Car&Driver test data

________________ 0-60mph __ Power ___ Weight ____ P/W ___ Price as tested

Subaru Forester
2.5XT ____________ 5.3 s ____ 210 hp ___ 3290 lb ___ 0.064 ___ US$ 26K

Subaru WRX _______ 5.4 s ____ 227 hp ___ 3100 lb ___ 0.073 ___ US$ 25K

Honda S2000 ______ 5.4 s ____ 240 hp ___ 2835 lb ___ 0.085 ___ US$ 33K

Infiniti G35 Coupe___5.5 s ____ 280 hp ___ 3500 lb ___ 0.080 ___ US$ 37K

Volvo S60R ________5.5 s ____ 300 hp ___ 3717 lb ___ 0.081 ___ US$ 42K

Dodge SRT-4 ______ 5.6 s ____ 215 hp ___ 2920 lb ___ 0.074 ___ US$ 20K

BMW 330i PP _______5.6 s ____ 235 hp ___ 3370 lb ___ 0.070 ___ US$ 40K

Honda Accord
EX Coupe __________5.9 s ____ 240 hp ___ 3300 lb ___ 0.073 ___ US$ 28K

Mazda RX-8 ________5.9 s ____ 247 hp ___ 2940 lb ___ 0.084 ___ US$ 28K

Nissan Altima
3.5SE _____________5.9s _____ 245 hp ___ 3220 lb ___ 0.076 ___ US$ 23K


All the above cars have manual transmission.

The S2000 and RX-8 have the highest power-to-weight ratio in this group. For some reason, the RX-8 is significantly slower than the S2000.

There have been discussions about this before. The other factors missing above are gearing, tire width, and power band.

Set the gearing low, and you increase acceleration while harming gas mileage. Add extra gears in the transmission, and you improve gas mileage, make it easier to stay in the power band for better acceleration, but lose some speed because you shift more often.

Power band is the RPM range for the engine where it is operating at or near peak torque. Ideally you want the power band to be as broad as possible, starting as low as possible.

S2000:
1st 3.133
2nd 2.045
3rd 1.481
4th 1.161
5th 0.971
6th 0.811
Final Drive ratio 4.11

RX-8:
1st 3.760
2nd 2.269
3rd 1.645
4th 1.187
5th 1.000
6th 0.843
Final Drive ratio 4.440

According to this, the RX-8 is geared lower than the S2000, which should be a mark in its favor. The difference, then, has got to be in the power bands. Anyone have a dyno overlay of the two available?

Hi Family Guy,

I see that you're getting the hang of the gearing thing no. :) There are several very important factors that have not been listed in Superchargers comparison though.

One of the biggest factors missing is whether the car is the drivetrain info. AWD makes a big difference in 0-60 times because the wheels don't really spin off the line. Another big factor is if a car is turbo or NA.

HP/wt comparisons between different drivetrain types are less meaningful as are comparisons between FI and NA cars.

Also note that although the RX-8 has higher numerical gear ratios, it has a large wheel/tire circumference. Although it may seem like the rx-8 is geared lower than the s2000, the s2000 is geared for better acceleration since the 1st - 2nd shift comes at a lower speed. The RX-8 was geared for a wide powerband, not for optimal 0-60 times.

Just about all of the other cars in the above comparison probably have 1st - 2nd shift points @ 3x mph and 2nd - 3rd shift points closer to 60mph.

Brian

Originally posted by Buger
Hi Family Guy,

I see that you're getting the hang of the gearing thing no. :) There are several very important factors that have not been listed in Superchargers comparison though.

One of the biggest factors missing is whether the car is the drivetrain info. AWD makes a big difference in 0-60 times because the wheels don't really spin off the line. Another big factor is if a car is turbo or NA.

HP/wt comparisons between different drivetrain types are less meaningful as are comparisons between FI and NA cars.

