I have been running my truck for the past year trying to sort it out. Took it to our local 1/8th mile track to work on the short times.

Truck is 3,300 with me in it, boost controller, ladder bars, Afco dbl adjustable on back re-valved by Mencer Motorsports for radials and single adj QA1 on front. Fronts are 3 clicks from full loose and Backs are full loose on extension and about middle on bump. Tires are 315/60/15 ET Pro with 17 lbs air.

Prior, I have gone a 1.42 leaving at 3,200 rpm on 4.5 lbs of boost and ran out to 9.91 at 135 on 14lbs of boost. I believe the truck should 1.29 when all said and done. Well, testing didn't get me close and I got worse. The track prep seemed to be pretty good, weather was a little hotter than I thought it would be, but wouldn't affect 60fts much. I tried to leave at 4,200 rpm (first vid) and then lowered it to 3,800 rpm (second vid), leaving the boost controller where it was.

I have an idea of what I think the issue/resolution is, but I would like to hear the experts (as I am know where near that).

First Vid I spun pretty bad and only went a 1.8x 60ft: https://youtu.be/gLF5ay9dIcs
Second Vid I lowered to 3,200 rpms and still spun and went a 1.56 60ft: https://youtu.be/COn8PqhZ2AY

Thanks to Scotty (member here) for the great slowmo vids on his new camera!

I’m not an expert and am just diving into this myself but to me looks like you have to tighten the front to leave at the higher rpm. It is hooked until the front topped out abruptly, before the rear had any real chance to separate.

Good evening:

Maybe a little less air pressure. I am on a 275 MT radial and started at 17 or 18 PSI. I am down to 13.5 PSI now to get the car to hook consistently. Extension on the rear shocks (single adj) are 2 clicks from full loose.

John

Have you treid a bias ply of the same size on your truck yet? If not, I would, and have on less than good tracks

I am far from an expert but you have almost zero separation in the rear and I agree with Blusmbl that the front is to loose. I would tighten the front down some first and see what the rear does from there.

That truck is awesome, I have always like it!

No claims to knowledge here, but I watched your vids multiple times and something doesn't look right to me...

Then I pulled up this NHRA Stock Eliminator video and watched a bunch of cars making passes: https://www.youtube.com/watch?v=htn-mn4lCOk

The only "conclusion" I can come to is your car seems to be wasting a lot of energy off the hit... you can see it jerk on the hit, then it doesn't move cuz it's just wadding up the tire at first. Then the front end kind of bounces like it's too loose on the compression after it extends... and your front wheel looks like it's just flopping around, too.

What size rims are you running? I think they're too narrow for that size tire.

What hole are the ladder bars in in the crossmember? How many are there? Are the ladder bars level or pointing up? I agree with slowing the front rise but you have NO rise in the rear. You have to plant a radial hard and stay on it.

First off this is good video. Others take note. Two things that I see. The front is to loose. There is zero tire spin until the front tire is off the ground. There is very little seperation in the rear. Raise the ladder bars to increase seperation. Then control that seperation by tightening the rear rebound. If you hit the gear icon on You Tube you can watch the video in 1/8 time.
Doug

Again no guru here and different set up but this is my mates RR with 10x29's@17psi, 8" wheel, caltrac/mono's rear with calvert shocks on 7 tight, 20yr old 90/10's up front , 3800lb car, mega block+11" drums and heavy street wheels/tyres, could be much better, some wasted motion there as well but not as bad as your truck when it tops out unloading rear, he's gone 1.42 60 best, and yes hit the tyre harder by moving the bars up and control the rebound with the shocks to keep tyre planted, tighten the front.


https://www.youtube.com/watch?v=9tnu9cSnf2U

You need a lot more rear rise, then you need to maintain the rise some, radials need to be hit hard / planted to the pavement to work best. Are they radial slicks or radial streets ? Can you raise the front eye in the ladder bar ?
My experience is with Caltracs and radial slicks, so no expert at all with ladder bars, but we were hitting a bias ply way to hard with our set up, despite the theoretically least aggressive settings. Changed over to radials and instantly picked up across the ticket. We also have Menscer Radial valved rears, we switched to Santhuff fronts from menscer / afco. The Santhuffs are a superior unit.
Below is a pic from the last pass of the season, basically testing stuff with new 3.73 gears in the dana. We run around 20lbs in the rears, though we have gone as high as 22lb on a hotter track. We've been 1.32 putting the fronts down before the 60ft, and 1.39 on the backs. car weighs over 4000lb w/d.

Nothing to add that hasn't been said already. Agree that the front is definitely too loose. Slow down that front end and it'll drastically affect the launch.

