ScaryFast

I added too much HP, so to stay within class limitations I need to add 134 lbs to my C4. There are specific rules as to how it has to be mounted:

All ballast must be of solid material (i.e. no lead shot), and safely secured in any location on the vehicle approved by safety inspectors. The preferred method is to use at least one 3/8" grade 5 bolt, two "fender" washers, and a locking nut sustem for every 15 lbs.

This seems like it's going to be a large ensemble. I clearly want to put the weight low and rearward, has anyone added ballast to a C4 that can offer some ideas? Also, is there anything smaller/easier than using barbell style weight plates?

Or, are any of you guys/gals 134 lbs, and do you want to ride with me whenever I go on track?

Aardwolf

I'll cut off two arms and a leg, then I ride with. For weight, if you want flat plates the ones for tractors would work well.

Slalom4me

How are your current fr:rr percentages with driver and fuel race-ready?

To make the least impact on polar moment I would want the extra weight
near the center and low. To offset the driver, perhaps add to the right of
center.

The rear of the passenger seat well offers possibilities. By limiting
seat travel rearward and downward, a space for weight can be created.
Attachments could be added to the seat frame or a bracket should
be sandwiched between the frame and the mounting studs so that
there is no need to drill through the seat well.

Lead - 0.410 lbs per cubic inch
Brass - 0.307 lbs
Steel - 0.283 lbs

One readily available source of lead is bar solder.

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ScaryFast

Sadly, I can not locate the paper with my weights on it. I just had the car corner weighed at the last NASA event and thought it had been placed with my other paperwork.

Frustrating.

Regardless, I know it was still biased toward the front. I am thinking of building a bracket for race day that I can put in the passenger compartment in place of the seat. It's only 4 bolts to pull it out, it will be low, and it's obviously opposite my weight. I'd like to get some further rearward, though. The battery is in the compartment behind the passenger seat, otherwise that would be a great place...

I'm also looking at some areas under the chassis, in the rear support and subframe.

Lead is softer, too. I could heat it and mold it into nifty shapes...

mrc24x

Here is a link w/ a few tips:

http://www.longacreracing.com/articles/art.asp?ARTID=20

As far as the ballast itself, Poske Performance sells 20lb lead sections that bolt to your roll cage. (Poske.com) 800-430-RACE Unfortunately the website is down.

I can only hope to have your problem of too much HP. Congrats!!

Hope to see you at MidOhio in July.

Slalom4me

The article's emphasis on biasing weight to the left suggests that the
intended audience is the left-turning circle track crowd.

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eogel

I have placed it where the passenger seat is normally located (full race car). A couple of holes already exist, or you can drill thru the lead and floor and bolt it down. Most any circle track supplier/car builder has lead, if there is one in your area. Also, Howe Racing Enterprises (www.howeracing.com) sells it in bars of 29-31 lbs in a couple of sizes for $34.50 to $41.50. Phone is 989-435-7080.
The idea for under the seat by Slalom4me is also a good one.

Slalom4me

I thought I remembered reading where you carried passengers
in the past, so I didn't suggest removal of the right seat.

Incidently, on my '89, the seat cushion comes out by releasing a spring
clip retainer. I have considered fabricating a mounting plate that would
nestle in the molded plastic seat base and be retained by pip pins.
Race day debris like an extinguisher, datalogger and so on could be
attached to the mounting plate. The pip pins would make R&R very
quick.

The attachment points for the tire carrier are
ready-made for a bracket to sling additional weight from.

Alternatively, what about building a rear diffuser - weight and downforce,
together. Blaine Fabrication may have something for the C4.

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vetracer

My C4 is very light on the right rear. Nothing I can do with the coilovers to correct it. I run an unlimited class, so unnecessary weight is the enemy...

I would suggest adding weight to the storage compartment behind the passenger seat. That's where I relocated my battery to.

Solofast

Get the weight low and aft of the diff in proper place to balance the corner weights. Polar moment isn't as big a deal with these cars and you aren't going to change it all that much with the weight you are adding unless you put way in the back where the mufflers were.

Look at the polar moment of a C5 with the tranny nearer the back of the car as opposed to where it was, on the CG in the C4. Nobody complains about polar moment of a C5...

C4's are nose heavy, and getting the cg aft is going to be a lot better in reducing understeer and putting power down off of the corners. I would put a couple of tubes across the rear frame where the spare tire was and set it up so that you can move the weight further aft or forward in that area and experiment with it back there.

With weight in the back you are going to be able to put down power earlier and harder coming off of corners and that is going to get the lap times down. Lots of folks think that polar moment is the biggest reason for mid engine cars, and it does help, make no mistake, but the other big, and maybe even biggest reason for an aft weight bias in higher powered cars is the ability to put down more power.

Slalom4me

In absolute or relative terms?

Corvette Action Center specs list the Weight Dist. F/R (%) as ranging from
50:50 to 51.5:48.5 depending on model years and CPE/Vert configurations.

As purchased, my used '89 scaled pretty much at 50:50 with changes the previous owner
had performed.

Other than this qualification, I agree with everything stated.

.

Solofast

In relative terms, they aren't that bad, but most the 10 that I had were all (as delivered) in the 51+% rather than 50/50. I was just thinking of stock cars and also I am sure with mods you can get to 50/50, but why stop there? A little rear weight bias wouldn't be a bad thing at all for a C4.