New Art Morrison IRS

[andrewb70]

It would surprise me if AM just copied the 5th Gen Camaro geometry. Yes, the rear spindles are from the Camaro, but the Camaro rear track length is about 64" whereas the widest AM IRS is 60.5".



Another thing to consider is that the AM IRS is probably designed for a much lower ride height than the stock Camaro, so I can see where the axle shaft angle issue would not be a problem here. Ideally, the rear axles should point down slightly (or be level) from the diff to the spindles at ride height. This way, as the suspension goes through it's range of motion, both in bump and rebound, the axle angle doesn't vary much from straight. I ca see how on a heavily lowered 5th Gen Camaro the axles might actually point up towards the spindles at ride height. This would be detrimental when power is applied and the suspension is further compressed and the axle angle increases even more.

Hopefully AM took all this into account.

Andrew

[David Pozzi]

Morrison has it in their 69 Camaro, Mary & I drove it & we felt nothing like wheel hop that would cause damage. The axles looked pretty level when I looked under it but we will know more when we install ours. Every link is beefed up compared to a Camaro. It uses Camaro outer aluminum knuckles & a similar layout but not exactly the same. There is a separate adjuster for toe-steer, & another for toe-in.

[j-c-c]

I am surprised by the few comments that have disdain for inboard discs, with the reason being brake cooling?, seems to me anyone running hard enough to overheat their rear inboard discs would: 1. find a way to cool them, since it has been done 2. really appreciate the reduction in unsprung weight of inboard discs, especially if they made the effort to convert to IRS in the first place.

[David Pozzi]

The rear axle housing would need to have caliper mounts on it.
The rear axles would have stress reversal pressures.
Brake torque would not be reacted through the suspension links, meaning there would be reduced anti-squat.
There will be a lot of heat thrown off by the discs, right ahead of the fuel tank, you'd have to figure out how to cool them plus divert the heat away from the fuel tank.

Not insurmountable, but is enough gained to be worth it? It's not something I'm ready to take on right now.

[silver69camaro]

Hi Guys,
Thanks for the nice words about our new setup. I haven't been on here much lately, mostly because for the past 3 years I've been eyeballs deep in multilink research and design. I'm proud to finally see this design come to life, and to have it perform above and beyond my expectations was just icing on the cake.

There were a couple things I wanted to say, although David has covered many things.
1. The geometry is not from a 5th gen Camaro. While it uses 5th gen knuckles, that's it - that's where it stops. I studied multilink design for a couple years, and while the GM design is pretty good (despite some issues that stem from bean-counters), it could use lots of improvement.
2. We chose not to use a 9" for a couple reasons. First, Strange did an absolute fantastic job with their Dana 60 replacement diff, it's beautiful and robust. Best of all, it uses OEM gears for zero noise. Guys have taken the stock diff into the 9s, and this could go further. This unit is light, durable, quiet, and well designed.
3. While I like the CTS front platform, I wasn't a fan of the rear. It had some issues that I felt weren't appropriate for what we are aiming for. It's great for the CTS, but just not what I was looking for.
4. CTSV, about the line in the catalog about being influenced in other designs, it's absolutely true. Several years ago Craig and I went to a high end Porsche shop and saw a multilink rear suspension that could possibly fit under musclecars...and that's where it all started. Just about every (if not all) high end manufacturers use multilinks in back, and some of the geometry properties that make those cars special have been put into this suspension. It just so happened that GM had a knuckle that was the height I needed, the general layout I wanted, accepted a Corvette wheel hub, was reasonably affordable, and had great brake options. I couldn't have been happier! I was looking for a good year for a knuckle that would work right and I was starting to think it may never happen.
5. I agree that solid axles are great for most people, we and DSE have proven they can work well. We have always wanted to take it a step further, but until the multilink became available, there wasn't an IRS design out there I was happy with. Good IRS designs will introduce toe control, camber control, and reduced unsprung weight that a solid axle can't offer. And while this suspension really shines on the track, the streetability was even better. Ride quality is excellent, very much reduced NVH, and turn-in is better than I had originally hoped for. But again, solid axles can work well too.
6. The sway bar is a two-piece design as packaging is so tight a one piece bar wont fit. The couple we designed IMO is a work of art and took a couple weeks by itself in design time.
7. Like David said, the UCA is bent to allow for rail clearance. The rear crossmember is bent just to give the rear diff bracket something to weld to.
8. While this fits great in Camaros, we will offer it in just about every chassis we make. Some trunk designs are very accomodating for ours IRS, some are not. In any case, every car should be able to retain the factory rear seat.
9. This does not use 5th gen Camaro hubs. They are C6, which still has the standard 5x4.75 bolt pattern. This also allows for the upgrade for ZR1 hubs.
10. The coilovers attach to the vehicle's frame, not the cradle. This allow me to select the type of forces the cradle (and it's bushings) will experience to improve longitudinal and lateral stiffness without resorting to very expensive custom cradle isolators.

