I think this is the right forum!

I got my restoration kit from Chevy, and in it there are lists of the base cars front and back weights, and then every option available and the amount it affects the weight.

Well, I came up with these #'s:

Front: 2063.1 lbs
Back: 1405.1 lbs

I know it's best to have a 50/50 setup... so what can I do to compensate? A 600 pound sound system in the back?

 

how drastic and how much money do you want to spend, money is really the key, put an all aluminum engine in, take out ac, aluminum radiator, fiberglass front end, battery to the back ,you can go as far as fiberglass doors, and lexan windows and lighweight rims.take out all the interior all the dash and make your own dash, prolly aluminum engine and aluminum radiator and no ac should help loose about 150 -200 lbs.and then the battery is some wieght.

 

Just stick with the simple things. A nice aluminum radiator and aluminum heads go a long way. Relocating the battery is another good option. Other than that do not sweat it. As long as you build your suspension correctly you won't feel the difference that much. My car hadles awesome and I could care less of the front to rear ratio. To much to worry about for a street driven car.

 

I would like to try to get mine a little bit closer. I think im gonna go with an aluminum radiator,water pump,heads,removed ac,might even remove the heater all together,removing emmisions,fiberglass hood, might put the battery where the back seat was. Anything else i dont want lexan windows or fiber glass front end none of that. I get the bottom end of the engine in 2 weeks.
Oh yeh when spohn comes out with the tubular k member i might get that also should be close with all that.

 

My car with 3\4 tank of gas is as follows;

Total: 3280lbs

Edit: 3460 with driver in car. Following wheel weights include driver.

Front: 1864lbs 53.7%

Rear: 1596 46.2%

Aluminium heads, Aluminium WP, Aluminium intake, Glass hood and battery relocated to trunk. No A\C...carbed car.

PS: Full 12 point cage in car.

Don't rely on printed literature. Rough guide only. Scale the car using some proper racing scales if possible.

 

Put the battery in the right spare tire well. The further back the better. Plus it helps load the right rear tire and offsets the drivers weight. Simple enough to build a bracket to mount battery.

 

Sounds like a good idea but for handling dont u want most the weight in the center.

 

I know that Jeg's has tubular K-members for 82-92 3rd gens for about $400, but I'll have to look and see who it's made by.

It says it knocks off about 30 pounds, and accepts all the stock hookups and such.

 

Yea you do but a little weight there won't throw the car that much out of balance.

 

In one word...No. You have to get as much weight to the rear as possible. Moving the battery 15 feet to the rear is equivalent to moving the engine back about six inches. Guess which is easier.

Front engine rear wheel drive cars are high polar moment of inertia cars. There is little that you can do to eliminate that. Nor would you necesarily want to.

Have a look at current Road Racing cars such as the ALMS Corvettes driven by Ron Fellows and Johnny O'Connell, or a current TransAm\GT1 car . Every thing possible is done to move weight to the rear... Battery, Fuel cell, Dry sump oil tanks, pumps, PS pump driven off transaxle and in the case of the C5 ALMS Vettes, even the gearbox is now located in the transaxle...not behind the engine. The result is a Front to rear weight ratio near 40% front and 60% rear.

F1 cars are also around 40% front and 60% rear. Interestingly F1 cars are built below the minimum weight rule and are ballasted with Tungsten ( Very heavy ) slugs. These slugs are usually placed as far forward as possible to tune the chassis for handling.

The low polar moment inertia idea is fine...in theory However you will find that most Road Racing cars actually have to spread the polar moment apart...to lessen the sensitivity of the chassis. At high speeds a low polar moment of inertia car becomes too twitchy for the driver to handle. Autocross is one area that a low-polar moment can be benefitial...but it is out weighed ( Good pun ) by the benefits of moving weight rearward in our cars.

This is all relative of course. An F1 car has a much lower polar moment of inertia than a Trans-AM car or GT1\ALMS Vette, however, an F1 car has a much more sophisticated suspension, much, much lighter weight and huge downforce. All that downforce aids stability which offsets the instability caused by a low polar moment of inertia.

One other mitigating factor on re-locating the battery....most sanctioning bodies prohibit having a battery located in the passenger compartment for safety reasons.

 

I was just goin by a post that agood3.1 wrote he said the more weight in the center the better. Also had a theory behind it.

 

Yep..and I'm familiar with the post. Theory is correct and Agood2.8 knows his stuff...but the main denominator is that you have to maximise what you have. And we have high polar moment of inertia cars with too much weight ( relatively speaking ) on the front end.

Getting weight off the front of the car takes priority over any slight gains in polar moment of inertia. Low polar mont of inertia street cars can be very, very tricky to drive. IE: early Toyota MR2's. Nearly 50\50weight split...low polar moment...and will spin at the drop of a hat if not driven correctly. Formula Fords are another good example. Low Polar moment...no stabilising downforce...and will spin very quickly if you get them out of shape.

