Motor question

[Guest PR0ject datsun]

Well i have a L28 block (dont know the code) with an N42 head. It's not put together yet, but i sourced the parts separately and the block has dished pistons...im building the car for all motor. Yeah, i know id make more power with flattops, but i want to work with what ive already got. What do you think would make more power?

 

Combo 1:

L28 bottom, N42 head

 

Combo 2:

L28 bottom, early E88 head

 

Combo 3:

L24 bottom, N42 head

 

or stock? what kind of power gains would i be looking at? or if anyone has any good suggestions, please post them up. Thanks!

[DeusEx]

If you haev dished pistons, you definetly want to chase compression, i believe that the early E88 would give the highest compression, but they are a primative head (the later ones are better) Personally i would go for the N42, good moden(ish) L series head, with decent compression.

 

Power figures are hard to estimate, what are you using for induction? Is the bottom end standard?

[Guest PR0ject datsun]

Stock bottom end, stock dual SUs w/ air trumpets, MSD 6AL, stock points, MSA header and 2.5" piping. But it would make more power over the stock L24?

[evildky]

the L24 heads (E31 and E88) both use smaller valves than the N42, the E31 has the smallest combustion chamber and therefore yields highest compression ratio and more power if it can flow enough air, via modifying the head to accept oversized valves, or you can take the N42 and a flat top L28 (you did not specify which you had (flat top or dished top pistons)) and get a high compression motor, the advantage of the L24 is it's short stroke and reviness, the L28 of course increases displacement, then it's a matter of getting a workable compression ratio, find and play with the L series engine calculator, very good starting point

[DAW]

Unless you're going to turbocharge, the dished pistons are worthless for making power. Even with a shaved E31 head you don't make significant compression and you've got those tiny valves to deal with. If you are building a n/a engine do yourself a huge favor and use flattop pistons, whether from an '80-'83 280ZX L28E bought as loose pistons or just find a shortblock from a 280ZX (F54) of those years.

 

There's one other approach which makes sense: Take out your piston/rods; remove pistons from rods; have a machinist turn down the edge of the dish-top until it's just gone and you barely have a flattop (with reduced pin ht.); reassemble pistons to rods but don't use the L28 rods, use L24 rods with 9mm bolts (2.6 mm longer rod than L28, makes up for lost pin ht.). You can bench-balance rod/piston matches in the process and the net result is that you've increased your baseline compression and have a simple choice of stock larger-valved heads (vs E88, E31 small valves) to use. P79/90 now gives you 8.8:1 and N42/47 gives around 10.0:1 on an engine that has an improved rod length/stoke length ratio than an L28E. For the highest hp/buck ratio and greatest fun factor/ headache ratio, this is the way to go. Hint: you can probably pick up a L24 shortblock for free if you haul it, or a set of L24 pistons (with rods) for less than you could for a set of rods on e-Bay (from someone who knows what they have). I've tried every approach you're considering and this one makes the most sense. DAW

[DAW]

PROject datsun, if you decide to go the route I suggested, here's some valuable info: you want to only consider L24 rod sources from engine # L24-096181-on as these have the 9mm rod bolts. Forget anything earlier as they would have the useless 8mm rod bolts. DAW.