Cobra weight distributions?

[RET_COP]

Can someone give me some information on Cobra weight distributions CG and so on with a SBF. I know there are alot of variables from different combination's and Cobra manufactures, I'm looking for front to back percentages, Center of gravity heights and locations etc.
I thought the cobra had close to 50/50 but when I think about how the spring weight ratings differ from front to back how can that be? Is the CG at the transmission near the top if it? Where is the 50/50 line?
I know your wondering " why does he want to know this"? but I never read any in depth discussions on this matter and I am curious?
OK the real story started when I had a discussion with my buddy who raced circle track tour Modifieds for some time. We were talking about spring weight ratings and rebound and compression on some shocks I was thinking about buying. It got deep and I was at a loss to answer some of his questions. I'd like to go back with some answers for a nice winter conversation over some beers.
Thanks
Lou

[Tommy]

My Everett-Morrison. Corvette suspension, 351W based Cobra was originally built as a dedicated SCCA racer. As such it was equipped with a lighter weight body than most EMs. It also lacked most accessories (e.g., no hood and trunk hinges, no windshield wipers, no carpet, etc.). About five years ago I disassembled and rebuilt the car to my taste. I added a few amentities (e.g., carpet and a racing seat) and I also moved things that could be moved to lower and redistribute the weight better. When I finished, the front/rear bias with half a tank of gas and me in the car is 52% front / 48% rear. I do not know the height of the CG, but my WAG is that it is about 21", or about 7.5" higher than the center of my wheels. .. For your analysis, keep in mind that my car may not be typical of many other Cobra kits.

[Tommy]

Lou,
If you haven't seen the info on this website, it might help in your next conversation with your buddy:
http://www.longacreracing.com/articles/index.asp

[RET_COP]

Thanks Tom on that very informative link. This spring I'll get my car to my buddies scales.
How mush does your EM weigh?
Lou

[Tommy]

Lou,
With me and a half tank of gas in it, it weighs about 2450. BTW, I mispoke in my earlier post. My weight distribution is 48% front / 52 % rear.

[RICK LAKE]

RET_COP Lou every car company builds there own frame and body. The best thing I can let you is to start with the spring rates the company comes up with when they sell the kit. After everything is togeather, all the fluids full, half tank of fuel in the car, battery in the r/r corner of the trunk, get the car weighted with you in it. Have a wheel alignment done after ride height is set and weights are done both diagonally and front to back. If you are rally serious have the bumpsteer also done so that both front wheels are turning the same radius. After this you need time on the drives seat and take pictures of the car going around turns, right to left weight transfers, see how much the car leans around shape turns. Fromt here you go to stiffer springs about a 30% rate increase over the ones that came with the car, better shocks like QA1 with dual control for compression and rebound. Your street setup will not work well on the track. You will also take a beating running a track setup on the street. Getting your self a Kirkey road racing seat will help alot by not having to hold your weight in place when driving hard. If you are going to track the car, 2 important things to look into
#1 pay a 2 or 3 quart accusump and have it hooked into the oiling system. this will prevent lossing oil pressure around high "G" turns. Also work great as a preluber for starting the motor.
#2 add 1 extra quart of oil to the motor for the same problem of high speed turn and oil not going back into the oil pan fast enough having the pickup uncovered and have the oil pump sucking air. This will not do any damage to the motor. There are a couple of suspension books to look at. I good driving school is another thing to look into. IF you have any guys around where you live that are into dirt track racing, they have scales and know alot about seting up cars and suspension ideas. There is about a 50/50 about weather to go with higher rated springs and small sway bars and the other idea is larger sway bars and lite spring rates. The angle of the coil over springs has somnethings to deal with too. Rick L.

[Dwight]

I have a 302 fuel injected motor in a Lone Star Cobra. I mounted my motor back in the car so my weight on the rear would be better.
I scaled mine at the local co-op on their drive on truck scale. I know it's not the best place to weight a car.

