Hoovey689

iTrader: (16)

There's always been the argument; "no replacement for displacement". Lately due to governemnt regulations and emission standards coupled with social view the trend has been to downsize and add forced induction.

My question is, with all these automakers dropping say their 3.0-4.0 six in favor of a forced induction 2.0-2.9 four, why not downsize the displacement but retain the same cylinder count. Why don't we see 2.0L V6's? 3.0L V8's? (Some exceptions like the Mclaren 3.8L V8 and Lexus 4.8L V10 and excluding racing engines like F1)

Having the benefit of two extra cylinders especially in a luxury car adds/retains that refinement. The 2.5L V6 in the IS may get dinged for being 'slow' but then would you rather have a raspy four which is not as linear. As long as one understands the IS250 is a four cylinder competitor with two extra cylinders for refinement.

Any thoughts? Correlation between Displacement vs Cylinders?

Discuss!

chikoo

That is the prime reason I purchased my IS250 - rwd with a small V6.

Keiffith

the idea is that an engineered for turbo 4 cylinder is equivelent to an N/A V6.

there is a 3rd dynamic here, and that bore and stroke ratio. heres some stuff copied from wiki

A square engine has equal or very nearly equal bore and stroke dimensions, giving a bore/stroke value of exactly or almost exactly 1:1. the 2jz is a square engine


An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length, giving a bore/stroke ratio greater than 1:1.

An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.


An engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.

At a given engine speed, a longer stroke increases engine friction (since the piston travels a greater distance per stroke) and increases stress on the crankshaft (due to the higher peak piston speed). The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. Because these factors favor lower engine speeds, undersquare engines are most often tuned to develop peak torque at relatively low speeds.

An undersquare engine will typically be more compact in the directions perpendicular to piston travel but larger in the direction parallel to piston travel.



these things are all considered when engineering engines. personaly, i believe displacement for a car under 3 liters is a waste. my favorite engine is the buick 3.8l turbo found in buick regals/ GN's from 85-57. the volumetric efficiency is such with the 3.8 that forced induction allows moderate streetable power numbers without putting too much stress on the motor. smaller engines can make the same power numbers, but are often not engineered for the amount of power output and can often lead to failures in the valvetrain/bottom end.

mmarshall

I'm with you, Hoovey. I've long-liked the idea of low-displacement for economy combined with more cylinders for smoothness/refinement. Years ago, although unreliable just like everything else the company built back then, GM had a nice 2.8L V6 in the X-Body front-drive compacts (Citation/Phoenix/Skylark/Omega). It could deliver 30 or more MPG in the road, even with carburetors and primitive throttle-body injection. Mazda did a dandy small refined 1.8L V6 on the early-90s-vintage MX-3 sport coupe, though it was a torqueless slug at low RPMs. And, more recently, both Lexus and Infiniti did normally-aspirated 2.5L V6s on their IS250 and G25 series. I wish Buick had done that on the Verano rather than simply use a standard generic 2.4L Ecotec four, though the 2.4 is generally refined by by in-line-four standards, and there isn't anything really wrong with that power plant.

corradoMR2

Ditto!


Loved the MX-3 Precidia's 1.8L V6. So smooth compared to the 4-banger competition. Friend had a '93 and I drove it (stick) several times - what a blast it was.

Loved my buttery smooth '08 IS 250, and again now for MY '14, over the TSX and German competitors' less refined (albeit more powerful) fours.

mmarshall

The GM/Buick 3.8L, as you note, eventually became an excellent powerplant, especially in turbo or supercharged form, but it didn't start out that way. It actually dates to the early-1960s Buick Skylark, where its 90-degree V-angle (rather then the more-common 60 degree for a V6), combined with the 6 cylinders produced small but noticeable harmonic vibrations in the block from the firing-order. It took years (even decades) of engineering work and fine-tuning to smooth things out and turn it into the power plant it eventually became. GM didn't give up up it, though....they stuck with it as long as the basic design and old push-rod technology could still meet emissions standards at reasonable expense.

bitkahuna

iTrader: (20)

what do you mean by 'social view'?

