Great question Mark,

Half of the answer needs to pull information from your current straight axle setup.  The other half will be IRS specific.

When you're laying out your basic geometry in a software program, two things you'll want to design in are your target anti-squat & rear roll center. Since you are already racing your car with the straight axle, let's pull some details from what you're currently doing. 

Questions for you:
A. What is your current Anti-Squat
B. Do you feel you need more rear grip on corner entry (under braking) or exit (under throttle)?
C. What is your current rear roll center?
D. Do you feel your mid-corner handling is most often neutral, tight or free handling?
E. Would you like to tighten up, or free up, the mid-corner grip with your IRS?

Lastly (for today only), what are your goals with transitioning to IRS? What do you hope to achieve?

I have a 67 Camaro that is equipped with Speedway Motors G-Comp X front suspension and Speedway Motors torque arm rear suspension. It has Penskes all the way around, 315/30-18 tires front and rear and I'm pretty serious about autocross and competing at SCCA Solo Nats in CAM-T class. I have a 6 speed trans and engine makes about 575 hp to the wheels. I am considering going full IRS and would be designing and building the whole thing myself. If I pull the trigger on this, I would run inboard brakes and would scratch build upper and lower control arms and the uprights using C7 Vette hubs. What should I consider for ideal geometry? Does the geometry of the front affect what I should do in the rear? My suspension is all entered into Performance Trends Suspension program, although I have made some changes and should probably double check all those measurements again.

Oh plumbing, how I love plumbing. Seriously, I do! It's always presented a challenge and I appreciate the mindset to make it look good. Bending, routing, and mounting hard lines comes into this in a big way. I'm probably going to catch some flak for it, but all my plumbing (yes, all) runs inside the car between the front and rear bulkheads. Oil feed and return, brakes, transmission cooler for a short run, and fuel. Being that the car is as flat a bottom as I could make it, room for lines under the car becomes quickly limited leaving the only real option being the tunnel. The idea of any plumbing running parallel to a driveshaft spinning up to 8500rpm sounded like a bad idea, along with exhaust heat. Lines inside the car are protected by the frame and roll cage just like the driver. Of the pictures following, all remains how it is to this day with the exception of the fuel line being re-bent in stainless steel.

Lets get started with the oil lines. I used aluminum straights and bends and welded it all together.


This was the beginning. After this I'm going to skip forward a little bit to the point where I had painted the interior of the car. It makes things much easier to see and because pretty. Aluminum tube and bends can be acquired from several places. This is all .065 thick, making it relatively easy to weld. The issue I ran into was the flared ends. Flaring up to 1/2" is easy. Inexpensive 37* flaring tools are available in both single and double flare. Over 1/2" is an issue. For my build I had some used BMRS fittings that I cut apart and welded in place. If anyone else is wanting to go the large hardline route, contact BMRS for flared ends. They offer flaring service on lengths of tube in AL or stainless that have one or both ends flared and leak tested. All you have to do now is add a tube nut and sleeve, and weld the ends on. They do offer complete bending services as well, but I've never had them quote out a setup for me.

Bending AL or stainless tube over 1/2" is also an issue. I recently tried a relatively inexpensive mandrel bender at work, from Woodward fab that can do up to 1" steel or AL tubing but the holding device needs some attention - it causes a sizable dimple in tube where its being held. Mitler Brothers offers a similar bender I want to try that uses a roller on the holding side that may provide a better product. If you can get one of these benders to work, the tubes could be made from one straight piece instead of welded together like I did. These tools were more than I could afford at the time. But..the product from hardlines....oooo




The short lines you see that dip under the oil lines are transmission cooler.


Near the rear bulkhead I did a mounted bulkhead block. Bulkheads are welded to a removable piece that continues the hardline for fuel and brakes, but changes to soft for oil feed and return.


The downward jog on the fuel line is why I ended up redoing the fuel in stainless. It was close to the floor and the very first time I drove the car there was a scrape on the bottom from who knows what. Not damage, just a scrape - right under that fuel line. I did a tight 90* fitting and brought stainless forward, as well as redoing all the rear lines in stainless too.



The scavenge filter mounted to the side of the oil tank was a cool idea I thought, and I like the way it came out, but checking the filter is a pain, even on a lift. That being said, I'm not a huge fan of the tube filter either. Cleaning the filter free of any particulate after inspection is a pain. I have a billet Oberg filter sitting on the shelf that I'm trying to find an easy accessible place for. The Clear View filters on the market are cool too. Little pricey and a little heavy, but cool none the less.



