Your dictionary is correct, Alex. 86.75 mm would be a .030" over piston. I don't
know what the cylinder wall thickness is on a 240-Z but I'd check it carefully
before going to 88 mm.
Check with a quality machine shop for sources of cast pistons. Most
high-performance pistons are forged, which usually require much wider
clearances, but a lot of the newer forged pistons will work with tighter
clearances than before. And if you have them coated with a thermal barrier, you
might be able to squeeze it down another thousandth.
Longer rods will (in theory) give a broader power band, because the pistons stay
in the vicinity of TDC a little longer, allowing more time for cylinder
pressures to build. Most engine builders say you'll never feel the difference in
a street motor. And I'd be very reluctant to shave a tenth of an inch off the
top of a piston. Check the thickness of the piston crown first. Usually going to
longer rods involves getting custom pistons with the piston pin hole set higher
in the piston.
Gordon Glasgow
Renton, WA
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of Alex Avery
> Sent: Wednesday, October 24, 2001 12:04 PM
> To: datsun-roadsters@autox.team.net
> Subject: Piston sources for Z car
>
>
> Ok, I know it's not a roadster topic, but I trust you guys and I need some
> advice. I'm trying to gather all the parts for my Z motor and I cast
> flat-top pistons. So far the biggest I can find are 0.04" overbore over the
> stock 86mm. I'd like to go to 88mm but it ain't critical. It'll be a high
> compression motor when its done, about 10:1, through a combo of increased
> bore and shaved P79 head.
>
> Any suggestions from you die-hard motorheads out there for companies that
> sell good cast pistons? Are there sources for Nissan cast flat-tops in 87
> or 88mm bore?
>
> A guy on the Z forum says he's got 86.75mm cast flat tops for $42 apiece
> plus shipping. Good deal? (He says 86.75mm is the same as 0.04" overbore
> from stock, but my dictionary says 0.04" = 1.016mm?)
>
> Thanks in advance for any replies.
> Alex in Virginia
>
> P.S. I've also got both the stock 280 connecting rods, as well as the 2.6mm
> longer 240 connecting rods (the good 9mm ones). I'm told that I'll have
> more torque with the 280 rods, but the longer rods will give me better rev
> characteristics. Any thoughts on which ones I should use? If I go with the
> 240 rods, I'll have to shave the flat top pistons 2.5mm.
>
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