350Z vs RX-8

[formerfordguy]

Originally posted by Iceburn
Third, torque rules in one sense, but high RPM torque is far better than low RPM torque. The reason is GEARING. If there are two engines with identically shaped torque curves, one produces 150 lb ft. of torque at 8,000 RPM and another produces 250 lb. ft. of torque at 4,000 RPM, which will have the most torque in a car? The one with 150 lb. ft. will. It's easy to picture if you simply add a 2:1 gear on the "lower" powered one that reduces the speed at the shaft to 4,000 RPM. That shaft will be able to twist with 300 lb. ft. of torque at 4k RPM due to the 2:1 gearing advantage. If you want a clear and simple description of this, click here.

I went to the site you mentioned and didn't see how it applied as your suggesting above. Too, identically shaped torque curves means peak torque would appear at the same RPM.

Finally, wouldn't the gearing advantage you mention work for the car with 250 lb ft of torque? Thus giving it 500 lb ft of torque at 2000 RPM? I don't think gearing matters -- or if it does it is a constant.

Example? The last Mustang I drove had 280 lb ft of torque, and I just test drove an Acura RSX. Their 0 - 60 times are close (within .7 seconds). The Mustang was effortless, hit the gas and you were moving. The RSX required double downshifts and a thrashing to get moving.

[rx8]

You all obviously know NOTHING about the RX-8. First, where did you all get the info about breaking down after 60K? Are the people who you were talking to reliable or against the RX-8? Rotaries will last forever, as long as you take care of it. You are all ignorant people and it disgusts me. Don't get me wrong... the Z is an impressive car, with sleek styling, but you don't see me talking bs about it. Do not start rumors that are not true.

[memmi]

While not much more than speculation can take place at this point about the longevity of the RX-8 engine, the old one's did tend to explode like clockwork at 60k. The seals would go out due to overheating. If you equiped your rx-7 with better intercoolers and gave them better seals they would last much longer but I've driven about 12 RX-7's and at least 1/2 had rebuilt engines.

So, While I would not go as far as calling the postings ignorant, they are speculatory and probably have some degree of acuracy to them.

[R1-rider]

Many posts here are factually but not 100%.

The rotary engine is a mechanical marvel as far as I am concerned, they can produce decent amounts of power and yet displace and weigh in at 1/2 that of piston engines. However, the rotary engine NEEDS alot of maintanence in order to provide it with a long life. The apex seals start to go bad at around 50K miles, so does it not make sense to change them around 45K? I have found that almost every single 13B engine that has been screwed up was due to neglect out of the owners part.

I think that both cars look fairly similar, and I don't exactly fall in love with either cars styling, however they are both very sharp looking cars for the market that they are aimed at.

Also, the RX-8 is not based off of the RX-7 sports car line, infact Mazda even plans to re-introduce the RX-7 back in America, either as latest gen FD, or possibly even a new RX-7.
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Ok i will try to explain now how that gearing situatin works with higher RPM engines.

We will use a 1 speed bicycle for and example.

Now as the rider of the bicycle, you can only pedal so fast. So at most you can only go 10mph because you can only pedal at say 100rpm.

now, your competition is a little kid on training wheels with the same gearing bike as yours. He can definetely not pedal as hard as you, however he can pedal twice as fast as you. So while you are limited to 100rpm, he can pedal at 200rpm. Now he can reach 20mph in first gear. However he cannot accelerate as fast as you because you are twice as strong as him. So in order to keep up with you, he will change his gearing to half of what it was, so now instead of him pedaling 200rpm at 20mph, he is now pedaling 200rpm at 10mph. So he can now match your acceleration.


So do you see how power is not everything, if your engine does not have the "legs" that maybe a lower hp engine does, you could get beaten. Why do you think motorcycles are so fast? (besides the silly HP/weight ratio)

Hope that helps some.

[Iceburn]

Originally posted by formerfordguy
I went to the site you mentioned and didn't see how it applied as your suggesting above. Too, identically shaped torque curves means peak torque would appear at the same RPM.

