Chassis Setup (corner weights)

[gnosez]

I've had extensive conversations with BSR crew members who said unless you move the engine or add weight to the right front the car won't corner balance with a driver in it.

 

The six piece custom exhaust made for the original 240Z number 33 race car would not fit in our 1972 because the tube for the number 5 hit the steering coupler.

 

If one was to move the engine about an inch to the right and say an 3/4 of an inch back and would you believe the car is perfectly balanced. It would mean you cut, shortened, added to, ground down, and painted with the correct paint code both engine mounts and did a small alignment adjustment to the driveline.

[74_5.0L_Z]

From the corner weights that I presented above, you can calculate the position of the CG as seen from above.

 

First, if you take moments about the centerline of the car and use my wheel base and track of 92 inches and 56.5 inches you get the following:

 

The sum of the moments about X = (1359lbf - 1278 lbf)(28.25 in) - (2632 lbf ) dy = 0

                                              

                                                            dy = (1359 lbf - 1278 lbf)(28.25 in) / (2632 lbf) = 0.92 in to the driver side.

 

Similarly, Moments about the rear axle yield the fore / aft position of the CG relative to the rear axle.

 

The sum of the moments about Y =  (2632 lbf ) dx - (1278 lbf)(92 in)  = 0

                                              

                                                            dx = (1278 lbf)(92 in) / (2632 lbf) = 44.67 inches ahead of rear wheels.

 

 

So, now you can go through the exercise of determining (roughly) how far I would have to move the engine, transmission and connected stuff toward the passenger side to balance the car such that the CG is centered left to right.

 

The Y position of a composite collection of rigidly connected parts is the sum of the y position of each of the separate parts times each parts mass divided by the total mass.  In this case, if we set Ycg to zero we can find out how far the engine and transmission have to move if we assume that they weigh a combined 600 lbs.

 

                                                          0 = [(-0.92 in)(2632 lb) - (Yei)(600 lb) + (Yef)(600 lb)] / 2632 lb

 

where Yef is the final engine position and Yei is the initial engine position relative to the centerline.

 

                                                        Dy = (Yef - Yei) = (.92 in)(2632 lb) / 600 lb = 4 in

 

As much as I would like a perfectly balanced car (left to right),  there is just no way that I am going to move the drivetrain four inches to the right.

Edited February 4, 2014 by 74_5.0L_Z

[jt1]

Well, if you move the engine and trans then that gives some room to move that lump behind the wheel!!!!!!!!!!

 

 

jt

[74_5.0L_Z]

Funny that you mention that.  I was just pondering what it would take to shift the entire engine, transmission, transmission tunnel, steering column, pedals, and the big lump behind the wheel about 1.5" inches to the right.  That way my new exhaust would still line up with the tunnel and the steering shaft would still fit inside my driver's side header.  I think I'll put that on my to-do list for the next car that I build.

Edited February 5, 2014 by 74_5.0L_Z

[clarkspeed]

I'm building a tube frame up now and did the same calculations. It takes a big move to get 50/50 l/r. I think I will center the engine and live with it.

[74_5.0L_Z]

I wouldn't try to center the engine, or try to get perfect balance.  I would align the centerline of the engine with the centerline of the differential as seen from above.  That way you will minimize the driveshaft angle.

[jt1]

Funny that you mention that.  I was just pondering what it would take to shift the entire engine, transmission, transmission tunnel, steering column, pedals, and the big lump behind the wheel about 1.5" inches to the right.  That way my new exhaust would still line up with the tunnel and the steering shaft would still fit inside my driver's side header.  I think I'll put that on my to-do list for the next car that I build.

 

Because that's exactly what I've been thinking about.  Somewhere between 1.5 -2 inches engine/trans/driver is doable.  I've concluded you would only have to cut up the left side of the tunnel, you could leave the right and keep workable driveline angles.  I'm struggling with the seat and belt mounts.  I think the pedals would be ok, not sure about the wheel.

 

But, still probably not going to get to 50/50, if you run equal offset wheels.

 

jt

[heavy85]

50/50 front to rear isnt that hard. Equal weights on all corners now thats gonna require just a wee bit of engine relocation.

 

http://www.solomatters.com/rolling_awesome_the_ver_mulm_camaro

 

.

[RebekahsZ]

Camaro =$ⁿ

 

Speaking of offset wheels, could you just run a huge wheel offset on one side and effectively more the entire car over a few inches?

Edited February 8, 2014 by RebekahsZ

[74_5.0L_Z]

That would cause other asymmetries with the car's steering.  I'll just have to suffer at the autocross events and find someone between 5'4" and 5'6" and between 115 and 120 ponds to sit in the passenger side to balance the car.  Blondes or brunettes are fine, but redheads are preferred.

Edited February 8, 2014 by 74_5.0L_Z

[jt1]

High maintenance, with a lot of varying requirements, some of them seemingly at random.

 

Also, weight creep is often an issue.

 

jt

[gnosez]

Maybe I'll out of line here, but most of the S30 race cars run back in the day were never corner balanced to 50/50 and within say 25 lbs L to R and yet the drivers of those cars seemed to win races. I've had the opportunity to crew at several vintage races with former SCCA National champions who managed to not only finish a race but win them in cars with only 3rd gear, or bad brakes or one that was set up for a 165 lb driver but was driven by someone 250 lbs.