Also note that although the RX-8 has higher numerical gear ratios, it has a large wheel/tire circumference. Although it may seem like the rx-8 is geared lower than the s2000, the s2000 is geared for better acceleration since the 1st - 2nd shift comes at a lower speed. The RX-8 was geared for a wide powerband, not for optimal 0-60 times.

Just about all of the other cars in the above comparison probably have 1st - 2nd shift points @ 3x mph and 2nd - 3rd shift points closer to 60mph.

Brian
Thanks for the great explanation, as usual.:)

Great to see you again Buger. Where have you been and did you get your 8 yet?

I think it's funny that a Subaru Forester was the quickest car in the bunch! :D And it's among the cheapest and heaviest. So much for slow, porky SUV's ;)

Originally posted by cueball1029

Thanks for the great explanation, as usual.:)

Great to see you again Buger. Where have you been and did you get your 8 yet?

I'm still around occasionally. :) I've previously posted about using my S-plan.

Several reports have Mazda corporate allowing dealers to accept S-plan in January (at their discretion). A local Mazda dealership reluctantly told me that the gt on s-plan would be around 2700 under msrp.

I have heard that my sport version will be around 1800 under msrp. I gave some of the details of how I got my S-plan in Nov of last year. I wonder how many people did anything with that info? :)

Brian

I don't remember that.:(

Maybe a link Buger?:)

HI Buger - I've seen you on several threads today. Are you back for good?

The sales manager at my dealership is also waiting for the S plan before getting an RX-8 - he said Jan or Feb is likely.

Car&Driver test data

__________ 0-60mph ___ 0 - 1/4 mile ____ Power ___ Weight __ P/W

Mazda RX-8 __ 5.9 s ___ 14.5s @ 96mph __ 247 hp __ 2940 lb __ 0.084

Porsche
Boxster ______6.0 s ___ 14.6s @ 98mph __ 228 hp __ 3024 lb __ 0.075


Both cars have NA engines, RWD and manual transmission.

This comparison suggests that the RX-8 tested by Car&Driver may have less than 247 hp.

Originally posted by Supercharger
Car&Driver test data

__________ 0-60mph ___ 0 - 1/4 mile ____ Power ___ Weight __ P/W

Mazda RX-8 __ 5.9 s ___ 14.5s @ 96mph __ 247 hp __ 2940 lb __ 0.084

Porsche
Boxster ______6.0 s ___ 14.6s @ 98mph __ 228 hp __ 3024 lb __ 0.075


Both cars have NA engines, RWD and manual transmission.

This comparison suggests that the RX-8 tested by Car&Driver may have less than 247 hp.

Keep in mind that the RX8 has peak torque 161 ft*lbs at 5500 RPM, while the Boxter has peak torque 192 ft*lbs at 4750 RPM. That's more torque over a wider range, and accounts for the difference nicely.

Originally posted by cueball1029
I don't remember that.:(

Maybe a link Buger?:)

I don't have the link off the top of my head but a serach of user:buger keyword:s-plan will probably find it. :)

Originally posted by pelucidor
HI Buger - I've seen you on several threads today. Are you back for good?

Hi Pelucidor,

The sales manager at my dealership is also waiting for the S plan before getting an RX-8 - he said Jan or Feb is likely.

My pregnant wife has a temp job this week so I've spent a little more time on the forum. We expect our little girl to arrive in about 6 weeks. :)

Brian

Originally posted by Supercharger
Car&Driver test data

__________ 0-60mph ___ 0 - 1/4 mile ____ Power ___ Weight __ P/W

Mazda RX-8 __ 5.9 s ___ 14.5s @ 96mph __ 247 hp __ 2940 lb __ 0.084

Porsche
Boxster ______6.0 s ___ 14.6s @ 98mph __ 228 hp __ 3024 lb __ 0.075


Both cars have NA engines, RWD and manual transmission.

This comparison suggests that the RX-8 tested by Car&Driver may have less than 247 hp.

