power to weight ?

My street driven '85 RX-7 (w/ driver) has a slightly better P/W than a 220hp 575lb Hayabusa with a 140lb rider

JoeyM wrote:

wearymicrobe wrote:

Keith Tanner wrote:

Toyman01 wrote: A Miata is in the 20:1 range.

Mine's at about 4.3.

4.3!!!!! That is better then my last modified viper.

Naked raccoon > snake

Somehow my new mission is to get that into the magazine or use it without context in real life.

W30 MR2 with about that power and at 2100lbs is a lot of fun, even less weight would be more so.

My Radical C sports racer is about 7#/HP and was low lap time of the event at a couple SCCA club races last year. It's quick but it's the aero and the mechanical grip that do the magic.

motomoron wrote: My Radical C sports racer is about 7#/HP and was low lap time of the event at a couple SCCA club races last year. It's quick but it's the aero and the mechanical grip that do the magic.

Yeah, the aero in a prototype-style purpose-built race car is going to win out over almost anything you could in a production-based car.

My Miata is about 8, which is fast enough that when it's cold out it spins the tires when the boost hits in third, and will spin them in 4th if it's not pointed completely straight. That's about as much as I'd want in a street car, I think. At least, not without AWD. :)

Toyman01 wrote: How about a video of the Abomination. https://www.youtube.com/watch?v=ggaD4nC8wec

Slightly off topic, but wtf is up with the videos related to yours??

clutchsmoke wrote:

Toyman01 wrote: How about a video of the Abomination. https://www.youtube.com/watch?v=ggaD4nC8wec

Slightly off topic, but wtf is up with the videos related to yours??

At a guess, Keyword Abomination. That probably pulls every freak out of the woodwork.

The Abomination is around 125 HP and 1700 pounds (remarked the guy who built it)and is somewhere between exhilarating and terrifying.

Something to keep in mind about HP to weight: it's only one piece of the puzzle. Two different, say, 10:1 cars which have vastly different vehicle weights are not going to drive or react the same. A 1500 pound car with 150 HP will be a completely different beast from a 3000 pound car with a 300 HP engine, even though both have the same p/w ratio.

Even though the heavier car will have the same power/weight ratio the vehicle's inertia will be much different thus it's not going to be as easy to drive or perform as well.

To get the 3000 pound car to accelerate as quickly as the 1500 pound car will mean a p/w ratio that would be better than 10:1. But this brings with it a whole host of other problems: you have to add mechanical grip so the tires won't just spin, then you have to deal with how to turn and slow down that extra weight and HP. Colin Chapman realized this way back when and that's why the Seven etc were the giant killers of their time.

Conversely, look at what happened with the Can-Am series. Big power triumphed.

They drive differently, that's been acknowledged multiple times here. Although I'm not sure I agree that the acceleration would be less on a heavier car with the same power/weight ratio. Once aero effects come in to play, the more powerful car would actually accelerate harder than the weaker one, as weight becomes less important than drag as speeds rise.

Although I've sworn that I've done my last engine swap, the thought of stuffing a 400 bhp Ecotec into a LBC (little British car) weighing around 2000 lbs. continues to entice me!

kanaric wrote: W30 MR2 with about that power and at 2100lbs is a lot of fun, even less weight would be more so.

Kanaric, how do you like your spyder? My wife's is a riot (214whp, pretty light, maybe sub2000?). It doesnt feel super fast to me but it puts down fast times at autox, seems to stay with my buddy's viper pretty well too.

Keith Tanner wrote: Conversely, look at what happened with the Can-Am series. Big power triumphed. They drive differently, that's been acknowledged multiple times here. Although I'm not sure I agree that the acceleration would be less on a heavier car with the same power/weight ratio. Once aero effects come in to play, the more powerful car would actually accelerate harder than the weaker one, as weight becomes less important than drag as speeds rise.

Keith, do you happen to know the difference in Cd*A between a typical sportbike and a Miata? I know the coefficient of drag is higher with the bike because of the exposed rider and wheels, but when combined with the lower frontal area, I'm wondering how close the final result is.

I suspect the motorcycle is still better aerodynamically, since it can reach high speeds with less horsepower.

Interesting question. I don't know what the Cd of a bike is, but it certainly has a very small surface area relative to a car. I agree, it would seem that the overall drag is lower, given the top speeds of some of these sport bikes.

DanyloS wrote: Something I put together and posted a few months ago:

There is no way a stock 996 is 2900 lbs.

Including me at 200 lbs the power to weight ratio of my Lotus Elise (2110/300) should have been 7 lbs/1 hp and the power to weight ratio of my 996tt (3600/520) should have been 7 lbs/1 hp, however my 996tt ran 11.7 where my Elise ran 12.7. Power to weight ratio is interesting but torque and AWD add a lot to the equation, also having a realistic idea of your cars power is essential as the dyno and the drag strip are know to break men's hearts. I weigh my cars at truck weigh scales and the local garbage dump so the weight should be fairly accurate but my horsepower numbers could be wrong.