Sulu

Why no low-displacement 6-cylinders? There is the factor that a 6-cyl has 2 extra cylinders over the same-displacement 4-cyl so it has 50% more cylinders, valves and other parts making it more difficult and more expensive to manufacture, and possibly heavier also.

But, as was said, the current fashion is to turbocharge a 4-cylinder, in the belief that a turbo-4 will give you the best of both worlds: 4-cyl economy AND 6-cylinder power.

Lexuslvr91

While I am not exactly sure of the refinement levels of the Lexus 2.5 V6 nor Audi/BMW 2.0T or even Lexus's new 2.0T I expect, if anything, that what these 2.0Ts lack in refinement they more than make up as far as power goes. The BMW 428i has seen times as low as 5.1 sec and that is ONLY with 240 hp in a 3500 lb vehicle with 33 mpg hwy. That is nearly 2 seconds quicker than the IS250 with better gas mileage. Also many publications note that it does in fact seem like the more refined of the 2.0Ts on the market compared to say Cadillac's 2.0T in the ATS 2.0T.

I'm not sure of the potential of the new Lexus 2.0T but I fully expect it to be much quicker than the 2.5 V6 with much better FE. The market for small displacement V6s in the US market is slim to none occupied solely by the IS250.

Another thing with the 2.0T, I'm sure it will be a cheaper engine to make for Lexus as it will go into multiple vehicles whereas the 2.5 only went into the IS(at least in the US market).

Och

iTrader: (3)

In most cases a 2.0 engine with 4 cylinders will actually make more low end torque than a 6 cylinder engine with same displacement. The 6 cylinder will make more maximum torque at high RPMs, but down low the 4 cylinder will have better response. And once the turbo spools up, it will have plenty of high RPM torque as well, and as a result the car will have more or less linear acceleration.

Keiffith

yes. i would say a large number of good V6 power plants even now stem from the engineering of the trusty buick 6. whats funny is the buick V6 can still hang with modern OHC andd VVT 6's of now when modifed correctly. their popularity is such that you could make the entire engine from the ground up with aftermarket parts. my dream car has always been a 3.8l turbo stuffed into the beretta chassis.

yowps3

Both the Camry & IS250 are 2500cc

One is super smooth and refined, while the other is refined by 4-pot standards but still has that raspy note to it..

It's all about profit and cost cutting. Lexus will do what the Germans do and fit their 2.0T in everything.

But from real world experience these force fed 4-pots are slower, use more gas, are far less refined and obviously less reliable than well made N/A sixes like Toyota's own V6 lineup today..

yowps3

The torque curve of the 2GR & 4GR (IS350 & IS250)



This is as good as it gets. Extremley linear, so linear that you're doing high speeds without notice. Silken engines these V6 from Toyota.

mmarshall

I tend to agree that cost of manufacture is probably the major issue. For a small V6 of the same size/displacement as an in-line four, the V6, of course, will generally have more valves, cams, pipes/tubes, spark plugs, heads, and gaskets.....plus probably need more complex robots/machinery to assemble it.

robert1408

While I love the smoothness and sophistication of the Lexus 2.5, It is a physically large, heavy and complex engine. To get much more power from it without a displacement increase (like the larger, rougher 3.5) involves boosting. That adds even more weight, cost and complexity and adds packaging problems as well. All that is possible and I would love such a car but the market wouldn't support it. Small displacement, multi cylinder, high output engines will remain only in low volume specialty cars.

I've driven three different BMW's with their 2.0 turbo. Only at high revs are these engines even a little rough. The overall smoothness and sound are surprisingly good and the plentiful torque makes them feel very powerful. I'm drinking the cool aide on this one. I can see why engines like this will become more common. Imagine an IS 250 with 40 more horsepower and tons more torque at about the same price as todays car. Imagine what a nice engine the new 2.0 Turbo will be withToyota's engineering and manufacturing talent involved.