Hi Supercharger,

I believe Rich posted something about some Bearded Clam's razor theory that had something to do not assuming too much.

It is true that the hp/weight ratio can be a pretty good metric. Of course you are aware that gearing can alter things a bit. We should all be aware by now that lower gearing (higher ratio) will give you more torque but will lessen the top speed in gear. Mazda designed the gearing ratios of the RX-8 to emphasize the wide powerband rather than quickest acceleration. Because of this the 1st-2nd shift comes around 40mph and the 2nd-3rd shift comes around 70mph. The RX-8 could have been geared for higher torque but I believe that Mazda wanted to avoid the "gas guzzler" tax that would have come if the combined epa figures were 1 or 2 mpg less. Mazda had the exact same dilemna with previous RX-7s.

With the above results, I would think that the Porsche Boxster that you quoted would have the 1st-2nd shift and 2nd-3rd shift come at a lower speed than the RX-8.

Since I know you like searching the internet for stuff :) , your mission (should you choose to accept it) is to find out the redline speeds in 1st and 2nd gear for the Porsche Boxster that you mentioned. It would also be interesting to find out the redline speeds in 1st and 2nd gear for the Subaru Forester 2.5XT that you quoted.

Even with AWD, that thing must be geared VERY low (high ratios) to get the 0-60 times that you posted. 2nd gear redline probably comes in a bit less than 60 mph for that thing!

Brian

Ok, enough post whoring for me. I need to get back to work and I'll never catch up with Zoom44 and Herules anyway. :)

Originally posted by Buger
Ok, enough post whoring for me. I need to get back to work and I'll never catch up with Zoom44 and Herules anyway. :)
:o

and Supercharger i have never seen you quote or post any stats incorrectly in th epast but could you double check that forester number please. are you sure it wasn't 5.8 seconds?

Originally posted by zoom44

:o

and Supercharger i have never seen you quote or post any stats incorrectly in th epast but could you double check that forester number please. are you sure it wasn't 5.8 seconds?

No, he got it right. 215 hp and like 240lb/ft. Check car and driver.

Originally posted by Buger


My pregnant wife has a temp job this week so I've spent a little more time on the forum. We expect our little girl to arrive in about 6 weeks. :)

Brian

Congrats! We expect our little boy in eight. :)

Oh, and I found the S-plan thread here (http://www.rx8forum.com/showthread.php?s=&threadid=1171&highlight=Buger+Splan).

Good luck with it... you could save a bundle.

Just another bit of info on that Forester ... 4.44 rear-end

That car is one hell of a sleeper.

http://www.caranddriver.com/article.asp?section_id=3&article_id=6854&page_number=4

http://www.hwysafety.org/vehicle_ratings/ce/html/summary_smsuv_overall.htm


Car&Driver test data

____________________ 0-60mph __ 0 – 1/4 mile __ P/W ___ Price as tested

Subaru Forester 2.5XT __ 5.3 s ______13.8 s ____ 0.064 ___ US$ 26K

Jaguar S-type R ________5.4 s ______13.8 s ____ 0.096 ___ US$ 62K

Porsche Boxster S ______5.3 s ______ 13.9 s ____ 0.084 ___ US$ 58K

BMW Z4 3.0i __________ 5.3 s ______ 14.0 s ____ 0.073 ___ US$ 45K


Fast, safe, affordable, roomy and versatile. The Forester 2.5XT can blow off most cars on the road.

Originally posted by Supercharger
Fast, safe, affordable, roomy and versatile. The Forester 2.5XT can blow off most cars on the road.

... and OFF the road!

While we're heaping praises on it, remember too that it's (as far as I know) the only vehicle thus far to receive a good crash rating on the front offset crash test AND the new side pickup/SUV crash test from

hwysafety (http://www.hwysafety.org)

Hi Supercharger,

You may have missed my previous post.

