Rear End Traction Recommendations Needed

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jimmyray

jimmyray

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OK. So I've read everything I could find about Caltracs, slapper bars, SS springs, and I just need some advice on which way to go next. Some background info on the setup:

Front: 1.00 TBars (like the firm feel)
KYB Shocks

Rear: 8.25" 4.11 Sure Grip, factory pinion snubber
Stock Leaf springs with 103,000 miles
Air Shocks
Nitto 450 17" 285's, 28" diameter and 11" wide

Problem: BAD tire spin. (see video link below) Front barely lifts on launch, and rear slighty squats. At this point, I want to leave the torsion bars as is.
I have a 8.75 with a 489 cased 3.55 Sure Grips that needs to be narrowed to fit in the car, but it is not ready yet.

Car has 408 Stroker 9.6:1 with Edel Heads (slight port & polish), M1 single plane (gasket matched both) and Holley 750 DP w/proform center 72/82 jets, into Hooker 1 5/8" and 2.5"to2.0" (after muffler) exhaust.
727 with 3000 stall and Manual Reverse VB. 12 degree mech advance at idle to 34 total all in by 3000rpm,

More can be done with exhaust. We reset float level and picked up 2 mph on top end. More can be done with timing and jetting, but need to fix traction issues first.

I have been launching around 3000 rpm, and feeding in rest of throttle after spinning stops.

Some details of my time slips:
Prepared track, 4/05:
60' time avg: 1.954 Best: 1.907
1/8 time avg: 8.316 Best: 8.236
1/4 time avg: 12.973 Best: 12.877
1/4 MPH avg: 104.643 Best: 104.84

Unprepared track, 6/07:
60' time avg: 2.229 Best: 2.286
1/8 time avg: 8.755 Best: 8.737
1/4 time avg: 13.357 Best: 13.314
1/4 MPH avg: 105.230 Best: 106.95

We found that the car was not opening all of the way at WOT. We fixed this, and the "prepared track" (raked, sticky stuff applied to track surface, no A/C drips, etc) times are NOT at true WOT. We fixed the throttle in the Unprepared times, and even with higher 60' and 1/4 times, MPH was up!

Tires heat up enough to have pebbles and such stuck to the tire when I return to the Pits. I also have a set of M/T SS Indy tires but there was no reduction of tire spin with those.

GOAL: Car is mostly a street car, but I like the track time, and would like to see 11's.

CONSTRAINT: With big tire, I need to pump up the air shocks. If too low, the tire hits the front of the wheel well opening. Currently at 28 ground to top of fender lip. (see pics below). I like the stance, but not sure what SS springs would do to it. Don't want it to be lopsided, either.

So my questions are:
Since I have LOUSY 60' times, what are the best options for traction?
In what order would you make the changes? (budget is $400, for now)

1. Slicks
2. CalTracs Only
3. Adjustable Pinion Snubber
4. SS Springs
5. Eliminate Airshocks
6. Install 8 3/4 with lower ration of 3.55 instead of 4.10 in 8 1/4.

Video of launch: http://www.youtube.com/v/AxQH5i3CpLo

02.jpg


DSCF3759.JPG
 
The KYBs must go. What do you expect from a $30 shock? The 1" torsions unload quicker than thinner bars, limiting the amount the front raises on launch. I hope you don't think the rear is supposed to squat. When that happens, it is the front leaf segments bending and the rear right lifting off the ground. The pinion pushing against the ring gear causes the pinion to move upward. If a pinion snubber is close to the floor, it can't move up, and instead, it pushes the axle down. SS springs have very stiff front segments. When axle torque tries to wrap up the front segments, they force the tires down since they can't bend easily. The driveshaft rotating counter-clockwise tries to rotate the differential counter-clockwise, lifting the right tire off the ground. That's why the right tire spins with an open differential. The SS springs reduce this also. The car doesn't have to sit lopsided with them. If the right rear sits high, raise the front left torsion, lower the front right, or both. I think your gear should be one that puts your RPM through the traps at your fastest shift point. If you shift at 6200, and you are going through the lights at 5400, your gear is too high. Raising the rear into the sky to fit a tire can't be the best thing in the world. This is what race cars with big tires should look like:
barracudatrack.jpg
nhra1290x200.jpg
 
He's gotta good point there. The air shock should not be used to fit in large tire. To adjust the car for a level ride.... OK, but thats really it. I've run them (Air shocks) for a vey long time (17 or so years) without the problems everyone screams about.

If it were me, I'd save the bucks for a full Cal-Trac deal. On the cheap you could do S/S springs and snubber. I have been hearing and reading about guys getting the Cal-Tracs dialed in and doing very very well with them.
 
I was hoping for more specific recommendations on what to change first, given the constraints I have. I can't change tires at this point, So I need the rear end up in the air. I'm not sure why the tire hits the front of the wheelwell, unless on a big bump, the axle wraps in a similar fashion as under hard accelration, and the lower stance allows contact.

DSCF3759b.jpg
 
That's just too big, both width and height, of a tire for a stock wheel well. How do you fix it without funds? If you want that wheel and tire, you need to move the leafs in and mini-tub. Metal's cheap. Your time's cheap to you. A friend with a MIG is about a six-pack or so to borrow it. You'll need a different offset wheel or a narrower diff, though. If you want a quick time slip, you may be able to find some cheap slicks used for the track.
 
