924Board.org

[Cbass]

I think the big thing being missed here, is that the weight reductions are not about acceleration. They are a cheap mod anyone with the time can do, for slightly increased performance in all areas of the car. If you can strip 150lbs out, by all means, do so! You will have a faster, better handling, better braking car! This is basic physics!

The 924 will never be a fast car with the NA 2.0 liter. This is just not feasable. Perhaps, if you had a stroker motor, with a 931 head, 12:1 compression pistons, a wild cam, and a stand alone engine management system, you could get somewhere near 200hp out of it. Perhaps. For the cost of these mods, you could buy a 951.

The other route to having a fast NA 924, is to swap in a big NA motor, as Porschev has.

[Peter]

Hi Teo,
I understand about elasticity. Thanks.

Cbass, dropping 150lbs gives you a faster 1/4 by a whopping 0.35 seconds! Not my idea of a faster car, but to each his own.
-Peter

[81turbo]

[quote]
On 2002-07-16 07:58, Cbass wrote:

The 924 will never be a fast car with the NA 2.0 liter. This is just not feasable. Perhaps, if you had a stroker motor, with a 931 head, 12:1 compression pistons, a wild cam, and a stand alone engine management system, you could get somewhere near 200hp out of it. Perhaps. For the cost of these mods, you could buy a 951.

Cbass I belive we are seing eye to eye here. These are the points that I have been trying to point out. I am by no means saying don't modify the 924. Heck I loved the car when I had one. That quote illustrates my points. bravo. -Ryan

one more thing The 931 is no blazing monster of speed but it is a big improvement on the regular 924.

[ This Message was edited by: 81turbo on 2002-07-16 09:14 ]

[Joes924]

I think 81turbos should lighten up, I enjoy cbass hes a very knowledgeable dude,
I dont know my is 2 cents all the mods I did to mine and making it lighter.. I could smoke a stock 924 till it caught up if it ever did. Theres a big gain in these things we do to our cars.

_________________
JoeD. 1979 924NA
MSD6 rev control/big bore TB/P&P.head
Bursche header/Schneider cam/dialcam


[ This Message was edited by: joes924 on 2002-07-16 15:13 ]

[Peter]

Just something I wanted to add. Many people stated that "a lighter car would be faster, that's basic physics, everybody knows that" in response to justifying removing 20lbs, 50lbs or 150lbs. When you actual apply these lbs to a program that converts rear wheel HP & chassis weight to 1/4 mile times, you see only a fraction of a second increase in 1/4 mile times. In fact, it takes a 200lbs reduction in the 924 to decrease its 1/4 mile time by nearly a full second. Yet it seems logical that any decrease in weight, even 1lb should produce a noticeable increase in 1/4 mile times. It should but it doesn't. Primary reason is that we are not physicists. Physics is a tricky subject and we attempt to apply the physics we use in everyday life to that of the automobile.
Let me give an example. Say you are at the gym doing a standing barbell curl with a 300lbs barbell ( wishful thinking). A reduction by 20lbs, 50lbs or 150lbs gives a noticeable improvement in your ability to lift it. Lighter weight is easier to lift. However, the greatest befit in weight reduction comes from the beginning of the movement to the mid point. From the mid point to the end of the movement leverage has taken over and you swing the weight up.
A car does not use leverage, but rather rotational movement. It always takes more energy to move the car the initial couple of feet than to keep the car going. For example, put your car in neutral (brakes off) and pull or push the car. Initially it's very hard. After it gets moving it becomes easier to keep the car moving at a constant speed and requires less energy to accelerate it. This is where our reasoning usually ends. We erroneously believe that if we dropped 20 -150 lbs from the car at this point, it will translate throughout the entire spectrum of the cars acceleration and therefore be a 1 to 1 relationship (i.e., decease in 1 pound = 1 mph increase in speed). This explains why people state that "a lighter car, even by 20lbs has got to be faster; that's plain physics." However, this is not the case. The energy requirements to maintain constant speed or to increase acceleration are not on a 1 to 1 basis with the initial energy required to move the car from a dead stop. This is why the calculations reveal that a 200lbs decrease in weight only gives you a 1 second decrease in 1/4 mile times.
In conclusion, although it seems contrary to us, every pound does not count; rather every 200lbs counts in reducing 924 weights to increase speed.
Teo, I think this is what you were getting at with your examples of 0-48mph times and 0-60 mph times and elasticity.
-Peter (beating the proverbial dead horse)

[Joes924]

Im tired to speaken of wheels though check this out.Why did I strip my interior???

https://www.discounttiredirect.com/secureindex.html

[ This Message was edited by: Joes924 on 2002-07-16 15:15 ]

[-nick]

do i really want to get into this...
[physicist mode on]

Peter you're getting things confused i think (or i'm getting confused). the basics are that the more massive an object is, the more resistive it is to acceleration. this is from Newton, and he was no dummy

what i hear people saying is pretty equivalent to this. you're example that it's easier to accelerate a car after it's already moving is where the problem is certainly a true statement. but you're adding in something about rotational inertia which i don't think is quite right. here's how it works for a car:

when a car accelerates it has to work against three separate forces: friction (from the wheel bearings and such), rotational inertia (from the wheels and any rotating parts), and air resistance.

