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Discussion Starter #1
This may be a bit off topic, but as i was going through various forums today they were talking about how great the high revving engines are. Admittedly I am not experienced with sports cars, racing, or even high performance engines, but i fail to see why a car that peaks (hp/torque) at 7,000 rpm would be better than a car that peaks at 2500 rpm. When driving my ford ranger with its 3.0 liter v6 that starts to move only when the engine is around 3500 or so rpm and my parents full sized van with a v8 that starts to move as soon as you touch the gas i find that i enjoy driving the van more (excluding handling, turning, etc. the thing is a bloated tank, slow and can't turn). That being said why would you want a car that you need to keep at 5-7000 rpm to get it to move instead of one that can move in the 2-3000 rpm range? I would think that by having such a high revving engine you would eventually run into long term durability problems when you revv so high.
 

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High revving engines can be a lot of fun to drive when going all out. I prefer more torque down low like I get in my Corvette though.
 

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You don't need a high revving motor, but in motors of similar size if tuned to use the high rpm you will make more power at 7k RPM than at 3k RPM. Smaller motors are designed to rev higher to achieve HP similar to a larger engine.
 

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Keep in mind that the IHP (internal horsepower or power lost to just turning the engine) goes up by the square of the RPM and the intake air velocity is liable to approach sonic (see "choked flow" )
 

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Discussion Starter #5
if motors that rev higher create more power then why don't most domestic engines spin faster to create more power? Also, when looking at larger engines they seem to like to keep the rpms low rather than high. I am just wondering what is the benefit to using an engine that needs high rpms?
 

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if motors that rev higher create more power then why don't most domestic engines spin faster to create more power? Also, when looking at larger engines they seem to like to keep the rpms low rather than high. I am just wondering what is the benefit to using an engine that needs high rpms?
Most of the reason American engines are lower reving is because of typical American driving habits. We don't like the sound and vibrations associated with high revs and we do like torque. Hell, most Americans don't even like to shift gears and thats another reason why we need engines that have more torque, to feed the energy sapping automatic transmission. Torque is created by having a longer stroke and there are limitations on piston speeds and rotational speeds involved with really long strokes having to do with the inertia of the engine components. Americans drive these types of engines because we can. The rest of the world uses smaller higher reving more efficient engines because their gas costs as much as 5-6 dollars a gallon.

Engines like in your parents van are large displacement engines. They make their power by the tried and true method of having more room in the combustion chamber for the fuel/air package. More package more power. The old saying goes "there ain't no replacement for displacement." These types of engines typicaly have more torque due to a longer stroke required to get that displacement and still get a compact engine size and effiecent fuel burn as well as make American buyers happy. These engines deliver the classic american hot rod experience. Step on the gas and your head snaps back. We like that.

Having said that, the down side of these engines are that they are big and heavy, and generally not as efficient as smaller high reving engines. (all things equal regarding aspiration and construction materials) A smaller 4 cylinder high reving engine is going to produce more HP to it's weight than a comparably equiped V8.

If you were to somehow put your parents van engine in the Solstice, it would no doubt give exciting 0-60 times, but you would also find it handled like crap and took considerably longer to stop. In addition your top speed would most likely suffer as well. Anyone who ever drove a V8 Vega or Corvair can attest to this. This increased efficeincy is also evident at the drag strip. In the amature "run what ya brung" racing you'll find highly modified Volkswagon Bugs turning in faster times than Cameros, Mustangs and even Vipers.

It all comes down to power to weight ratio. Of course you can modify Cameros and Mustangs with even bigger power plants, but you will give up handling. In the case of Nascar you'll notice that while these bigger cars also use V8 engines, and can handle well, those engines are operating at very high RPMs. In general with engineering, if you can operate a system at a higher freqency then you improve efficiency. Think of the processor in your computer, a higher frequency processor gets more work done in a shorter time than a lower frequency one.

I don't know if I am explaning this very well, and I'm sure this thread will spin off into a very technical debate on engine theory, but the bottom line is you have to ask yourself what kind of driving experience you hope get. The Solstice is a classic roadster, meaning to be in precise balance of all the qualities needed to traverse all types of roads in the most efficient manner and still deliver a spirited driving experience. If fast 0-60 times and lighting up the tires in the parking lot is more your thing, then I would say the Solstice is not for you. I would suggest the new Mustang (which I think looks awsome) or the Pontiac GTO for that kind of driving.

