I am trying to sort out the suspension on my AWD V8 Merkur XR4Ti. I have been drag racing it off and on for a few years and now I also want to AutoX it. I really seem to be able to spin the rear tires pretty easy even though the car is AWD. My 60ft time when launching in the 1/4 mile is nothing to write home about at about 1.7sec.

After doing a bit of research on suspension design and looking at the stock 3dr cossy rear setup I have it is rather obvious that it is not an ideal setup for drag racing The obvious thing to do is modify the rear beam to a 6 degree setup to minimize the toe and camber changes when the car squats during the launch. Which, this finally gets me to my point. Looking at the stock rear setup the trailing arm mounting points are at best level with the center of the wheels when stock and if the car is lowered at all the pivot axis of the trailing arms will be below the wheel center axis. This is bad from a traction standpoint is it actually generates pro-squat. This means that the rear suspension geometry actually helps the car squat rather then trying to resist it.

To decrease the amount of pro-squat and hopefully add in some anti-squat to make the rear bite, the trailing arm pickup points would have to be raised higher by several inches. I have scanned all of the pictures of the various versions of the "6 degree beam" and nobody seems to raise the pickup points. Why is this? It does look like the inner pivots would interfere with the floor if raised much above stock. This would require modifying the floor-pan under the rear seats a bit.

Thoughts?

 

Sorry I can't be of any help, but I would love to see some pictures of your car

 

Speak to mark at Mk motorsport, he produces the best beam and knows his onions

 

What was different with the rs500's I'm sure they had addition mounting points for the beam to sit different when in touring car guise?

 

Thanks for the responses guys. Mark, your V8 setup looks great.

Here are some specs on my car:
Here is what I have now:
Engine
327 SBF( 4X3, still has stock bore)
R302 short block built by Keith Kraft
Older Style AFR185 heads with upgraded Brian Tooley springs Ti retainers
8.5:1 Compression Ratio
Totally stock Edelbrock Performer RPM2
75mm Accufab TB
226/226 - .545/.545 - 114 LSA custom cam
Precision 74mm Turbo with the “GTS” turbine, .81 AR ratio
3.5in downpipe to 4inch exhaust.
Custom A/W using Garrett 1000hp core

Car
86 Merkur XR4Ti – Converted to All Wheel Drive
T56 six speed with Viper Gearset (2.66 first gear, .5 6th)
4:10 gears front and back
GMC Syclone Transfer case with viscous center differential
8.8 IRS in back with a Torsen
GM 7.25 in the front with an open Diff
The car is not light; it weighs about 3500lbs with gas but without driver.

As the car sits, my best time was an 11:008 @ 128.5 with a 1.7 60ft and 15lbs of boost on 93 octane pump gas.

Here are some pictures:












If you look at this group A square beam, it looks like the mounting points are much higher then stock.



Thanks,
Tim
XR4X4Ti

 

Car looks fantastic

Some clever engineering gone on to pack all that in and the weight is pretty good considering !

My daily driver Audi S4 is AWD V8 and it weighs in at 3660 lbs

I see what you mean about the group A beam and can only repeat what Caddyshack said, give MK Motorsport a try.

I assume you want to keep an IRS and not go for a live axle ?

This guy was running 12.2 with a worn out Cossy engine making around 260bhp using a 8.8 Mustang axle









Have you considered a WRC beam ?
I know it's not designed for the 1/4 mile, but I'm sure MK would be able to advise.

Pic of a MK version

 

You have a cool car matey.

What car is the gearbox out of?

 

It is a T56 based unit, but it is sort of a Frankenstein. It is basically a Viper Spec unit that has a Ford front cover and an input shaft modified to fit the SBF pilot bearing. The output shaft is from a Camaro along with the shift rod. The tail housing is from a C5 Corvette. I made the adapter between the tail housing and the transfer case which also houses the shifter. The shifter is a Ford style unit since they are shorter then the Camaro unit. It took a lot of thought to lay it all out.

Here is a better picture of the setup when I was fabricating the adapter.



I don't want to go solid axle. Even though that would be the best thing for drag racing. If I was going to do that, I should have just built a Mustang They are easy to get here!

 

Very nice car!!!
Do you have a tread, where you show all the details?
That would be nice to see.

Thanks
Mario

 

Very cool car.

 

Aren't the hubs pointing the wrong way in that pic?

 

Yes, the hubs are backwards

 

Thanks for the kind words.

Unfortunately I don't have a web page up at this time. I do have a domain name and plan to get it setup again, but my old host shut down and I have been to busy to get my web page going again.

 

I have been really considering this direction lately. But rather then using a strut, I would add an upper arm and try to keep the coil over rear damper in the stock location. This setup would make it easy to dial in anti-squat, camber curve, roll center, etc. I really like how this setup transfers the longitudinal loads directly to the chassis mounting points.