Art Morrison IRS, 73 Camaro

[David Pozzi]

It's way better right out of the box! Sure footed is the best description I can give of it. The car isn't upset as easily and the street manners are outstanding!
Mary has done two local autocrosses and one in San Diego where she won the new SCCA Tour CAM (Classic American Muscle) class.

[fleet]

Very helpful info David.

Feel free to post much, much more on the subject.

[Damn True]

Awesome stuff.

[mfain]

Very nice. When you can share, I would be interested in your thoughts on the roll center height versus spring rates and whether you are running any toe steer with bump.

Pappy

[David Pozzi]

I don't have the roll center height data but they say it's very stable which is the main consideration, it moves 1:1 with the body.

We are starting from scratch on spring rates and shock valving. The motion ratios are different from the stick axle we had, more like the front now. We are at 450 in spring rate which is what Morrison runs on their 69 Camaro. It works very well, I doubt we will be far from that in a year from now, but time will tell.
We started with an aggressive toe steer setting (toe out in bump) we found that to be too much and backed it down to pretty close to what Morrison runs on their 69 right now. We will experiment further.
I'm not much up to speed on the "numbers" yet, we have been so busy just getting it into the car. I'm not sure my Performance Trends software can even handle this type of suspension. I kinda doubt it.

[mfain]

Originally Posted by David Pozzi

I don't have the roll center height data but they say it's very stable which is the main consideration, it moves 1:1 with the body.

We are starting from scratch on spring rates and shock valving. The motion ratios are different from the stick axle we had, more like the front now. We are at 450 in spring rate which is what Morrison runs on their 69 Camaro. It works very well, I doubt we will be far from that in a year from now, but time will tell.
We started with an aggressive toe steer setting (toe out in bump) we found that to be too much and backed it down to pretty close to what Morrison runs on their 69 right now. We will experiment further.
I'm not much up to speed on the "numbers" yet, we have been so busy just getting it into the car. I'm not sure my Performance Trends software can even handle this type of suspension. I kinda doubt it.

Thanks David. I use Performance Trends for various IRS designs. The data enters like a double a-arm front suspension with X,Y, and Z measurements of the pivot points. It will yield moment center, instant centers, camber gain, and the like. I am anxious to see Mary's car perform in person.

Pappy

[David Pozzi]

Originally Posted by mfain

Thanks David. I use Performance Trends for various IRS designs. The data enters like a double a-arm front suspension with X,Y, and Z measurements of the pivot points. It will yield moment center, instant centers, camber gain, and the like. I am anxious to see Mary's car perform in person.

Pappy

That's encouraging, I have to get all the measurements for it.

[Ron in SoCal]

Thanks David. Great to see a straight up review.

How's the First Gen coming? I think we need a project thread on it

[David Pozzi]

Originally Posted by Ron in SoCal

Thanks David. Great to see a straight up review.

How's the First Gen coming? I think we need a project thread on it

Ron,
I have my rear IRS in the shop for my 67 Camaro & will begin the install within the next week. I've been told there is very little cutting needed compared to a second gen. My engine should be done in a month so I can start building my headers then. It's a tall deck RHS block. I think I'll get it running before doing the body work, then finish the fenders to suit my wheels and tires, then tear it down over winter and paint it. Autocross is ending at Marina by the end of the year and I'd like to run the car a few times locally & work on the setup before I have to start towing longer distances to events. If I don't get it running by late year, I'll just paint it, then run it next year. I'd love to have it in good shape for the USCA events next year.

I'll start a project thread when I make some progress on the IRS install. Not much to see right now except the junk I'm throwing out/moving in my shop, I'm making room so I can move my Camaro around.
The nice thing is, our cars will be the same under the skin, Although I'm running the LG drop spindles and Mary isn't.

Morrison recommended I get new frame rails with my IRS. They make their own first gen frame rails. The assembly comes as shown below and I was advised to fit it in the car as a unit. They recommend cutting out the factory frame rails but leaving the spot welded flanges in place. This gives a thicker area to weld the new rails to. I'll sand blast the stock rails before cutting. The paint on Mary's frame rails was tough to remove, it's whatever JCG used.

The suspension comes aligned so you can measure from the hubs to the fender openings to get it centered up.
My IRS:

[Damn True]

Originally Posted by David Pozzi

Autocross is ending at Marina by the end of the year and I'd like to run the car a few times locally & work on the setup before I have to start towing longer distances to events.

HOLD THE PHONE!

WHAT?!?!?!?!?!?