I said identically shaped curves, not identical curves. You can take the shape of a curve and scale it to a different size to get different peak torque numbers and different RPM values. For instance, imagine a square that's 2 inches by 2 inches. Another square could be 4 inches by 4 inches. Same shape, different scale. As for not seeing how the site applies, the only thing I can say is to read it again. The fact that an "engine" that has 2600 lb. ft. of torque simply couldn't drive a car to 60 mph (or even 30, probably) makes this point more clear than anything else I can think of.

Originally posted by formerfordguy
Finally, wouldn't the gearing advantage you mention work for the car with 250 lb ft of torque? Thus giving it 500 lb ft of torque at 2000 RPM? I don't think gearing matters -- or if it does it is a constant.

Nope, it's not. You can't just gear it down as much as you want because you lose RPM (and thus speed) each time you do. The water wheel example at that site is a good example. It had 2600 lb. feet of torque, but at 12 RPM. If you made an engine that behaved the same way, it wouldn't be able to reach 60 mph because when you geared it down it would have 43 lb. feet at the output. That hugely torquey engine only has 6 HP!

If you take your examply of the 500lb ft of torque at 2000 RPM, you have to do the same thing to the high revving engine. The reason you have to match the RPMs when comparing the torque is because (and this is the key) the RPMs are the SAME at the wheels, assuming the same tire circumference! So, you can take advantage of the torque multiplication that gearing gives you more times (or at a higher ratio) the higher the torque is produced. I'll give an example. I will compare 2 cars that are both going 40 mph and accelerating at their maximum capabilities, assuming equal tire size, and no drivetrain losses. Acceleration from a stop has too many other factors including wheelspin, clutch, flywheel, etc. to make a simple comparison. The point is the same at ANY RPM, however:

12 RPM at the wheels is approx. 1 mph in a car (I took this from the web site I cited. If wrong it just changes the final number, not the comparison).
Let's say both cars are geared so that max torque is available at 40 mph in 2nd gear.
That's 480 RPM at the drive wheels.
Engine 1: 150 lb ft. of torque at 8,000 RPM
Engine 2: 250 lb. ft. of torque at 4,000 RPM
Engine 1 is geared (this is just derived from the 3 above points) so that:
150 lb. ft. * (8,000/480) = 2500 lb. ft. at the drive wheels
Engine 2 is geared so that:
250 lb. ft. * (4000/480) = 2083 lb. ft. at the drive wheels

The engine with lower torque at higher RPM gets more power to the drive wheels, because it can take advantage of *gearing*.

Originally posted by formerfordguy
Example? The last Mustang I drove had 280 lb ft of torque, and I just test drove an Acura RSX. Their 0 - 60 times are close (within .7 seconds). The Mustang was effortless, hit the gas and you were moving. The RSX required double downshifts and a thrashing to get moving.

That's a bit of a misleading comparison, even though it makes my point. The Mustang had 280 lb. ft. of torque, probably at lower RPM than the RSX's much lower torque number (160?, 180?), yet they accelerated to 60 in similar amounts of time. However, since the weights, gearing, tire size, aerodynamics, flywheels, etc. are all different, it's not really a good comparison. The comparison on the cited site with the LT1 and L98 does a better job, or the base vs. GS-R integra comparison. Then you're comparing basically the same car, just a different engine.

As for the reliability of the rotary, I'll repeat that other than the 3rd gen. rotaries, the rotary engine was incredibly reliable. The 3rd generation rotaties were (and still are in Australia and Japan) very reliable if they didn't overdo the boost levels. Look around next time you're driving. There are still plenty of early 80s RX-7s on the road. When Mazda added the high power turbo to the third gen. RX-7s there were some heat problems. However, the RX-8 is a non-turbo. None of the RX-7reliability problems should occur with the RX-8, since they're a different engine and one was a turbo, the other isn't.
Saying the RX-8 will be unreliable because the RX-7 was is like saying a Mustang can't be powerful because the mid-90s Ford Escort wasn't powerful.

[starrdog69]

okay, anyway, besides all that torque mumbo jumbo, the Z has been tested as a faster car, both in 0-60 and in the 1/4 mile. The cars are quite different, and its not quite fair to compare them. The RX8 is steered more towards families who need speed as well. Otherwise Mazda just would have sent the RX7 back. The Z is a two seat pure sports car. I do dislike the tail lights however, they remind me of a ford focus.