I think that's about it. I could go on and on about details but I simply don't have the time. Thanks guys.

[Cdog]

Hi Guys,
Thanks for the nice words about our new setup. I haven't been on here much lately, mostly because for the past 3 years I've been eyeballs deep in multilink research and design. I'm proud to finally see this design come to life, and to have it perform above and beyond my expectations was just icing on the cake.

There were a couple things I wanted to say, although David has covered many things.
1. The geometry is not from a 5th gen Camaro. While it uses 5th gen knuckles, that's it - that's where it stops. I studied multilink design for a couple years, and while the GM design is pretty good (despite some issues that stem from bean-counters), it could use lots of improvement.
2. We chose not to use a 9" for a couple reasons. First, Strange did an absolute fantastic job with their Dana 60 replacement diff, it's beautiful and robust. Best of all, it uses OEM gears for zero noise. Guys have taken the stock diff into the 9s, and this could go further. This unit is light, durable, quiet, and well designed.
3. While I like the CTS front platform, I wasn't a fan of the rear. It had some issues that I felt weren't appropriate for what we are aiming for. It's great for the CTS, but just not what I was looking for.
4. CTSV, about the line in the catalog about being influenced in other designs, it's absolutely true. Several years ago Craig and I went to a high end Porsche shop and saw a multilink rear suspension that could possibly fit under musclecars...and that's where it all started. Just about every (if not all) high end manufacturers use multilinks in back, and some of the geometry properties that make those cars special have been put into this suspension. It just so happened that GM had a knuckle that was the height I needed, the general layout I wanted, accepted a Corvette wheel hub, was reasonably affordable, and had great brake options. I couldn't have been happier! I was looking for a good year for a knuckle that would work right and I was starting to think it may never happen.
5. I agree that solid axles are great for most people, we and DSE have proven they can work well. We have always wanted to take it a step further, but until the multilink became available, there wasn't an IRS design out there I was happy with. Good IRS designs will introduce toe control, camber control, and reduced unsprung weight that a solid axle can't offer. And while this suspension really shines on the track, the streetability was even better. Ride quality is excellent, very much reduced NVH, and turn-in is better than I had originally hoped for. But again, solid axles can work well too.
6. The sway bar is a two-piece design as packaging is so tight a one piece bar wont fit. The couple we designed IMO is a work of art and took a couple weeks by itself in design time.
7. Like David said, the UCA is bent to allow for rail clearance. The rear crossmember is bent just to give the rear diff bracket something to weld to.
8. While this fits great in Camaros, we will offer it in just about every chassis we make. Some trunk designs are very accomodating for ours IRS, some are not. In any case, every car should be able to retain the factory rear seat.
9. This does not use 5th gen Camaro hubs. They are C6, which still has the standard 5x4.75 bolt pattern. This also allows for the upgrade for ZR1 hubs.
10. The coilovers attach to the vehicle's frame, not the cradle. This allow me to select the type of forces the cradle (and it's bushings) will experience to improve longitudinal and lateral stiffness without resorting to very expensive custom cradle isolators.

I think that's about it. I could go on and on about details but I simply don't have the time. Thanks guys.

