Need your opinion please

charlandk · #1 (**permalink**) 03-27-2010, 07:58 AM

Going with a Roush 427 sr/tw and T56 tranny, would you go with an open rear end or LSD and why?

Thanks,

Kevin

Snakebit · #2 (**permalink**) 03-27-2010, 08:50 AM

With that size motor and torque I would get LSD to get the power to the pavement.

Ron61 · #3 (**permalink**) 03-27-2010, 09:38 AM

With the light weight on the rear end of these cars I would go with the LSD on any car regardless of what motor you use. And especially if you plan to do any track time with it.

Ron

Silverback51 · #4 (**permalink**) 03-27-2010, 09:57 AM

I would go with the best available LSD system, short of a spool that will fit your rear end.

dcdoug · #5 (**permalink**) 03-27-2010, 01:58 PM

Madness to go with an open rear end, unless you want your driving experience to be burning up one tire at a time.

I prefer to burn up two tires at a time....

Gunner · #6 (**permalink**) 03-27-2010, 03:20 PM

Aye, with an open diff you'll burn one tire every time you start off with any level of fun. It will be a life of carefully easing up to speed or you'll break one tire loose and burn it until you lift throttle. A decent LSD is not an option on these cars.

patrickt · #7 (**permalink**) 03-27-2010, 03:51 PM

Don't stop with just a limited slip -- make sure it's paired with a fully independent rear suspension. A live axle in these cars is a ticket to the morgue.

charlandk · #8 (**permalink**) 03-27-2010, 05:39 PM

It will definately be paired with an independent rear suspension!

CoolCarl · #9 (**permalink**) 03-28-2010, 12:21 AM

OK, so I realize that IRS is better than a straight axle. My question is how much better? I'm in the process of researching kits, checking options, (and most important of all...saving money in the mean time). IRS seems like a pretty big expense.

Would it be justified for someone like me? I plan on just cruising around, 99.9% street use. I'm leaning towards a 9" rear end with LSD but I'm open for suggestions (not sure if my pocketbook is though).

undy · #10 (**permalink**) 03-28-2010, 04:43 AM

Quote:

Originally Posted by CoolCarl

OK, so I realize that IRS is better than a straight axle. My question is how much better? I'm in the process of researching kits, checking options, (and most important of all...saving money in the mean time). IRS seems like a pretty big expense.

Would it be justified for someone like me? I plan on just cruising around, 99.9% street use. I'm leaning towards a 9" rear end with LSD but I'm open for suggestions (not sure if my pocketbook is though).

Don't pay any attention to some of our member's sensationalistic opinions and "pot stirring". The live axle is just as suited to this car as the independent setup is. Both have their strengths and weaknesses. The IRS will do "a bit" better on an open track where the live axle kicks butt, 1/4 mile at a time. For the street it's probably a wash.

I wouldn't go with a LSD setup if you want the best track and street hook-up. Try Detroit's True-Trac. It has no clutches, just gears and has a better "posi" effect. It also has no noise like the Detroit "Locker" but hooks just as well.

patrickt · #11 (**permalink**) 03-28-2010, 05:11 AM

Quote:

Originally Posted by undy

Don't pay any attention to some of our member's sensationalistic opinions and "pot stirring". The live axle is just as suited to this car as the independent setup is. Both have their strengths and weaknesses. The IRS will do "a bit" better on an open track where the live axle kicks butt, 1/4 mile at a time. For the street it's probably a wash.

I wouldn't go with a LSD setup if you want the best track and street hook-up. Try Detroit's True-Trac. It has no clutches, just gears and has a better "posi" effect. It also has no noise like the Detroit "Locker" but hooks just as well.

No pot stirring here. He's not circle tracking, and he's not drag-stripping. Putting a solid axle rear in a car like ours that, sooner or later, see's heavy acceleration on uneven streets, will put you in to the trees. I believe it to be a huge safety issue. But hey, it's your life....

undy · #12 (**permalink**) 03-28-2010, 05:20 AM

Quote:

Originally Posted by patrickt

No pot stirring here. He's not circle tracking, and he's not drag-stripping. Putting a solid axle rear in a car like ours that, sooner or later, see's heavy acceleration on uneven streets, will put you in to the trees. I believe it to be a huge safety issue. But hey, it's your life....

...uneducated opinion based solely on internet experience and hear-say.

Mine's probably seen much harder acceleration than yours (more HP and M/T drag radials) and I've NEVER had a problem with a live axle and never ever even come close to going "in to the trees". Actually, my IRS C6 Z06 is no more stable on bumpy roads than the Cobra. The situation you're describing could provided the same results, IRS or live axle. Posi is Posi.

blykins · #13 (**permalink**) 03-28-2010, 05:11 AM

Definitely go with a positraction rearend. You'll never get any power to the ground whatsoever with an open diff.

Unless you're racing, it would be hard to make a bad decision on what diff to use. The Ford Trac-Lock would work well along with the Auburn diff, or the Detroit True Trac as Dave pointed out.

