Wouldn't it be safer to use nitrous with less boost, then your not stressing
the turbo, and the nitrous will help control knock with the cooler charge?

OK, but engine is completely rebuilt(at least I think so). Would 100
HP over be a problem for it?!? How much it would cost me ?!?

Whole set up is about maxed out with everything nicely matched and
specified to the power it's making now.  To increase the boost it
really needs bigger turbos as they are only rated for 50bhp more.
Injectors can only cope with 550bhp and at 500bhp have a nice safe
50bhp margin to ensure they do't go lean. Fuel pump can only deliver
fuel for 500bhpish so that could do with uprating anyway.  If used as
it is, should get a few dyno runs, a drag strip once a month, some
track days and maybe 20-25K miles before the rebuild.  (Steve will say
"As much as that?")  Run it on 10w40 for daily use, 10w50 when it's
going be used hard.  Needs careful warm up for reasonable life
especially when on 10w50, allow to idle for first 30 seconds, don't
exceed 3000 rpm in first 3 min, don't plant your foot on the gas until
fully warm - oil temp not water temp.

300ZX is supposed to be able to take 600bhp on stock internals.  No
one has ever reported for how long, could need a rebuild every 5K
miles or may only last a dyno run and a few runs on a drag strip.
Putting extra 100bhp in using N20 will give 100bhp more exhaust gas
flow, that will drive the turbos to pull in more air which gets
metered by the AFM and you get more than 100bhp.  So you put about
75bhp N20 in and get 25bhp more from the turbos = 100bhp.  ECU has to
put 25bhp (=525bhp) more fuel in for extra air but that runs fuel
system close to limit and it may go lean.

More boost, wet or dry N20 it needs a bigger fuel pump.  The injectors
won't flow enough for even a 30bhp dry N20 system and are really too
close to the limit for a 75bhp wet system.  So for 600bhp max it needs
N20 jetted for about 75bhp - the turbo will make it up to 100bhp, fuel
pump(s) and injectors - should flow 650cc for dry and 600cc for wet.
Or forget the N20, fit fuel pump and 650cc injectors, increase the
boost and accept reduced turbo life.  As Steve says use race fuel to
compensate for higher inlet temps and higher effective compression
when boost is set high.

For 700-750bhp it needs stronger rods, forged pistons, thicker metal
head gaskets, bigger turbos (disco potato) with dump pipes, 800cc
injectors and fuel pump.  As Steve says no point in going with N20
when the required mods to take the power will deliver the power by
boost alone.  But internal mods cost a lot more in labor than bolt
on's and you are going to take a loss on selling secondhand JWT turbos
and 555cc injectors.

--
Peter Hill
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