Matt,

Great post. So we have installed the AM Tri-4 link in my 69 Camaro we are building to get back out there with the pack. Will this new IRS work with the AM frame portion of the tri-4 link? If so can you illustrate how it would install?

Thanks in advance.

[silver69camaro]

Matt,

Great post. So we have installed the AM Tri-4 link in my 69 Camaro we are building to get back out there with the pack. Will this new IRS work with the AM frame portion of the tri-4 link? If so can you illustrate how it would install?

Thanks in advance.

Yes it works great with your subframe and is the same setup we have in our Camaro. At a minimum, remove the forward LCA brackets and the rear cross tube (by the fuel tank). We elected to remove the sway bar and UCA frame brackets as well, just to make it clean. From there:
1. Mock up the IRS in the car with the frame brackets bolted on.
2. Center the wheel in the wheel arch, check for square.
3. Tack the frame brackets to the subframe.
4. Remove IRS then fully weld brackets.

On a first gen, there are two small sheetmetal areas that need to be cut - and thankfully they are small and easy to patch. I'll see if I can dig up some photos. The rear seat can stay as well as the stock fuel tank. If a person were to buy the rear subframe from us along with the IRS, all the bracket fitment will be done here at AME.

The cradle can be removed with just four bolts. It's very easy. If you're interested and need more info, PM me and we'll go from there.

[Cdog]

Yes it works great with your subframe and is the same setup we have in our Camaro. At a minimum, remove the forward LCA brackets and the rear cross tube (by the fuel tank). We elected to remove the sway bar and UCA frame brackets as well, just to make it clean. From there:
1. Mock up the IRS in the car with the frame brackets bolted on.
2. Center the wheel in the wheel arch, check for square.
3. Tack the frame brackets to the subframe.
4. Remove IRS then fully weld brackets.

On a first gen, there are two small sheetmetal areas that need to be cut - and thankfully they are small and easy to patch. I'll see if I can dig up some photos. The rear seat can stay as well as the stock fuel tank. If a person were to buy the rear subframe from us along with the IRS, all the bracket fitment will be done here at AME.

The cradle can be removed with just four bolts. It's very easy. If you're interested and need more info, PM me and we'll go from there.

Thanks for the info. We’re going to build the 69 with the tri-4 first then look at this as an evolution with the car. We had a meeting over last weekend discussing our build time frame. I brought the new AM catalog to show it off. Needless to say we’re big fans. We need more Art Morrison products over at Starlite Garage.

[andrewb70]

Matt,

Thanks for chiming in.

Can you elaborate more on things like camber and toe curves as well as the anti-squat characteristics?

Also, I would like to know how this system integrates with the A-body frames and the front suspension used on them.

Andrew

[silver69camaro]

Sure thing Andrew.

Camber gain is a consistant 0.520 degrees per inch of travel, antisquat is similar to our 3-link, about 40% but that changes pretty easily depending on the vehicle. Roll center movement is 1:1 with chassis height, and lateral migration is on par with our C6 front suspension.

The toe curve is a bit different than what you may be used to, and this may sound a bit silly, I'm not sure how many details I want to divulge as it is a bit of a trade secret. It will toe out and toe in by various amounts in order to steer the rear axle into a corner, but large amounts of bump travel (say a pothole or similar) will toe in about 0.017" for stability. The magnitude of the roll steer is adjustable by an eccentric on the cradle, and will be pre-set at a conservative amount here at AME. Careful tuners will really find this helpful as they can fine-tune handing woes caused by various factors (too much/little rear grip, too much/little power, very short/long wheelbases, extra tight autocross courses, etc). With street driving, as David had mentioned, the rear turn in is very sharp and may feel almost alarming at first but the amount of grip is amazing.

Because of the sensitivity of the cradle toe-link location, our lead shop man built a tool for the cradle that has astounding accuracy. After every component is welded, side-to-side pivot measurements are typically within .008" of each other - something that I wouldn't have thought was possible. It's quite amazing.