"Since I know you like searching the internet for stuff :) , your mission (should you choose to accept it) is to find out the redline speeds in 1st and 2nd gear for the Porsche Boxster that you mentioned. It would also be interesting to find out the redline speeds in 1st and 2nd gear for the Subaru Forester 2.5XT that you quoted."

If you choose to look it up, the answers will be a service to the forum as another good example of how gearing can affect acceleration performance.

Brian

http://www.caranddriver.com/article.asp?section_id=3&article_id=6854&page_number=4

http://www.roadandtrack.com/assets/download/592003155629.pdf

I copied the info from the links that Supercharger gave.

Subaru Legact 2.5XT

DRIVETRAIN
Transmission: 5-speed manual
Final-drive ratio: 4.44:1, limited slip
Gear ... Ratio ... Mph/1000 rpm ... Max. test speed
I ... 3.45 ... 4.9 ... 32 mph (6500 rpm)
II ... 2.06 ... 8.3 ... 54 mph (6500 rpm)
III ... 1.45 ... 11.8 ... 76 mph (6500 rpm)
IV ... 1.09 ... 15.6 ... 102 mph (6500 rpm)
V ... 0.78 ... 21.8 ... 129 mph (5900 rpm)



Boxster 5-speed manual

Gear.....................................Ratio/Overall/(Rpm) Mph
1st, :1 . . . . . . . . . . . . . . . . . .3.50/12.46/(7200) 43
2nd,:1 . . . . . . . . . .. . . . . . . . 2.12/7.55/(7200) 71
3rd, :1 . . . . . . . . . . . . . . . . . .1.43/5.09/(7200) 105
4th, :1 . . . . . . . . . . . . . . . . . .1.09/3.88/(7200) 137
5th, :1 . . . . . . . . . . . . . . . . . .0.84/2.99/est (6350) 157
Final drive ratio. . . .. . . . . . . .3.56:1

So the XT gets to 60 in the same amount of time as the Porsche even though it has an extra shift. Then, it leads by .1 second through the quarter despite the brick-like aerodynamics. Impressive for an SUV/wagon/econobox. *grin*

I want that engine and tranny in my RS. :cool:

Gear _________ Speed at Redline

________ 247 hp RX-8 ___ 228 hp Boxster

1st _______ 39 mph ________ 43 mph

2nd _______ 65 mph ________ 71 mph

3rd _______ 89 mph ________105 mph

4th _______124 mph ________137 mph


The Boxster can keep up with the RX-8 despite having taller gearing and a lower power-to-weight ratio.

Conclusion: The Renesis probably produces less than 247 hp.

Hi Supercharger,

The results are interesting. The crazy gearing and better traction of AWD explain the Subaru Legact 2.5XT fast times but I would have thought that the Porsche Boxster would be geared a little lower. Knowing nothing else, it makes sense to assume that a higher hp car with the same shift points will be a little faster.

I went to the link with the R&T Boxster stats and was surprised to see that the Boxster has some crazy rear wheels/tires. 265/35zr-18's are not a common tire choice to say the least. The width of those tires and the rear weight bias of the Boxster do a good job of adding more traction off the line.

When you consider the margin for error (results taken from different magazines and conditions), it is a bit presumptuous to come to a conclusion based on a single comparison.

I would have thought that the first comparison you would have made would be between the G35C and the (preproduction) RX-8. Both are more similar in price and purpose and Road&Track already did the work of putting their test results side by side. They even graphed their acceleration curves together (April 2003). The power to weight ratios on the 2 cars are very close and Road&Track said that the (preproduction) RX-8 was a little faster than the G35C in 0-60 and the 1/4 mile.

Magazine comparisons with the preproduction RX-8s aside, we will have to wait for Mazda's response on the dyno testing results that have production RX-8s missing some torque (and thus horsepower) above 6250 rpms.