Here's the before and after on the fuel line.






This is getting a pit lengthy so, one more note on hard lines - Mounting. Hard lines need to be frequently mounted to prevent vibration, fatigue, and failure. Planning for mounting points is something I actually planned out! Wow! Lol! I welded 1/4-20 x 1/2" bolts all over the chassis for plumbing and harness mounting. the harness mounting studs also make great grounding points. I have seen several builders weld the lines to each other for rigidity which also works well. If you thumb the line over a long run like a guitar string and it vibrates, you need another mount.

Cant help myself, couple more pics. This is the Racepak display dash mount I made.






Until next time!

Quote from: Ryan Kennedy on Mar 21, 2026, 01:24 PMThe green and black DIY set with rollers are the ones I'm trying. I too am concerned about the amount of camber that they can handle. The same company makes a few other things for E36 BMW. Assuming that's what they originally made them for, they usually run a lot of static camber. Have to see what they're capable of once they arrive! Didn't mean to highjack your thread, PJ!

I think you'll be able to open up the middle section & give the uprights more room to camber.  Let us know after you get them done.

The green and black DIY set with rollers are the ones I'm trying. I too am concerned about the amount of camber that they can handle. The same company makes a few other things for E36 BMW. Assuming that's what they originally made them for, they usually run a lot of static camber. Have to see what they're capable of once they arrive! Didn't mean to highjack your thread, PJ!

My Race-Warrior customers with Centerlock hubs use these HERE, with adapters. 

Where Allstar discontinuing their inexpensive version, you may want to build your own.  Paco Motorsports sells 4 of the mounts for $200. Then you could make the adjustable part however you want. Website here.



Here is another "weld it yourself" option.


I like the rollers, but frankly we'd need to modify the plate to allow for more camber.

Quote from: Ryan Kennedy on Mar 19, 2026, 12:14 PMThe levelers and roll-offs are the one I was considering before looking more into hub stands. In your opinion, is the foot or so you're able to roll back enough to unload the wheels? Levelers and roll-offs are still more expensive than what I'm trying with the hub stands, but you still have me with the cost of nearly nothing using greased slip plates. Longacre also has their billet levelers with rollers so the scales move with the tires. Hadn't seen those before. Cool but pricey.

The hub stands are kind of a multi-use item IMO - countless times have I wanted to have the car at an accurate ride height and be able to work or measure in the same space that the wheel is occupying. Just the way I'm going about it.

I also like hub stands, but not the billet non-adjustable type.  With those you can't change ride height (hub height). But I'm a big fan of the adjustable height versions.  Allstar used to offer them quite affordably. See image.  But they've been discontinued.



The Wehr Machine setup plates are off the hook great.  They act as your hub stand & toe plate together ... plus they're adjustable for height & have rollers to ensure there is no tire or suspension bind. See image below.  Website HERE. We sell Wehr & use a lot of their stuff.  When we add a tool section to our catalogs, these will be in there. Not super cheap. $700 for 2 or $1400 for 4. (RSRT offers free shipping on this item)

Quote from: Ryan Kennedy on Mar 19, 2026, 12:14 PMRamps aren't one I've found can be used by yourself.

Agreed. If one person was working on doing this, we'd use jacks to lift one side of the car, then put the two scale stands (with scales) under one side. Then the other. No ramps needed.  Just don't let the car roll off the scale stands!  LOL

We put thick aluminum stops on each end of the stands so that wouldn't happen, unless the car was pushed with power.

Yay, some discussion!

Ron, making slip plates as you've described is something I've done before and it seemed to work well. The roll-offs and ramps are also an option. I was looking at cost and ability to use by yourself. Ramps aren't one I've found can be used by yourself. Had them at a Mazda shop I worked at and it was the best way. Only thing is, there's no amount of roll that can happen before you start rolling down to ground level and then need help getting the car back up onto the scales.

The levelers and roll-offs are the one I was considering before looking more into hub stands. In your opinion, is the foot or so you're able to roll back enough to unload the wheels? Levelers and roll-offs are still more expensive than what I'm trying with the hub stands, but you still have me with the cost of nearly nothing using greased slip plates. Longacre also has their billet levelers with rollers so the scales move with the tires. Hadn't seen those before. Cool but pricey.

The hub stands are kind of a multi-use item IMO - countless times have I wanted to have the car at an accurate ride height and be able to work or measure in the same space that the wheel is occupying. Just the way I'm going about it.