truckdoug

iTrader: (25)

this is my first attempt at a 4 link in a drag car (well, truck)

I have the bars close to racked out for anti-squat.

still seems to squat. or rather if you look closely at the video it doesnt squat on the hit, but about 40 feet out it sits down hard on the axle snubbers and spins until i let the wheel speed slow enough to hook back up.

set up is: 4.8, 224/228 .57x/.58x 114+2 lca, 7875, 4l80e w/3500 stall, 9" 3.50 gears. 275-60/15 nitto 555's

boost is limited to 12psi



shocks are qa1 DA promastars with the "recommended" factory settings of front: 18 clicks compression, 8 rebound
rear: 6 compression, 10 rebound

this video is pretty typical of the problem(s)

svslow

What was the tire pressure?

truckdoug

iTrader: (25)

17 psi

slocaddy

With what I've been trying to learn with my car, witch I know doesn't compare to an actual "drag setup, or anything for that matter,( It just needs to be low and do incredible burn outs), I intentionally set my upper bars with "squat" in mind(you know, the kinda $hit and git!) my understanding to accomplishing more "anti-squat" comes mostly from the upper link bars pointing upward to where they will mount on the frame basicly lifting the chassis. I know there is more involved c/g bla,bla, bla.....just figured I'd chime in.
Post some pics of your suspension

Nathaninwa

Part of it might be the track! Do you know where your instance center is? I've bought into performance trends 4 link calculator and worked around a bunch and found the Dave Morgan sweet spot to be very close. I've worked mine high than most would call for as well

My lower bars is down in the front with like a 45 inch length and 8ish inches high

Also get slowmo from the side and email it to qa1. They would be more than happy to help as well

truckdoug

iTrader: (25)

these are the most current pics i have of the set up. the only changes from pictured (aside from bar angles) is the watts link bars are now horizontal, in plane with the axle.









in the video the bars near totally racked out to achieve more than 100% anti-squat.
http://www.dragstuff.com/techarticle...inktuning.html

I'm trying to drive the tires into the track so it'll hook. if I leave on more than zero psi it just spins as long as I have my foot down.

I had one more hole to go down on the top bar, axle side so we'll see what that does next weekend.

I think part of my problem is the front of the truck (the whole truck really) sits much lower than my build diagram and suspension geometry were built for.

also it appears the front end has nearly zero rise, so I need to loosen the rebound up front I think.

truckdoug

iTrader: (25)

thanks for the reply, i was hoping you'd chime in.

i wish i would have spent the $$ on the software now. it's very reasonable compared to rebuilding from scratch.


yes my IC in the video is just above and behind the AS line. I have now moved it higher by dropping the rear of the upper bar (but now it has less than 3" of leverage to CL of the axle...so i think i'm losing something there)

i will try and get a better video for QA1. it's difficult since they don't let anyone next to the lanes at PIR

and yeah I know our track isn't all that great, but hell my 60' is like 2+ seconds so I shouldnt be spinning that hard...i'm only making like 450hp!

Rudy72

iTrader: (2)

Listen to this man, he is a Guru and has lots of advice, this will get you started and touches on many issues you definitely have, probably a good idea to listen to all his suspension video's and get a note pad! you will learn terms like pre-load, flats, and roll center, spread and many others...

Good advice by Nathaninwa also ;-)

Tim McAmis

stinkybutt

Also your 4 bar system is typical of street rodder style. Parallel 4 link upper and lower bars = spin city. You will learn that your geometry is way off for a good 60'.

Again not how much you spend, but how you spend it.
You will get it figured out from the above posts.
Good luck and keep us posted.
Aleck

Nathaninwa

He said his bars are not like in the picture. What ems are you using? I've installed a Denali suspension sensor and can tell you exactly what the front and rear do

If to much antisquat, and you top the shocks out from having the wrong spring, then you lift the tires off the track. We need weight to transfer, tbh I'm running a 90/10 front strut with a 14 inch 125lb spring to store as much kinetic entertainment as possible

Out back we want the spring to sit 60% compressed with zero preload, and use shock mounting to adjust ride height. I went from a 130lb spring to an 80lb spring with great resuslts

I'm convinced/not convinced about lower bar angle. Mines less than 1* down in front and feel it helps drive the 1/4 panels into the track, then given the antisquat the setup resists the dive providing more weight on the tires. I'll measure mine but my lower bar is close to axle centerline

I helped a friend this weekend setup his links, moved bars around to get IC as high as we could with a downward angle and off the trailer went 1/2 second faster!

