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Building a 3.1 (Advice)


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-- Group Message from "Dan Baldwin" <danbaldwin@hotmail.com> --

>I was thinking of building a 3.1 liter.

A fine ideer!

I already have a 2.8 with a P79

>head. I was wondering if this is a good head to ues or not.

Not the best head for performance. Low compression and poor exhaust

port design. N42 is what I'm using. Higher compression and the

preferred square exhaust ports. Others prefer the P90 turbo head,

which also has square exhaust ports.

I would like to

>be able to drive this car on the street and be able to use pump gas.

With the N42 head and a 2mm HKS head gasket, I'm at 10.14:1. somewhat

steep, but I ran mine like this with the stock cam (hotter cam allows

more compression) at something like 10-12 degrees ignition advance at

idle and had no pinging problems using 93 octane pump. With a hotter

cam, I now run more ignition advance, ~17 or so.

With a P90 head and 1mm HKS gasket, you'd be at 9.75:1. Shouldn't

be a problem.


>any suggestions on where to get the crank, rods, and pistons besides Nismo

>and MSA would be appreciated, they are kind of expensive($1800)

Time to scour the junkyards, or post to this list and the big list

(go to www.zhome.com to find out how to join it) for the desired

parts. 240Z rods, diesel crank from a diesel Maxima, and get new

KA24 pistons. If you're gonna be racing or doing a lot of high-rpm

usage, you might consider having the rods shot-peened and having

the pistons cryo treated or something. If you're breathing through

stock FI or SU carbs, you won't be revving high enough to worry with


FWIW, my 3.1 breathes through 240Z SU carbs which, in spite of a

290/.503" cam, limits my rpm to 6500 or less (6500+ in lower gears,

just over 6000 in 4th). before the cam, I was limited to 5000-5500.

I don't know how much more the stock FI flows than SUs.

BTW, I didn't have my rods shot-peened or pistons treated when my

motor was built. If I was doing it again I probably would.

3.1 with SUs (or with FI) is a KILLER street setup. I do a fair

amount of track work, though, and find myself in need of more.

Still, even at the track it's great to have a ton of low-end, and at

the high end even though torque falls off, it's still ahead

of a stock L24, and monster torque is only an upshift away.

I really need 3X2 44mm or 45mm carburetion to take full advantage of

the motor, though.

Dan Baldwin

'71 240Z 3.1


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