Does this one comparison mean that the G35C probably produces less than 280hp? Margin for error and different testing conditions are 2 major reasons why magazine racing does not always yield reliable results. Go and drive the cars Supercharger! You know you want to! :)

Brian

Originally posted by FamilyGuy


Keep in mind that the RX8 has peak torque 161 ft*lbs at 5500 RPM, while the Boxter has peak torque 192 ft*lbs at 4750 RPM. That's more torque over a wider range, and accounts for the difference nicely.

If you'll forgive me for quoting myself, I think this explains why the Boxter does better than the RX-8. It has more torque to play with earlier. To put it into other terms, the Boxter has 173 of its horsepower available at 4750 RPM. If the RX8 has 160 torque at 4750 RPM - and it probably has less - than it would only have 144 horsepower. Even if the RX8's peak horsepower is higher than the Boxter's, for a big chunk of the RPM range the Boxter has the edge.

For a further example, the Forester has one of the lowest horsepower ratings in your little comparison - but it has one of the highest torque ratings.

Originally posted by FamilyGuy
If you'll forgive me for quoting myself, I think this explains why the Boxter does better than the RX-8. It has more torque to play with earlier. To put it into other terms, the Boxter has 173 of its horsepower available at 4750 RPM. If the RX8 has 160 torque at 4750 RPM - and it probably has less - than it would only have 144 horsepower. Even if the RX8's peak horsepower is higher than the Boxter's, for a big chunk of the RPM range the Boxter has the edge.

For a further example, the Forester has one of the lowest horsepower ratings in your little comparison - but it has one of the highest torque ratings.

Hi FamilyGuy,

You are forgiven but I thought you would understand that engine torque without gearing and tire size information is meaningless by now. Think wheel torque and tire size NOT engine torque!

If you remember, gearing was discussed in your thread about your V6 Impala in February. In one of my posts in your thread (http://www.rx8club.com/showthread.php?s=&postid=29615#post29615), it was pointed out that the RX-8 is geared about twice as much as the Impala in first gear (16.71 vs 8.35). The end result is that the 159 ft-lb RX-8 has almost much more wheel torque than the 205 ft-lb Impala.

Your comparison which you quoted yourself on might be valid if the drivewheels for the RX-8 and the Boxster were bolted onto the output shaft of their engines. Unfortunately, things are not that simple and both cars have gears.

As an exercise to further understand that things are not that simple, we can use released figures and some simple math. Note however that Mazda released figures seem to differ from production results at high rpms right now:

Boxster:
engine torque ................... : 192 ft-lbs
1st gear .......................... : 3.5:1
final drive ......................... : 3.56:1
total gearing ..................... : 3.56 * 3.5 = 12.46 (in first gear)
approx peak wheel torque ... : 12.46 * 192 * .8 = 1914 ft-lbs (in 1st gear)
approx weight .................. : 3000 lbs

RX-8
engine torque .................. : 159 ft-lbs
1st gear ......................... : 3.76:1
final drive ....................... : 4.444:1
total gearing ................... : 3.76 * 4.444 = 16.71 (in first gear)
approx peak wheel torque ... : 16.71 * 159 * .8 = 2125 ft-lbs (in 1st gear)
approx weight .................. : 3000 lbs

You can see that the 159 ft-lb RX-8 has more peak wheel torque in 1st gear the 192 ft-lb Boxster. The wider rubber of the Boxster gives it a little more traction off the line however.

Now if you want to compare the peak wheel torque of the Porsche to the RX-8 at the same speed...

Boxster in 1st gear:
wheels/tires .................................. : 265/35r18
Speed @ redline .............................. : 43.5 mph @ 7200 rpm
Speed @ peak torque ...................... : 29mph @ 4750 rpm
approx wheel torque @ 4750 rpm ..... : 12.46 * 192 * .8 = 1914 ft-lbs

RX-8 in 1st gear:
wheels/tires .................................. : 225/45r18
Speed @ redline ............................. : 41.6 mph @ 9000 rpm
eng rpm @ 29mph ........................... : 6250 rpm
eng torque @ 6250 rpm ................... : approx 157 ft-lbs (according to Mazda)
approx wheel torque @ 6250 rpm ...... : 16.71 * 157 * .8 = 2099 ft-lbs

Given the gearing and wheel/tire size of the Boxster 7200 rpm calculates to 43.5 mph. The 1st gear speed at peak torque (4750 rpm) is approx 29 mph.