PS, Portland just blows. At toutle I went 1.29 sixty at 5.35, couple hours later was at Portland and was almost going 2.0's in the sixty with about 6 fish tales down track while trying to apply power. Same setup went 1.31 at Pacific with a 5.41 1/8th. Get to a better track for more testing!

PSS, my compression is 3 and rebound is like 14 with my front lifting like 5 inches and my rear squating no more than 1/2 inch

truckdoug

iTrader: (25)

wow thats all good stuff. i'll have to read it a couple times to digest and make a reply

but I will say I have been watching a lot of 1320 "no-prep" videos and the industrial park tracks they slap together for a few hours racing appear to be much stickier than PIR

Nathaninwa

You may also have my same problem. Your to light in the rear. Being light is cool and all, but weight also provides traction! I'm supporting something like 600lbs out back plus the axle. So I'm limited on the boost and rpm i can launch at

Try adding 50/75 or even 100lbs over the rear axle. I'm going to start with 40 or so lbs for this grudge event coming up

truckdoug

iTrader: (25)

yes I have something in the works for that. just need to figure a clean way to add plates and what kind of increments i want to work with.

roastin240

iTrader: (13)

How about moving the weight to behind the axle, like in the rear bumper. Should have a greater affect on the normal force applied to the tire contact patch. Ultimately requires less weight for the same result.

QA1_Damien

truckdoug, a video from the side would be very helpful, but from what I can see the truck doesn't do much of anything. What spring rate do you have in the rear? Lighter rate springs will have more stored energy to help the rear of the truck separate when you launch. Softening the rebound setting will allow the back of the truck to separate as well if you have over 100% anti-squat.

What do you have for springs and shocks up front? How are the front shocks adjusted?

Damien

truckdoug

iTrader: (25)

Hi Damien thanks for the reply. I'll try and get some video of the launch directly from the side soon.

The rear springs are 12" 170lb

The front shocks are the older type, i think i recall them being roughly equivalent to the current DD401 and the spring is 450lb

I'll have to double check but I recall setting them middle of the road for drag racing according to the instructions. ~14 compression and 3 or 4 on rebound.

I really oughta write this stuff down somewhere!

truckdoug

iTrader: (25)

Oh another thing I was just thinking of is how I ended up moving my shocks at an angle out back to fit under the stock bed. I think that increased my spring rate a fair bit and is probably adding to my problem

Nathaninwa

Angleing the shocks makes them weaker. Do you have front to rear weights at all? My suspicion is the springs are way to stiff. I bet you only get like 2 inches of front compression on the springs at the most. This won't let the front lift at all since there is no real stored energy. My 125lb springs compress like 5.5 inches, this stores the energy and helps the front lift on the hit. You're new spring oh maybe stiffer than mine, but your current setup isn't helping. Google it, lots of links out there on the subject

Longer and softer! You can measure your current compressed spring to its free length and times that by the weight to get the front suspended weight, same with the rear

truckdoug

iTrader: (25)

aye aye aye, thats what im learning...apparently i didnt do enough homework before I cobbled this thing together.

but thats my motto! i do it nice because I do it twice!

QA1_Damien

The older style shock would be a DDR4855B which has 24 adjustments per ****. Being that your are not transferring weight i would loosen the rebound on the front.

The rear springs could maybe be a little lighter. I'm basing this off the weight of my '83 C10 which is 1,621 lbs. on the rear with dual tanks and leaf springs. I think a 150 lb./in. spring would be reasonable, maybe less depending on the actual weight of your truck.

Keeping a log book is going to be your best tuning tool.

Damien