questions about size of engine

my take...

traditionally, larger displacement engines had much better low end torque and power deliverly (just look at their torque curves), and could move a heavy car from a standstill faster than a smaller engine, simply due to quicker power application. as multivalve engines made their way into the mainstream, horsepower figures rose, but not proportionally to torque -- torque seemed to get only minor boosts. as a result, a lot of cars with the new multivalve engines saw dramatic increases in speed when the engine was allowed to breathe, but again, only marginal increases were evident off the line. the larger, lower-tech engines still held this domain.

as multivalve design became more prevalent, larger displacement engines began using it (a good early example is the taurus SHO), and they -- due to a good cubic displacement AND better intake technology -- exhibited a flat torque curve not normally associated with a multivalve, high-revving engine. still, big v8's coupled with powerful and intelligently-engineered trannys would beat the smaller, though multivalved, engine in shorter sprints. if the engines were allowed to stretch out a bit, the delta between the two diminshed.

today, we have intake/timing refinements to simple multivalve technology that can drastically change the performance of the engine. variable valve timings that respond to throttle demand help the engine tailor power delivery to the situation at hand -- low-speed, high-throttle situations had one set of valve timing/fuel delivery parameters; open road, higher-speed situations another set. torque curves are flatter than they every have been with multivalve engines due to this accessory technology, and their performance will surpass most reasonably-sized pushrod v8 engines.

of course, most v8s today have the same multi-cam/multivalve heads, so we don't have a smaller-displacement revolution here, we have an industry-wide engine EVolution. it's iterative.

for your particular question, well, it depends on the cars, the transmissions, the drivers, etc. a car making a ton of power and good torque can be crippled by an inefficient tranny or (even worse) a bad driver. i don't believe there is one magic rpm point where a vtec or similar engine will begin to overtake a lower-tech, larger engine, as each multivalve engine has it's intake tech tuned to different flashpoints. my cl-s opens its second intake plenum at ~3800 rpm, and the vtec kicks in around 4400 rpm (i don't know exact numbers...embarrassing), but that's not true for all engines with similar enhancements.

anyhoo, hope this helps.

wow, thanks guys and geoff for that detailed explanation.

are almost all engines nowadays multivalved?

erick, didn't u JUST get that GS400?

For 0-60 times, power to weight ratio and traction are probably the most important factors. Low end torque helps too, but you can use clutch "feathering" in a manual trans to launch at higher RPMs.

As you go faster, max HP and coefficient of drag start to become more important (as wind drag starts to limit acceleration).

Since the IS300 has a good "C.D.", and 215hp max (more than most of the other cars you mentioned), then - YES - I would expect that (as speeds increase) the IS300 would start to overtake some of the lighter smaller cars which have less HP.

The number of cylinders is not really much of a factor here. Looking at vehicle weight, engine output curves, coefficient of drag, tire traction and transmission characteristics are the main things you need to know.

The main benefit to having 6 cylinders (instead of 4) is in engine smoothness.

One benefit to have a broad, flat torque curve is that gear selection is less important when requesting passing power. With the IS300, you should be able to hit the gas at 50 mph and get to 70mph (for passing) without much concern. In a car like the Integra Type R, you better hope that you are in the right gear (say 3rd) to have the engine revving high otherwise you won't be getting alot of response when you hit the gas.


[This message has been edited by TEG (edited October 08, 2000).]