Drag Racing IRS In-Here, Need tips

[ClubVenom1]

Here's a video of a SRA Cobra with a nice launch.

Notice how the body separates from the tire/axle after a very short amount of movement forward. And note the planting of the tire into the track.

[video=youtube;jjp0I1in1YY]https://www.youtube.com/watch?v=jjp0I1in1YY[/video]

 

[ClubVenom1]

Now look at an IRS Cobra launching with no wheel spin or smoke show. Fwd to 0:35 for launch.

You tell me if the experts were right or not in those articles I read.

[video=youtube;WOl5noeLiYs]https://www.youtube.com/watch?v=WOl5noeLiYs[/video]


Front end comes up and the rearend SQUATS thru the run until he shifts. But even then as soon as he applies the pedal after the shift, it Squats all over again.

 

[ClubVenom1]

This is the same Cobra but from a rear view. Car was faster on this run too. Squats and Goes. Fwd to 0:58 for launch.

[video=youtube;Qd8NEL-vgZU]https://www.youtube.com/watch?v=Qd8NEL-vgZU[/video]

 

[TxCobra76]

Great info fellas. Just got my first cobra a couple months ago and plan on taking it to the track in the spring. Learned a lot from this thread. Thanks

 

[Stage 4.6]

Very good info!

 

[Jack Hidley]

I'd like to correct a few of the comments about using an IRS in a drag racing situation.

Given a clean sheet design, using an IRS will make the car much more consistent for drag racing than a solid axle. This basically comes down to the fact that numerous crutches need to be used to make a solid axle rear suspension work well due to their unequal rear tire loads on launch. An IRS needs none of these fixes.

In the case of most production IRS', they have a very low amount of antisquat (AS). If you build an IRS with 100% AS, the car is going to have brake hop and a lot of roll steer. This is why you don't find this on OEM IRS designs. Changing the AS of an IRS is a lot of work as many pickup points need to be moved.

With an IRS, there is no difference in left/right rear tire loads on launch as the driveshaft torque is not reacted by the rear suspension the way it is in a sold axle rear car. The driveshaft torque is reacted through the engine mounts, frame, IRS subframe and directly into the gear carrier. This means that installing a larger rear swaybar, smaller front swaybar, or airbag in one side of the IRS are all going to have zero affect on rear tire traction at launch. Note that no matter how hard an IRS car launches, there is never any body roll. This is because the rear suspension doesn't react any driveshaft torque. There may be a tiny amount of roll due to the inertial affects of the engines rotating mass.

Installing softer front springs and struts does help traction at launch a little bit, but only about 1/3 as much as it does on a solid axle car. On a solid axle car, less front roll stiffness results in more equal rear tire loads, which equals more grip. This is the main affect of softer front suspension, which doesn't exist on an IRS car. The second benefit of softer front suspension is that the rear axle torque can raise the front end higher. The higher the front end is raised, the higher the cg is, which results in more weight transfer to the rear tires, which results in more rear tire traction. This occurs with a solid axle or IRS.

 

[black-plasma]

I'll be going for 1.3x 60's with my IRS this year. Best so far with nonadjustable suspension was a 1.44. Now running full MM setup in front with Tokico D spec struts and Viking DA shocks and stock springs in back. Video's in my sig.

 

[ClubVenom1]

Jack you have confirmed most of what I posted earlier from the tech articles I quoted. Thanks for your insight too.

 

[tt335ci03cobra]

A properly setup 99-04 IRS sn95 can click off 1.7-1.5 60fts with a small collection of minor mods.

If it's taken a few step further and some reinforcing is done, minor tweaks, adjustable components, tubular suspension up front, skinnier et al, guys have clicked off 1.2-1.3's with our, uh, limited, irs subframes.

The new s550 chassis likely go 1.07-1.15's in a dedicated race application, irs and all.

When you get into 1500-2000wtq, ya, irs isn't going to be as easy, but for street cars, done right, irs is honestly a great way to go in my opinion.

My car hooks hard, squats, and just moves out. Even, uneven, bumpy, smooth, just hooks and books.

Stock shocks, but mm coil overs and full front suspension, full tilt boogie racing rear with a low mileage 04 subframe, ford racing diff cover, Detroit trutrac, and toyo tq's right now, but nt05r's, nt555r's, bfg gforce ta's etc in the past.

Illuminate deflection, minimize sloppy characteristics, drive it smooth and fast at the launch, no clutch drops or side steps, but quick smooth launches and a speed shift to 2nd, wot shifts 3rd and up, and the IRS honestly feels like a millions bucks in my experience.

I've driven heavily modded solid axles and I didn't feel as planted or comfortable driving them hard and fast on city streets in sn95 cars, more hoppy/bumpy on my roads. Rocky Mountains up here, and potholes/broken pavement, choppy roads, etc take their toll on a solid axle up here.

In a state like Kansas, Ohio, Nebraska, I could see solid axle being awesome. Lots of nice smooth road.

Neither is terrible unless they are left stock or put together with unproven components. Irs has more handling potential, sra is eventually the stronger/more reliable setup, but it's a ways on end before that matters on a properly built up street IRS.

920wtq in the past over here, blew up a t56 a time or 2, but the IRS was still alive and well.

 

[ClubVenom1]

black-plasma nice vid of your car. Squats and Goes. Noticed that your car does bounce back up on the rebound. Bet the DA viking shocks will help out in that. Keep us posted as to your results on the DA Viking shocks.

By the way... whats your RWHP and RWTQ if you dont mind posting. Just intrigued by the times you ran on that vid.

 

[black-plasma]

With the 2.9 I made 777/744 but its a pig at 3855lbs. On my 2.3 it made 644/677 and went 10.3, so there is a lot left with the 2.9.