Automobile Engines With a Long Stroke

What gasoline car engines have a relatively long stroke? I was looking at the LS7 C6 corvette Z06 engine that has a stroke of 101.6mm. The only other performance oriented engine I could find with a stroke over 100mm was the V10 viper with a stroke of 100.6. Are there any other engines both past and present that have long stroke crankshafts from the factory?

British cars of yore tended to have long strokes, as they were taxed on the size of the bore.

The AMC 258 straight six had a 99mm stroke. Not quite 100mm, and not quite a performance engine, but it has an excellent reputation. It evolved into the 242 (4.0L) with a slightly shorter stroke that’s considered by many to be the ultimate bulletproof gasoline 4wd powerplant.

V-type engines usually aren’t going to have terribly long strokes because with the opposed cylinders, longer stroke makes for wider engine. The classic “undersquare” (i.e. stroke length longer than bore diameter) engines are usually inline engines. I can’t really think of any performance-oriented cars these days that have large displacement inline engines. The most recent BMW M3 with a straight 6 had a 91 mm stroke, which is pretty big for their relatively small 3.2L of displacement.

The Chrysler 225 slant 6 had a 104.6 mm stroke. The Cadillac 500 V8 had a 109.3 mm stroke. Both had good low-end torque for their size, but really weren’t high performance engines.

A lot of transverse mounted engines use a longer stroke and a narrower bore in order to reduce the overall engine length, giving the engineers a bit more room in the engine compartment for other things like making space for the wheels to move back and forth while steering.

The old Chrysler 225 slant 6 engine had a narrow bore and a long stroke (104.8 mm according to wikipedia) and also slanted the cylinders 30 degrees. This shortened both the engine’s length and height. Slanting the engine also allowed them to offset the water pump to one side, further reducing the engine’s length.

As GreasyJack said, these long stroke and narrow bore engines are often called “undersquare” engines. Undersquare engines have a natural tendency towards great low end torque, but not necessarily so good high end performance. The inertial stresses are greater in a longer bore engine, which generally prevents them from being revved as high, though there are exceptions. The narrow bore also limits the size of the intake and exhaust valves, which also chokes high end performance. Oversquare engines can have larger valves, have less inertial stress, and all other things being equal, can rev higher, thus producing more power. Oversquare engines are also longer in length and shorter in height than undersquare engines, again, all other things being equal.

(ETA - Ninja’d on the slant 6 - I type too slow)

This.

It’s not so much that some modern engines have a “long” stroke as that the ideal designs have evolved to where usually bore approximately equals stroke. Stroke grows as overall displacement grows.

High RPM engines like F1 and crotch rocket motorcycles are oversquare (short stroke) but pay for the performance advantage in decreased durability and low RPM torque. Long stroke engines have long, heavy rods and more piston inertia to control.

Fiat’s 1911 effort , the “Beast of Turin” (two were built), had cylinders of 7 litres EACH !
Only 4 cylinders but still its a 28.3 litre engine…probably the largest petrol (gasoline) engine ever , and also largest cylinder size of a petrol engine, and therefore, longest stroke of a petrol engine…
There was a damaged chassis stored in Australia, and Fiat kept an engine,
and so … there is now a working Beast of Turin …

http://theoldmotor.com/?p=122246

Ok the Beast of Turin engine wasn’t in fact the largest engine total, but it would have had the largest cylinder size.

The larger total sized engines used 12 cylinder designs, eg the 37 litre V12 Rolls Royce R.

Echoing Greasy Jack’s comments, a very common modification to a small block 350 cid Chevy engine is to replace the 350 crankshaft with a small block 400 cid crankshaft, which has a 1/4" longer stroke. With a .030 overbore the displacement is upped to 383 cid. You give up some rpm, but you gain a lot of low end torque.

The Bentley 4.5 Litre is a good example: 140 mm stroke.

If we’re limiting this to just cars, yes; but then there’s the 71 litre, 28 cylinder, Pratt & Whitney R-4360 Wasp Major.

Actually, I decided to look that up to see if radial aircraft engines (at the pinnacle of their size and development) were over- or undersquare, and it’s neither, 146 x 152 mm. Checking a few other aircraft engines, it looks like the early ones (WWI era) were undersquare and current ones are oversquare.

A fun fact:

A consortium of automobile companies, mostly German, have come up with a bore/stroke/liter ratio that is considered optimal for balancing efficiency/power/torque/power curve and which lends itself to being turbocharged (or force inducted).

2.0 liter 4 cylinder, with a stroke a little longer in length then the bore size (a modest stroker engine). <— this surprised many, who expected an oversquare engine or 1:1 bore:stroke ratio to win)

This ratio carries over to 3.0 6 cylinder and 4.0 liter 8 cylinder, all modest strokers.

You will see a lot of 2.0 fours, 3.0 sixes and some 4.0 Eights.

WHY SOME PERFORMANCE CARS ARE STROKERS (e.g., Viper. Vette):

They’re lineage is traced to big American iron, which was often mated to simple 2 or 3 speed transmissions. A stroker engine is torquey and just what you need to pull a heavy car with just two gears to play with.

Viper: Makes use of a modified truck engine, and truck engines (boats, too) are best suited to be torquey.

Opposite end of the charts: Ferrari is famous for oversquare engines mated to as many gears as they can squeeze into a transmission and lofty 9000 RPM redlines.

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<highjack>
The Wärtsilä RT-flex96C (Wikipedia) displaces 25,480 litres … used in the biggest cargo ships.
</highjack>

Yes we are discussing gasoline car engines here. Let’s try to keep this on topic.

Ford 5.4L engine has a 105.8mm stroke.

ETA, Carroll Shelby said it was the best engine Ford ever made.

As mentioned above, British cars used to be taxed on their ‘RAC horsepower’ a curious calculation, used by no one else, based on the cross-sectional area of the cylinder bores. The result was that British engine designers kept the bores as small as possible and tried to compensate with a long piston stroke, producing tall and inherently fragile engines. This basis for taxation was not finally abandoned until the late '40s, although manufacturers tended to quote the RAC horsepower and the brake horsepower, which gave a much better assessment of the engine’s power, for a lot longer.

If you have 2 single cylinder engines one oversquare and one undersquare but of the the same displacement would they not have the same torque at low rpm? Assuming, of course, everything else being equal.

The longer stroke of the undersquare giving a greater moment at the crank would be offset by the lesser area of the piston given equal pressure in the cylinders, conversely a lesser moment at the crank compensated by the greater area of the piston in the oversquare design. The actual situation is quite complex but in general, contrary to what seems like common sense, in an “on paper” sense they should have equal torque.

I think the general impression that long stroke engines have inherently greater torque comes from practical examples that people are familiar with. These engines are designed for lower rpm operation in the name of longevity namely ring float and inertial loads due to high piston speeds. Cam timing is designed around low speed operation as is the induction system.

Subjectively the lower the rpm the peak torque is reached the greater it feels to the rider or driver. A racing engine that is way oversquare and develops its peak torque near the hp peak will feel less torquey even though of the same peak torque as an undersquare engine.

I have always wondered what one would get with an engine whose cylinders varied in bore and stroke, but had equal displacements. For example, an inline six with three undersquare cylinders and three oversquare. How about a V8 with an undersquare side and an oversquare side? Would one get the best of both types, the worst of both, or something in between?

I think there would be much difficulty in balancing such a weird crankshaft.