Great post, I've been contemplating moving mine, but love sticking stuff in those rear holes so they don't fly all over the place when driving enthusiastically...off topic Powerlabs, but curious how much time on an avg autox course you've shaven since the addition of the supercharger?

 

...ever corner balance your car? It would be interesting to see how the 21lbs in the right rear corner shakes out in the math. In the case of the ZR1, Z06 and LS3 GrandSport it is more a matter of real estate than performance...the oil reservoir needed a home.

 

Don't let the questions bewilder you. You could have answered the question without the underlined part. It would have changed the comments from mean spirited to friendly. Just my 2 cents.

Yep, it has been tried. I stopped a Ferrari one day for doing 75 in a 40. He told me the accelerator was stuck. He further stated he was a Ferrari Mechanic and could prove the accelerator was stuck.
I gave him two, one for speeding and one for Reckless Driving. He got nailed for both in court. The reckless driving stuck because he "KNEW" the accelerator was a problem and drove the car anyway.

 

Guys I'm not trying to bash what he has done here...just looking for the data that supports the claim that this change has improved the performance of the car. If the car has been weighed and the numbers show he needs 21lbs in the right rear then great...awesome idea. But, if the rear was evenly balanced prior to the change then it wouldn't seem to be the right thing to do. I'm all ears....educate me!

 

Nice work Sam

Relocating the battery is a great mod, beneficial in many ways. You really dont need any scales to recognize the benefits. The stock battery is heavy and mounted up high (in relation to the center of gravity) and all this weight is near the right front wheel. And this is on a car thats heavy in the front, and likes to understeer when hard cornering...

IMO moving the battery is another key to a well built car. Adding horsepower is easy, but optimizing the cars balance, suspension, braking and tires is the key to a top performing car.

 

Battery relocations have been around as long as sports cars. Kits are sold from every car part place from Jeggs to Summit. Weight transfer being the reason and many having tried it note an improvement in traction. Your terminology suggests you really havent spent much time at a drag track. Moving a 40lb battery off the front to over the passenger rear wheel helps the car squat down. To aid with this you even remove the front sway and use 90/10 shocks. Weigh a car to see if he needs 21lbs on the rear wheel? The reason for the weight is due to the TQ twisting the car on the launch, which you cant weigh statically on some scale.

If you dont think moving weight backwards aids in weight transfer and you dont think weight transfer does anything for performance, I doubt you can be convinced.

If you are seriously saying you dont think battery relocations help weight transfer or you dont think weight transfer helps acceleration, search "battery relocation weight transfer".

 

Have to agree, would hate to see you on "vacation" again.

 

How do we know the shift in weight transfer is helpful in this case? It Seems to me the weight is being moved behind the rear axle not onto the rear axle where it would actually help traction.

I do agree he did a great job moving the battery to the rear compartment.

 

In drag racing, this is a pretty standard concept but here goes: Weight transfer is best when the relcated battery is as far back as it can get. If you extended a 5 foot bar behind the car and put the battery on that, it would benefit the car more than where he put it. The concept is to fully load the rear tires with only enough on the front wheels that you can control the car.

What you seem to be misinterpreting is that you think the battery's actual weight is what is pushing down on the rear tires when its the physical lifting of the nose of the car that loads the rear tires to the tune of 1000 more pounds because the front wheels are just short of lifting up. Think about it this way, you have a really heavy thing up front that keeps the rear tires from loading so if you had a really long fulcrum, a realatively small shift in weight can move the center of balance back. Its like a fat kid weighing 200lbs is trying to use a teeter totter with a 80lb kid. If you move the fat kid toward the center it will work. If the fat kid is fixed (like the engine is) you make the skinny kid sit as far back as he can and if you can make his lever/half of the teeter totter longer, they can again find a center that allows the teetering to work. In this case the battery is behind the fulcrum to effectively make the same result as if you moved the engine backward on the frame 10 inches.

Now for those of us that added a supercharger, we gained 50 lbs in front of the engine. Exactly what a car doesnt need when you add 300HP. A battery relocation can effectively make it feel more like it did stock for which the car was designed for both weight and balance.

 

I don't think so... The driver weights several times more than the battery... Plus the extra cable run to put it on the driver's side would weight more...

That is my plan. WORSE case scenario I'll put it back in the stock location just for drag racing. Whatever the case, I'll report back here...

I can't tell much of a difference so far; in an SCCA sanctioned autocross you're never really out of 2nd gear and corners are sharp and spaced closely so the supercharged horsepower presents little, if any advantage because I can almost never put the throttle to the floor. The car is still very driveable and I have a blast with it while doing reasonably well, but the blower is not much of an advantage there. It does much better on longer courses where you can use the power.

And that is the whole point: these cars are not perfectly balanced from the factory: According to GM's specs for the Corvette: 51% of the weight is located up front, and that is before the driver sits in front of the center of gravity. Now put a 60lbs supercharger in the nose and the bias shifts even more. Meanwhile you've got tires that are two sizes narrowed in front than in the back; it is the recipe for a car that consistently understeers at the limit. Safe, but not ideal for performance. Moving more weight to the back makes the car feel more neutral at the limit, and that makes it faster.

 

You should be fine with the rear mounted battery, atleast as far as NHRA and ORP are concerned. I checked with them when I did my car and found out that if the car came stock with a rear mounted battery, that it doesn't require an external cut off switch.

Even if a tech inspector is corvette savy enough to know that your car didn't come stock with the rear mounted battery (unlikely). I doubt you would have any problem, especially if you had a couple pics in your glove box showing it's an OEM setup.

 

This is the next mod on my DIY list. PM sent for write up!

 

Spin did a great job of explaining this. Another way to think about it is you should move all the weight rearward as possible to allow you to pull the front tires off the ground with a hard launch. But just enough so that the front wheels come back down softly after the hard launch. Think about it, if the front wheels are off the ground, that means that the total weight of the car are on the rear tires. And Spin is right, the best place to mount the battery would be off a 10 foot pole hanging off the back of the car in order to leverage the front wheels off the ground using the rear axle as a fulcrum.

And to Sam, once again a GREAT JOB!!!!

 

I don't agree that the weight transfer issue can be described as simply as it is in this thread. You forget to mention that in order to place the weight in the proper place you would need to make many calculations. Since the acceleration rate of a car is not linear, the placement of the weight would be different under different circumstances.
Simply stating that moving as much weight as far back as you can would be optimum for acceleration is not a true statement. Your reference to a fulcrum is inaccurate due to the many other forces acting on a car chassis under acceleration.

If you think it is that easy, I have a few physics and math books you an use while I search for reference to "battery relocation weight transfer " articles.

 

Sam,
The Braille batteries are the exact same batteries (made by EastPenn) as the Deka or Big Crank. The difference is the price. The Braille brand name costs twice as much (at least). I posted this information about a year ago when I replaced my stock battery with a Deka. I opted for a lighter battery but mine is under the hood, so I think your choice is probably a good one. It is a good battery, no matter what name it bears.

San

 

I think when you consider Sam has a supercharger, moving weight to the rear is a lot more important due to the weight of the supercharger, not to mention where the weight of the supercharger is carried.

San

 

...all 60-ish lbs carried pretty much forward of the front wheels

 

Have you, or Powerlabs, had any starting issues with the smaller battery. Is your car a DD?

 

The only issue I've had is when I haven't driven the car in three weeks or more the motor turns over, but sounds slightly hesitant. For a daily driver there aren't any issues I've found. I have three vehicles so I don't really have a daily driver.

San

 

Great job Sam... I've needed to do this to add an extra battery... thanks for reminding me...