As for rear suspensions, I prefer the solid axles. Less chance of wheel hop, axles are stronger than half shafts and CV joints, better selection of parts (especially when you compare an 8.8 or 9" Ford to a Jag or Dana 44 rearend).

RICK LAKE · #14 (**permalink**) 03-28-2010, 05:36 AM

charlandk Kevin, The way I read this question is are you running an open carrier read or looking at a posi one?

If this is it, Posi over open, reasons why are many. Depending on which carrier you get, it's about putting power to the rear tires and movement. Posi in a straight line both tires work, open rearend in a straight line the r/r tire works only. There are 4-5 kinds of posi's. clutches, air, worn gears, mini lockers, mini spools. The question is what kind of HP is the motor going to have, what are the trans ratio's in the trans you are looking to run, what kind and size tires are you going with?? IMO a posi is needed in any cobra with 300hp or more for control of the car.
Kevin if you have the info on your car on another thread, it would be nice to know. You have not really said what you plan to use the car for?? Cruising, Shows, autocross, road racing, stress release, or chick magnet???
The other question is without knowing the HP and more important thing, TORQUE you are leaving more questions that need answers. A stock rebuilt Jag rearend is good for about 450HP and Torque. Some other rearends will take more or less power limits before breaking. If you normal drive the car, no additional improvements need to be made. If you are going for heavy abuse you need to look at better output shaft assemblies that are good for 750-1,000HP. Chromemoly stub shafts in the carrier. Better sidegears in the carrier and even blueprinting the unit itself. OVER BUILT your car.

This way it will take some extra abuse and not break down on the side of the road from a drive train failure. The rearend in my car is all heavy duty parts. Chromemoly shafts, 30 spline locker, heavyduty end supports, gridle for the carrier caps. HP rating is in the 650 range. Been racing this setup for 12 years and no failures. The first year I broke a stub shaft bearing, have had no failures since then. Have gone from 448ft of torque to over 600ft of torque, same rearend and tires. Time will tell about failures of these parts. Rick L.

blykins · #15 (**permalink**) 03-28-2010, 05:15 AM

Patrick....

It doesn't matter what rearend you have with a Cobra. If you have 400-500-600 hp like most of them do, if you don't show any respect or sense when driving, you'll end up in the trees anyway. Lots of power application on an uneven road will you get you wheel hop in an IRS car and if it's a positrac car, it's going to be spinning both tires anyway. I've driven enough modified 03-04 Cobra Mustangs to know that if there's a low spot in the road and it's spinning, the rear's going to go to the low spot. Having an IRS doesn't change any of that.

The rearend doesn't have any bearing on it whatsoever in my eyes.

patrickt · #16 (**permalink**) 03-28-2010, 05:19 AM

Quote:

Originally Posted by blykins

Patrick....

It doesn't matter what rearend you have with a Cobra. If you have 400-500-600 hp like most of them do, if you don't show any respect or sense when driving, you'll end up in the trees anyway. Lots of power application on an uneven road will you get you wheel hop in an IRS car and if it's a positrac car, it's going to be spinning both tires anyway. I've driven enough modified 03-04 Cobra Mustangs to know that if there's a low spot in the road and it's spinning, the rear's going to go to the low spot. Having an IRS doesn't change any of that.

The rearend doesn't have any bearing on it whatsoever in my eyes.

A newbie experiencing solid axle torque steer in a Cobra is a just a newspaper story waiting to happen. Advising somebody not to get an IRS in these cars is irresponsible. Period.

TButtrick · #17 (**permalink**) 03-28-2010, 02:17 PM

Quote:

Originally Posted by patrickt

solid axle torque steer

Patrick,

Are you making up technical terms again?

Pics of suicidal solid axle racers...

patrickt · #18 (**permalink**) 03-28-2010, 02:28 PM

Quote:

Originally Posted by TButtrick

Patrick,

Are you making up technical terms again?

Well I'll be damned, I googled the exact phrase "solid axle torque steer" and my use of it was the only result.

But it's a real thing, nonetheless. I bet you googled it too before you posted that.

blykins · #19 (**permalink**) 03-28-2010, 05:22 AM

So you're saying that adding an IRS suspension to a Cobra with any amounts of horsepower will take away all chances of wrecking due to irresponsibility and lack of experience? Please.

You can use whatever punctuation that you want at the end of your paragraph. It doesn't make a hill of beans difference. If someone gets in a 500hp car and puts the pedal through the firewall, it's going to spin and most likely go a little sideways, no matter what. Period. Question mark. Exclamation point. Asterisk.

patrickt · #20 (**permalink**) 03-28-2010, 05:25 AM

Quote:

Originally Posted by blykins

So you're saying that adding an IRS suspension to a Cobra with any amounts of horsepower will take away all chances of wrecking due to irresponsibility and lack of experience? Please.

It's a serious safety related issue, IMO. If you were building a Cobra for your son, who has limited experience with a high horsepower/short wheel base type car on the street, would you want him to have an IRS? Of course you would.