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So is the amount of torque per vehicle weight useful?

If so, is the unit expressed as a linear distance (feet, as in ft-lb per lb) or as the inverse (inverse feet? ft^-1? ).

I've been in vehicles with a peaky hp curve and no low end torque (Quad-4, Honda S2000), and I've been in cars with engines that have higher torque at the expense of hp (2.4 l version of the Q-4 comes to mind, called the twin-cam?, in the Sunfire - gained something like 20 ft lb torque but lost 25 hp).

I prefer the cars with more hp, once I learn where the working range is. I'd love to get into the new Honda S2000, they got a bit more power but a decent amount of extra torque.

On a track, hp is extremely important, on an autoX course probably Tq is more important. I think that the range of RPM from pk torque to pk hp is probably most important, (larger is better), IMHO.
 
How about this, you guys let me drive all the cars in question, and I'll tell which one sucks me in my seat best while putting the biggest grin on my face. That what sells a car for me! I will give your such technical specs like, well the Z seemed more balzy to me and the Corvette got the most girls in the car in da hood. lol :D
 
The important thing as I mentioned is the *area* under the torque curve and I have never seen an expression for it. Probably to most, the shape of the curve is most important because that is what makes the car "feel" fast.

Many associate the felling of a steadily increasing torque curve (and associated high HP value) with high performance, a really flat curve may actually be faster (the 3800 is a good example) on the time slips but seems slower.

To make a peaky engine work properly, you need have lots of gears and shift a lot to keep it "up on the cam". On the race track, the car that wins generally has a broader curve than the one that sets the fastest lap, partially because it is much less tiring for the driver and is usually better mannered in traffic.

Mountain motors like those used in the old Can-Am series often had intake stacks of different lengths to broaden the torque curve by having different cylinders peak at different revs.

Now making a street engine live at least for the duration of the warrenty and meet CAFE rules means you want to have the efficiency at 2,000 rpm (average cruise on Amerrican highways is going to be in the 1600-2400 rpm range) and that means you want the torque near the peak there since IHP (Internal Horse Power or pumping losses) is minimised.

Back in the bad old daze of 400 cubic inch engines turning 3000 rpm at 60 mph a good part of the 13-15 mpg was that as much gas was expended turning the engine as moving the car.

One of my experiments at GMI involved a 67 Camaro ragtop, 275 hp 327 & wide ratio (3.11:1 first) 4-spd fitted with a Rochester FI and geared for 70 mph at 2000 rpm. Would give in the mid-20s mpg on the Interstate, very close to the "official" club 2nd Gen Firebird with 250 cid 6 and a turbo. The difference was the amount of tire smoke (and it had posi) available in lower gears (with much shorter tires was also a successful autocross car).

So one way to get acceptable MPG with an engine that has excess power is to turn it slowly when possible.

Add in "drivability" and with a five speed you have three "performance" gears (first is for starting up hills and top is for MPG) and the torque curve had best match them. (With an automatic you have a torque converter to spread the gears a bit but not with a manual trans. OTOH a manual is smaller/lighter/less expensive to manufacture but tends to have a higher incidence of warrenty work.

With a six speed you can have four usable gears but what I see out of Detroit is that both fifth and sixth are usually overdrive ratios. Personally I would just as soon have only three shift gates to worry about and preferably with a lockout or ramp on first and reverse.

A good rule of thumb for classing an engine is to look at the stroke: close to or under 3" and you have an engine that can wind to the moon but is likely to be peaky. Over about 3.25" stroke and you will have more torque than revs and the rest of the drivetrain should be designed accordingly. The 2.4 EcoTec apparently has about a 3.7" stroke (2.2 is a 94.6 mm stroke and I doubt that the 2.4 will be less)

Nothing really magical about the above, just a matter of what you can do with a spark ignition engine running on pump gas.
 