Think of it like a current day fighter plane plane such as the F-35 JSF or the F-22 Raptor, compared to earlier varients such as the F-14 or 15. The latest planes are built so that they are flight unstable ( very low polar moment of inertia combined with aero instabilities ). They rely on constant computer corrections to maintain stable flight. The advantage is that in combat manuevers they will change direction far faster tha a higher polar momt of inertia aircraft, such as the F-14 and F-15. However...they are impossible to fly with out computer assistance.

This is all greatly simplifled of course, aero configuration plays a big part...but the principle is the same.

If you really want to get a migraine...pick up the Febuary issue of Race Car Engineering. Has a new mathematical view of yaw moments ( stable yaw moments vs unstable yaw moments ) that is causing quite a stir in the racing community...Particularily F1....even some of the Nascar boys are looking at it now.

Makes for some mighty interesting reading.

 

wow... you really know a lot about handling! thanks, I think I know what I have to do. Spend $! lol

 

Hey i learned today that weight in the back makes a big difference on hookin up lol. I had 250 lb friend that sat in the back and damn it would hardly spin at all just hooked.

 

Agood2.8 is into autocross. That is a low-speed, very sharp turn kind of thing. Not at all the same as road racing. That was one of the things that got him banned; he didn't understand how specialized his knowledge was, and how little application it has to anything other than that narrow, non-real-world specialty.

Imagine chasing a baby around a dining room, under all the tables and chairs... I don't know if you've ever had a baby, and I don't know how strong or agile you are; but I guarantee you, no matter how goo dof shape you're in, that 14-month-old will kick your mortal buttocks at that game. That's about what autocross is like. That's why Miatas and Mini Coopers are unbeatable in auotcrossing, even though on real streets they're just ordinary cars.

Road racing, F1 or T/A style, is something completely else. The car has to be tuned for stability and predictability, not just raw agility.

 

1864+1596=3460lbs Not 3280lbs

My car is
1760+1485=3245lbs

Jerry

 

Oooops...those figures were with driver in car. Car weighs 3460 with me in it. Subtract 180lbs for driver = 3280.

 

Just to open your eyes alittle.
http://www.cardomain.com/memberpage/518752/4

He also owns a Mini Cooper. bottom of page
http://www.cardomain.com/memberpage/518752/3

 

Theoretically the best way to place weight effectively in a 4 wheel vehicle is having it as low as possible in the senter of the car (strip from front to rear) with no weight protruding in front of the front tires or behind the rear tires. Think Indy/Formula 1 cars.

Of course this is impossible in any street car - an accident would ruin things very quickly without any real protection. But you can apply the ideas to a street car in a predictable manner. Remove anything in front of the front axle and behind the reat axle (or lighten up the pieces). Any parts high in the car should be either replaced, move down, or removed. Any weight removal should be done with durability in mind - a track made aluminum wheel will be turned into a wreck over potholes. You should move the battery to the center of the trunk area, not to the spare tire well - to balance out the extra mass in the rear.

 

paul,

that is a great theory when you are just trying to change directions as fast as you can, when you are dealing with high speeds like on a road course, or in chickenmans case, hill climbs. you need to have the car stable, and predictable, when you start dealing with 120mph + speeds, very small steering inputs = very fast and changes. this is why chickenman is saying the ability for it to make those sudden changes isn't so important as balance is. in road racing you are making very smooth, very precise changes in direction, and relative high speeds, in auto-x you are at very low speeds, and making very quick, radical changes in direction. the priority of what you are looking for changes.

 

Correcto mundo Dewey... one other thing to consider...and some of you straight liners may want to try this as well.

All of the really fast Hillclimbers and Autocrossers always run with a full gas tank. Even in a Hillclimb...hauling all of that extra weight up the hill, is more than offset by the extra traction gained exiting the corners. Big HP, RWD cars need as much weght as possible over the rear wheels in order to put the power down without spinning the tires.

#1 rule in racing. He who puts the most power down First .....WINS.

I Autocross...Hillclimb and Road race. Looking at any of the top line Front Engine RWD Autocross cars ( Prepared and Modified classes ) or Road Racing cars. You will always find the battery ( and everything else that can be legally moved ) as far to the rear as possible. Balancing the car weight and getting as much weight over the rear wheel as possible takes precedance over ANY slight decreases in Polar Moment. Even in Autocross at low speeds....this is true.

BTW...regarding F cars....until very recently, F1 designers were putting Tunsten ballast in the front wings of the cars in order to balance them. As far ahead of the front wheels as possible. That practise was quickly banned by the FIA, due to safety concerns should a wing go flying off in an accident. But it illustrates the importance of achieving overall chassis balance and stabilty over any reductions in Polar Moment.

