Brettus

iTrader: (2)

I agree with 4 yrs . Your car could weigh 10 pounds and it would still have an almost identical top speed as the 3200 pound car . Weight is not a factor with top speed only air and rolling resistance .
And rolling resistance will only be very slightly more on a heavier car

staticlag

So your telling me that a car with a weed-eater engine that weighs 3200 lbs is going to have the same top speed as a car that weighs 10lbs with the same engine?

Brettus

iTrader: (2)

if it had the same rolling resistance then yes . However - at that power level the relatively (relative to how much power there is) large difference in rolling resistance will make quite a difference .

Brettus

iTrader: (2)

I should not have used the 10 pound figure as weight will obviously affect rolling resistance . Was just trying to make the point that weight is not a big factor when it comes to top speed .....

JB_Rotary

I think I understand what you are saying. In a top speed environment (140mph+) Actual power greatly exceeds weight in terms of just how fast you can go. the difference between a 160 mph car and a 170mph car can be as much as 200hp just to overcome rolling and air resistance. Regaudless of weight. It's the diffeerence between 'get up and go' and 'going faster'. Yes a lighter anyhting will have better pick up but once at speed (especially high speed) weight becomes less of an issue and things like air/rolling resistance become the issues.

staticlag

well, its pretty easy to see when we look at gravity as our force.

Imagine two objects falling(due to gravity) in a vacuum. One of them is a feather, the other is a bowling ball. Which will hit the ground first?

The answer is both because without air resistance the outside force (gravity) will affect both objects the same reguardless of total mass.

Same thing as for a car. Both of them have the same engines giving the same force so they should have the same top speed.

staticlag

However, practically, increasing the mass on an object such as a car will increase the friction that the bearings and tires will experince and will limit the top speed accordingly.

Brettus

iTrader: (2)

agreed - but increasing the mass by 10% might only increase the rolling resistance by 0.1%(guess) and the top speed difference will be negligable

JB_Rotary

the faster you go it becomes almost exponential how much power you need to go faster

speeddemon32

I can see this going around and around.....

I am not going to fight it much. this was not even the point of the thread anyways.

but its simple yet complex. but simply put, weight, power and drag, all play key. assuming all things being equal, you have a car the weighs less then the other and the one that weighs less will out perform the one that weighs more in every aspect. acceleration, top speed, handling and braking.

the focus on the last few post was weather or not one car with a top speed of say 160 would have a higher top speed if you took say 500 pounds out of it.... (of course assuming the limit was NOT gear ratio)

I say yes, you have more power on tap to fight the resistance.




ok, so you have an RX-8 that will top out at 160 MPH in stock form. you don’t change a thing, but you put a 1000 pounds in the car. now we all agree that the acceleration, handling and braking will be severally affected negatively right? (good, cause if not we have a real problem) but do you think that the car will still top out at 160? no way. the car is just to heavy for that power. the engine could no longer fight the weight of the car AND air resistance. at 120 (?) the air resistance would become to great. (Disclaimer: 120 is a guess... but probibly close)

well same thing the other way. You got a car that tops out at 160, you take off weight, and you then have more power on tap to fight the air resistance rather then the weight of the car itsself.


Now with that being said, will 50 pounds help top speed…. Not really, it would take more then that. But still. A car that weighs less will be better in every way, shape and form.

the original question in mind was NOT top speed… how did it even go that way anyways?

Brettus

iTrader: (2)

my guess would be 155-158 . it really won't make that much of a difference to top speed .

max5roadster

Now factor in the likely event that your car will experience "lift" created by the air resistance and gravity will not behave the same... i.e. rolling resistance will vary.

Brettus

iTrader: (2)

An easy way to test would be to put 3 big fat fellas in the car and take it up to full speed - take them out then try again .
Any volunteers ? heh

TrochoidMagic

i don't need this book... but its still a fun read when compared to reading automotive textbooks, and its highly recommended regardless of your outlook on this subject.

"how to make your car handle" by fred puhn.

once that book is read, then those who still thinks weight is not a contributor of performance... well, what can you do?
there are always gonna be the few of us who buy performance parts, only to cancel out the performance with heavy sound system. let them waste their money...its not mine. just my 0.2 cents.