Is it just me or is the rear tire toeing in on the hit? Probably just an optical illusion, but I see it in both videos.

It LOOKS like it is, but it may just be the tire distorting making it appear the rim is moving?

Thanks all who have replied. I will answer the different questions here.

But first, yes, I believe I need to tighten the front shocks! Also want to make sure I am not topping out the rear shocks.

Blusmbl : First post and you nailed it!

gearhead01: I am still playing with pressure a bit but based on what I have tested, air pressure is close.

Cab_Burge : Do not have a desire to ever go back to bias ply!

Bad340fish: Thanks for the compliment! Tighten the front it is!

Brad_Haak : I don't see it wadding up the tire and being a radial, that would be very tough to do at 16.5 lbs of air, but I will double check. The rims are 13". The front "action" you are seeing is the result of bump steer. Not much I can do about it with the stock front end.

fbs63 : I have the bars up as high as they will go but don't remember the plotting. IMO, the rear does separate about 2 inches but then when it starts to spin, it looses the separation. But....I do wonder if I am topping out my shocks. I will check that.

dvw : Yup! Slow the video down even more? lol

rb446 : Maybe the rear shock is too short..have to check that

Tig : You need more help than I do, but for a different issue! They are Radial Pro tires. The front of the ladder bar is as high as it will go. I may need to invest in some good D/A front shocks vs my single adjustable QA1.

an8sec70cuda : Chip!

justinp61 : Illusion. If it is moving at all, I am in big trouble! The truck goes very straight and the beadlocks helped a bunch!

I had two sets of M/T ET Street tires, one set of radials and the others were bias ply, same size, 315x6x15 on both, ten inch rims.
The radials were quicker (from .012 to .18 ET) and faster than the bias were on a GOOD track, not worth a hoot on the average no prep track or on the street, once they started to spin I had to let off to get them to stop spinning and going up in smoke
The bias plys would spin maybe from a 1/4 turn to maybe 1 3/4 turn and the hook on the same tracks or streets that the radials would not hook on at all
I did not try to make that car hook on any surface on the radials , I'm sure that there are cars that will hook well on radials on the street and average tracks but I wasn't one of them
My Duster weighed 3450Lb. with me in it and had 50.3 % weight on the front tires and 49.7 0n the rear tires, ladder bars with Strange Engr. double adjustable coil overs with 300 lbs. springs, stock 6 cylinder torsion bars up front with double adjustable front drag shocks, 1.42 best 60 ft. times
I ran big bias plys only on my last S/P car, 14x32x15 and 15x33x15
My new car will get 16x16 inch rims with either15x33x16 or bigger rear tires

100% without a doubt the fronts are waaaaay too loose.

A good rule of thumb is you should try to get between 1/2 to 1 full rear tire revolution before it starts to pick up the front tire off the ground.


The rear MIGHT need more separation, but start with the front first. You might find the rears don't need any change. It's hitting the tire decent, so it's not too far off.

It'll only need more rear separation if the front's don't fix the issue.


For what it's worth, High boost/low RPM, was WAY WAY WAY better than Low Boost / High RPM in my car. 22PSI was worth 9.50's@142mph on my car @3700lbs. That was leaving on 12-14psi on a 275/60, 3.55 gear, and 727 trans, good for 1.37 60ft.

Here is a good example of DVW's car.

Notice how far out it gets before it's got daylight under the front tire. Watch the stripe on the rear tire for rotation... somewhere between 1/2 and 3/4.

https://www.youtube.com/watch?v=rC7EASI6ihY

As said front is way to lose and for a radial I would think more rear separation would be a good thing. Check to make sure its not topping out in back for sure.

oh yeah I thought you sold this thing

Very True, we are into 5 figures now repairing stuff from several big wheelstands , the car isn't even that quick I don't know if its a Caltrac thing, but we have tried tightening the front up and / or limiting front rise to stop the wheelstand. Always ends up knocking the tyres off or rattling them some.
We can spend most of a qualifying day chasing our tail if we get it wrong. We cant take any more rise (anti squat) out of the car mechanically, it just seems to need to have a loose front and anti squat in the rear to run it's best. We're going to have to get a handle on it quick with potentially an extra 700 hp (bigger engine + 500 hp N2O dual fogger). IF we ever bust out of the 8.50 cage cert, we will make the rear more adjustable for ride height next time round but keep the caltracs and small tyres.

I did! about 5 years ago and then bought it back about 2 years ago and let it sit...again. I just started to play around with it this year and my son is starting to get interested in it so that makes it better.

I am in the process of getting all the measurements, etc., as we speak..