IRS vs. Solid Axle Quarter Mile performance? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 9 Old 04-15-2002, 09:10 AM Thread Starter
kc
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IRS vs. Solid Axle Quarter Mile performance?

Is there anyone out there who has swapped from IRS to a solid axle on a Cobra (or put a Cobra IRS in a GT) that has good before/after data on the quarter mile ET/Trap speed differences between the two?

(Preferably no other changes than what was necessary to make the swap, i.e. same gear ratio, etc.).

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kc

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post #2 of 9 Old 04-15-2002, 10:12 AM
 
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Well I ran a 14.4 in my stock 01 Cobra with the IRS . . . mostly because I didn't know how to drive but also because at 2k rev it hopped like CRAZY so I had a crappy launch of 2.511 60' time!!!

After the live axle I just ran last week and got a 13.21 time with a 1.753 60' time!! Now I also had sticky tires and 4.56 gears and fortified my rear end!! However, the problem with the IRS isn't that is CAN'T work because Joe Lynch has proven that it CAN work as a drag car!!

The problem is MONEY!! It cost LOTS of money to make it work!! For example if I were to get 4.56 gears with the IRS I would NEED sticky tires to get any launch at all!! Well with sticky tires more pressure is put on the halfshafts which are not made very well so you have to replace those - and your talking $1,000 just for that!!

I got the live axle for FREE and only spent $900 on parts in the rear and was launching at 6K at the track with ET Streets and NO wheel spin!! For me as a drag racer the live axle is the way to go . . and to be honest I don't notice that much drive difference and neither does anyone else I know that has Cobra's and has ridden with me!! Just IMO

Hope this helps!

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post #3 of 9 Old 04-15-2002, 12:22 PM
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All things being equal, the solid axle is easier to launch, weighs less, and costs less to setup.

But, it is possible to get 1.7 60's with 17" DR's using the IRS, if it's setup correctly, I've done it.

In a drag only car, I'd go with a solid axle, but I enjoy all the capabilities of my car, and the IRS made it a better car.

p.s. I probably wouldn't have swapped in a T-56 either (weighs more), but it also made the car much better overall.

98 Laser Red/Black Cobra Coupe (T56/IRS)
12.483 @ 110.94
95 Pearl White Thunderbird SC 5spd
12.879 @ 106.66
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post #4 of 9 Old 04-15-2002, 05:05 PM
 
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I did the swap but unfortunately changed other things as well. Before the swap w/ the IRS I got a best of 13.7 @103 w/2.01 60' STOCK.
This past weekend w/ the mods in my sig I ran a 13.304 @104 w/ 1.987 60'
I love the solid axle it just hooks and goes, no more wheelhop for me. Then again I also love the ET Streets I can run now.
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post #5 of 9 Old 04-15-2002, 05:16 PM
 
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I believe the IRS on cobra works good and with minor upgrades and work great. I have run a best of [email protected] at a horable track. All the IRS requires is practice launching, many people just want to stomp on the gas and go. With a good driver these cars are great.
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post #6 of 9 Old 04-15-2002, 09:53 PM Thread Starter
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Thanks, guys. I appreciate the input.

Purely from an acceleration standpoint, I would expect the solid axle to perform slightly better due to reduced parasitic losses and less weight, along with potentially less wheel hop.

Just trying to quantify what the true advantage would be. If anyone else has good before/after results, please post.

kc
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post #7 of 9 Old 04-15-2002, 10:16 PM
 
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My biggest justification for swapping was $370 per halfshaft or $600 for a complete solid axle. I just didn't want to dump the money into the IRS and still have the hop. I don't regret this mod at all
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post #8 of 9 Old 04-16-2002, 12:42 AM
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KC,

You can make it work at the strip, but like it has been said above it costs more. Don't try hard launches on the stock axles!!! They will break. I have R-axles and have been pretty fortunate but am probably living on borrowed time. I consistantly have 1.8 60ft times and can usually get a 1.7 every now and then. I've been happy with the IRS but of course now want more so I'm going to switch to a live axle. I'm keeping my IRS if I ever want to swap it back and use the live axle in a future project. See the times in the sig.

Couple of recalls by Ford, TOTAL RECALL by me
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post #9 of 9 Old 04-16-2002, 02:06 AM
 
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Joe Lynch isn't the only one who has made it work with the IRS, I followed Joe's lead and went with aftermarket 1/2shafts (Raxles), MT ET Streets on 16x10 diamond wheels and HAL 12-way adjustable shocks/Tokico 5-way adjustable struts. I can cut consistently good 1.7 60' times launching at 5k rpm's (not dumping the clutch) and last May ran a 12.7 @ 107 and later ran an 11.6 @ 120 with the JMS/Compucar dry nitrous kit. I have added a ported and polished lower intake manifold this past week and an AJE tubular K-member is going on the car tomorrow. I found out the throttle blades weren't opening all the way since I put the WOT microswitch on the TB, that problem was corrected when the new intake went on.

I ran the car at Road Atlanta this past weekend and it feels much stronger in the upper rpm's now with the new manifold. I plan on going to the track this weekend, weather permitting, and make a few passes on the motor only and see how low I can get into the 12's, then try the nitrous. The 99/01's can be decent strip cars with a little traction, I have no wheel hop at all with my setup, you just can't bounce off the rev limiter on the launch I made a big mistake last year by trying a 6k rpm launch on stock 1/2 shafts, it wasn't pretty...
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