The tire is hitting the front because the torque of the rear axle is bending the front of the spring pack actually making it shorter and causing the axle to move forward slightly especially if they are the originals with 103,000 miles on them. Super stock spring have stiffer front sections and will limit wrap up. It will also raise the rear end of the car so you won't have to run so much pressure in the shocks to keep the tires clear.
 
Just my opinion, but seeing that you cant afford much at the moment (believe me your not alone) that the cheapest option for you to "help" is going to be an adjustable pinion snubber. If you have it adjust properly it should take the little bit of upward body travel you have at the front and force the dif in your favor (downward). Other than that concidering the budget and the tire and wheel combo, everything else is going to cost more than it seems you are able to do.
Just give it a try anyway, I think you'll be impressed. When I had a 7 1/4 I made one and the rear acted completely different. About 50% of the time both tires would spin if I was screwin' around with it. Point being it planted the tires evenly and made even an open dif work harder.
 
To clarify, I can let all of the pressure out of the air shocks, and all is clear, and I can drive the car normally. It's when I hit a big bump or pothole that the tire contacts the front wheelwell lip. Mintubbing and moving springs in won't help at all unless I move the entire wheel in so that the tire would clear the front wheelwell lip, about a 3.5" inset. Not an attractive or feasible option. I see my options as one of the following, all of which should be under $400:

1. Caltracs with stock springs and airshocks (no wrap and maintain height)
2. SS springs and adjustable pinion, 50/50 shocks (no wrap, will raise rear 2", probably clearing but making rear level uneven.
3. New tires - drag radials, and new shocks. Smaller tire to clear, better grip but still axle wrap. Stance won't look as good, though, IMHO.

I am leaning towards option #2. Some suggest that the torsion bars can be adjusted to compensate for the rear level uneveness. Is this safe? Does it reduce the effectiveness of the axle loading, etc.?

What do the 90/10 front shocks do to the handling of the car in cornering, etc?
 
if you want cal tracks ..you can make your own for a lot less money than buying them ...its not to do , just time and a little welding, drilling ,to fab up the pieces... there should be more info in the archives.... or pm me and i ll send it to you ...Ron
 
I ran 90/10 shocks on my Duster for awhile and did not really notice much ill effect in normal driving. But (big but), it did affect cornering, making the car want to push a little more that I liked, so I took them off since I drive on the street mostly anyway. I would not recommend running them for any type spirited driving.
 
Ace said:
I ran 90/10 shocks on my Duster for awhile and did not really notice much ill effect in normal driving. But (big but), it did affect cornering, making the car want to push a little more that I liked, so I took them off since I drive on the street mostly anyway. I would not recommend running them for any type spirited driving.
Click to expand...

Thanks for the input. I suspected as much because of the special application nature of the shocks.
 
GOAL: Car is mostly a street car, but I like the track time, and would like to see 11's.
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if its mostly a street car then i personally would side on the street part of the compromise. think i would start with tires. i go a 1.69 60' with a 26x9.5-14 hoosier qtp. and that was with small blk torsion bars and beat shocks up front and 100k slant 6 leafs out back with air shocks.


what i would do first i think is tires. something that is gonna stick. the video looks like you get no traction. i know i ran a 12.81 on street radials the same way you say your launching and that is a pain in the ***. put the hoosiers on and it was instant 12.30's. after tires i think i would maybe got to espo 6 leaf springs. you can get stock height or 1" to 2" inch over so that would take care of your height problem. then an adjustable snubber. everything is a compromise when its a dual purpose car. i would rather sacrifice a little at the track for a better street car.
 
Jim I have the extra HD mopar springs from Mancini's and they also make the car sit a little lopsided like SS springs but not quite as bad. I cranked down the front left torsion bar adjustment to compensate and it loaded the RR tire and hooks much better than it did with the original stuff. Drives perfectly normal too. Sorry but I don't have any numbers since I didn't run it at the track before and aft but I can sure tell it's hooking better on the street. Next I plan on building a set of Cal-tracs. I picked up the heim joints off of e-bag for less than $50 shipped and here's a link to the build showing dimensions

http://www.hotrodsandhemis.com/Traction.html
 
You can move the axle forward or back 1 to 1 1/2 inches by drilling another hole in the spring perch and shock plate for the spring center bolt.
 
C130 Chief said:
You can move the axle forward or back 1 to 1 1/2 inches by drilling another hole in the spring perch and shock plate for the spring center bolt.
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That's an idea I had not thought of. That is a much cheaper option than a new driveshaft when I install the 8.75 I have in the wings. Reckon how that affects the driveshaft to tranny spline engagement on the current rear?
 
jimmyray said:
That's an idea I had not thought of. That is a much cheaper option than a new driveshaft when I install the 8.75 I have in the wings. Reckon how that affects the driveshaft to tranny spline engagement on the current rear?
Click to expand...


ya but dont forget your tires might hit if you move your rear forward, so thats why maybe it would be easier to get the drive shaft
 
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