L18 Long rod or L20b motor?

[datzenmike]

Running the pistons 180 (backwards) changes the piston pin offset and can add some small percentage too. OK for race motor, rattle like hell till warmed up in a DD though.

 

I was reading Smokey's stuff when a teenager. I remember seeing a motor he was tuning on a dyno. The headers had small holes drilled in them. Best anyone could figure was it was a good way to see the color of the exhaust flame. This was way before O2 sensor exhaust gas analyzers and cheap temp thermocouples.

Edited October 13, 2009 by datzenmike

[freaky510]

I have/Had a long rod motor it was pretty cool it would come up on the R's real fast:eek:

 

I plan on puting back together here soon. all I can say it was a fun motor had good power and pulled hard when i bought it, it had a down jetted holley 500 cfm carb on it :lol:

 

the only problem I belive was the timming i blew the rings out of the #1 piston:mad:

[Dudeman]

I also just noticed that Z22S and early Z22E pistons have the same 35.5mm pin height, but a 2mm bigger bore and a 9.32cc dish. Does anyone make flattop Z22 pistons, and then you could punch out your L18 2mm? That's a little over .050 overbore, will the l18 even handle that?

 

And on a related note, I'm familiar with American cars being bored in thousandths (.020, .030, etc.) but I've seen people talk about boring datsuns both in thousandths of an inch as well as in mm. Are they close enough that it doesn't matter (i.e. 1mm=.030) or do they make oversize pistons for both types of overbore measurements? Perhaps a bit off topic, but that's just something that has always confused me

Edited October 13, 2009 by Dudeman

[zed]

That's a little over .050 overbore, will the l18 even handle it?

Honsowetz book says maximum overbore for a L16/18 should be .080. But I have seen an L18 advertised for sale here in South Africa bored to 89mm. Wonder what pistons would be used in such a build.

[datzenmike]

1mm is a C hair under 0.040". I would not advise anyone to over bore a motor without the pistons in hand. The person doing the boring should measure each new piston and bore accordingly. Just because it is 1mm or 30 thou over, or whatever, does not mean it's exactly that. The cylinder should be, (I think) about 2 thou smaller all the way around the piston for proper ring sealing.

 

Even Nissan grades their pistons and block bores, thats why there is a number stamped on the piston top. Pistons are mass produced and fall within a tollerance range, the same as the bores in the block. The block will have a number punched in the top and the assembler reaches into the parts bin and selects the piston that most closely fits the bore. If a bore is just slightly over, a slightly over size piston is installed to keep the clearance within spec.

[ggzilla]

If you sonic test the bores, you can tell if they can take a bigger overbore. Sometimes they can even offset bore them safely.

 

But without such testing, .080 overbore is the most a "typical" L18 can be expected to take. Remember, by overboring .080 you are gaining almost 9 CCs. So instead of a 1770 cc L18, you get a 1779 cc L18. Wahoo!

Edited October 13, 2009 by ggzilla

[zed]

Remember, by overboring .080 you are gaining almost 9 CCs. So instead of a 1770 cc L18, you get a 1779 cc L18. Wahoo!

 

I work it differently:

 

volume of cylinder = area of base x height of cylinder

=22/7(pi) x 42.5mm^2(radius)x 78mm (L18 stroke)

= 442.61cc per cylinder x 4

= 1770.44cc standard L18

 

For .080 (2mm) overbore:

22/7 x 43.5mm^2 x 78

= 463.68cc per cylinder

= 1854.72cc

An 84.28cc gain.

[DISLEXICDIME]

check out ozdat there are some neat stroker's on that site

[datzenmike]

I work it differently:

 

volume of cylinder = area of base x height of cylinder

=22/7(pi) x 42.5mm^2(radius)x 78mm (L18 stroke)

= 442.61cc per cylinder x 4

= 1770.44cc standard L18

 

For .080 (2mm) overbore:

22/7 x 43.5mm^2 x 78

= 463.68cc per cylinder

= 1854.72cc

An 84.28cc gain.

 

 

Close enough to make no difference.

 

BTW 2mm isn't exactly 0.080". This is why I cautioned that the pistons be measured before boring.

[ggzilla]

Thanks for the correction. 84cc will make a noticeable difference. Not as much as an L20B, but good enough.

[Doctoraudio]

Okay, It turns out I have a exact same motor in my car!
Took a while to figure out some of the things.

I am using a Weber 32/36 for now.

Like, I have been driving around with the wrong jets in the carb.

Since changing the jets it seems to run smoother than ever and has more bottom end power.

I like it and it is perfect for daily driver and getting on the freeway and cursing at 70 mph.

I don't have any problems passing anyone. Well within reason!
This is a great motor!
 

[EricJB]

If you are building the car to compete in a class where you are weighed based on engine size, some people would choose an L18.

 

Same car, same weight, same gears, same head and externals, I would go with an L20b. It's not hard to make an L20b spin past 7k.

[Doctoraudio]

It took me all this time to find out all that is in my engine.

This one came in my car and still has less than 35,000 on the motor!

Double and triple checking stuff.

Last engine I had something to do with building was a L20B.

May look around for a L20B block to bore out again.
But this engine is great for coming with the car and preforms very well under all conditions.

I get good gas mileage too, so no complaints. YET!
Later!

 

[Stoffregen Motorsports]

Will a L18 Long rod perform as good as a standard built L20b?

Trying to decide which route to take given that I already have both L16 and L18 components to build a L18 long rod less the pistons.

 

 

 

Long rod L18

flattop Z20S pistons and peanut chamber head for 9.7:1 CR, better rod/stroke ratio for higher RPM.

