The Next Generation. 3G T.A.

[cornfedbill]

The C5/C6 does place the transmission in front of the rear wheels, unlike the Porsche/Audi transaxles that hang behind. It meets your design criteria. The torque tube does limit the torsional load on the frame so it does not need to be designed to support that load.

[RobNoLimit]

The C5/C6 does place the transmission in front of the rear wheels, unlike the Porsche/Audi transaxles that hang behind. It meets your design criteria. The torque tube does limit the torsional load on the frame so it does not need to be designed to support that load.

This was our plan. At first. We thought we had it all figured out, but, to make use of the C5/6 torque tube we would have to raise the engine some. Also, we could not offset the eng to the pass. side for weight balance.

[RobNoLimit]

Our next idea was to use the C5/6 trans axle without the torque tube. It is easy enough. Machine a front mount that carries a support bearing and mount a yoke to the input shaft. Then, run a driveshaft from the engine back to the transaxle. But, that leaves gear changes out, and we really want to be able to do that. BTW, we went pretty far with this idea. I have the plate/bearing/yoke design all ready to go. I may do this on another project. We made a last minute call to go to PRI (which is way better than SEMA) to do some scouting. And we found, among other things, this awesome gear box - transaxle. It checked all of the boxes. front side gear box, 'low side' mounting, IRS CV bells, even sequential shifting! It's even fairly light @ 110 lbs. wet. We were so excited. Then, we heard the price. $37k US. Hmm, well, that's almost half of the total planned budget. It was like getting one kiss, from a smokin hot chick in Italy, and she hops on the train and heads back to Sweden. Only the heartache is left. Ahhh, it was an awesome gear box though. And, we kept on walkin.

[cornfedbill]

This does not check all the boxes because the gears are behind the rear axle centerline. But it is was cool and has lots of potential and the ability to transfer lots of torque. And it's "only" $18,500.00. That's a lot of money and not likely within your overall budget. But not bad considering the alternatives.

While it is not what you are looking for because of the placement of the gears, I do think it would be great for some builds though.

https://www.ppgearbox.com/single-pos...xle-conversion

[RobNoLimit]

In the end, gear change (ability), availability (parts and repair parts), weight and cost won out over pure desire. We decided on a Speedway Engineering Quickchange IRS center section with a Platinum-Drive diff unit. This was built to accept Porsche style 934 CV joints with 33 spline axles. This checks off quite a few boxes for us. Serviceability and the option to do a gear change in less than 15 minutes came in as the overwhelming pros. Cons may be the mounting, as not much comes with it, but we do have a fab shop. In our initial set up, we mounted the diff so that the axle center height was at 11.5". This is 1.25" lower than the wheel/hub/CV center at 12.75. This was done in an effort to lower the overall CG of the car.

During the design phase, we set a driveline angle target of 3* max. In this configuration, we have four "drive shafts". 1) engine/clutch to trans 2) trans to diff 3) LH CV axle 4) RH CV axle. Our goal here is to have a max of 3* angle on any joint at it's spec ride height, and try to stay under 5* (CV axles) at full suspension travel. *** Less than 3* is for parasitic HP loss reduction, and the 5* limit is to reduce driveline NVH, or "busyness". Vibration can be reduced or eliminated by matching angles, but the 'busyness' or 'verb' from higher angles cannot. Once the rear suspension was in full mock-up, and we had actual CV's and axles, we decided to raise the diff to an 11.800" centerline to keep the axle/CV angles within range at full stroke of the suspension. All in all this was a big step forward. It cemented the driveline direction and allowed us to move forward into full fab.

[RobNoLimit]

Wow, that last pict shows how empty the back of the car was!

The rear chassis design was again from 'function' first. In the design, we had to plan for Exhaust, Muffler/s, Fuel tank, Aero, and allow for shock tuning, spring swaps and sway bar adjustments. The lower chassis tubes have to mount the LCA, the lower Diff mounts, fit to the belly pan, and clear the exhaust. The upper tubes hold the UCA, upper diff mount, rockers, coil-over mounts, and are spaced to allow the fuel tank to sit in. You can spot the sway bar in a few picts, I'll get to more on that later.

At first, we planned on using the C5 lower arm (LCA) But, in the end, shock/spring and sway bar mounting locations were not correct, and, the arm geometry was a compromise. So, we built new LCA's. The adjustment on the lowers is for 'wheel base' squaring only. Once the car is set square, we won't be touching them. BTW, our new arms are 2 lbs lighter than the OE C5. The UCA was always planned to be fabbed. we wanted LH/RH adjustment for rear camber. Also, these arms are a little shorter than the C5 for quicker camber gain.

[SSLance]

Ball joints and tie rod ends...on the rear knuckles... For rear toe adjustments I'm assuming?

[RobNoLimit]

Ball joints and tie rod ends...on the rear knuckles... For rear toe adjustments I'm assuming?

Yes, this is OE C5/C6 'vette stuff, well the knuckle anyway. Careful lay out will allow us to tune the Roll-Steer of the car, as well as set a baseline Toe-In on the rear. The C5 uprights will end up with C7 UniBearing hubs (direct bolt in). The C7 hubs are stronger, and take a 33 spline stubshaft, stronger than the C5/C6 28 spline unit.

