Can IRS handle a 514?

Jahred · #1 (**permalink**) 03-05-2002, 04:02 AM

I am curious on thoughts on this. I have a Ford 9in with Moser axels and the Power Trac locker rear end.

The SVC rear end is also pretty heavily braced/triangulated. Very solid off the line. Kicks out a bit in first and second but seems to apply as good a traction as the rubber can handle.

A guy in my neighborhood (have not run with him yet) has a 514 with IRS. He has suggested he can't get traction in 1-3, has suggested his tires arent soft enough.......and I assume his can't get traction is partly bravado.

I have heard though, that with too much low end torque/HP that IRS will create "lift" on inner or outer edge of wheels causing at least temporary loss of traction.

How severe is this problem and is the IRS really suited for 600+HP application?? Is it a function of which IRS you have?

cobrashoch · #2 (**permalink**) 03-05-2002, 10:27 PM

This one has been hashed out on this board a few times. It really comes down to personal preferance with a eye on what you want to do with your car. I guess my question is what do you mean by can it handle a 514? If you are talking about keeping a IRS glued together the answer is yes. There are many guys that have used them very successfully in many Cobras. I would spend some time here inspecting them from time to time dependent on your abuse level though. If you are talking about traction control though that's another animal. Again the choice is dictated by your use. The 9 inch live axle will by in large take more abuse but on a cobra the IRS will give you more compliance and a bit of a better ride. If you drag race I personally lean to the live axle. If your into road racing on rough surfaces the nod goes to IRS. Not talked about much here is that a live axle can indeed work well on road course racing if the going is not too rough.
I personally have had bad things happen on half shafts of IRS setups. No one has shown me yet half shaft universals/cv's that can live long on 650/700 lbs of torque. Lots of guys will argue that with me though. When one of those things breaks under throttle or hard breaking the nasty result is a very rapid and hard forced turn. So if you go that way be sure to insect this weak spot regular. The NHRA now requires half shaft loops as well as drive shaft loops on IRS cars to.
A few years ago the NHRA required cars that had over 600hp to use a live axle. This has changed of recent due to Vipers and high horsepower stock Corvettes and other cars, as they had to do something with those cars. It doesn't change the wisdom of that thought process of old, at least in my mine.
So my answer is to weigh what you are doing very carefully and for crying out loud research it better than on this forum. It's your life we are talking about here.
cobrashoch

Jeff Frigo · #3 (**permalink**) 03-06-2002, 12:05 AM

If you are using street tires, don't worry about it. If you are going to use sticks, cheaters, or BFG drag radials, you had better use chrome moly. stub shafts (not to be confused with half shafts). That is the weak link in a Jag rear end. Click on the link below and call these people. They can help you more.

IRS Parts

HighPlainsDrifter · #4 (**permalink**) 03-07-2002, 08:00 PM

NO. The 9" ford you have is many times stronger and more reliable than an IRS with U joints and half shafts.A jag rear is made for 250 ft/lbs of torque,not the 600 you have.A t-bird is made for 300 ft/lbs. You can get a custom built 9" IRS from a number of suppliers,but then you need a road racing expert to set the camber and caster on the rear end. All factory cars with IRS are set up with oversteer as a comprimise so the driver doesn't put it in the ditch. Set up as a performance alignment will be much more reactive and you will need to pay attention as the car will let go too fast for most drivers.
Perry.

Jeff Frigo · #5 (**permalink**) 03-08-2002, 05:57 PM

HighPlainsDrifter:

You mean understeer. Also there are many cars that run well into the tens with Jag rear ends.

HighPlainsDrifter · #6 (**permalink**) 03-09-2002, 05:16 PM

If someone is foolish enough to run that fast and have a rear link break,they can kiss his $ss goodbye as he turns into the guardrail at 120 mph and rolls over 5 or 6 times before sliding to a stop. They would not run on a sactioned track.