Power-to-Weight Ratio Comparison

[Supercharger]

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.

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[FamilyGuy]

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?

[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

[cueball]

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?

[Schneegz]

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

[Buger]

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

[cueball]

I don't remember that.

Maybe a link Buger?

[pelucidor]

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.

[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.

[FamilyGuy]

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.

[Buger]

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.

[Buger]

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

[Buger]

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

[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.

[zoom44]

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?

[Shard]

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.

[FamilyGuy]

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.

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

[Keshav]

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

That car is one hell of a sleeper.

[Supercharger]

http://www.caranddriver.com/article....&page_number=4

http://www.hwysafety.org/vehicle_rat...uv_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.

[Keshav]

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!

[FamilyGuy]

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

[Buger]

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

[Supercharger]

http://www.caranddriver.com/article....&page_number=4

http://www.roadandtrack.com/assets/d...2003155629.pdf

[pelucidor]

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

[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.