You wanted to compare the HP of the Boxster (@ it's trq peak) to the RX-8's HP at the same speed. Notice that the RX-8's 1st gear rpms are 6250 @ 29 mph (not 4750).

Boxster @ 29mph has approx 173.6 HP (4750*192/5252)
Boxster 1st gear wheel torque @ 29 mph (assuming 20% dt losses) is 1914 ft-lbs

RX-8 @ 29mph has approx 186.8 HP (6250*159/5252)
RX-8 1st gear wheel torque @ 29 mph (assuming 20% dt losses) is 2099 ft-lbs

Note that this comparison is in no way trying to denigrate the Boxster (which is another great car). It is only meant to demonstrate that engine torque by itself is meaningless.

Once again, a couple of things to remember:
1. HP is a better indicator of wheel torque.
2. HP/weight is a pretty good metric if cars are geared to shift at the same speeds.

Lastly, please note that the Subaru 2.5XT gets it's wheel torque by tremendously low (high ratio) gearing. It was geared for more torque but less range in each gear. The entire reason I wanted somebody to find out the speed @ redline for it was to demonstrate this. You can see that 1st gear only has a range up to 32 mph and 2nd only goes up to 54 mph. The tradeoff to gearing for more wheel torque is less of a range in gear.

This was much longer than I meant it to be. I think I'm done for awhile.

Brian

Originally posted by FamilyGuy


If you'll forgive me for quoting myself, I think this explains why the Boxter does better than the RX-8. It has more torque to play with earlier. To put it into other terms, the Boxter has 173 of its horsepower available at 4750 RPM. If the RX8 has 160 torque at 4750 RPM - and it probably has less - than it would only have 144 horsepower. Even if the RX8's peak horsepower is higher than the Boxter's, for a big chunk of the RPM range the Boxter has the edge.

For a further example, the Forester has one of the lowest horsepower ratings in your little comparison - but it has one of the highest torque ratings.

Short version:

Absolutely wrong. The Boxster does not have more torque to play with earlier. It is a fallacy that the Boxster has a big chunk of it's RPM range at higher HP than the RX-8. Gearing affects the RPMS that the cars should be compared at.

The Forester has one of the lowest horsepower ratings in Superchargers comparison but it has AWD and it has been geared for more torque and less range per gear. Peak engine torque by itself is practically meaningless.

Brian

Buger,

Thanks for clearing me up on that. My mistake. I was trying to make things simpler than they are. Allow me to summarize the situation then, as best as I understand it - and I'm welcoming correction here, this is how I learn (I may get lots of things wrong, but I think I've come a long way since first reading this forum):

When comparing two cars' performance in straight line acceleration, you have the following factors:
peak horsepower
RPM point for peak horsepower
peak torque
RPM point for peak torque
drivetrain losses to horsepower and torque (usually 20%)
final drive ratio
transmission drive ratios
combination of where the transmission 'tops out' in each gear.
tall gearing reduces effective torque to the wheels but
offsets that by getting a larger mph range out of each gear,
short gearing does the opposite
AWD, FWD, or RWD and the presence or absence of
a limited slip differential (LSD, no not the drug)
vehicle weight
tire radius
(and of course) driver skill

Did I miss anything?
Here's two questions.
1. All other things being equal, if you put tires with a 5% larger radius on a car, does that mean you get 100/105 = 95.24% of your previous effective torque to the ground? Is that totally wrong, or is there another formula you can use?
2. How much does the weight of your tires factor into this? Heavier tires would require more energy to accelerate in rotation, yes?