I don't mean to sound stupid but those posts of yours padgett... I read them three times and I still have no idea what you are talking about!!! I mean, I read it and I understand the words but when it comes to putting it together for the 'big picture'... I'm more lost than a virgin boy on prom night :confused

Keep it up though, I'm sure it's helpful and enlightening for someone here. :cheers
 
Discussion starter · #26 ·
I see where he is going with all that, basically hes saying that tourqe is important more than exretmely high HP, really with lots of HP comes lots of tourqe too. lots of american V8's have more touqe than HP thats whats hes saying. little 4 cylinders have to hit high RPM's to get max HP but that dosent change the fact that there 4 cylinders. so there gonna put out little tourqe. thats basically whats hes saying.

and I love the virgin boy on prom night analogy.:cool :cheers
 
padgett said:
<snip>
One of my experiments at GMI ...

<snip>
GMI? As in the GMI in lovely Flint, MI?

Did you graduate from GMI-EMI, Gen Motors Institute, or Kettering U? Are you a GMTE?

What year? (don't mean to hijack thread topic, but found this interesting)
 
Sorry, will try to back it down a bit. Basically it is HP that makes trap speed but torque that determines how fast you get there.

They are related: HP=Torque*RPM/5252. Obviously the higher the rpm for a given torque value, the higher the HP.

Further, what a dyno measures is Torque (the classic ones even look like a big scale). To get HP you apply the above conversion.

Where it gets confusing is that peak HP only has a meaning at a specific RPM. Acelleration OTOH is how fast you can *change* the rpm. Apples and Oranges.

Now if you could just keep the engine at peak revs the whole time then it would have meaning but in a car you can't (as a sidelight you might look up Continuously Variable Transmissions which tried to make it possible but generally were only successful in cars under 1 liter (61.5 cid)).

Since you can't, what matters is the torque available while you re in each gear. Diesel trucks have a very narrow operation range which is why 10, 12, 15, and even 20 speed transmissions are common. - Not really 15 speeds but a 5 speed connected to a three speed with over, under, and sideways drive and both hands with an elbow hooked to the wheel needed for speed shifting...

Meanwhile a typical five speed has a starting gear often good for about fifteen feet and one bounce out of the gate, three accelleration gears, and a long mpg gear. (In my Sunbird V-8, first gear was so low that the engine could not rev fast enough with the stock flywheel and would acellerate faster starting in second).

OK, you take the jump in first and pull (or push depending on the linkage) hard on the shifter and bat the clutch. Right foot flat on the floor (or forget the clutch and bat the throttle, depends on technique - personally I do not care for the "hit the rev limiter and pull" style, feel like the limiter upsets the engine for too long).

Initially you get a jump from the engine inertia at 6500 grand suddenly droping to 4k but after that it is how much torque you have *at every point* from 4k to 6500 again that determines when it is time to row your boat again. (Honda S2000 owners multiply by 1.5).

Now you may not care but the general does how much is available at 2000 rpm as well because that is important from a CAFE and emissions standpoint. Internal friction goes up by the square of the RPM so economy and "gas guzzler" tax avoidance demand the RPM to be kept as low as possible during normal driving.

Ideally the toque would be flat from 1200 rpm to 6500 but it does not work that way. While there are tricks you can play on an engine to spead the curve, it remains a curve. Further combustion parameters (a whole 'nother semester) being failrly fixed for pump gas (93 PON burns slower than 87 PON, it doesn't have any more "power") and various losses increasing with rpm, this means that a longer stroke engine will peak at a lower rpm than a short stroke engine

Just to mention the Honda S2000 again, for 2004 the stroke was increased from 84 to 90 mm to make the car "more streetable" at the expense of a few rpm.

In comparison with an 86 mm stroke, the s/c 2.0 l Ecotec is really going to wind (though boost can correct a lot of issues) while the 98 mm stroke of the 2.4 positions it much more as a low rpm torque engine. That stroke difference between the two engines is really going to change the character completely.

Must admit I find the 12 psi claimed peak boost for the s/c version incredible for a street engine particularly with 9.5:1 cr and a 6500 rpm cutoff, will be interesting to see what it does on the road.

Does this make more sense ?

BTW yes spent a number of years commuting from Anderson. IN (home of Delco Remy) to Flint when it was still GMI and we were employees, not students. Once dropped a loaded Suzuki 750 water buffalo on glare ice in the middle of I-69 during a commute. Didn't know I could pick it up until then but an oncoming semi made a number of things possible.
 
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