Hello, new guy has serious questions about drag racing this rear suspension

[Manic Mechanic]

My names Vernon, I'm from Texas, and I'm visiting your site in hope of getting some information regarding how well the independent rear suspension of the LS and late model T-bird handles a hard launch. I just bought a crate rear suspension on Ebay and plan on installing it in an 89-95 Thunderbird chassis. The suspensions are very similar and based on preliminary measurements I can fit it in rather easily with some fabrication work. The main reason why is this: wheel hop. Our IRS units don't have a triangular upper control arm like the LS. Our upper is just a straight flat link with a long bushing on each end. When you push the suspension hard from a dead stop the tires shove the spindles forward until the bushings bind and snap back. This will continue until you break an axle, let up, or gain enough speed to hook up and go. We call it wheel hop because if you're watching from the side the wheel bounces back and forth and inside it feels like you're riding a jackhammer. I'm a master mechanic who's been a life long hot rodder so I always check out performance cars and like to see what they've got and will do. The first time I put an LS on the lift and got under it I realized that this was the evolution of the chassis under my T-birds. Very similar but further advanced design. The rear suspension was a "holy cow" invoker. Well I just got back from our annual shootout drag race and witness several broken axles and lack luster launches and decided to actually look into a LS suspension swap. I found a shop on Ebay that must have scored a bunch of these suspensions from Ford still new and bought one from the '03 T-bird due to the cable operated parking brake. So I'll be getting my hands on it in a week or two and already have one of my birds up for a trans swap so it's a go.

Now that I've given you my whole story and if you've been kind enough to read through all that (I can type fast-lol) here's my question for you LS owners. I know the V8 has traction control of some kind because I've worked on and driven enough of them now to have first hand experience with the control on and off. Both ways the car seems to have excellent traction with smooth and drama free WOT acceleration. But it is a wee little V8 with a bunch of valves, so though it makes a ton of HP it does so when the crank is wound out and the valve train is singing a sweet song. Our supercharged Birds make big block like torque curves with a no waiting throttle response. So overpowering anything short of a narrowed straight axle with slicks is always an option. I've yet to get my hands on a V6 5-speed LS so I have no idea to how they would react to a hard launch. All I know is that from the looks of it the rear suspension would be a world of difference for the better in forms of rigidity at launch. Have any of you guys pushed the car hard enough to offer any experience in this regard. I was searching the forum first and didn't find much if any discussion on this particular subject. So either it's not a problem for you guys and you don't know how good you've got it or nobody’s driving these luxury sedans like a crazed drag racer to see how hard they are to break and who they can outrun at the light. In any case if there are any of you guys out there who like to drag what's your experience in the rear suspension department? Am I on to something good here?

Thanks,
Vernon

 

[pepperman]

:W to :V the LS owners will give you the info you need!!!!!

 

[mespock]

Yes Weclome to LvC.... I am sure you will find the information that you need.

As Pepps said our LS owners will be posting you quickly.... We have a good number of very active LS owners who really know their :q:q:q:q when it come to the LS...

I know very little on the LS sorry I can't help you out..:W

 

[Fla02LS]

The way the LS is designed it strongly prohibits a "hard" launch. Between the traction control, gearing, engine, and 2nd gear start w/SST there isnt much availability for any power induced wheel spin, its possible but not close to the launch you are talking about. As far as the 5-speed goes, with our rev. limiter i'd think that would also limit the ability to get a good rev. and drop the clutch for a hard launch with the manual tranny. I think the only sure way to test the LS's IRC is to match it to another chassis and drivetrain and hit the track.

 

[Quik LS]

your biggest issue is the open diff - we gotta do something about that if are are going to get serious.

on my pass of 13.9350 @ 109.04 - I really spun the tires for almost the first 80'....

 

[Manic Mechanic]

Big thanks for the welcoming attitude and responces. Quick LS you just reminded me, I was planning on swapping in our 8.8 differential. I'm hoping it would be just a little of this and that to change over. Has anyone tried putting one in the LS yet? They came in the SC and 5.0 birds and the Cobra. I've got a few of them with various gears and posi.

I'm going to put it together an test it one way or another but I wasn't sure if any of you guys could have used them like this yet. The way they build cars now is pretty controlling. My Silverado has a 496 in it but it will barely lay rubber. But about half way through 2nd gear you feel the full power come in and a 7000 pound crew cab smokes anyone in sight LOL.

Vernon

 

[astroboyzx12r]

05 Mustang Diff work in LS?

You might investigate whether a new 05 Mustang differential would work in the LS.

Ford has been pretty good about having common rear gear/rear diff parts and althought the Mustang is solid axle rumor still abounds that a few special models will have IRS. Since it's based on DEW98 chassis, same as LS, it's quite possible the solid axle unit uses gears/differential compatible with LS IRS with little or no hammer adjustments.

Just an idea...

Good luck,

Mike

 

[Quik LS]

Since it's based on DEW98 chassis, same as LS, it's quite possible the solid axle unit uses gears/differential compatible with LS IRS with little or no hammer adjustments.
Mike

Mike - the new Mustang is not based on the DEW98 chassis. Ford did intend to re-use the LS chassis but:
- they could not get the cost of the platform down into the Mustang target cost range
- the T-bird proved that the DEW98 chassis was surprisingly unstable once the roof was cut off. The T-bird required a bunch of extra bracing and is still on very stiff. A mustang convertible was a must....
- the engine bay could not accomodate the larger engine platforms to be loaded from underneath the car - which is the way it is loaded at the factory.

at the end - the only parts of the floor pan and some other smaller bit made it into the Mustang.... ;(

 

[2001LS8Sport]

The way the LS is designed it strongly prohibits a "hard" launch. Between the traction control, gearing, engine, and 2nd gear start w/SST there isnt much availability for any power induced wheel spin, its possible but not close to the launch you are talking about. As far as the 5-speed goes, with our rev. limiter i'd think that would also limit the ability to get a good rev. and drop the clutch for a hard launch with the manual tranny. I think the only sure way to test the LS's IRC is to match it to another chassis and drivetrain and hit the track.

The 2nd gear start is moot...the car will launch in 1st gear when you mash the throttle on 00 to 02 models and the lag is undetectable. 03's and up start in first regardless of throttle position.

Turn the TC off.

Now, as to your original question on the IRS. The IRS can be made to be reliable on the drag strip, but it's costly and not the best set up for a drag strip car. It's lack of tunability compared to a straight axle is one huge reason. The Cobra boys have a ton of experience with this. The serious drag strip cars switch to a straight axle. The part time drag racers stay with the IRS and add axles, bushings, a brace, and sticky tires. Tires do a LOT to cure the ills of the IRS. If you don't, you get wheel hop that is deadly to the IRS. I would think that with the kind of hp these cars are capable of at this time, there would be no need to do much more than bushings to stiffen it up a bit. But if you start adding converter and tires, all that goes out the window. But you need to remember, there are several 10 second Cobras that run the IRS successfully. And there are some 11 and 12 ones that haven't. It all depends on what you are willing to spend to make it bullet proof.

Quik has mentioned the #1 inhibitor to this axle....and that's a posi. Until that happens, you won't find a way to make this rear end a serious contender.

Interesting idea about the Mustang 3 link. Although the new Mustang chassis has some similarities to this chassis, it is in fact different. The main reason being engine room. But if the diff will bolt up to this car, that opens a huge door for the guys that want to drag race. However, I would HATE to lose or change the way the LS handles....it's just too good.