The gear ratios and power curves for the RX-8 are available, so it is possible to do a comparison of acceleration between the 8 and the Z. Though it is just an "on paper" calculation, it is still a relatively good indication of how the cars will match up. The first interesting point is that the Z and the 8 have very similar torque curves. Second, Mazda seems to have chosen some funky gear ratios...not quite optimal for 0-60. Some people are guessing that this was done as a compromise in favor of economy...the car is a four door after all. After plotting acceleration through the gears for both cars, here are my predictions:

0-60, stoplight races, or anything at low vehicle speeds: The Z will own the RX-8. Like I said, the gear ratios are funky in the 8. If Mazda revises the ratios later for quicker low speed acceleration, Zs may have some difficulty.

Anything above 50: The 8 and the Z have nearly identical acceleration. What this means is, if you own a Z and want to race an 8, don't do it from a roll on the highway...neither one of you are likely to pull much on the other. This also means that if the 8's handling is up to snuff, the Z will have stiff competition on the road course.

Anyway, those are my predictions for a Z vs. 8 match-up. I'll be the first to say that this is entirely bench racing, so like many others have said wait until the 8 comes out before making any final judgements.

One final interesting note is that one of the reviewers who was present at the RX-8 Laguna Seca press day borrowed a 350Z to do a comparison between the cars. On the subject of torque, he said the 8 had "good low-down torque" while the Z "lacks much in the way of low-down torque". Things may not drive the way you expect them to, so wait till you can drive both before you make a choice.

Both cars carry 90% peak torque over a significant percentage of the rev range. But don't be fooled by the torque numbers...the Z doesn't really have all that much more torque than the 8. The area under the torque curve is what really matters for acceleration. While the height of the Z's torque curve is greater, it does not span the rev range that the 8's curve does. Compute the area under the curves, and you'll find that the torque of the two engines is much closer than you think. To make a more simplified comparison between the 8 and the Z, consider the 8 to make 240 lb-ft with a 6000 RPM redline and 90% peak torque coming in by 2166 RPM. This will tell you how the car drives and accelerates. Of course, 240 lb-ft is still less than the Z's 274, but please remember that the Z also makes ~40 more HP than the 8.

Like I said, I think the Z is going to own the 8 from a standing start...but the reason is because of the gearing Mazda has chosen, and not because of the Z's (perceived) torque "advantage".

the 350Z curve is much taller than that of the RX-8, but the RX-8 curve is significantly broader. Visually try to compare the area under the curves, and you'll see it's not that big a difference.

They don't use a similar amount of RPM range on each gear shift. As an example, the Z upchanges from 1st gear to 2nd at redline, and the tach drops to ~4250 RPM. That means that the entire 2nd gear pull will cover a rev range of 2350 RPM. In contrast, the RX-8 makes the upchange to 2nd at 9000 RPM in 1st, and the tach drops all the way down to 5250 RPM. The 2nd gear pull for the RX-8 will cover 3750 RPM on it's way back up to 9000. The RX-8 will sweep 1.6 times the revs the Z will during 2nd gear. That means the RX-8 torque to the wheels is getting multiplied ~1.6 X more than in the Z, since gearing directly multiplies torque. It's like the RX-8 was making 1.6 times it's torque with a lower redline...1.6 x 160 lb-ft = 255 lb-ft. Like I said, they really aren't that far off.

Originally posted by Supercharger
You can figure out the best shift points from a TF-S graph

Originally posted by Buger
It all really depends on the weight of the RX-8. I haven't really posted many simulations recently because I've been hoping to hear something about the final weight of the RX-8.

At this late stage of the game, the weight should already be known since all of the production dies and stuff are already finalized. Mazda has previously advised that Job1 will be in before the end of their fiscal year which is March 31. I'm not allowed to mention the exact date.

From what I have done, the 350z is still faster than the RX-8, even at higher speeds. The 350z was built for a different purpose than the RX-8 and any acceleration comparisons should really be done with the G35.

Still, every single comparison I have previously done with RX-8 (weights ranging from 2850 to 3011 lbs) has the RX-8 beating the 350z from 50-70. This is because the RX-8 can stay in 2nd gear (higher wheel torque) while the 350z can't. The RX-8 and the 350z will also probably be neck and neck from 0-70 (A 3000 lb Rx-8 that shifts at 9500 rpms actually comes out .01 faster).

Because the RX-8 was built for a different purpose than the 350z, it was geared for a different purpose as well. The rx-8 gearing ratios seem to be chosen to emphasize the wide powerband of the renesis more than to emphasize maximum acceleration. Hearing the statement "1.6 x 160 lb-ft = 255 lb-ft", any 350Z enthusiast could point out that the 350Z engine already makes 274 ft-lbs so doesn't need any "additional" gearing.

Redrotaryrocket is a member of this forum as well as the Rx7forum. I'm sure he can probably post some of his stuff up when he has the time.

Brian

Originally posted by Supercharger
Tractive Force:

Originally posted by Supercharger
Traction Force and Tractive Force are the same thing.


.

From what I have done, the 350z is still faster than the RX-8, even at higher speeds. The 350z was built for a different purpose than the RX-8 and any acceleration comparisons should really be done with the G35.

Originally posted by rxeightr

G35 0-60mph--5.5sec 0-100mph--14.2sec 0-130mph--26.8sec
5-60mph--6.2sec 30-50mph--9.2sec 50-70mph--8.8sec

In the 4/03 Car & Driver comparison article between the RX-8, the G35 Coupe & the Mustang Cobra, this is what their 3 days of testing came up with ---

Originally posted by rxeightr
Quote from Buger:
In the 4/03 Car & Driver comparison article between the RX-8, the G35 Coupe & the Mustang Cobra, this is what their 3 days of testing came up with ---

RX-8 0-60mph--5.9sec 0-100mp--15.8sec 0-130mph--33.5sec
5-60 mph--7.5sec 30-50mph--10.8sec 50-70mph-10.0sec

G35 0-60mph--5.5sec 0-100mph--14.2sec 0-130mph--26.8sec
5-60mph--6.2sec 30-50mph--9.2sec 50-70mph--8.8sec

Cobra 0-60mph--4.6sec 0-100mph--10.6sec 0-130mph--18.4sec
5-60mph--5.4sec 30-50mph--8.2sec 50-70mph--7.6sec

Originally posted by Buger


Hi rxeightr,

It appears that the 30-50 and 50-70 times were done in top gear.
Brian