 

What you are all overlooking is "rules". Those cars are all governed by rules. It has been proven that an indy car can run much faster than it does when not under rule resrictions. Mario Andretti proved this by coincidence (they were not intentionally trying) in a documentary he and his son were filming. They outfitted one of his older chssis with a heavy carmera unit and he ran with Michael as they documented the next years new chassis debugging. With the weight rule restriction on the older chassis not an concern, they were able to retrofit the weight bias of the older chassis anyway they pleased to incorperate the camera equipment- it turned out that the Michaels new season car could not touch the unrestricted older Mario car. (they striped the car completely of excess weight before fitting the camera- then end result with camera was still much lighter.

F1 cars the same are restricted to downforce angle limitations as well as tire widths and tread pattren front to rear to keep things slower. If they could, they would strip the Tungen weight altogether and balance the chassis entirely differently other than polar weight over the front.

If you can strip the weight and remain legal, then strip it- mostly at high speed banked tracks were you will suffer less from spring compression in banked forces. The less weight you run, the less the change in compression at speed compared to the slower sections of track, the more consistent the chassis will feel at all speeds.

D

Ps- you guys are being way to critical on a heavy car that will never suffer from a lack of so called "low polar weight". You move that battery to the back and the car will continue to turn on the yaw axis and cause tration break sooner than you would with it in the center of the car. That will cause you to loose tration- equally cancelling out any gain in straight line traction you might gain from the extra rear weight- also while additionaly sliding the car loose sideways more unwantedly. Drag race acceleration yes, cornering acceleration no- move it to the center of the car.

 

Sorry we disagree... Balance is the key. Polar Moment is of secondary consideration to overall car balance. You are wrong about the battery causing an yaw condition. It just doesn't happen in reall life. Same situation as running with a full gas tank. The increase in traction given by the increase in grip created by extra weight over the rear tires EXCEEDS the extra centrifigal forces created by the added mass at the rear of the vehicle. This is a basic tire engineering fact...well utilised in the racing world...but seldom understood by the layman.

You've got to look at the BIG Picture..which is: Our cars ( and Most Front engine RWD cars ad -nauseum ) are too heavy in the front and too light in the back. ANTHING that you do to move weight off the front and transfer that same weight to the back will help the balance of the car and bring lap times down. That is the main point...and ONLY point to consider.

Theories are fine...as long as you understand them.... you can't just pick and choose which theory you want to define....vehicle dynamics is a very,very complex isssue, There are hundreds of variables. Polar moment is only one variable...and a small one when dealing with cars of our size. That is critical to understand.

The only truth is to do whatever it takes to make the car faster...


I've seen enough Pro Road Racing cars ( and worked on enough ) to know the trade offs. I've also done enough testing ( over 25 years ), to know what works and what doesn't. Battery in the back spare tire well works ( on our cars ). Battery beside driver in Passenger seat doesn't... Been there...Done that already. I can also feel the difference 25 lbs less fuel in the car makes in the car.....my bum is very sensitive LOL.

 

ware are you guys weighing your cars like that at....

 

Intercomp Digital Scales. Longacre and Rebco are also make digital car scales.

Pitstop USA

I will be corner balancing my car this weekend for the Seasons first test and tune. I'll post figures later.

 

the other thing that you are not taking into account is the driving of the car, slow in fast out...

if you are driving properly, the back-end coming out should only be a concern when you start to apply power, assuming that is when you are worried about the car becoming unsettled forward traction becomes a big deal.

like chickenman said, this is a complex issue, there are ALOT of variables, and the rear geomitry becomes a huge issue here, too little weight transfer, it is hard to put the power down, too much and you have issues under braking, and transisitions. i guess it comes down to what you are looking for, in my book i will take a 50/50 distrabution with "high polar-weight" over a 70/30 car with "low polar-weight".

 

im kinda waiting on spohns k member and A arms...

between thoes, alum heads and a few other things, i want to see the weight diff.... if it can take 300# or more off the nose of the car, i'll do it... and if it cant, i wont.


in anycase, the better answer is not to shift weight, its to remove it.. if the front is too heavy, remove stuff from the front.

i was sure someone would have already said that yesterday when i read this thread, but i just re skimmed it know, and i didnt see anyone mention it.. athough halfpint kinda did by mentioning they removed the ballast in the indy car...

 

to a point, you want less weight. BUT there are things youc can't get rid of. you need an engine, you need a battery, you need fluids, you can't get rid of those things. the only option here is to relocate them to a better location, the argument here is were that location is.

 

alum engine/ (block intake heads whatever) , dynabatt battery, ect.....


lol, yea i got that point, i was just talking about the flip side..

 

Anyhoo...another good discussion. Got the old minds a thinkin'...and that is the whole idea.

 

My head feels kinda warm after reading this.. Good stuff soaking in tho.
So did you ever get those figures?