Parts: L18 crank, L18 block, L16 rods, Z20S pistons

s/2+r+p: 207.66mm

piston deck height: -0.29 (below deck)

-.29 (below deck)? and 9.7:1 CR?

[Doctoraudio]

I read it somewhere, it means .29 below the top of the cylinder!

Otherwise, you could smack the piston with a valve.
Or you could end up with higher compression.

I don't remember which one it was but, I can be corrected!

[Stoffregen Motorsports]

I guess what I was saying was that it is probably .029 inches below deck or maybe .29 mm below deck.

 

If it was .290" (over a quarter inch) below deck it wouldn't have hardly any compression at all.

[datzenmike]

Deck clearance is not the distance below the head to the piston.  It's the distance from the piston top, up or down, to the top of the block.

 

 

 

 

Long rod L18

flattop Z20S pistons and peanut chamber head for 9.7:1 CR, better rod/stroke ratio for higher RPM.

Parts: L18 crank, L18 block, L16 rods, Z20S pistons

s/2+r+p: 207.66mm

piston deck height: -0.29 (below deck)

 

L18 crank, L16 rod and Z20S piston totals 207.56mm from crank c/l to piston top.

The L18 block is 207.85mm tall.

 

So... 207.85 - 207.56 = 0.29mm of clearance below the top of the block.

 

This space above the piston and below the block top becomes part of the combustion chamber. 0.29mm is about 1.644 cc of volume. Doesn't seem like much but it can raise or lower compression quite a bit. You could mill the top of the block if you wanted to to remove this and add to the compression. Generally you could remove even more and allow the piston above the block. But not more than  1/3mm.

 

 

Will a L18 Long rod perform as good as a standard built L20b?

Trying to decide which route to take given that I already have both L16 and L18 components to build a L18 long rod less the pistons.

No, it won't perform better than an L20B....

 

It will still be a 1.8 liter motor but with a longer rod. Longer rods don't do much... the piston decelerates sooner and accelerates later than a shorter rod and is traveling slower near TDC. This would reduce stress and side loading on the piston but on a stock L18... you won't notice anything.

 

The L20B will always be 11% larger displacement with about 10 more hp and torque.

[Dime Dave]

No, it won't perform better than an L20B....

 

It will still be a 1.8 liter motor but with a longer rod. Longer rods don't do much... the piston decelerates sooner and accelerates later than a shorter rod and is traveling slower near TDC. This would reduce stress and side loading on the piston but on a stock L18... you won't notice anything.

 

The L20B will always be 11% larger displacement with about 10 more hp and torque.

 

Like my Dad always says, "Ain't no replacement for displacement."

[EastBay521]

saved me some time.my day dreaming of this motor was shot down after Troy Ermish told me they don't make roadster clutches to put behind this thing anymore nor do they make flat top pistons for the l18 (unless you want to pay to have a set made) because all of the z20 pistons I am finding are dished

[datzenmike]

You want Z20E only available on the '80-'81 S110 (200sx)and but for 4 small eyebrows for valve clearance are flattop 85mm. (and stock over size)

 

 

This would be a great motor if limited to 1.8 liter in your class, and if with multiple carbs and big cam..

[Doctoraudio]

I don't have another engine to compare it too.
It scoots and I beat on her and she responds.
 

This would be a great motor if limited to 1.8 liter in your class, and if with multiple carbs and big cam..

[hosestop@msn.com]

L18 track motor will see more rpms like 8k and bury the tach I have one here with comp six bolt crank ,built by tilton from a car we disassembled , also have a L18 12 to 1 Venolia piston motor , sitting on three L18s for a race car project ,Castillo crank is down here where they knife them and lighten.

[EastBay521]

1mm is a C hair under 0.040". I would not advise anyone to over bore a motor without the pistons in hand. The person doing the boring should measure each new piston and bore accordingly. Just because it is 1mm or 30 thou over, or whatever, does not mean it's exactly that. The cylinder should be, (I think) about 2 thou smaller all the way around the piston for proper ring sealing.

 

Even Nissan grades their pistons and block bores, thats why there is a number stamped on the piston top. Pistons are mass produced and fall within a tollerance range, the same as the bores in the block. The block will have a number punched in the top and the assembler reaches into the parts bin and selects the piston that most closely fits the bore. If a bore is just slightly over, a slightly over size piston is installed to keep the clearance within spec.

so is this the reason my l18 has the number 3 stamped on the top of each piston except for cylinder 3 wich has has the number4 stamped on top.? is cylinder 3 slightly bigger?

[datzenmike]

Most likely. The difference between the largest and smallest pistons is only 0.050mm or 0.00125"   The differences are very small but the largest oversize piston will not fit in the smallest undersize bore. This allows a wider production range of parts to fit. If it was a perfect world an L20B would be exactly 85mm bore with an 84.985mm piston. Way to hard to mass produce these in those exact dimensions.

 

Pistons fall between 84.985mm and 85.035mm and these can be measured and given a grade of 1 to 4?

Blocks fall between 85mm and 85.050mm and are also graded 1 to 4. Usually stamped on the block or maybe measured during assembly. If the block falls in the #3 range a #3 piston is selected from the bin and perfect (or very close) match. This cuts down on rejects.

 

An L20B with the largest allowable stock L20B pistons is only just over 1/2 cc larger than the smallest. It's nothing.

[Doctoraudio]

I am understanding most of what your saying Mike.

Is it possible for a L20B to get better mileage than the Long rod 18?
 

I like performance and mostly gas mileage.
Trying to find the right balance for me.

Wouldn't the L20B burn more fuel?
I like what I got in there.
Just trying to clarify it.