New Art Morrison IRS

[CraigMorrison]

The only reason I am talking about the ZL1 rear diff is because the Strange can only go down to a 3.50 gear, while the ZL1 is offered in a 3.23.

Andrew

Andrew, it should definitely fit, but keep in mind that we are building a new back cover for both the OE Camaro diffs and the Strange diff. The stock Camaro configuration has it's rear mount offset to one side. Because we are doing multiple track widths, we have centered that mount, if we hadn't we definitely wouldn't have been able to pull off the 55.5" option.

[dontlifttoshift]

What is the maximum wheel backspace with an 18" wheel?

Would it be safe to assume that the widest track width may offer the best suspension geometry?

[silver69camaro]

What is the maximum wheel backspace with an 18" wheel?

Would it be safe to assume that the widest track width may offer the best suspension geometry?

Yes, wider is typically always better. However, our multilink can get away with narrower track widths because the links provide direct load paths that efficiently transfer forces to the cradle. Because of this I'm comfortable suggesting a track width that is a couple inches narrower than what a typical IRS can allow - unless the person has an extremely powerful engine with sticky tires.

18" wheels, assuming the hoops are spun aluminum, will allow a backspace of 7.5".

[andrewb70]

Yes, wider is typically always better. However, our multilink can get away with narrower track widths because the links provide direct load paths that efficiently transfer forces to the cradle. Because of this I'm comfortable suggesting a track width that is a couple inches narrower than what a typical IRS can allow - unless the person has an extremely powerful engine with sticky tires.

18" wheels, assuming the hoops are spun aluminum, will allow a backspace of 7.5".

So Matt, ideally, on a GM A-body would you run the 61.5" rear with the biggest offset wheel possible?

Andrew

[silver69camaro]

So Matt, ideally, on a GM A-body would you run the 61.5" rear with the biggest offset wheel possible?

Andrew

For ideal geometry, yes. But for this suspension a 59.5" would work great too.

[andrewb70]

For ideal geometry, yes. But for this suspension a 59.5" would work great too.

I guess using a slightly narrower rear will allow the wheel to have more of an outer lip which tends to look better on older cars.

Andrew

[CraigMorrison]

I guess using a slightly narrower rear will allow the wheel to have more of an outer lip which tends to look better on older cars.

Andrew

Exactly!

[PPG TRIGGER MAN]

Well I've been reading this thread with interest because I recently bought an entire ZL1 rear setup. I looked at the AM piece, and it is awesome, but the price was more than the budget would allow. I was hoping someone else had taken the ZL1 rear and utilized it already so I could get some feedback. I got the whole setup with 14" brembos for less than 4k so it was too tempting to pass up. The other thing is i'm using it in a big car that will see more street time than anything else. The car is a 62 Buick Lesabre. for the front i'm using mustang II from Hiedt. I'm going to build the rear rails higher in the car so hopefully I can get the stance low while maintaining good geometry on the cv's. Here is a couple pics of the unit.

[David Pozzi]

Simple. Mary and mike are very fast. If Mary, or David, would have beaten Mike by a good margin, I would say that the new rear is worth it's weight in gold.

In general, this makes sense. One issue though is Mike, like us, is always improving his car so what beats what today may not hold up next weekend. At Del Mar last year, Mary beat Mike by .003 seconds, so any improvement by him could possibly put him ahead, but she won't be competing against 2013 Mike, with the old lower HP engine, it will be 2014 Mike with the Roush engine back in the car. BUT! She now has the IRS! :-)

[andrewb70]

There are several reasons why I am even discussing the ZL1 rear. First is cost, and probably least important is cost. A new ZL1 diff can be had for under $2000. Secondly, in my instance, I really want to run a gear ratio less than 3.54. The auto ZL1 gear is 3.23. Lastly, I want to use a CV joint at the rear and The Driveshft Shop make a simple adapter that bolts to the ZL1 3 finger flange that will accept a CV joint.

I am eager to see how Mary does this year as she learns to drive with the new rear and it gets tuned.

Andrew

[silver69camaro]

There are several reasons why I am even discussing the ZL1 rear. First is cost, and probably least important is cost. A new ZL1 diff can be had for under $2000. Secondly, in my instance, I really want to run a gear ratio less than 3.54. The auto ZL1 gear is 3.23. Lastly, I want to use a CV joint at the rear and The Driveshft Shop make a simple adapter that bolts to the ZL1 3 finger flange that will accept a CV joint.

I am eager to see how Mary does this year as she learns to drive with the new rear and it gets tuned.