[RobNoLimit]

The last picts were pretty clear. It was only the base IRS parts. One pict here is just of the LCA on it's Ride Height stand. The rod end adjustment on the LCA is only for "Wheelbase" alignment, not camber. We wanted the ability to make the car perfectly square. (actually a rectangle through the tire contact patch centers, but you get the idea) So, next came the rocker mounts and rockers. The rocker mounts use a set of needle bearing rollers. The rockers are currently 1-1 ratio, and although we thought about milling them in aluminum, modeling showed fabbed steel units to be lighter than aluminum (simple 3 axis milling).

[andrewb70]

Awesome. In for undated.

Andrew

[RobNoLimit]

NSRA Louisville was last weekend. If you are not going to this, and you like to get in some AX laps, you're missing out. You could easily get 20 runs per day, for three days. I had a few discussions with some people who's opinion and knowledge I value, and most of those discussions included "weight" as a topic. Total weight vs. unsprung wt vs. rotating wt. ...... And, then I had a 5 hour drive home with some alone time to think about it. AX and Road racing share some things, but short track (AX) is it's own beast. Rapid and radical acceleration and deceleration are keys, but also total direction change. For these actions, two factors rise to the top as 'most important' (IMHO). Traction, and Total Mass (weight). When you want to "change" vector force - (direction/speed), weight is a huge deal. Think of a Ping-Pong table (a really strong one), if a Ping-Pong ball is coming at you at 20 MPH, you can use the paddle and hit it back. - Change it's direction, it's Vector Force. If it was a golf ball, you could not change it's direction as well, and if it was a cannon ball at 20 MPH, I doubt you could change it's direction at all. Your car is the same thing. You want to charge down the lane at full throttle, stop at the last minute (change) and turn 90 degrees left (change) and then accelerate as fast as possible (change). Mass or weight, is making you're performance desires very very difficult. So, you may start to think that 'Lighter is better" no matter what, BUT, this may not be so. We need traction to apply the force (torque) to the ground. At some point, the car would be too light to allow the suspension to work efficiently.

I have thought for some time now (and still do) that the relationship is based on a percentage of unsprung vs. sprung weight (or total weight) Like the Ping-pong ball, if you want to hold the tire to the ground, you need a sufficient overwhelming force to do so. As we AX and Short-Track more and more, my own thoughts are that the minimum balance number is around 14 or 15%. BTW, it may shock some to realize that a Trophy truck weighs in at around 6500 lbs, just for this reason. So, I look backwards. If the total unsprung weight is 90 lbs per corner (wheel/tire/brakes/spindle + 1/2 of the LCA/UCA/spring/shock) and for example, lets say an IRS with the same rear figure, then the total unsprung is 360 lbs. If this is 14% of the total, then the lightest the car can be is 2571 lbs (360 divided by 14%) If the car gets ant lighter, the unsprung weight has to be trimmed as well. Now, if the car is heavier, it is easier to get the suspension to plant the tire, but harder to "change" direction.

Anyway, here are a few shots of the rear suspension. The guys at ridetech sent me a test shock to use, it has no fluid or gas charge, so I can open and close them easily. It may not look it, but the shock/rocker/pushrod assembly is "on plane" so that there is little or no side load on the components, and also, there is less than a 3% side shift on the pushrod through the entire stroke. At this point the travel is too much, and we will limit it with bump rubbers for tuning.

[SSLance]

Rob, am I correct in assuming that when using a rocker arm setup like the above you are moving the weight of the shock\spring combo from unsprung to sprung weight? Or does that line always exist in the middle of the spring no matter what?

[Streetbu]

That would be considered sprung weight from my understanding

[JayinMI]

I was thinking that it seemed like doing that would laos have the added benefit of moving weight toward the center of the car and away from the outside corners...then I realized that that would probably be considered unsprung weight. Am I correct in my assumption?

Jay

[RobNoLimit]

I was thinking that it seemed like doing that would laos have the added benefit of moving weight toward the center of the car and away from the outside corners...then I realized that that would probably be considered unsprung weight. Am I correct in my assumption?

Jay

I think it's a mixed blessing. The shock/spring become sprung weight, but 1/2 the rocker and pushrod weight are unsprung. So, the unsprung weight is reduced, but the total weight is up a bit. Also, we did move the weight 'up' in this design (bad). In the game of compromises, the ability to tune in 15 min or less, and the reduction of unsprung weight won out over a gain in total weight and raising the net CG. ** This car will have a LOW CG, due to many of the other design elements. So, in comparison to other platforms, even though this decision raised the CG (appx .13" net says the E-box) we are still way down from a traditional build.

[RobNoLimit]

Over the last week I have been thinking about another build going (not ours) and the test days they have had. I think a short timeline gave them fits. I'm sure they will get it sorted, and I'm sure it will be fast. But, I have my own feelings on the car in total. It's light, it's a wide big tire car, it's got lots of HP, and to me, it's old news. They didn't push the envelope. Nothing there that hasn't been done. So, awesome car, and a proven approach, but a little less excitement to me.