Hope that helps a little, not sure I did. :leaving
 

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A deceptively simple question that has a very complex answer, but there are two main elements:

the first is the physics of a piston engine, compressible flow dynamics of a gas (air), and the combustion characteristics of gasoline coupled with current accepted design practices that makes the optimum cylinder size something between about 300 and 600 cc with a stroke between 3.1" and 3.6" and peak efficiency around 2000 rpm. Yes you can go beyond that in any direction and computer controls help a lot but this is what American technology supports at the moment.

Motorcycle engines can turn very high rpms with much smaller cyinders (because they have much smaller cylinders), relatively short cranks (see "rocking couples" and first & second harmonics), and needle or roller bearings (added cost) Also with a very small cyinder, the accelleration forces (what used to be referred to as "piston speed") reach the limits of a rod material or bearing capabilities at a much higher rpm than for a larger size.

At increased cost, you can improve the materials (e.g. go from cast to forged pistons, plain to roller bearings, desmodromic valve gear) that can live at higher stresses but you are fighting declining efficiency (the internal HP required to spin an engine increases with the square of RPM).

Somethings you can make act differently - the current rage for super and turbosupercharged engines is to make a smaller engine with reduced internal lossess put out the power of a much larger normally asperated engine. Something not commonly understood is that the larger combustion chamber of a boosted engine which lowers the static compression ratio is necessary to increase the combustion volume for maximum power. As a side effect, detonation is reduced if you do it right but that is not the primary purpose.

The downside is that (turbo)superchargers are expensive and add complexity/warrenty costs.

One thing we have today is complete control and feeback information on the operating condition of the engine and is a major component of increased efficiency. Particularly the feedback (o2 sensors) and learning capability of the computers help a lot. Keep in mind that the cntrol priorities designed in by the manufacturer are not always the same as those of the owner.

The other major factor is governments. In europe a combination of very high taxes on gasoline and on engine size plus countries often the size of our smaller states led to development of very small, high efficiency engines and a logistics train (service stations, mechanics, and parts) to support them.

OTOH in the US until recently the engines were designed to be large, relatively slow running for 100k miles and rebuildable in a barn using hammers. The 4.5-7 liter V-8 was most common in mass market cars where 1.0-2.0 liter four cylinder engines were common in europe. With gasoline prices under 30 cents a gallon before 1973, except for a few fanatics, MPG was not an issue.

This is true today with gas prices approaching $2/gallon, most people just do not care and the GALB (Great American Land Barge) still exists in SUVs and Suburbans.

The big difference is that in 2004 the average US engine is now about half the size of those in 1970, cruises at about 2/3 the rpm, gets double the mpg, and lasts for 200,000 miles. All of which are important but has little to do with performance.

The bottom line is that not only are there physical and dynamic reasons for the current engine sizes and typical speeds (anyone notice the Vibe GT has peak HP at 7600 rpm ?), but political and logistical ones as well. Part of the reason for incredible service prices is that few really know how to work with computer systems (and those who do are making more money and staying a lot cleaner installing computer LANs).

So yes, a W-12 4 litre 1600 hp 12,000 rpm engine is possible but the cost would be incredible and require a riding mechanic. Real world American engines right now are going to be going to be as mentioned above and stem from certain design constraints.

Just as an example, current motor oils are limited to 60-70 psi because at higher pressures the oil can erode the current bearing materials. Tolerances are also much tighter than they were in the Muscle Car era which means if you want the oil to get everywhere, you do not use a 20W50.

This limits the load per square inch a plain bearing can support so the real variable is bearing size (width and diameter). This is a function of the crank geometry and a larger bearing requires a heavier rod and increases the rod bolt stresses and increases rod angles. All of this means that there are certain standard rod bearing sizes and everything else builds from that.

This is also the reason a boosted engine that is expected to live has a LOT of attention paid to the bottom end.

Have covered more than I expected to and didn't even come close to explaining all of the factors but there are reasons that you don't turn a production small block over 10,000 rpm. At least not more than once.
 

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Hoo boy, I took too long composing that one 8*).

About AeroDaves comment, I resemble that remark. We currently have a Reatta, a Bonneville, and a TranSport van all with essentially the same 3800 powertrain and one I really like. Maybe there were too many 3.4 and 3.8 Jags in my yout but that size has always seemed perfect for the street.

