67 inlet valve becomes
choked(no more air/fuel can be flowed) at approx 5550rpm. This was
calculated with the stock L20B block specs(85mm bore). Changing only the
bore to 87mm, drops max power to 5300rpm due to bore to valve area ratio
changes etc. Put an optimum lift camshaft in this engine and it will
lift it to approx 5650rpm. Put 44mm inlet valves in for approx 6280rpm
before valve choking. As long as ports/manifolds and carbies flow enough
for the valve thats the approx. max power rpm to expect. It will also
vary depending on you valve seat internal diameter/minimum port diameter
aswell.
I can't see anyone estimating power/torque figures accuratly, there are
just so many variables.
I'd recommend using closed chamber head on any L series. The added
squish/quench area creates turbulence that assists in mixing the
air/fuel better, and also increases the burn rate. Mixing the air/fuel
better reduces the amount of lean pockets of air/fuel which leads to
reduced knocking/pinging allowing higher compression ratios. From memory
Nitrous Oxide emissions can be kept lower with low compression ratios
which is probably why Nissan designed the L20B the way they did.
A friend has an OZ L20B in his 180B it's ~86mm dished pistons, U67 head,
~10.5:1CR, stock Cam, 3angle 42mm valve, stock ports, twin 38mm SU's,
ram tubes, extractors into 2" exhaust. Assembled in a hurry, not ported
& no attention to detail. Doesnt pull past 6000 at all, power from about
3000-5500 i'd say. Pings @~6deg without AVGAS. 10-12deg with AVGAS I
think. L18 Dizzy used needs regraphing too.
Hope that helps.
Craig.
Japanese L20B blocks seem to be the go otherwise don't bore the Oz block
very far.
> abrahamk wrote:
>
> I am/was rebuilding an ex-TRX Bluebird black rocker-cover L20B for
> PRC/club motorsport until I read the disparaging comments about this
> type of motor on the list. I would like to know more about the
> relative merits of the L18 vs. the L20B before I continue.
> Firstly let me get my facts straight.
> -The L18 block has a higher nickel content than the (Australian) L20B
> block and so is more wear resistant. The L18 is also oversquare and so
> should rev better and respond to a cam change better than the L20B.
> The PRC rules forbid connecting-rod changes e.g. L16 rods into L18.
> Now,
> -What are the power/torque/maximum rev. limit figures for these two
> engine types using twin 1-34" S.U's ( 1.50" port size), extractors,
> 9~9.5:1 compression ratio, open-chamber head and 248 degree L20B/SSS
> cam ( i.e. a fairly average 'mild' setup )
> -I would expect 80-85 kW from the L20B, lots of torque, easy to drive,
> relatively easy on fuel, which will pull hard to about 5500-6000 with
> a 6500 rev limit.
> -What is this talk of A,B, and C type L20B cams? I have acquired a 'B'
> stamped cam from a 200B but is has the same profile and duration as
> the Bluebird (according to the manuals) i.e 248 degree 16/52-54/14.
> -A 280 degree camshaft re-grind costs ~$100. What kind of power
> increase do you get, if any, with a medium-low compression ratio and
> open-chamber head (engine spec. as above). Any detonation, fuel
> consumption, driveability etc.. effects to worry about?
> -Also, was the HA-10 Stanza homologated with an L18?. I've been
> told that a L18 Stanza will pass registration without an Engineer's
> report, but CAMS only has homologation documents for L16 and L18
> versions (that I know of).
> -What are the weights of the Datsun 180B and 1600?
>
> Thanks - Nick.
>
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