On the other hand, we are trying things. And, we may fail because of this. We are taking some risks this way. There are a dozen or more hings on this car that I have thought about, and never tried. So, it has a higher percentage of failure than a build on a known plan. Because of this, we cross our fingers a lot. Also, there's nobody to ask. No info to find. So we spend a lot of time researching and figuring. Here are some shots of this.

To divorce the trans, we chose a small bellhousing/clutch with a reverse mount starter, This also helped with clearance to lower the motor. On the "clutch" side, we have an input housing from a TKO (thanks to Mark Bowler). to support the "Clutch Shaft" (as we call it) we are using a wet roller bearing from a M22 4 speed, and to support the output and slip yoke, we have a TH400 tail housing. We started with a 1 1/2" thick chunk of aluminum and carved out the merge plate. It is complete with a seal set, oil reservoir, vent and drain. Too many hours to count for such an item, but having it all fit was a great payoff. We are having a custom shaft made to fit (two actually, so we have a backup). There is a pict of the front LCA mount tabs. I chose to duplicate the OE style adjustment of the LCAs (for CL squaring only) So first we needed a hole to center the mount, the later we knocked out the sides to make slots (this requires a little work with a file to get nice and smooth). Last is a pict I ran across while looking for these. The F100 is owned by Kai L. of "Street" Magazine in Germany. The 'effe sits on one of our "Big-10" chassis with a floater, 406W and 6 speed, and has been around the Ring and Hockenheim many times. It is always a shock to the other drivers how quick it is. Remember, this is supposed to be fun.

[rustomatic]

I just wanted to say thanks for continuing to show great ideas, engineering, and perhaps most importantly, depth. It is what this hobby (not a business for most of us) really needs, especially with the easy access we have to information and great tools these days. I think I know which "build" you alluded to early in your post, and I really hate the way that cluster went; the results were totally unnecessary. More importantly, who needs a $200k track car with a stick axle?

Again, thanks for doing what you're doing! By the way, what happened to your crazy aluminum chassis Cobra project?

[jlcustomz]

Nice to see this level of work going into a 3rd gen. Had a friend that put 80k or so into one about 10 plus years ago as a combination of show & go. People at shows would say why on a 3rd gen, I'd say why not. But like with so many builds done 10 or so years ago in a sort of pro street/pro touring/custom style, the chassis & aftermarket suspension really couldn't handle & make proper use of all the heavy big block power, leaving it an underused showcar.


Don't look like you'll have that problem.....

[RobNoLimit]

I just wanted to say thanks for continuing to show great ideas, engineering, and perhaps most importantly, depth. It is what this hobby (not a business for most of us) really needs, especially with the easy access we have to information and great tools these days. I think I know which "build" you alluded to early in your post, and I really hate the way that cluster went; the results were totally unnecessary. More importantly, who needs a $200k track car with a stick axle?

Again, thanks for doing what you're doing! By the way, what happened to your crazy aluminum chassis Cobra project?

Jenny (the Cobra) is resting during the Fbird build. Honestly, last year I had too many projects, so I idled some to clear my plate. The Roach Camaro is done, Tina's Mustang update is done, and my C10 driver is almost done. Once the Bird is closer, fab done, the Cobra will come back out.

- - - Updated - - -

Nice to see this level of work going into a 3rd gen. Had a friend that put 80k or so into one about 10 plus years ago as a combination of show & go. People at shows would say why on a 3rd gen, I'd say why not. But like with so many builds done 10 or so years ago in a sort of pro street/pro touring/custom style, the chassis & aftermarket suspension really couldn't handle & make proper use of all the heavy big block power, leaving it an underused showcar.


Don't look like you'll have that problem.....

Thanks. I think we will see more 3rd gens and G-bodies very soon.

[RobNoLimit]

Here's one. Years ago I stumbled onto a link for Mercedes Benz tech archives. There's something like a million + pages of their research and testing base. A few articles that I read stuck with me. On the sides of the "tech" findings, (very well written and charted), we're the engineers notes and comments (off the cuff stuff). One article was focused on their testing to chart "Ride Frequency" as it related to human ergonomics and therefor comfort, security and driver experience. They spent years developing test environments and machines, testing thousands of people, blah blah blah. In the end, an engineer linked something very basic. They found, that the average "most comfortable motion cycle" to humans was around 1.1 cycles per second. The side comment was something like this. "Brilliant! Six years of testing and over $30,000,000 spend has led us to understand that people, on average, are comfortable at 1.1 Htz. That's amazing. To think that we are most comfortable at a cycle that matches the average human walking step is almost unbelievable. After all, Humans have only been walking around for a few hundred thousand years. Bravo MBz." OK, so, don't overlook the obvious. That's the lesson I got out of that. They had other great stuff too. Crazy formulas for calculating the intake runner length from pulse tuning based on rpm/cyl size/torque..... Exhaust Db calcs for muffler volume, shock resistance formulas, sound canceling..... it's all there. Crazy to me that they spent all that time/money on learning this stuff, and then keep it in a public access location. So, the info is out there, we just have to find it.