What do sub frame connectors really do...

[SN65]

I have been studying a bit of data covering the structural analisys of a NASCAR chassis.

A lot of it applies to unibody construction.

For example. The major chassis members are...

The rockers and central cross brace (on a unibody the rockers and the seat pan that runs from rocker to rocker) are the major lower structural members.



They tie from the rockers to the frame rails with structural tube. (Torque boxes on a unibody)

Then they have the frame rails front and back with a cross brace at the front and rear suspension mounting points. That is it for the chassis.

The major torsional members in order of sensitivity to torsional loads translated from NASCAR to unibody are

1 the roof structure that runs from the "A" pillars at the windshield to the "B" pillars behind the drivers door.

2 The strut towers and any reinforcement that runs from the tower to the firewall at the "A" pillar.

3 The "A" pillars themselves.

4 The front frame rails from the firewall to the core support.

5 The rockers and the torque box structure.

6 The structure at the top of the windshield.

7 the structure at the botom of the windshield or cowl area.

8 the frame rail extension that runs from the firewall to the seat pan structure.

Addressing these 8 areas is where the best bang for your buck will be in reducing torsional deflection.

I find it interesting that, under torsional loads, the area under the greatest stress is the roof structure at the edge of the roof just over the side windows.

Of course if the "A" pillars and other areas of the car are not correctly reinforced none of the loads will transfer to the roof, etc, etc, etc...

We have just about finished all of our modifications and we have reduced torsional deflection to just over 1/8".

Wayne is sanding and primeing now, but as soon as the chassis is in primer I will post some more shots.

[David Pozzi]

Bob,
Have you calculated torsional rigidity in foot lbs per degree?
That would be more informative.
David

[SN65]

Bob,
Have you calculated torsional rigidity in foot lbs per degree?
That would be more informative.
David

Thanks David, When we set up for our final test, we will generate that info for you.

I am guessing that lbs/degree will generate some type of curve. But, in order to make the data acurate, we are going to have to use a dial indicator to take the measurment. We are down to about 1/4" deflection at this point. I am hopeing for a little less when we are complete.

[David Pozzi]

I cheat and use a digital angle finder with two decimal place accuracy. I had one with .1 deg accuracy but with me standing on a piece of tube across the front of the car, the car only deflected .3 deg, so any improvements were going to show 1/3rd, to 3/4 change.

A dial indicator in different positions along the chassis length is good. I also thought of using a laser level along the chassis, but it would take more calculations to convert it to degrees.
David

[SN65]

I guess if we were smart, we would have used the laser measuring system.

We will have to take that route next time we do this. It will not only give us deflection at the frame rail but also key points along the chassis.

[SN65]

Here are come AutoCAD drawings I worked up showing the changes we have made and the cage we are working up. The cage is still a work in progress.





Green is the original structure.

Red shows the additions

Yellow are the mechanical modifications.

The suspension (front and rear) is all custom. The torque arm is designed to handle over 1,000 ft lbs of torque.

More to come...

[David Pozzi]

Just installed the DSE weld-in subframe connectors in our 73 Camaro. I haven't driven it yet, but my wife has run one Autocross, and two open track days. She says she can't tell the difference seat of the pants. No change in handling or feel. We'd already installed front "G" braces which made a huge difference. GW solid subframe mounts were installed long ago.
Just our experience, we are glad we did it for the long run. Hopefully the roof cracking will not get worse.
David

[saunacrank]

So what kind of shoes will be in this so called box we speak of.......

[JEFFTATE]

So what kind of shoes will be in this so called box we speak of.......

Carbon Fiber .

[SN65]

We have been moving along and now have the cage installed.

For giggles, we put it on the frame rack and performed a quick torsional stability test...

We supported the chassis at the 4 suspension mounting points (the rear frame rails just behind the rear axle and the front frame rails at the CL of the front wheel)and let them all float. We started to lift the chassis at the front left mounting point and measured the deflection when the left rear moved off its perch.

Total deflection was at .06"

[jaybee]

'Total deflection was at .06" '

That's impressive!

[SN65]

Well, we really won't know what the real "improvement" is until we test our completed car against a totally stock 65 coupe.

The installation of the motor and the shock tower brace, etc... will have an impact on the final numbers.

Also, we weill set the car up for a standard test to see how it really compares against cars with a known lbs/degree number.

When complete we are guessing that the car will weigh in at about 2,700 to 2,800 lbs....

Bob

[47lt1]

OK, i got my button up shirt, popsicle sticks, shoebox, glue and scissors, but now I'm really confused.

I did however notice that adding subframe connectors to my car changed the seat feel a lot! acceleration, braking and handling, even jacking up one side to work on something, it seems much more rigid.

[mrn2obelvedere]

Just out of curiosity, has anyone played around with using the engine block as a structural member? They do this with motorcycle engines. If you properly engineered your engine mounting scheme then it seems that it would be possible to substantially stiffen up the front end.

[JRouche]

Just out of curiosity, has anyone played around with using the engine block as a structural member? They do this with motorcycle engines. If you properly engineered your engine mounting scheme then it seems that it would be possible to substantially stiffen up the front end.

Using the engine block as a structural member has been around for some time. The issue that should be looked at is the overall stress that will be placed on the tabs and ears of the block. If it is a production case that was never designed for the purpose of suspension loads along with the ability to support its own stresses there is a certain failure.

I am amazed at some of the apparent loads being placed on a Formula One engine and gear box. I have a nice article showing some of the configurations on those cars. Its a large PDF file. I could email it to you, I think its kinda large.

But what I see is some deep engineering to use the case of the engine and gear box to take the suspension loads. And these cars are very light. The drive train amounts to a larger percentage of the overall weight of the car compared to a street car. Same with the high tech motorcycles today. The drive train is a major portion of the entire weight of the vehicle.

A street car has so much more weight that is not the drive train.

The production blocks just are not meant for it. They are a small part of the weight equation compared to a F1 car or a race ready street bike.

A V8 is just not designed to withstand the force of 750Lbs springs, there is no place on the case that can withstand that force.. Better to focus on the frame and advancing its abilities I think... JR

[mrn2obelvedere]

I can't find anything there to argue with. Clearly production based blocks aren't designed to have suspension loads directly applied to them. What if you use a creative set of front and rear engine plates in conjunction with other frame members? With a bit of creative triangulation, you could create a stiffer front end, with the engine effectively being a zero load member. The rear plate could really tie in to the fire wall, and give a nice distributed loading to other parts of the unit body.

I'm just bouncing ideas around here. As you will come to see, I am constantly thinking of different stuff. Sometimes I think of good ideas, other time not so much.

[Bjkadron]

I can't find anything there to argue with. Clearly production based blocks aren't designed to have suspension loads directly applied to them. What if you use a creative set of front and rear engine plates in conjunction with other frame members? With a bit of creative triangulation, you could create a stiffer front end, with the engine effectively being a zero load member. The rear plate could really tie in to the fire wall, and give a nice distributed loading to other parts of the unit body.

I'm just bouncing ideas around here. As you will come to see, I am constantly thinking of different stuff. Sometimes I think of good ideas, other time not so much.

I think most race cars already do that.?