FamilyGuy,

Car&Driver did an 8000rpm clutch drop standing start to get the 0-to-60 time of 5.9s for the RX-8. The RX-8’s engine rev never drops to 4750rpm in that run.

0-to-60 and 0-to-1/4 mile are not low-end torque tests. 5-to-60 is.


______________ 5-60mph

228 hp Boxster ___ 6.7 s

247 hp RX-8 _____ 7.5 s

Originally posted by Supercharger
FamilyGuy,

Car&Driver did an 8000rpm clutch drop standing start to get the 0-to-60 time of 5.9s for the RX-8. The RX-8’s engine rev never drops to 4750rpm in that run.

0-to-60 and 0-to-1/4 mile are not low-end torque tests. 5-to-60 is.


______________ 5-60mph

228 hp Boxster ___ 6.7 s

247 hp RX-8 _____ 7.5 s

You're right, I was wrong. :)

Car&Driver test data

______________ 0-100mph ___ Power ___ Weight ____ P/W

Volvo S60R _______13.9 s ____ 300 hp ___ 3717 lb ___0.081

Dodge SRT-4 _____ 14.0 s ____ 215 hp ___ 2920 lb ___0.074

Subaru Forester
2.5XT ___________ 15.0 s ____ 210 hp ___ 3290 lb ___0.064

Honda Accord
EX Coupe ________ 15.2 s _____240 hp ___3300 lb ___ 0.073

BMW 330i PP _____ 15.3 s _____235 hp ___3370 lb ___ 0.070

Mazda RX-8 ______ 15.8 s _____238 hp ___2940 lb ___ 0.081


All the above cars have manual transmission.

Road&Track test data

________________ 0-100mph ___ Power ___ Weight ____ P/W

Honda S2000 _______14.2 s ____ 240 hp ___ 2835 lb ___0.085

Porsche Boxster S ___14.4 s ____ 258 hp ___ 3080 lb ___0.084

Infiniti G35 Coupe ___ 14.9 s ____ 280 hp ___ 3435 lb ___0.082

Porsche Boxster _____15.7 s ____ 228 hp ___ 3000 lb ___0.076

Mazda RX-8 ________ 15.9 s ____ 238 hp ___ 3000 lb ___0.079

BMW 330i __________ 15.9 s ____ 225 hp ___ 3340 lb ___0.067


All the above cars have manual transmission, NA engine and RWD.

A pre-production RX-8 probably has less than 230 hp.

AUTOCAR (U.K.) test data

______________ 0-100mph ___ Power ___ Weight ____ P/W

Honda S2000 ____ 14.3 s _____ 237 hp ___2780 lb ___0.085

Alfa Romeo
156 GTA Sedan ___15.1 s _____ 250 hp ___3110 lb ___0.080

VW Golf R32 _____ 15.6 s _____ 237 hp ___3260 lb ___0.073


All the above cars have manual transmission and NA engine.

Originally posted by Supercharger
Car&Driver test data

__________ 0-60mph ___ 0 - 1/4 mile ____ Power ___ Weight __ P/W

Mazda RX-8 __ 5.9 s ___ 14.5s @ 96mph __ 247 hp __ 2940 lb __ 0.084

Porsche
Boxster ______6.0 s ___ 14.6s @ 98mph __ 228 hp __ 3024 lb __ 0.075


Both cars have NA engines, RWD and manual transmission.

This comparison suggests that the RX-8 tested by Car&Driver may have less than 247 hp.

Or maybe porche has more than 228Hp

FamilyGuy, don't forget that the width of the powerband is also important. Just imagine the extreme example of an engine that only makes considerable horsepower in a span of 100rpm. Basically that peak is useless because it would be impossible to maintain that rpm as you accelerate (unless you have tons of gears).