TrochoidMagic

*sigh* speed, why bother? i give up.
thanks for agreeing with me though. i think we both know the answer as to how weight mmay/does affect top speed. or even ease of achieving top speed.
that said, i think my pulley is a cheap mod for the performance. the best $ spent and the wisest.

what pulley you're running? any tips on what you personally like to use for your autox car?

see, smile guys. lets change the subject, or purely just focus on the subject...

o and btw, lighter parts will help save gas there, i still said it.

speeddemon32

none the less your still agreeing with me.

this topic was not how much it will help, but someone said that it will not help no matter what, weight does not effect top speed.... and that’s wrong.

either case, both my number and your number was a guess. but we both agree it will make a difference. that was my point.

I was the first one to say, "at top speed will 50 pounds make enough of a difference..... no, not on a street car". i mean come on, how often do you hit top speed in your daily driver. once maybe? but if you were a top speed racer at a track like the Bonneville salt flats, you WOULD be concerned about weight because it WOULD effect top speed..... period.




I find it funny that this is what we are arguing considering top speed was not even magic's intentions. he is trying to improve acceleration, handling, and braking. all of which we ALL know is greatly improved with the loss of weight.


and just for the record again, would I personally stress the 15 pound stock radio and speakers in my daily driver... no freakin way. a street car is a street car, a race car is a race car.

I DO think there are mods worth doing on a street car that can give you performance AND not have a down fall. Pulleys, Flywheel, light wheels, intake, exhaust, etc. no real down fall to these mods and it makes you feel like you have a faster RX-8 then the stock RX-8 sitting next to you at the stop light.

speeddemon32

I went with the UR pulley. the reason I went with that one is because I wanted to keep A/C... see again, on a street car, even one I autocross, I was not willing to give up A/C when there is a happy medium. I was able to keep the A/C and still loose some weight off the rotating mass. (plus underdriven)



as for what I liked to use on my auto cross 8. here is what I had. keep in mind I ran BSP. what class you run determines what you can do.

Koni Yellow struts
Sprint springs
RB sways
K&N intake
UR pulleys
ACT prolite flyheel
RB flash
Enkei RPF1 18x9.5" wheels
Kumho Ecsta V710 R compund tires 285/30/18
drilled and sloted rotors and other small stuff that didnt really do anything.

TrochoidMagic

[QUOTE=speeddemon32;2245243]none the less your still agreeing with me.

I find it funny that this is what we are arguing considering top speed was not even magic's intentions. he is trying to improve acceleration, handling, and braking. all of which we ALL know is greatly improved with the loss of weight.





actually...i think this was an argument based on HP and/or MPG savings from pulleys...but then it turned to lightweight parts flywheels/ wheels/ car, etc.

TrochoidMagic

thats what he stated... however, its really not like i can "actually" prove him wrong. a pulley is such a minor piece and can only contribute such small gain. but its the same reason why mazda gone with light weight aluminum rotors in the renesis. its the same concept...and thats how you get more HP and MPG at the same time...its what i've been saying over and over again. top speed or not, even if weight does affect a role in top speed...in which case i agree with demon that it does.

weight from rotating parts, static parts and any other can contribute to mpg savings and probable horsepower gain...or the less use of horsepower to accel and maintain speed.

^^how's that for rephrasing? lightweight parts are still there to perform a function.

BoosTED

iTrader: (2)

Let me rephrase to clarify my original point: I have not seen a MPG increase since having the UR pulleys installed.

I like my pulleys and endorse them but like I said I had never seen or heard of a MPG increase on the RX-8 with lighter or underdriven pulleys.


I was hoping you would understand my other point that quick is different than fast but it was overlooked. I will stop trying to explain because I am not looking for an arguement. Besides you probably know better than me anyways.

The rotors on the engine are not aluminum.

The rotors on the brakes are not aluminum either.

The rotor housings are.

Razz1

Let's get back to pullies and not areodynamics, MPG etc..

BoosTED

iTrader: (2)

Is pulleys spelled pullies or pulleys?



I finally spell checked it even though I am sure I have spelled it both ways.

Microsoft says the correct spelling is "pulleys"

Enjorren

http://www.vividracing.com

Has the Agency Power 3 pulley set with belts for $143.00

Picking mine up on Monday as this is a smokin deal.

You have to call them though as the website is misleading.

d j

I believe that's only for the e-shaft pulley + belts. AP never produced alt & H2O pump pulleys, unless that's a new product that they're offering...

Enjorren

Scratch that the guy I talked to didn't know what he was talking about. Since the crank pulley is techincally two pieces stock it makes it seem like the AP pulley is two pulleys.