Moving on to the A-body, they will require a bit of sheetmetal work behind axle C/L, but nothing in the front. Fuel tank is fine, rear seat is fine. I can't say much about about the aftermarket front suspensions other than ours, as I don't have detailed data on critical metrics.

[andrewb70]

Matt,

I sent you a PM.

Andrew

[CTSV]

Ok i was really looking this over again today in the AM catalog i received and this question is for AM direct or its reps

it looks like this IRS rear cradle has 4 mounting locations with pressed in rubber bushings almost like a modern OEM type rear IRS subframe.

How does this work on a 69 Camaro? what is involved making this bolt in or is this welded in while replacing the rear OEM frame rails?

Also im just a bit confused are you making these IRS for various cars or just one system as shown in your catalog that must be retrofitted to any car? Will you be offering this IRS on your full chassis in place of the 4 links you currently offer?

i think it looks great i am just wondering what this will take to install in lets see a Mustang, Camaro, Chevelle or Corvette. Please fill in those details as I am in the process of building another car with IRS and i had my mind set on a Fast Track Chassis.

[silver69camaro]

When using our IRS, you have the option of purchasing our brackets (that weld to the stock frame) in which the IRS cradle bolts to, or you can purchase a subframe/full frame from us with those brackets already integrated. In terms of a Camaro, we've had our rear subframe available for a couple years that only requires the OEM frame rails to be removed. That same subframe can be outfitted with the cradle brackets (like our car has). While you could weld to the OEM rails, they are very thin and I don't recommend attaching much of anything to them. You could reinforce the rail, but by the time you are done, it would have been faster to install our subframe. So in short, every frame we currently offer (builder's platform or bolt on, sans trucks) will have the IRS available.

The amount of cutting required, if any, is determined by the OEM sheetmetal profile. No way around that. Some cars have more room than others. We have one cradle design that is extremely compact and will work very well in most cars, but it can't fit everything.

Does that answer your questions?

[HellPhish89]

..this is going to possibly be a pie in the sky/stupid question but... any plans to make it work (with a weld in bracket kit) in later generations of FBody? like say.. a third generation car?

[andrewb70]

..this is going to possibly be a pie in the sky/stupid question but... any plans to make it work (with a weld in bracket kit) in later generations of FBody? like say.. a third generation car?

The cradle looks easy enough to adapt to a wide range of chassis. I bet if you found a competent chassis shop in your area it wouldn't take them a lot of work to make the mounts for the cradle in any chassis.

Andrew

[silver69camaro]

..this is going to possibly be a pie in the sky/stupid question but... any plans to make it work (with a weld in bracket kit) in later generations of FBody? like say.. a third generation car?

The only thing we could do in that case would be to:
1. Draw up a weld-in clip complete with frame rails with cradle mounts already attached (we've done a few for those cars, but mostly drag 4-links)
2. Give you cradle brackets that you weld in to your factory unibody rails (provided they are in good shape and are of sufficient thickness)

[David Pozzi]

Nearly done with the install, I'll post some details once I'm finished. It's been way more cutting & welding than a first gen, but turned out pretty nice.


Frame supports are 2" wide on each side of the flat panels. I put some bead rolls into them to stiffen them up.


I raised the floor placing it on top of the new crossmember. The raised floor allows space for the mufflers, there is around 1/2" clearance. There is a factory kickup in the area of the crossmember, so the forward edge of the stock floor lays on top of it.

Below, you can see the edges of the old floor along the edges of the frame rails. I think it may have worked better to have placed the frame braces farther inward closer to the edge. It would look cleaner.


Thermo Tec insulation added.


I cut the corners off the trunk which gained a lot of access room to get at the subframe bolts and upper shock mounts.
I still need to cut holes for the shock reservoirs to pass through.

[jtwoods4]

That is beautiful. Nice job.

[MrQuick]

Nice work David. So its a bolt in cradle? Can't wait to hear some feedback on the new set up.

[David Pozzi]

It goes in & out pretty easily with just 4 bolts.
We should have the car at Pleasanton Goodguys.