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how much to skim block?


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I need advice.... again. Can I skim .030 off my L18 block? How much 'out of the bore' can an L18 piston be? Problem is, my block is bored out to 86mm. The only gasket available here for that is .055" thick compressed (55 thou). The machine shop guy says the motor is going to ping/detonate. Or make poor power. Because the clearance is too big between piston and head - so there will be no 'squish'.

Standard L18 deck height is -0.021" + 0.055"(gasket)=>0.077" clearance. That is too much.

any advice?

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It should only ping if the compression is too high, if the gasket is to thick it would lower compression? I dont really understand what you are asking? you could always go with a head that has smaller combustion chamber to rais compression if that is the problem or change your pistons, or turbo it :) and yes you can have the block shaved

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Can I skim .030 off my L18 block?


YOu mean bore out?

Yes u can go 2mm over no proplem.


I had my L16 bore out to a L18/20 which is 85mm.


1mm over is usually theStock size on the 280zx L28 motors(86mm). Of coase this is in the USA and I dont know what they have in Africa.


a stock L18 piston is 4cc dished 85mm

a SSS L18 is a O dished

a 81-83 280zx TURBO is 86mm but 10.9cc dished

a 81-83 280zx NON Turbo is 86mm 0 dished


If possible you can bore it out to 86mm and use the flatops on a "CLOSED) chamber head A87/W53/SSS no proplem. Just need to maybe find a 87mm head gasket as it gets close to the bore. Datsport in Austrailia has made in Japan one for sael as they made L mootrs up in mid 80s in Austrailia.


But if you run a Open chamber head I cant guareentee that it could ping/detonate as I dont know what octane gas is sold there cause Open chamber head tend to detonate ezer than the closed chamber heads.

best to ask some one who has done this.


hope this helps




If your machinist can get .030 in stock L18 pistons then you can get those if you want.


I had 2 motors done and there was always one piston that was out of tol. so a rebore was needed w/new pistons

Edited by banzai510(hainz)
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Ok, sorry I'm not clear here...

I'm trying to get 10:1+ compression, without pinging on 93 gas. So I gotta have good 'squish' - 0.040" to 0.060" clearance.

But, the problem is the only available head gasket is .055" thick. So, the only way to bring the pistons closer to the head now is to skim the block(head is already skimmed .020") By how much can I skim the block without pistons hitting valves or other shit?

(Hainz - the block is already bored out to 86mm)

Edited by zed
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Well, I read a lot that raising the compression is the easiest, cheapest way to boost power. Fuel economy is also important - gas costs R8,00 per litre here - that's about US$4,50 a gallon. Out here, hot cams and carbs are hard to find, and very expensive, and there are no experts to fix them if they go bad. I went to every scrap yard within 300 miles - not one L18 motor could I find. But there is a machine shop, and I can get basic Datsun/Nissan engine parts quite cheap.

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im sure they have sr20 motor's or ka24de's there.


if your looking for substatial increase in power you may want to just do a swap.


The old saying that theres no replacment for displacment is not always true.

Newer technology can render that saying moot.

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Here's what I got:


L18 bored to 86mm using flat top zero dish pistons, 1.4mm crushed gasket thickness and stock 41cc closed chamber head... 9.66 compression.


You say you have milled the head by .5mm. I don't know the cross sectional area of a closed chamber head, but we could assume it is about half that of an open chamber and this works out to about 1.5 to 2cc smaller in volume. This will raise the compression to 9.91 (or more).


I see where you need to get the piston a little closer to the head in order to take advantage of the quench area. The L 18 piston/rod combination measures .55mm below the top of the block. Removing .55mm will remove 3.19cc of combustion volume and raise the compression to just over 10.5. A bit high... too bad the head was already milled.

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