the only difference between accelerating from rest and accelerating from motion is that your friction changes from static to kinetic. and kinetic friction will provide less drag than static friction.

the other forces:

rotational inertia: like i said this is present anytime you accelerate. removing weight from rotational parts _can_ have a profound effect on acceleration. this is because the force equation is not simply the good old F=ma. the force equation of rotational inertia includes Coriolis, transverse, and centrifugal forces that make things very complicated (and confusing).

and then there is air resistance which is not a function of mass at all. this force increases the faster you go (it is roughly proportional to the square of your speed).

so where does this leave us? well if we're not talking about removing rotational mass then we can treat a car as a point mass. so we can use F=ma. if 'm' decreases and 'F' stays constant (where 'F' is the force the engine is providing) then 'a' will increase. ta-da. it's just that easy! or course we're not adding in our other forces of friction, rotational inertia, and air resistance, but it really doesn't make any difference if you're just comparing unsprung weight.

when you decrease weight from a car your acceleration times will decrease. it doesn't matter if you empty the pennies out of your ashtray or build a carbon fiber engine (there's one for you...). if you're using a program that tells you otherwise then the program is wrong. (yikes! how's that for uncompromising).

i hope this is at least helpful, or has convinced you whether or not to pursue the field of physics

-nick

[Body Shop Rob]

I don't care about 1/4 mile times. I don't care about top speed.I care about getting around that semi truck that has stuff hanging off of it on the highway. I care about avoiding women in SUV's who are on the cell phone who blindly drift into my lane. I care about getting by elderly people who can't hear or see but still drive.
Its those split second moments that you either punch it or not, that I care about. Being able to pull away quickly and safely IN EVERY GEAR is more important than any 1/4 mile time. Weight reduction makes the 924 a quicker car in those moments that really count.

BSR

[tmb-racing]

Wasn't there a post awhile back asking what everyone's average age was? Somepeople need to start acting like it.I rarely post on the board but feel compelled to do so.I feel alot of people hear give bad advice or comments.Would I publicly humiliate them? No. Was the carrera GT replica on ebay last month a ultra rare pre-production test mule from the factory that just happened to be built years before any thought was given to racing a 924 by the factory as suggested by someone on this board? OF course not! The truth of the matter is for how much sifting thru this site I have to do to get past all the BS every once in a while I find something of interest. I have sold parts from this site. I have found parts off of this site.I have made friend's off this site.Do I think a franco cam gear is going to give me 944 performance? No-but I do appreciate knowing that it exists and is an option for me to buy at my own risk.924S muffler on a normal 924 for horsepower? Interesting? You bet!It is an option.No one here is God or the website police-if you believe everything you read- you are an idiot.I quite frankly disagree with almost everyone here on any given subject.But usually everyone has a little tidbit thrown out somewhere that is worth a second thought.No one needs to be blasted for sharing an opinion which is what 99% of this forum is.To say the 931 is the best car is an opinion.I personally believe the 924S is the best 924 until you get to maintenance costs-how can you argue it is not? There is a reason Porsche made the 931 for just 2 year's.Yes I like 931's. As far as the whole weight thing-Why do they make the winners of the speedvision touring races add ballast when they win.10 bag's of sugar does make a differnce folk's! Would I strip out a street car like my road race car? NO! Noisy-hot-and a few other inconveniences but does that mean someone else should not? That is not for me to decide.I can only offer my OPINION.I see both sides of the argument guy's but if you don't have something nice to say-keep your mouth shut.It makes it easier to sift thru and find the good stuff this site has to offer!
Andrew


1 of 100 M471 Sebring car's
1 of 1288?? Sebring 79's
69 911T
73 914
96 Volksmonster Jetta

[Joes924]

Body-shop Rob by any chance have you been driven in my town you nailed it to a Tee and tmb besides noisy,hot you forgot about smelly
[oil and gas fumes].

[Cbass]

Thank you TMB, that's the message I was trying to convey in an earlier post...

Let's not forget, that acceleration is not the only benefit of weight reduction. Rather, any acceleration gain will be the smallest performance improvement from a weight reduction. The handling, braking, and fuel economy will be affected more than the acceleration.

[eturbo924]

Some where in this large post some one must have said this but, reducing the weight by say 100 pounds in a car with 2600lbs and 110hp will make a much larger difference than in a car with say 3400lbs and 300 hp. The car with less hp would benefit greatly from reduced weight. Hasn't anyone here ever run a race... oops but not on the road.... with a passenger in the car.... and then with out some one in the car... other than driver of course. My car has always seen a very large impact with passengers in the car. I have not seen this with as much effect in a Carrera or 928 as in my 924. With such a small amount of hp the weight makes a big difference. Be it initial movement or quickness or not. I can feel the differnce. Now noting that I have not stripped my interior or much of anything else. I have not replaced the hood insulation since my paint job and also take out the spare tire, jack, tools and rear hatch mat if I think I might have a go. It makes a difference.... do I think my car is a 1/4 mile monster.... hahah NOPE. DO I think it is much faster than it was from the factory....yes. I have done the typicle head work and such to add to some minor weight reductions. Just wanted a bit more that is all.

Peace every one.

Eric

[larso]

[larso]

[larso]