Gemini engine capacity (taken from forum)

[Adam]

I know this has been said before, but it seems to be said regularly. Half of the time I read posts about gemini engine sizes I have to laugh. Everyone is aware of:
g161z has 82mm bore and 75mm stroke.
g180z has 84mm bore and 82mm stroke.
g200z has 87mm bore and 82mm stroke.
g161z capacity is actually 1548cc
g180z capacity is around 1850cc
g200z capacity is around 1950cc

The maximum overbore I've ever seen in a 2 litre is 60 thou or 1.5mm. Someone may know of a bigger one but i doubt it cos there is barely enough cylinder wall to seal when its bored 60thou over.

Working with the rough size that the difference between a g180 and a g200 bore size is 3mm and that gives 100cc, a 1.5mm overbore should give you and extra 50cc correct? Therefore the largest possible non stroked g200 capacity will be 2000cc exactly.

So why do people talk about boring motors to 2.3 litres? And if i fit 2 litre pistons to a 1600, I barely get 1750cc. And while im sure it is possible, I am yet to see or have proven to me that stroking a gemini motor is possible. People talk about hilux cranks and corona cranks, none of which come close to having the right journal spacing to fit a gemini.

So unless you know things I dont, and I know alot of engine reconditioners in queensland, I would pretty much rule out stroking a g180z or g200z. Be happy with your motor, its not the size that counts, its how good the head is that matters!

[TXcoupe]

ok capticy for the motor are
1600 = 1584
1800 = 1825
2000 = 1994

so given that a bore of 120 thou on a 1800 take u to 1994 then by boring out a 2000 60 thou takes it to about 2100

[Mark]

Just because wrong information shits me........
from the ACL parts catalogue, a g180z is 1817cc and a g200z is 1949cc. 120thou (3mm) gives 132cc. Therefore a 60thou bore which until proven otherwise I will take as the maximum allowable overbore, would give half of that 132cc, yes? Therefore we have a capacity increase of 66cc.
1949cc + 66cc = 2015cc. This is the maximum capacity of a gemini engine. If anyone cares to argue my maths or figures by all means go ahead.

[MR_GEMI]

Well here's the calculation I used.
82mm bore. STD
75mm stroke. STD
pi times radius squared = area of piston
times height = volume

3.142 X 41 X 41 X 75
------------------------------ X 4 cyl. = 1584cc (std gemini capacity)
1000

add 120 thou bore or 3mm, then you get;

3.142 X 42.5 X 42.5 X 75
----------------------------------- X 4 cyl. = 1702cc
1000
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[Stock TE]

A 2L bored 60 thou equals 2063cc

[Poida]

So the correct figures are in fact:
G161Z - 82mm bore and 75mm stroke. (1584cc)
1604cc @ 0.5mm O/S
1623cc @ 1.0mm O/S
1643cc @ 1.5mm O/S
G180Z/G180W - 84mm bore and 82mm stroke. (1817cc)
1839cc @ 0.5mm O/S
1861cc @ 1.0mm O/S
1883cc @ 1.5mm O/S
G200Z/G200W has 87mm bore and 82mm stroke. (1949cc)
1972cc @ 0.5mm O/S
1995cc @ 1.0mm O/S
2018cc @ 1.5mm O/S

I wonder if some of you actually bothered to calculate the volumes using the figures you state.... do the maths!!!

Now the only question I need to ask is;

Why are we talking in inches when the Isuzu engine is formulated in millimetres??

You can only buy pistons, rings and bearings measured in millimetres for these engines so why complicate things and calculate in inches???

Oversize pistons/rings are available in
0.5mm, 1.0mm and 1.5mm

NOTE:
Since 1975 Australia has been metricated. Lets all speak the same language!
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[Poida]

Most of us are over boring to increase the engine capacity and gain power.

There are limits to how far you can safely over bore an engine.

The cylinder wall thickness varies from engine to engine. An engine with too thin a cylinder wall will more than likely fail prematurely. Cause of failure can be a split bore or a deformed bore due to the inability to dissipate heat to the coolant. The ideal engine should also have a rust and scale free cooling jacket.

Removing metal from the bore also removes the engines ability to transfer heat. Think of that cylinder wall as a heat storage vessel. If the heat cannot be carried away by the cylinder wall it means the engine will overheat eventually damaging rings and pistons.
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[ATG23Q]

....