 

Perhaps spending more time and money on instructions and seat time would allow you to improve regardless of what vehicle you might be driving. Just a thought....

[RebekahsZ]

Ouch. I would don a wig for you any day if it meant I got to take a ride-along. The 120# would be a problem-does that make me a weight creep?

Edited February 8, 2014 by RebekahsZ

[heavy85]

Maybe I'll out of line here, but most of the S30 race cars run back in the day were never corner balanced to 50/50 and within say 25 lbs L to R and yet the drivers of those cars seemed to win races. I've had the opportunity to crew at several vintage races with former SCCA National champions who managed to not only finish a race but win them in cars with only 3rd gear, or bad brakes or one that was set up for a 165 lb driver but was driven by someone 250 lbs.

 

Perhaps spending more time and money on instructions and seat time would allow you to improve regardless of what vehicle you might be driving. Just a thought....

I would put money on the fact they corner weighed Z's back in the day. You are correct that first you need seat time and instruction. However there are some of us on the pointier end who will tangibly benefit from getting weight distribution as good as you can and then setting corner weights. Without radical things like that Camaro you likely arent going to get equal weight on each corner but there are some things like battery, seat, etc that can be tweaked to help. Setting corner (cross) weight is simply an exercise to tweak spring perch heights on scales. Doing so netted me 0.6 sec lap times and my starting point wasnt even that far off.

 

Cameron

[tube80z]

 I've never worried about side to side much on my car.  It's more important to get the car balanced so it corners the same both ways, unless you have a specific reason to try asymmetry.  I had a sports racer for a brief amount of time and it could be balanced side to side with ballast but I found that it worked better using the ballast for setting front to rear balance and allowing it to be uneven side to side.  Even with same size tires front and rear it is better to have a slight rear bias if you can get it.  As the power goes up you'll get faster running more rear weight and tire if you can add it.

 

The Camaro is cool but it's like bringing a plastic spork to a machine gun fight.  It's too big and way to heavy.  There's already a really cool corvette that's built the same way (Sam Platt) and it's miles off the leaders times.  But I'm sure it will put a smile on the owner's face and maybe that's all they wanted.

 

Cary

[gnosez]

Of course they corner balanced race cars back in the day and to get to the holy grail they moved things that would likely result in a penalty or a DNF today.

 

As to being on the pointy end of the stick.........been there and still doing that.

 

With the new seat and the accusump, the race car will get corner balanced again to as good as it can be gotten (should have left the battery up front) and then I will drive the piss out of it.

[clarkspeed]

Gnosez, you are so correct. Driving skills are monumentally more important. And i think one advantage to the S30 is abilty to get 50/50.f/r pretty easy.

[JMortensen]

Because that's exactly what I've been thinking about.  Somewhere between 1.5 -2 inches engine/trans/driver is doable.  

I've got 1.25" on my LSx, and that's about as much as I can get out of it.Might be able to push to 1.5, but it would be TIGHT. The T56 is the issue, might be able to go further with a smaller trans. I don't have to worry about exhaust either, since I'm going side pipes out the front fenders.

 

The alignment of the pedals and seat doesn't really matter that much. I wanted to try my race seat in my Miata so I made a really crude mount for the stock rails and drove it. Didn't have any problems with it and honestly never noticed it when driving, but in looking at it later the seat was something like 3" left of where the stock seat was. 

[74_5.0L_Z]

Well,  just got back from a weekend at Sebring running autocross with the Central Florida SCCA.  It was great to get some seat time as this was the first time I have had the car out in over two and a half years.  The car has been sitting while I finished my Masters degree and while I weathered the storm of lay-offs in the space industry.  Now that I am fairly comfortable that I am not going to lose my job in the near future, I feel a little more responsible spending money on race tires.

 

As far as corner balancing goes, I consider it a necessity.  I would no more mount a new set of Hoosiers and go racing without a corner balance than I would go racing without a proper alignment.  I want to make the most out of my tires and make them last as long as possible.

 

As you guys stated above, that Camaro is cool.  But he will get his rear-end handed to him by the 1800 pound beasts that dominate this class.  I spent the whole weekend racing Brunton Stalkers.  Those little things are hard to beat.  Scott Minehart (the owner of the Brunton Stalker company and a national level driver) was there with his new Stalker M-Spec.  Basically it is a Lotus 7 clone with a LS1 engine.

Edited February 10, 2014 by 74_5.0L_Z

[gnosez]

The easiest/hardest thing to do: get your S30 under the weight limit and then add weight where you need it. It helps if you limit your own personal weight as well which makes getting the critical LR to RF cross weight so much easier.

 

A driver tells his crew chief the car isn't doing what he wants/needs it to do. Adjustments are made, the car feels and handles better, the driver has more confidence, but those changes could have likely altered the pre-race set-up (like say corner balancing,alignment, tire pressure, etc.). Does the driver even know or for that matter care if the car is no longer 50-50 and within 5 lbs side to side? Hell, no. You start with a set of specs and go from there. If 50-50 makes you feel more confident you race harder so perhaps it's a chicken and egg sort of thing.

Edited February 10, 2014 by gnosez