LS Coupe on the scales

[mmarshall]

I finally found the time to set up our club's Intercomp scales to find out what all my work did for me. I still had my R-comps on from the last race so the numbers are a little skewed as the race tires are 11.5 lbs each lighter than my street tires.

Here are the new numbers vs old:
Total weight: 2260 vs 2427
F/R % 48.9F/51.1R vs 45.8F/54.2R
L/R % 49.6L/50.4R vs 49.7L/50.3R

New numbers were taken with no driver, no gas (trying to ensure I can't bust my minimum weight limit for XP), and race tires. This simulates a worst case senario of rolling into the pits and onto the scales at a national event low on gas. With the 5.7L LS1 my minimum weight limit for XP is 2226 lbs. This means I have a 30 lb buffer as I roll into impound even with no fuel.

It appears my efforts were sucessful in shifting weight towards to 50/50 goal and the weight loss is right on target. I plan to lose a little more weight and use a reasonable fuel load to "make weight". While the 3% weight shift did not totally cure my oversteer issues, the car does feel much better balanced and will be faster once I adapt to the new feel.

[mmarshall]

I got the cross weights all set now. I ended up at 50/50.

LF/RR 1221 lbs
RF/LR 1216 lbs

I went 1/2 turn on all 4 corners to get it set. I calculated that on Konis 1/2 turn on each shock changes the cross weights by about .4%. I 1st did the RF/LR (1/2 turn each tighter) and the cross weights changed by .8% in the right direction. I then did the LF/RR 1/2 turn looser and it changed by another .8%. Just a good rule of thumb we can use in the future!

Comparing the weights to the scaling we did last year I took 150 lbs off the car which nearly all of it was off the rear. The front weight is nearly identical.

Front weight old/new - 1161/1158
Rear weight old/new - 1431/1280

[stengun]

Howdy Mike,

Pretty interesting. Thanks for posting the info.

I moved the engine in my Spyder forward about 1 1/2" and I hope this will help to balance it out better.

Paul

[Jetsbaby]

Mike that is very good info..I am 90% sure I am putting in an LS2 engine in mine..Looking at a left over crate engine this weekend..

[xlr8or]

Nice balance you got it to. Why not set the final cross weight with some fuel and you in the car?

[mmarshall]

Originally Posted by xlr8or

Nice balance you got it to. Why not set the final cross weight with some fuel and you in the car?

The cross weight numbers above were with me in the car. I also realized that I did not get all the gas out of the tank and it probably had a couple of gallons in it. The gas should not change the cross weights any as the fuel is centered over the rear axle.

I would eventually like to switch over to a small fuel cell and a surge tank so I can run just a few gallons of gas during competition. I think fuel is one of the worst types of weight to have in the car. The only time the sloshing won't hurt the stability of the car is if the tank is near full or near empty. I also hate to carry around 100 lbs of fuel when I really only intend to burn about 10 lbs of that 100.

[Shawnski]

MM, so the old weight included you in the driver seat? Trying to get my head around how you lost weight in the rear by going with an aluminum block motor?

[mmarshall]

Weights in post #1 were empty to ensure I don't bust my minimum weight for XP class. Weights in post #2 were with me in the seat to balance the suspension via setting cross weights.

I lost weight in the rear by:
1. Moving the new engine setup forward by 2"
2. Deleting the side pipes which means all the new exhaust is forward of the CG of the car.
3. Removing the 35lb battery from the hatch area and installing a 19 lb battery under the front X-brace.


The old weight of 2427lbs was with street tires and about 3 gallons more fuel so about 66 lbs of the 150 lb weight loss was from a configuration change. The rest was actual weight loss in the chassis. I do know that the new engine weighs exactly 50 lbs less than the 302 as I weighed them side by side on the same scale plate.

[Jetsbaby]

From your pictures I thought you moved your battery to the front of the passenger side foot box..Did you move it now to the front of the X-brace?

[Cone Basher]

mmarshal: Weights look good. Just curious,how are the Hawk HP+ pads working for you now that you have them broken in. My experience is with a manual system, I jump on mine hard with my left foot for initial slow down and they work fine. They are dirty however and if you want clean wheels you have to give them a wipe prior to the event but they improved my braking a lot.
Keep us posted:
CB

[mmarshall]

Jets I did move the battery to the pax footbox, but then my exhaust plans changed so I had to move it again. The battery was only about 3" from the muffler. I have redone the exhaust, batttery and air intake a few times now. I am getting good at this fabrication stuff!

CB the HP+ pads are much better. I don't have many street miles on them yet so I am waiting to see if I get all the noise people complain about. If the noise stays the same I will put them on the 2-piston PBR's on the rear. So far they are more quiet than the rest of the car!

[Shawnski]

Originally Posted by mmarshall

Weights in post #1 were empty to ensure I don't bust my minimum weight for XP class. Weights in post #2 were with me in the seat to balance the suspension via setting cross weights.

I lost weight in the rear by:
1. Moving the new engine setup forward by 2"
2. Deleting the side pipes which means all the new exhaust is forward of the CG of the car.
3. Removing the 35lb battery from the hatch area and installing a 19 lb battery under the front X-brace.

Good to see these changes altered the balance for the better. Although I too have most of my exhaust underhood (to provide better exhaust scavenging via proper collectors), the battery placement (Odyssey) has evolved on my build from the hatch area, to atop the passanger footbox (once I learned of the rear bias), and as proven by your results I am now certain to place this in the middle of the front "axle". No need to bring my motor forward since its already plus 50 lbs in the right direction

[mmarshall]

Shawnski the right front tire is the lightest of the 4 so I would suggest offsetting the battery toward the right side of the X brace.

With my battery offset to the right the LF is at 24.7% and the RF is at 22.8%.

[Shawnski]

Originally Posted by mmarshall

Shawnski the right front tire is the lightest of the 4 so I would suggest offsetting the battery toward the right side of the X brace.

With my battery offset to the right the LF is at 24.7% and the RF is at 22.8%.

Thank you Sir!

[turbodon]

Mike

Do you disconnect the sway bars when setting weights?

[mmarshall]

Yes but then re-weigh the car with the swaybar connected as that is how it will be driven. When I re-connect the bar I try very hard to set them up with no tension while static as that will constantly be trying to put some twist in the suspension.