Car&Driver test data

__________________ 0-100mph ___ Power ___ Weight ___ P/W


Acura TL (manual) _____14.6 s _____270 hp ___3521 lb ___ 0.077

Mazda RX-8 (manual) __ 15.8 s _____238 hp ___2940 lb ___ 0.081


TL report: January issue Car&Driver (p.120)

Originally posted by Supercharger
Car&Driver test data

__________ 0-60mph ___ 0 - 1/4 mile ____ Power ___ Weight __ P/W

Mazda RX-8 __ 5.9 s ___ 14.5s @ 96mph __ 247 hp __ 2940 lb __ 0.084

Porsche
Boxster ______6.0 s ___ 14.6s @ 98mph __ 228 hp __ 3024 lb __ 0.075


Both cars have NA engines, RWD and manual transmission.

This comparison suggests that the RX-8 tested by Car&Driver may have less than 247 hp.

You forgot to mention something very important, boxter is a mid engine car.

Originally posted by Keshav
So the XT gets to 60 in the same amount of time as the Porsche even though it has an extra shift. Then, it leads by .1 second through the quarter despite the brick-like aerodynamics. Impressive for an SUV/wagon/econobox. *grin*

I want that engine and tranny in my RS. :cool:

It is basically the same engine as the STI without the bigger turbo and intercooler. Same short block.

Originally posted by Supercharger
Gear _________ Speed at Redline

________ 247 hp RX-8 ___ 228 hp Boxster

1st _______ 39 mph ________ 43 mph

2nd _______ 65 mph ________ 71 mph

3rd _______ 89 mph ________105 mph

4th _______124 mph ________137 mph


The Boxster can keep up with the RX-8 despite having taller gearing and a lower power-to-weight ratio.

Conclusion: The Renesis probably produces less than 247 hp.


You have to look at the torque not just horse power.

Originally posted by Buger

Boxster @ 29mph has approx 173.6 HP (4750*192/5252)
Boxster 1st gear wheel torque @ 29 mph (assuming 20% dt losses) is 1914 ft-lbs

RX-8 @ 29mph has approx 186.8 HP (6250*159/5252)
RX-8 1st gear wheel torque @ 29 mph (assuming 20% dt losses) is 2099 ft-lbs

Note that this comparison is in no way trying to denigrate the Boxster (which is another great car). It is only meant to demonstrate that engine torque by itself is meaningless.

Once again, a couple of things to remember:
1. HP is a better indicator of wheel torque.
2. HP/weight is a pretty good metric if cars are geared to shift at the same speeds.


Brian

Don't forget the Boxter has a mid engine layout therefore less dt loss, I would say more like 10%.

Also from standing still your formula doesn't apply since you can rev the engine up at neutral and drop the clutch at any rpm you desire. It only applies going from 1 to second gear and so on.

Originally posted by FamilyGuy
Buger,

Thanks for clearing me up on that. My mistake. I was trying to make things simpler than they are. Allow me to summarize the situation then, as best as I understand it - and I'm welcoming correction here, this is how I learn (I may get lots of things wrong, but I think I've come a long way since first reading this forum):

When comparing two cars' performance in straight line acceleration, you have the following factors:
peak horsepower
RPM point for peak horsepower
peak torque
RPM point for peak torque
drivetrain losses to horsepower and torque (usually 20%)
final drive ratio
transmission drive ratios
combination of where the transmission 'tops out' in each gear.
tall gearing reduces effective torque to the wheels but
offsets that by getting a larger mph range out of each gear,
short gearing does the opposite
AWD, FWD, or RWD and the presence or absence of
a limited slip differential (LSD, no not the drug)
vehicle weight
tire radius
(and of course) driver skill

Did I miss anything?
Here's two questions.
1. All other things being equal, if you put tires with a 5% larger radius on a car, does that mean you get 100/105 = 95.24% of your previous effective torque to the ground? Is that totally wrong, or is there another formula you can use?
2. How much does the weight of your tires factor into this? Heavier tires would require more energy to accelerate in rotation, yes?

Weather condition, temperature, altitude, tyres (stickyness of the tyres), and engine layout (where the engine is located).