Maybe the gearbox is a significant factor
 

in the higher-end performance area.

Just for fun, I've been comparing the gear ratios of the 6-speed S2000 and the 350Z and it appears that these two cars have "better" gear spacing in 4th, 5th and 6th. By "better" I mean geared more for max performance all the way to top speed.

The 8 doesn't lose much ground against these cars up to about 60 or 70 MPH, but seems to drop back more quickly beyond that point. Interestingly, when comparing the gearing of all 3 vehicles, the S2000 and 350Z take advantage of quite even gear spacing in all 6 gears while the 8 seems to use only 1st through 5th to top speed with little or nothing to gain in 6th. This makes 4th and 5th gears in the 8 "taller" (higher gear ratio) than the others.

http://pacer.calpoly.edu/tri/pacer/rx-8comp.html

No intent to start another "straight line" dragster war. Just a curious observation.

1.3L

Interesting...

Interesting comparison. I think Mazda considers 6th gear in the RX-8 as a, more or less, overdrive gear. This comparison would certainly tend to confirm that anyway. And the difference between engine rpm in 5th and 6th is very small, so thinking about it, I'm not sure what the actual purpose of 6th gear really is, other than a marketing feature.

your 5th and 6th gear top speed for the 8 is misleading, the 148mph is the electronic governor, that's why it stopped there. IIRC the 'redline' speed of 8's 6th gear is 160 or something...

if the 8 had enough power to overcome wind resistance, 9000 in 6th would have you at 186, and by the time you reached fuel cut off, you'd be in the 190s.

also, i don't remember where, and not that it really matters, but i saw someplace that the skidpad numbers for the 8 were 0.91g.

the speed for the rx8 are wrong i know from experiene that it'll go 96 in 3rd, 137 in 4th, 155 in 5th and 6th ?? seen DMP dyno 184 in 6th. fastest I've gotten my 8 is ~167 in 6th.

I think you missed my point. All 3 vehicles, for whatever limiting reason, have virtually the same top-speed (150, 148 and 152). The limiting factor may or may not be different for each vehicle (governor, drag, RPM), but who cares? That's as fast as they will go.

My point is, the S2000 and the 350Z make very good use of all 6 of their gears to reach their top-speeds. The RX-8 does not. The RX-8 only uses 5 of its gears to reach top-speed. My thinking is that the S2000 and 350Z better keep their engines "on the boil" by simply utilizing all 6 gears right to the limit. The RX-8 simply does not. Mazda engineers decided, for whatever reason, to space the gears differently which ultimately left 6th completely out of the equation when making a max-performance run to top-speed. Not really a flaw, but it does leave the 8 at a slight disadvantage when one compares all of the numbers.

And again, this is just a gee-whiz, who cares, observation.

1.3L

I suppose, but I'm not going to get into nit-picking over the numbers. I gathered all of the performance numbers from various road test reviews made by some well known magazines. I think everyone well knows that those figures can vary because of many factors and those include:

driver
track/street conditions
ambiant air temperature
altitude
vehicle variances (is it new, old, thrashed?)
tire condition/brand/inflation

and on and on...

1.3L

PS. dynos lack the air resistance (drag) factor.

I care...I really do, lol...

So, in theory, could swapping out the tranny in the 8 increase performance? When people say gear ratio does that equal the rear end? What I mean is...I hear people saying they have 4.44 gear ratio (maybe I'm wrong...sorry) so does that have to do with tranny or rear diff?

If we wanted to increase acceleration in the 8 could we change the rear end or tranny?

Also, something I've thought about...

Do you think our carbon fiber drive shaft/axle is flexing somewhat causing the 8 to accelerate slower? Tech me guys...tech me...

I might be a little confused about what you're saying, so my apologies if I am...

Are you suggesting that it would be better to make as many shifts as possible during a "max-performance run to top-speed" than as few shifts as possible? :confused: Whether top speed is electronically, mechanically or drag limited, in an acceleration run to an arbitrary speed, you want to be able to do it with as few shifts possible. Adding shifts adds time.

Did you compare all of the numbers or just the ratios and speeds attainable? Did you plot where each upshift at redline places the car in its powerband in the next higher gear? Those are all numbers that affect the quality of the gear ratio choices from a "by the numbers" approach. And, of course, there are the practical real world considerations that account for how the cars are actually used that must factor into the decisions as well.

Yeah, it's a who cares kind of observation in some ways, but it's still worth thinking about why they are the way that they are. ;)

something isn't right about the numbers for the 8. Mathmatically, the numbers should be...

9000 rpm speeds
1 - 42mph
2 - 69mph
3 - 95mph
4 - 132mph
5 - 148*mph
6 - 148*mph

*limited speed. calculated numbers are 5 - 157 and 6 - 186

judging by the speed the gearing allows, it appears to be that the driver in the tests for the rx-8 was shifting too soon.

*looks at speed/gearing chart*

yup. based off the posted speeds, the driver of the 8 was shifting at 8500.

I agree... the 6th gear on this thing does nothing. I think this is part of the reason people get such bad gas mileage (that and we rev high :) ). If the RPMs were lower in 6th, gas mileage, especially highway miles, would benefit.

Here's an example. At 55mpg:
- In my Acura TL-S in 5th gear, RPMs are around 1600 or so
- In my RX8, in 6th gear.... RPMs are around 3300 or so

Same speed on both cars, RPMs are twice as high on the RX8 as they are on the TL-S. The end result is that the bigger, heavier, higher HP (around 300hp with mods) TL-S has been averaging over 33mpg (85% highway) since the end of March while my RX8 has been averaging 20mpg (85% highway) since I got it end of April, and I drive the same in each car.