In reply to Cody_D:

Power to weight is less important as drag increases. so the power becomes a bigger factor than the weight as drag increases. The power of your 996 overcomes the drag better than your elise. (also, tell us more about this awesome elise! Is it 300hp @ wheels or crank? 2zz turbo? rotrex?)

carbon wrote: In reply to Cody_D: Power to weight is less important as drag increases. so the power becomes a bigger factor than the weight as drag increases. The power of your 996 overcomes the drag better than your elise. (also, tell us more about this awesome elise! Is it 300hp @ wheels or crank? 2zz turbo? rotrex?)

http://grassrootsmotorsports.com/forum/build-projects-and-project-cars/multi-project-thread-lotus-porsche-and-viper-oh-my/75408/page1/

It and the 996tt are no longer mine, I buy a car at a time and both of these ones are gone. I should say that my 300hp claim is unsubstantiated, I've just always called it 300hp as that is what the supercharger kit designer claims, likely the car is mid 200's. It was an Eaton M62 with water to air heat exchanger on a stock 2ZZ motor. I'm currently putting a TVS blower on a friends Exige 240 S which the kit manufacturer claims is good for 400hp, I am booking dyno time for it this month so we should see some actual numbers. Before he bought this kit he was running a Secant kit on it which I don't care for, I only managed to run a 13.7 with the car, before I modified my Elise I was running 14.5. I think the Exige will run 11's this summer.

I should add the trap speed for the Elise was 110mph and the 996tt was a little over 120mph, can't remember exactly. Just to throw some non modified times out there for our elevation (weights include me), I ran 13.8 with my NSX (3200/280), 14.5 with one of my 964's (3200/250), 13 flat with my SRT-10 Viper (3400/500) (surprised me), 10.4 with my R1 (600/180), 13.5 with my C63 (4200/450), 13 flat with my friends CTS-V with both of us in it (4400/560).

Sounds like you've had some kick@SS cars man! Keep up the good work.

carbon wrote: Sounds like you've had some kick@SS cars man! Keep up the good work.

Thanks, if I buy cars at the bottom of their depreciation cycle I can sell them the next year with little loss and try something different, I've been doing it for 8 years now.

I love the idea of power to weight as removing weight is usually a lot cheaper than adding power.

Cody_D wrote:

carbon wrote: Sounds like you've had some kick@SS cars man! Keep up the good work.

Thanks, if I buy cars at the bottom of their depreciation cycle I can sell them the next year with little loss and try something different, I've been doing it for 8 years now. I love the idea of power to weight as removing weight is usually a lot cheaper than adding power.

Does your state have vehicles sales tax, or do you just eat that cost/sell for more?

Here's a little chart I keep up with:

www.tinyurl.com/power2weight

OSULemon wrote: Does your state have vehicles sales tax, or do you just eat that cost/sell for more?

We only pay tax on used vehicles when buying from a dealership. I usually eat some losses just because I have no patience when selling and any modifications I have bought.

Warren v wrote: Here's a little chart I keep up with: www.tinyurl.com/power2weight

Very cool chart, one thing is the Enzo's weight is 50% of it's real weight on the chart.

I think it's funny that the only car i own out of that list is the last one. But i think thats because all of my faster cars have been built not bought and actually started out too slow/plain to make such a list.

In reply to Cody_D:

Thanks for the catch, must have been a typed-in-the-wrong-cell error. 1515 was XP-3s weight before we traded the wings for a passenger seat.

First on the subject of bike an average sportsbike has a CD of .50 which explains why many middle weight bikes run in the 10s but trap speed and top speeds are lower than one would expect. A perfect example is my dual sport Beta enduro, 265lb bike +140lb rider, 50 hp and 0-60 in 4.5 seconds (with knobbies!) but it would be very hard put to top 110mph, when you get up to around 80 you can tell it's really starting hit the aero wall. Same goes for my Datsun 1735lbs with me in it and 80 whp (round 100 bhp) coming off turn 2 at my local track it goes for 60 to 85 in about 100-150 yards but takes 200 yards to go from 85 to 95. As a comparison in my old D Sports Racer, 1016 lbs with me in it and powered by 175 hp Yamaha engine, at track days it would just out accelerate a stock Viper or Z06 but the car would do 135 mph tops........all that lovely aero that let you pull 3Gs on the brakes and over 2Gs cornering saps loads of power.

I'm a big fan of light cars but the reality is that as low as 60 mph you start paying for the lack of outright power.........I think shifter karts would be the best example of this.

 Tom