2jzGTE Square engine

Toyota's 2JZ-GE/2JZ-GTE is a square engine, with a bore and stroke of 86mm

When people forge the engine they generally hone the block out to a larger bore , but is it enough to cause the engine to be Oversquare?

If the bore is larger than the stroke, the engine is considered to be oversquare.

What are the implications?

A better question might be , why it was not made an over square engine? (Short Stroke)

I'm sure I've read somewhere on here about this when Chris Wilson was trying to discourage the use of a Stroker Kit....

I'm sure he will be along to answer your question in due course..

A better question might be , why it was not made an over square engine? (Short Stroke)

Because it was probably easier just to build on the 1JZ platform, which is an oversquare engine, than starting from scratch all over again.

The 2JZ has the same 86mm bore as the 1JZ, the stroke was lengthened to 86mm in the 2JZ to give the extra 500cc and the hike in torque.

Damien has already given a good and similar answer to what I would have done. Just to say increasing stroke relative to bore increases piston speeds in a none linear manner, adding to rod loads and skirt friction. Long stroke engines are not synonymous with being free revving, but the extra lever arm effort of the longer throw crank does boost torque. It's a balancing act.

An over square 2J would've required a longer and 'twistier' crank and also a longer block and head, all of which would be heavier and none of which would be desirable.

Large bore sizes are not particularly desirable on supercharged engines either, for various reasons of combustion propagation. Nice to see you back David.

Damien has already given a good and similar answer to what I would have done. Just to say increasing stroke relative to bore increases piston speeds in a none linear manner, adding to rod loads and skirt friction. Long stroke engines are not synonymous with being free revving, but the extra lever arm effort of the longer throw crank does boost torque. It's a balancing act.

Thanks Chris , I find the topic fascinating especially when you start to add in Stroker kits and oversized pistons ; with the intent of changing the engine design from maybe undersquare, square to oversquare, depending on what you want it for.

From what I am reading is it ideal to have a square engine , for the sake of simplicity if we just say for a road car or in an ideal perfect world? The benefits of a square engine is having a good balance between rod loads and ...(please fill in here ) ?

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Because it was probably easier just to build on the 1JZ platform, which is an oversquare engine, than starting from scratch all over again.

 

The 2JZ has the same 86mm bore as the 1JZ, the stroke was lengthened to 86mm in the 2JZ to give the extra 500cc and the hike in torque.

Thanks Dude!

Supercharging wasn't part of my answer, just responding to the O.P. even though my input to his question has been ignored?

I'm the only nutter with one of those.

Talking of nutters and being back, I have been locked up in a high security Asylum for the last 2 weeks with rubber gloved heavies trying to force feed me antipsychotic drugs.

However, they all learned the hard way that when I say no, I mean no.

I have had to resist breaking myself out, because that would have given them excuse to section me.

Now after 2 weeks of Judo practice fielding my wicket night and day, being careful not to cross the sectioning line, they have now decided that I was never in need of antipsychotic medication, just a good nights sleep that Judo 24/7 was preventing me from having.

Which is what I told the Knobheads when I was first detained.

I have kept up with my p.m's on my mobile, but telephone posting is a PITA and I have been a tad busy fielding my wicket.

I'll update the saga page when I get around to it, there's a chapter or three to be told about Civil Service corruption yet.

Oversquare engines:

Advantages:

Low mean piston speed

Reduced friction

Reduced inertia forces on rod, piston and pin (not withstanding potentially increased piston mass)

Shorter engine (packaging height)

Better NVH (also L/R dependant, but easier to achieve if stroke is shorter)

Able to package larger valves.

Able to achieve same piston force with lower cylinder pressure (see also disadvantages)

Disadvantages:

Worse charge preparation at low speeds (reduced bottom end torque).

Increased mechanical loads for a given cylinder pressure (i.e. requires a stronger piston, rod and pin)

Heavier piston (will partially offset the mechnical loading benefits of having a shorter stroke, although still overall benefit).

Longer engine (packaging length).

Higher heat rejection to coolant (larger combustion chamber surface area near TDC)

Lower average cycle torque for a given cylinder pressure curve.

Increased burn time.

Suited to: High revving engines with lower peak cylinder pressures. Engines where low speed charge preparation is not critical (i.e. port fuelled engines). Also 60degree V6 engines tend to be oversquare because the packaging is driven by the length of the crankshaft which in turn drives a large cylinder spacing. Making such an engine square or undersquare would be very inefficient, package space-wise.

Undesquare engines:

Disadvantages:

Higher mean piston speed

Higher friction

Increased mechanical loading

Taller engine (packaging height)

Worse NVH (sensible L/R harder to achieve)

Smaller combustion chamber (valve packaging)

Increased piston specific loading for a given cylinder force (i.e. requires a heavier / stronger piston crown and top land).

Advantages:

Better charge preparation at low speeds (improved bottom end torque).

Less heat rejection to coolant (smaller combustion chamber surface area).

Higher average cycle torque for a given cylinder pressure curve.

Shorter engine (packaging length)

Decreased burn time.

Suited to: Boosted DI engines where charge preparation at in the off-boost / low speed area is important. Engines where efficiency in the drive cycle region is important.

Despite the apparently long list of disadvantages in undersquare engines, the trend in passanger cars is overwhelmingly towards going undersquare. This is enabled by the fact that modern piston materials and design has alleviated many of the issues related to piston strength and mass. Also, with peak cylinder pressures heading towards 120bar, having a smaller piston crown area makes life a lot easier for the piston, pin and rod. Modern approaches to bore honing and piston coatings are reducing the friction issues, as is the now commonplace offset cylinder bore (which reduces piston side forces). The advent of DI has also meant that as you do not get the fuel mixture preparation by injecting further back in the intake system, the combustion system is reliant on in-cylinder charge motion instead. This is inherently better with longer stroke engines because the mean piston speed is higher.

Thanks Digsy

What does NVH stand for & L/R (sensible L/R harder to achieve)

NVH is noise, vibration and harshness.

L/R is the ratio between the stroke and the actual con rod length.

Mainly dependent on how high up the piston relative to the crown the piston pin is, in many cases it intrudes into the oil control ring land or even higher.

Excellent post by Digsy

An over square 2J would've required a longer and 'twistier' crank and also a longer block and head, all of which would be heavier and none of which would be desirable.

Thanks David, sorry missed your post

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NVH is noise, vibration and harshness.

 

L/R is the ratio between the stroke and the actual con rod length.

 

Mainly dependent on how high up the piston relative to the crown the piston pin is, in many cases it intrudes into the oil control ring land or even higher.

 

 

Excellent post by Digsy

thanks again Sir

Would you recommend any books on thus topic