Automatics: in daze of yore, automatics were mostly 2 (Powerslide) or 3 (THM) speed boxes with a 3% efficiency loss in the torque converter alone and the equivalent of a large passenger in weight penalty. I can R&R the Muncie in my Judge while lying under it, something you cannot do with a 400. They went down the road at 3000 rpm even if you ordered the economy axle.

Today's automatics are much lighter and typically have five speeds (four plus lockup) and are geared for 2000 rpm at 70 and have no trouble. Many racers are now using five and six speed automatics with paddle shifters because they not only last longer than manual transmissions, they do not require three feet to operate (a muffler bracket can make a nice heel and toe extension).

With the right valve body/electronics a good automatic will do what you want, when you want it, and stress the rest of the car less than a manual while doing it.

V-8s. I agree with reservations. What you were referring to were somewhat archaic converions involving iron V-8s. Go from a 300 lb engine (I can lift a Corvair) to a 600 lb V-8 and things will be upset particularly if you use (was is Crown ?) a conversion that hung the engine out the back, another flopped the trasaxle and put the engine in the back seat (Avenger ?)- those can handle very well.

For that matter I had a V-8 Sunbird (glorified Vega) that could run with the Porches in autocrosses.

The modern equivalent is the 1984-1988 Pontiac Fiero that started out with the engine in front of the transaxle and has received everything from small block chevvy sidewinders (V-8 Archie) to Northstar conversions. If my 2.8/4-spd ever fails I'll probably drop a 3800/4T60 in there. And those conversions can be made to handle very well indeed.

As to efficiency (and BTW the original quote was by Augie Pabst in 1957 "There (is no) substitute for Cubic Inches") that depends on the engine. An all aluminum small block will not weigh any more than an iron block four but everything else (trans, axle, suspension, driver) may be overstressed). However the efficiency is a function of design and while a larger displacement engine (I would not want a V-8 smaller than 3.5-4 liters) will consume more fuel, it can be just as efficient as a four with the same bore/stroke relationship.

So while what you say was true of the engines of the sixties and seventies which were designed to fit the needs/wants of the time, todays engines, particularly the aluminum ones with port fuel injection, feedback computer control, and VVT are something entirely different.

I take that back, there was one V-8 engine of the early sixties that, like the V-6 Buick, is still around, just not here, the 215 cid BOP V-8.
 

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Holy geez Padgett, your posts are informative, but probably only useful to people who alredy know the answer. LOL
I'll try to dumb it down for the rest of us. Feel free to correct me if I mess up.
The "work" or "power" an engine produces is a rotating force and therefore measured as torque. To calculate HP from torque use the formula: TQ x RPM / 5252. (Ex. 100lb/ft of torque x 2000 rpm / 5252 = 38 hp) if that same engine is producing the same "power" (100lb/ft) at 4000rpm it is producing twice the amount of "work" in the same amount of time (one minute) Ex. 100lb/ft x 4000rpm / 5252 = 76hp. Numerically, tq and hp cross at 5252 rpms, so 100lb/ft at 5252rpms = 100hp. So if you follow that, and engine (within limitations) will produce more hp if you move it's peak TQ further up the rpms.
 

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But don't forget internal friction (the power it takes to spin the engine, can model as a big air pump). This goes up with the square of the RPM so you can take a low reving engine (torque peak at 2000 rpm) and by adjusting the intake, exhaust, and valve train move the torque peak up to 4000 rpm, chances are it will not be as high as it was at 2000. The HP will be higher but the efficiency will drop and you pay for it in MPG.

This is part of the reason the US changed from Gross HP measurments to Net HP in the early 70's. In the old style some ratings were more hope and marketting than reality. Today it is more of what you see is what you get.

When they say that the new 320 hp GTO is the "most powerful ever", they are not kidding, under the old measurement it would be well over 400 hp and the RA IV was only rated at 370 gross hp (of course they were underrating it a bit)

What really matters in 0-60 or the 1/4 mile is the area under the torque curve for the rev range used. For those who have had some calculus, it is the integral of the curve in each gear times the gear ratio.

Further, you shift when the torque times the gear ratio in the lower gear crosses the same curve in the higher gear and some times that is in odd places. Wind it out all the way and go slower. Computers are really good at figuring this out and is part of the reason that the NHRA bans them otherwise we would have bracket racers clicking off within .001 second of breakout nearly every time.