Andrew

Andrew, why not look at the aluminum diffs? They'll save lots of weight, and notice on the Z/28 they switched from the iron ZL1 diff to the aluminum case again. Granted the Z/28 used a different gear, but we do offer the smaller aluminum diff in 3.23. If the OEM diff saves about 30lbs over the Strange aluminum diff, I'm sure it's 50+ over the ZL1. The OEM diff is pretty durable, and if you're road racing, add a fluid pump (it would be easy to do).

Just a thought.

[andrewb70]

Andrew, why not look at the aluminum diffs? They'll save lots of weight, and notice on the Z/28 they switched from the iron ZL1 diff to the aluminum case again. Granted the Z/28 used a different gear, but we do offer the smaller aluminum diff in 3.23. If the OEM diff saves about 30lbs over the Strange aluminum diff, I'm sure it's 50+ over the ZL1. The OEM diff is pretty durable, and if you're road racing, add a fluid pump (it would be easy to do).

Just a thought.

Good thought Matt. I am concerned about durability. Is the ring gear size the same on the aluminum diffs as it is on the ZL1? I thought the ZL1 had a bigger ring gear.

Andrew

[silver69camaro]

Good thought Matt. I am concerned about durability. Is the ring gear size the same on the aluminum diffs as it is on the ZL1? I thought the ZL1 had a bigger ring gear.

Andrew

The ZL1 is quite a bit larger, yes. The standard diff is 8.6", the ZL1 is about 9.9". Best I can tell, the Z/28 uses the smaller diff. I have a couple sources that I can ask, that info doesn't really seem available yet.

[keithq69]

I'm not sure if the Z28 is going to use the 8.6" aluminum section or an aluminum version of the ZL1 differential.
I have been trying to find out too but can't find any information.
The ZL1 has a built in cooler in the housing and the Z28 is going to have a cooler also so I'm thinking it may be a new housing.
Would love to know the specs if anyone had an inside track.

Keith.

[andrewb70]

I'm not sure if the Z28 is going to use the 8.6" aluminum section or an aluminum version of the ZL1 differential.
I have been trying to find out too but can't find any information.
The ZL1 has a built in cooler in the housing and the Z28 is going to have a cooler also so I'm thinking it may be a new housing.
Would love to know the specs if anyone had an inside track.

Keith.

Keith,

One way to tell would be if the part numbers for same ratio ring and pinion gears are the same between the ZL1 and the Z/28. The manual ZL1 gets a 3.73 gear as does the Z/28, however, it doesn't look like the R&P area serviceable items. I did a little looking around and it looks the the rear end assembly is sold complete.

Ultimately, I am just splitting hairs here. For the vast majority of power train combinations a 3.54 or numerically higher gear ratio is perfectly suitable. In which cace, the use of the S60 rear is ideal because it is both lighter and probably stronger than even the ZL1 rear end. It is just that for what I have envisioned (for my particular combination), I need huge torque capacity and something like a 3.08 or 3.23 gear.

Also, cudos to AM for using the gen 5 Camaro rear knuckle assembly. If it ever needs to be replaced it looks like the cost is less than $140 each!

Andrew

[keithq69]

I think the Z28 might use a 3.91 gear like the 1LE car does.
There are no part numbers or information available yet for the Z28.

[CraigMorrison]

Also, cudos to AM for using the gen 5 Camaro rear knuckle assembly. If it ever needs to be replaced it looks like the cost is less than $140 each!

Andrew

Thanks Andrew, but the thing that's really great about this part is that it's so darn compact. With the top to bottom height being relatively short it lends itself to be packaged into a lot of applications where extra fab work is at a minimum.

[silver69camaro]

I'm not sure if the Z28 is going to use the 8.6" aluminum section or an aluminum version of the ZL1 differential.
I have been trying to find out too but can't find any information.
The ZL1 has a built in cooler in the housing and the Z28 is going to have a cooler also so I'm thinking it may be a new housing.
Would love to know the specs if anyone had an inside track.

Keith.

My sources say the ring gear is the small diameter, and the housing is "similar if not the same" to the current production SS aluminum housing. The Torsen diff is a big plus, it is well tuned. A cooler would be easy to add to any housing.

[andrewb70]

Matt,

Do you have any insight as to how this set-up might work in a drag racing scenario? I realize that an IRS is far from ideal for drag racing (I am familiar with some challenges having owned a second gen RX7 and trying to drag race it), but how do you suppose it might work?

Andrew

[silver69camaro]

Andrew,
To be perfectly honest it's tough to say without trying it in a real high HP with sticky tires. One thing I can say is, it should work better than a Gen 5 Camaro does. Geometry is different, and the bushings are much much stiffer. I suspect it will do well, obviously not like a true 4-link however. I'm not concerned about strength, as the load paths are very efficient and axles are extremely strong.