[sinfestboy]

rx-7
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300zx


350z
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rx-8


the only reason the rx-8 isnt gonna spank the 350 is because mazda doesnt want to make a sports car, they want to make a touring car.

oh, and cause ford fucked up mazda.

[Fliquer]

okay, anyway, besides all that torque mumbo jumbo, the Z has been tested as a faster car, both in 0-60 and in the 1/4 mile. The cars are quite different, and its not quite fair to compare them. The RX8 is steered more towards families who need speed as well.

Correct. End of argument.

[ArtemisEntreriR34]

My opinion is, the 350Z is better looking and from what I have heard more powerful. The 2 major thoughts when looking for a car is performance and looks and the 350Z beats the RX-8 in both categorys.

[Pennzoil GT-R]

i read a review recently on the Z which says it is a brilliant pure driving machine, and stays to true to the original 1970 car. i also prefer the looks so the Z gets my vote

[Iceburn]

Originally posted by starrdog69
the Z has been tested as a faster car, both in 0-60 and in the 1/4 mile. The cars are quite different, and its not quite fair to compare them.

Wrong facts, correct conclusion. The RX-8 hasn't been tested yet. Road and Track did get to spend a little bit of time in a very pre-production version, but wasn't allowed to hook up any test gear. Keep in mind, the RX-8 is still almost a year out.

Originally posted by ArtemisEntreriR34

My opinion is, the 350Z is better looking and from what I have heard more powerful. The 2 major thoughts when looking for a car is performance and looks and the 350Z beats the RX- 8 in both categorys.

I can't believe you really believe this. If you do, are you driving a Ferrari F50 or a Mclaren F1? Some people buy for performance and looks, others buy for comfort, others buy for price, and others buy for safety. There are as many different sets of priorities in buying a car as there are cars on the road. The simple fact, as stated by many others, is that these cars are aiming at different markets. If there's someone out there that LOVES the 350Z but simply can't have a 2-seater, the RX-8 will be a good choice for them, as would the Infinity. Also, there are lots of people that think the Z is ugly as sin, as there are people that think the RX-8 is hideous. You know, eye of the beholder, and all that?
Last, just becase a car is more powerful does not mean it will perform better. Stock Miatae often smoke Civic SEs in autocross events, and I've seen a few of them beat Camaro SSs and late model Cobras. The 350Z, as sweet as it is, is still really, really heavy. I think it weighs close to 3300 lbs.!

After checking, I found these weights here:
Model MT/AT
350Z 3188
Enth 3197/3210
Perf 3217
Track 3225
Tour 5AT 3239
Tour 6MT 3247

The RX-8 was estimated at 2970 in R&T, but the rumor mill has it that Mazda's putting it on a diet. We could very well see a >300 lbs. advantage for the RX-8 and a 287 to 250 horsepower advantage for the 350Z. Of course, straight line acceleration is the least interesting of the performance characteristics, so we'll have to see how they stack up in the important ones later.

Anyway, the whole point I'm trying to make is that they're very different cars, aimed at different buyers. However, they shouldn't be seperated by much in terms of performance. I'd guess, and it's only a guess since there are no stats, that the 350Z will be a hair better than the RX-8 in most performance categories. They should be close enough in performance that on the autoX course the driver will be the biggest performance difference in their respective abilities. The styling is an issue that will have to be judged on an individual basis.

[carlson]

As an owner of a high reving car, I would say on the freeway, high reving cars are fun. In the city driving, it is not quite fun to get it off the line, unless you rev it up to 6K and drop the clutch.
Torque rules in the city, high reving rules on the freeway.

I am gonna give up my high reving car to the 350Z, really soon.

[HerculesMO]

Hey guys, I hope you realize torque doesn't mean too much.. at least not from where I'm standing. Look at the Honda S2000. Does 0-60 in 5.3 seconds, with a weight of 2810 lbs. The torque is 153lb/ft@7500, with a horsepower rating of 240.

The RX-8 has a weight of 2970lbs (probably Mazda is trying to trim some more, last I heard). The torque is at 162lb/ft@7500, horsepower rating of 250.

With only about 170lbs of difference in the cars, but greater torque on the RX-8, I wouldn't be suprised to see the RX-8 make its way into the mid 5s for a 0-60, keeping up with the Nissan Z.