Just remember that a car is the sum of all of its components and if you raise the torgue peak on an engine with a heavy flywheel, you may go slower.

The only way to go really fast is to have all parts being all that they can be. You can still be fast even in discord, but not as fast as possible.
 

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Discussion Starter #12
Thankyou, i understand now how the smaller engines make the power and why most engines from foreign countries are small, but why would you want to put a high rpm engine into a sports car rather than a low reving one. For example if i had 2 solstices and one had an engine that had its torque peak at 3000 rpm and another that peaked at 7000 why would i want to use the one with the higher rpms? is there a benefit to one over the other, or is it just because foreign cars makers are used to small high rpm engines and that is what they use in their sports cars. Basically what i am asking is there an advantage to one type over the other? And to answer some of the questions, no i would not want to see a v8 in the solstice i just would like it to quick enough where i am not worried about getting beat by a ford taurus like a miata does with its 0-60 of 8 seconds.
 

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Basically, as Padgett said, an engine tuned for low rpm torque is easier to drive for lazy N. Americans. The power is instantaneous and it works well for our love of automatics. You typically want a higher revving engine in a sports car because the idea is you will be driving it "sportily". In other words driving it hard and keeping the revs up where you can extract all the power out of that type of engine. In daily drivers people rarely crack 3k rpm when accelerating away from lights.
 

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Padgett,

Don't forget to model the 0.22 seconds each shift takes... that small loss in acceleration if you have to run through several gears in the 1/4 mile hurts - and another consideration for how to gear your vehicle. :thumbs
 

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.22 seconds ?! You have never seen me shift when in a hurry: Grab T-handle, pull back as hard as possible, bat clutch (right foot never leaves floor), great YALP & side wiggle from back end & repeat as needed.

Learned on XK Jags with Moss gearboxes, had to use a torch to straighten the bent shift lever to be able to exert force properly. Muncie is like slicing butter in comparison.

Will admit that some friends have expressed horror at the floorboard shake but have spares and after all, what is a Judge for ?

That said, a modern electronic automatic can be even faster. When I worked at Remy's we had an electronic automatic that would bark the tires on every shift. Instant. Just not something the public would like.

The reason for the name "Padgett" is because that is how I be yclept. Have been signing e-Mails that way since before there was an Internet.

As to where to put a torque peak, that depends on your intended use. For example for maximum MPG you want it low and to use real long gearing. For maximum HP for top end you want it high, and for maximum accelleration, you want it somewhere in the middle.

For road racing and particularly endurance racing you may trade top end for accelleration out of a corner. Accelleration from a standing start for a bit better MPG (and when you are talking 3-5 mpg, even a small change is a large % and may mean one less pit stop).

When the flag drops only one thing matters, getting to the finish line before the other guy. Doesn't matter if (s)he slides through every corner a tenth faster than you if the tires must be changed often (also why a fast pit crew is just as important as the car or driver). Matters even less if something breaks.

Now sometimes you have a car that acts as a rabbit to try to get the opposition to overextend. You optomise that one for speed and do not expect it to finish. Thats where you see lap records set while the car you plan to win circulates somewhat slower but within striking distance.

Pesonally I dislike bracket racing. The entire concept of "breaking out" is foreign to me. In that case you want a car that is dead reliable and tuned to run a precise speed which is below the actual capability but repeatable (and why the NHRA bans computers - would make it too easy).

So where you want an engine to peak and what the torque curves look like depend on what you want it to do. If you want a ringer specifically for fuel economy rallys ('nother long story), that can be arranged. :jester
 

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Long time ago I raced a Mazda 808 in Showroom Stock Sedan. Was giving up 400 cc to the Opels but could jump a few feet on every shift. They say the hand is quicker than the eye :devil

With my aunchient GS Buick I had a different technique. Pull back hard and just blip the throttle. Never touch the clutch. But that was with a 26 spline close ratio M-22 Muncie (wasn't that it could crush rocks, was so called because it sounded like you were crushing rocks), my Judge has a M-20 wide ratio. Never got around to installing a kill button for a really fast shift.

ps regularly beat Z-28s in Autocrosses with GS. Always registered it as a "Buick?" :patriot
 
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