Strange....but gearing has to be partially involved....

Mathmatically speaking, you are probably correct. The mag articles didn't specify shift points (could've been at max power RPM or redline), but in any case, it doesn't make much difference when refering back to my initial point that the 6-speed RX-8 is basically a 5-speed in an all-out acceleration attempt to max speed. As I mentioned, the S2000 and 350Z utilize all 6 of their speeds right to max speed. Even with variances allowed for all 3 vehicles, it seems apparent that the 8's gear spacing is wider in the last 3 (top) gears.

1.3L

Not as many shifts as possible, but enough to keep the engine in its best power band. Obviously, a 2-speed would be a dog and a 16-speed truck tranny wouldn't be an advantage either.

I think the numbers show pretty clearly that the S2000 starts pulling away more quickly from about 90 MPH on up. From 89-90 on to top speed, the RX-8 uses 4th and 5th. The S2000 uses 4th, 5th and 6th (one shift more than the 8). It seems that an extra shift is an advantage in this case.

1.3L

i think a larger factor is when the car was shifted. it seems, at least with the 8, that they were shifting at peak power, which might not be the optimal shift point for the 8.

shifting at 8500 drops you to a lower rpm than shifting at 9250 (just before fuel cut off). thats pretty obvious and somethign that i think we all can agree on.

now what needs to be looked at is the power at 9250 and the power after shifting. if the 9250 hp is more than the power produced after shifting at peak power, then in terms of acceleration, it is more adventagous to shift higher up than at peak.

also, the earlier you shift, the longer it takes after the shift to get to the point where the tertiary ports open.

all these things may on make a slight difference, but do them over and over, and they will add up. so, going off the numbers in the comparison chart, i think it is less of a gear box issue and more of driver technique issue.

anyways, thats my hypothesis on the data available. ;)

there is no limiter in the us hi power car. i had mine to 155 in 5th. forget about a limiter. 6th is and was always meant to be an overdrive gear. it is not meant for acceleration. in that you are correct. what point you are try to maker isstill not clear to me.

Was my question so dumb no one touched it...lol, sorry guys...at least let me know what you think about the carbon fiber driveshaft (is that what you call it) flexing...can that be possible?

Having driven both the S2000 and the RX-8 extensively, I completely agree with you. 6th on the RX-8 is like 6th on a Corvette--useful only for optimal fuel mileage on the highway. Now, that's a good thing, but it really means that this is a five-speed, for performance purposes, while the S2000 is a six-speed (and gets better gas mileage anyway :D ).

If anything the carbon driveshaft would increase performance due to it's light weight. Carbon fiber can be stronger than steel, so I don't think flexing would be an issue unless Mazda cut some serious corners on it's design.

My point is, when considering best acceleration all the way to top speed, having a transmission that is designed to use all 6 gears to reach top speed is better than one using only 5 (out of 6). The 6-speed transmission in the RX-8 was not designed to need 6th gear to hit top speed. That gear is too tall. It seems quite clear that the RX-8 reaches its top speed in 5th gear while the S2000 and 350Z reach their respective top speeds in 6th.

As to the RX-8, utilizing only gears 1 through 5 may make no difference in the ultimate top speed, but I believe it makes difference in how quickly it gets there. Again, notice how the S2000 starts pulling ahead more quickly around 100 MPH and beyond. I believe the closer gear spacing of the S2000 in 4th, 5th and 6th enhances its already great performance. If the S2000 tranny was designed like the RX-8's I believe the race to ~150 MPH would much closer. Or if the 8 had a tranny like the S2000's...

1.3L

what is an electronic governor?

You guys are only looking at this from a performance perspective. Gear ratios are chosen by the manufacturer to provide a balance between performance and fuel economy. If Mazda chose all the gear ratios with pure performance in mind, they would lose roughly 2-4 MPG on the EPA fuel economy rating. The EPA procedure specifies a vehicle speed versus time trace that must be followed closely during the test. By choosing ratios (for all gears) that emphasize performance over economy, the engine will be revving higher and consuming more fuel during many portions of the test, thereby degrading the fuel economy rating. This is a HUGE thing to a manufacturer, as a certain target level for fuel economy must be met in order for the program to be viable. Why can Honda get away with gearing the S2000 more aggressively? Because their engine is much more fuel efficient than the Renesis.

No, the flexing of the drive shaft has little to do with acceleration for the most part; however, the axle/wheel hop phenomenon is related to torsional windup of the shafts, which causes displacement of the differential mounts. Stiffer shafts aren't really going to fix the problem though, because more load will be simply be placed on the diff mounts.

I'd much rather than 6th was WAY steeper and was an actual overdrive. It's so close to 5th it's almost pointless.

your point is that the cars accelerate differently because the transmissions were designed diffeently? thank you good point


excellent point also buckeye. one that was made 3 years ago when the gearing was first found out. buger was all over that and Rich was pissed thatthey didnt gear it for best acceleration performance

ok maybe that was a bit sarcastic 1.3L . you had an idea, did an analysis and came to a coclusion. thats good work. but what does it get us? try plugging in diiferent gearing in 1-5 and see what effects there are on acceleration . and if you can the fuel economy. there must be some equations around to use.