Just trying to get an idea as to where I want to go next with the suspension mods....I want my car to LAUNCH HARD.....I'm not really interested in anything but 1/4 mile racing with this car so what would make the rear end REALLY plant and go??? I'm building this one from the suspension up this time...I already have lowered it and SFC'd it.....what comes next????

 

To answer that question: I would say the combination of high torque at low rpms, combined with tires that do not allow the force to overcome the coefficient of friction between the road surface and the tire.
u=coefficient of friction ~0.9
F=force at the wheel torque @flywheel X 1st gear ratio X Final drive ratio X radius of tire.
W= weight of wheel + weight of car @ wheel. ~3500/4 (assuming 50/50 weight distribution, and no torque of the car, (which puts more weight on one rear tire, less on opposite side) =875 lbs.
u= F/W so the more force you apply. (more mods you make upping the hp and torque of the motor) is inversely proportional to the weight transfer to the rear tires of the car.
In conclusion you must choose tires that maximize the coefficient of friction between themselves and the road, or enough weight transfer to the rear to provide more force (weight) on the tire to minimize the force (torque) that is trying to overcome friction.

Check my math, it's been awhile.
Tony

 

Great tires - wide slicks probably. Tires let go
not just from the basic compound's friction
characteristics but also tread block deformation.

Traction bias - a good drag differential or even
a spool. Torsen max torque split is no good once
the first tire lets go. Weight bias onto the lifting
prone passenger's wheel, like a drag bag.

Instant center - downforce from drivetrain/wheel
torque reaction. LCA relocation, torque arm mount
relocation. Perhaps stiffer components to preserve
the nominal geometry under high stresses (LCAs, TA).

Weight transfer - light in the front, throw more
weight to the back, high center of gravity, tricks to
improve transient weight transfer and let the sprung
weight rise while the unsprung weight drops - drag
shocks, disconnected front sway bars, etc. Maybe
weak rear springs to let the body roll back easier,
but this could fight against optimum instant center.

Weight reduction (with preferential removal off the nose).

More rear wheel power / torque - gears, converter,
power adders.

Want to do it over and over? Almost certainly a beefier
rear end and probably a transmission too. Before or after
you have to trailer it home the first time?

 

DAMN....I have a LOT to learn about making my piggy launch hard!!! You guys provided GREAT info..!!! I thought maybe it was as simple as LCA's and relocation brackets......great info...! Thanks!!!

 

Also should be mentioned that a stock clutch and rear arent gonna last long pulling har launches on slicks.

 

Actually, I was just being a smartass. Concentrate more on what JohnnyBlue said. What I put is the scientific equivalent to the method that he posted. But in my opinion, to make the car really launch, you have to make a few sacrifices.
To start off with.
1. Get rid of the Hotchkis springs. Look into a set of drag springs, or 6cyl springs for front. Rear Hotchkis springs are too "hard" they won't allow the transfer of weight as well as stockers. Drag shocks will allow front to rise, transferring weight to rear.
2. Slicks, on stock diameter wheels. Preferrably a set which decreases unsprung weight (better for the end of the quarter though)
I could go on, but I'd be repeating all of Johhnyblue's info. What you referred to with LCA's and relocation brackets was covered in his 3d paragraph.

Tony

 

A set of drag wheels will do the trick for weight reduction . Drag shocks will work wonders for launching also. Like the other 2 guys said, weight off the front of the car is important to allow it to rise easily and plant the rear like you want.

 

What about HAL's?? Will that make a huge diff?? Also, is a 16" rear 15" front weld drag lites a good combo or should I go with 15's all four cormers?

 

Basically, what PSU said in his first post was drag tires and soft suspension.

Really though, good text book explanation of WHY you need these things. I'm always a fan of understanding the why and how, as well as the what.

the only technically incorrect portion was using coefficient of friction. Traction is just so much more than u (mue), but it's also so much harder to understand (in fact, the professionals all pretty much agree that we still don't completely understand it). It's just important to realize that traction is more than friction because, based on the formulas using friction, contact patch isn't a factor, and anyone that knows anything about performance automobiles know that larger contact patch = greater potential traction (and I say potential because you need the proper suspension to realize that potential)

 

4:10 gears
spec stg.3 clutch
bfg drag radials
lca w/brackets
good springs or an airbag
as much tq as you can make...as in h/c package, headers, etc....
weight reduction!!!!

and after a couple of those hard launches.....a 12 bolt.

 

NITROUS, AND LOTS OF IT!!!!!!

 

BYE-BYE stock rear end...... kaboom

 

I like to know the HOW as well.....I'm gonna look into some nitto's as soon as I know the rain is gone for a while....I found some 4:10's for 100.00 and I'm gonna grab those asap....

 

A big enough pair of ***** to dump the clutch at 6500+ RPMS!

 

you wont hook on nittos and 4.10's.