[Stock TE]

I dont know what i did before but yeah it equal 2017cc

[Poida]

Once again... Why are we speaking in inches???

In Japan the system of measurement is METRIC. Isuzu engines are measured in millimetres.

Is the G161Z known as a 96.6 cubic inch engine???

No machine shop is going to machine your engine in thousanths of an inch because there are no parts made for it in inches!

If you convince the machinist to bore/mill/grind it in inches, don't be angry when it doesn't match the clearances of the bearings/rings etc...

If you need to know the theoretical volume of your rebored engine read my earlier comment where all the calculations have been done and you can simply read off the chart and the answers are there.

Forget trying to bore out beyond the available piston sizes. It's generally inpractical attempting to match pistons meant for different applications and you're better off buying a bigger capacity engine to begin with.

It's no problem spending three times the amount trying to build your 1.6l into a 2l... the machine shop will thank you graciously. You'd be better off beginning with a 2l block.
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[Stock TE]

Just give it a rest. Let them use whatever style of measurement they want, who cares if the G161Z is Japanese, this is australia. Most people I know use imperial measurements when describing how bored out their engine is. Also I know somebody that works in an engineering workshop, and they use imperial just as much as metric.

[Poida]

Stock TE,
the reason I keep pointing it out is that the chance of making a mistake multiplies with conversions as you are changing from one scale to another then back again. Did you not notice the number of mistakes in the comments posted. They stood out to me!
The other reason is, machine shops DON'T refer to a metric engine in imperial measurements. Why would they?
I have been employed in a number of different engineering based industries in my life and I am confident using both imperial and metric measurements.
I am no youngster Stock TE.
I was well into my working life when Gemini cars were introduced to us in Oz. I worked at GMH in my first job when the last of the XU-1 Torana's were on the line. I watched them win Bathurst.
I am familiar with imperial measurements in everyday life. Do YOU remember imperial measurements? Do YOU remember pre decimal currency?
Talking imperial measurements with a Japanese engine is on par to shopping in Oz, calculating the price in Euros then paying in US$.
Is it not helpful to guide someone less experienced or knowlegable and point out the truth?
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[Stock TE]

I didnt say engineering shops refer to a metric engine in imperial measurements, I said they use both. This means they use whatever measurement you give them, eg. if you give a machine shop a Gemini block and say bore this 40thou they are going to bore it 40thou not say this is a Japanese engine give me a metric measurement. I do not remember pre decimal currency, and I dont remember imperial measurement but its quite easy to convert. Most of the mistakes are made because of assumptions and starting with the wrong number, but look at the actual tip, he has got the conversion right and still made mistakes. And yes it is helpful to guide someone less experienced or knowlegable and point out the truth and you did, you told them to do the maths. Doing this, giving them the formula and giving them a basic coversion table would do. So here goes.
Pi times half the bore times the stroke times 4 equals Displacement. If you are using millimetres divide by 1000 after this to get cc's.
Eg. 3.141 * 1.614 * 1.614 * 2.952 * 4 = 96.6ci
Or 3.141 * 41 * 41 * 75 * 4 / 1000 = 1584cc
And 1 millimetre equals 39.36thou (40thou if you need to do it in your head). Hope this helps.

[Poida]

Yeah Stock TE.

I am not having a dig at anyone in particular so long as you understand that.

Your comment on machine shops is nearly right.
A machine shop will work in both imperial and metric standards. They have to. But the catch is they work in the standard each individual component was manufactured to.
A holden RED motor was always manufactured in imperial measurements so thats how you work with it.
A Gemini motor was always a metric engine.

The machinist might listen to you ask to 'bore this .040" for me mate, knowing you want it bored 1.0mm. In reality he'll be thinking, this guy hasn't got a clue (wanker), but he isn't going to tell you that!

Anyway the gist of my post was to alert everyone to the fact mistakes were being made. From my understanding the point of this "workshop' area is to post usefull facts we can refer to. Thinking about overboring a block 3.0mm is just not feasable. Therefore why bother speculating on what capacity it will give?

P.S. (nostalgia)
I remember the days when I could buy eight licorice blocks for a penny. These were real licorice blocks measuring an inch square and 1/4 inch thick... times have changed.
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