The Z is nice for a lot of people, personally I love the interior of it, the seats and all. But the exterior still looks like a retarded Audi TT, and there is no back seat, and little trunk space. That's what makes the RX-8 an easy choice for me. That, and I feel it will be a more agile and tossable car than the Z, because of its special LSD, and 50:50 weight distribution.

Of course, time will tell in this area. But let's not rule out the RX-8 as a non-contender to the Z.. I think the Z will get a run for its money yet.

[volvo4me]

Originally posted by Iceburn
Third, torque rules in one sense, but high RPM torque is far better than low RPM torque. The reason is GEARING. If there are two engines with identically shaped torque curves, one produces 150 lb ft. of torque at 8,000 RPM and another produces 250 lb. ft. of torque at 4,000 RPM, which will have the most torque in a car? The one with 150 lb. ft. will. It's easy to picture if you simply add a 2:1 gear on the "lower" powered one that reduces the speed at the shaft to 4,000 RPM. That shaft will be able to twist with 300 lb. ft. of torque at 4k RPM due to the 2:1 gearing advantage. If you want a clear and simple description of this.


I agree that higher torque rules at higher RPM. However your case above is not well stated.
In fact you say above that 150 ft-lbs of torque is more than 250 ft-lbs of torque. This can never be true. You also talk of putting a 2:1 gear ratio on the lower "powered " one. I think you should have said lower torqued one.
What is true is that the engine producing 150 ft-lbs torque at 8000 RPM will be producing more horsepower than the engine producing 250 ft-lbs @ 4000 RPM at that point in time.

You also need to qualify the two torque curves with respect to their peak torques.

Is the 250 ft-lbs torque at 4000 RPM the peak torque? How steeply does it fall off above 4000 RPM. e.g. what is the torque of this engine at 8000 RPM? Can this engine turn 8000 RPM? If it is more than 150 ft-lbs at 8000 RPM then this engine will win not only off the line but will win in the long run as well.

Since our friend Isaac Newtom proved that F = MA then this also means that any engine that produces more torque will cause greater acceleration.

When we apply this to a car we need to understand that the winning vehicle will be the one that can maintain the highest torque at the highest RPM. (Factoring in of course gross vehicle weight and the total drag coefficient) Whenever you have to shift to a higher gear, so as to maintain this high torque, you would want to do it at peak horse power NOT peak torque. At peak horse power is where the vehicle can do the most work (i.e. keep the car going the fastest in that gear). Note that at peak horse power you will not be maintaining peak acceleration since you have exceeded your peak torque. You will also need to factor in the next gear ratio and where on your torque curve you will end up at the speed that you actually shift. This may cause you to decide to shift a little earlier or later in RPM so as to be in the optimum torque range in this next gear. So it all a matter of torque and speed (RPM)

Peak horse power will occur when the slope of the Torque versus RPM curve reaches -1 such that any increase RPM is offset by the corresponding decrease in Torque.

[Iceburn]

Volvo4me, you're 100% correct. I should have said lower "torqued" one, my bad.
What I meant by more torque "in a car" should have been stated as "more torque at the rear wheels". Again, you're correct.

The only thing I disagree with you on is I think I did qualify the two torque curves with respect to their peak torque values. Twice I specified that the curves are identically shaped, just different in scale.

" If there are two engines with identically shaped torque curves"
and again:
"I said identically shaped curves, not identical curves. You can take the shape of a curve and scale it to a different size to get different peak torque numbers and different RPM values. For instance, imagine a square that's 2 inches by 2 inches. Another square could be 4 inches by 4 inches. Same shape, different scale."

If peak torque in one was 4k and the other was 8k, then we could hypothesize redline at 5k and 10k for each engine. If one reaches 90% of peak torque at 2k, the other would reach 90% at 4k, etc. Without identically shaped curves, the whole comparisson falls apart.

Last, I'd like to clarify that the only point I was trying to make is that simply looking at the fact that the RX-8 is supposed to have "only" 162 lb. feet of torque is misleading. There are a whole host of other issues that are at play, including torque curve, engine RPM, gearing, weight, flywheel, etc.... It sounds like you understand these issues well enough that you'd agree with that point, perhaps?

That's it, nothing more. Thanks for catching my poor wording! I'll be more careful next time.