I drove the front wheels onto the scale, then the whole car and then the back half. Did the math and came up with 52% rear and 48% front with half tank of gas.

car 2315 lbs

with full tank and me 2660 Lbs

Dwight

[RET_COP]

Rick,Dwight thanks for the posts.
So three cobras
Front/Rear with driver
Tom 48/52
Rick 49/51
Dwight 48/52

Being that the driver sits behind the center of the car F[0"------90"]R dashboard is about the center 45" and driver butt is about 70" these cars are built about 50/50 without driver.
Is 50/50 optimal?
I think of a car like the GT40. with the mid engine, it must have been rear heavy yet I read where it cornered great
Lou

[olddog]

I have an A&C with a 5.0/347 stroker - aluminum heads and intake.

Full tank of gas no one in the car -- 2370 lb.

Rear wheels on the same scale the same day (no one in the car) 1200 lb.

That calculates to 1170 lb on the front wheels -- not measured.

[Tommy]

Lou,
It's not wise to make generalizations about the handling of a car based on something as simple as weight distribution, but here are a few thoughts about the GT40. For accelerating, the more weight on the drive wheels (rear in this case), the better. When braking, the effective weight transfer to the front means a car with more weight on the rear will become more balanced under braking. And for a car with significant aero downforce, that force can be used to balance the actual weight of the car when cornering at speed.

[STL Mark]

Superformance MKIII stock suspension, with BBFord 460 stroker, TKO600, full tank of gas and driver (me) at 220 lbs. Weight about 2900 lbs.

50/50 front to back - dead on.
Plus - 50/50 side to side - dead on.

Just sayin. Stock suspension, good install.

[RET_COP]

I see where your coming from Tom. There is alot to Road Racing, I'll get it in time. Thanks for your help and knowledge.
Lou

[Dominik]

50/50
2200 lbs car, with driver.

The difference in spring rates, amongst others, can be attributed to different motion ratios (distance from damper mounting points in front are typically different to rear, as well as angles).

Ride comfort is typically dictated by front coil (rate).

[scottj]

Originally Posted by RET_COP

Rick,Dwight thanks for the posts.
So three cobras
Front/Rear with driver
Tom 48/52
Rick 49/51
Dwight 48/52

Being that the driver sits behind the center of the car F[0"------90"]R dashboard is about the center 45" and driver butt is about 70" these cars are built about 50/50 without driver.
Is 50/50 optimal?
I think of a car like the GT40. with the mid engine, it must have been rear heavy yet I read where it cornered great
Lou

Mine is 45F/55R w/driver and 10 gallons of gas. I can get 57R with a full load of fuel. The driver accounted for +1% rear...

Scott

[vector1]

Originally Posted by STL Mark

Superformance MKIII stock suspension, with BBFord 460 stroker, TKO600, full tank of gas and driver (me) at 220 lbs. Weight about 2900 lbs.

50/50 front to back - dead on.
Plus - 50/50 side to side - dead on.

Just sayin. Stock suspension, good install.

how do you get 50/50 side to side--with driver?

[mickmate]

Offset the drivetrain to the passenger side. It also helps line up the driveshaft with the offset pinion flange.

[mdross1]

My CMC Cobra 460 powered after having it scaled found at that time with iron heads intake and water pump was 52 front 48 rear.Now everything is alumium.

[Ron61]

When I had mine with the small block, after putting it on the scales and making adjustments I had almost a 50/50 distribution. But it would be closer to call it 51 front and 49 back. I set the engine back about an inch and lowered it just a little.

Ron

[scottj]

Originally Posted by vector1

how do you get 50/50 side to side--with driver?

I'd like to hear how that's accomplished also. Regarding install... I built my car from the frame up on a set of Longacre scale pad levelers. First to insure I was always working on a level plane and second so that I was constantly informed of weight distribution when placing components. With the tight clearances in the engine compartment and trans tunnel, I was able to offset my motor 1" to the right and that was only made possible by fabbing my own headers. I also have the drysump tank and battery inline with the RS tires. The P/S tank and all the lines and cables are on the right side as well. With the driver at 160lbs, I'm LS heavy by 40lb.

[Ron61]

It could be done with lead weight like the NASCAR cars use. Move the weights until they counter balance the drivers weight. I tried to find my book that has all of the pictures and explanations of how to balance a car for road racing but I must have let it go when I sold my Cobra. It came with the dyno program that I had back then which was the same one that NASCAR and the NHRA used. It cost quite a bit but it was extremely accurate so long as you got the figures for everything right.

Ron