4-link preload

>> Then I looked at this earlier video.....

Disregard the early video. When I first took it out, the back was way too
stiff and bounced badly! I changed the rear coilovers, springs, and 4-link
setting since then. The video from last Fri is using the new parts and its
not bouncing anymore. I'm running 8 psi in the MT14-32s and they do
wad up hard at the hit. If I run more psi they start to spin. It pulls left
hard enough that I have to drive the car back in the groove after the
front wheels come down. I'm dying to turn on the NOS but afraid it
could get really ugly left???? So want to get it straight first!

I'm going out again Fri to test. I'll flip the tires and see if that changes
anything? If not I'll put some negative preload in the upper bar and
see what that does. May stiffen up the front shocks 1 click to lessen
the wheelstand?

Rich

I checked the circ of both slicks and they measured exactly the same.
So I swapped them side to side and set everything back to neutral again.

Side note about neutral: I tried the "hanging" method as suggested here.
No preload with top bar free while hanging on the fully extended coilovers.
However, when I set the car back to ride height the top bar was tight again
and took 4-5 flats to free it up (sorry dont recall which direction?). So I am
very skeptical about using the "hanging" method and feel its NOT realistic
to what the car sees. So I went back to setting it neutral at actual
weighted ride height like I've always done.

First pass - car pulled to the RIGHT pretty hard. Remember it
was going HARD LEFT before!!! Made a second pass just to
confirm and it did it again even harder. Okay I'm thinking it was
definitely a tire problem? Not something I can fix here at the track?
BUT decided to adjust for it anyway rather then go home. So I put
2 flats of preload in the upper 4-link bar.

Third pass - still pulled RIGHT pretty hard. Seemed about
the same. ETs the same. I've always had better success on other
cars preloading the coilovers and not the 4-link. So took the 2
flats of 4-link preload back out so it was free and neutral again,
and put 2 full turns up in the pass coilover platform.

Fourth pass was a lot better! Still pulled RIGHT just a little
but not bad! ET was better too. So put 1 more full turn up in the
pass coilover platform.

Fifth pass - STRAIGHT AS AN ARROW! NICE!!! Made another
pass in the opposite lane to confirm - perfect again! Got on brakes
really hard on top end to see if it had any ill effects stopping
and it felt great and stayed straight.

So turned the NOS on for 5 sec for my last pass.
NICE!!!!
(NOS results in another thread coming soon....)

Will leave the tires and coilovers the way they are for now.
Pretty interesting.....

Good job, glad you got it launching straight. Just goes to show that every car is different. It's been a long time since I last needed to resort to trying a staggered spring seat height to straighten a crooked launch on a 4-link car. But back then it was a 4-link car without an anti-roll, so that did play a part.

As for what you observed when you tried the "hanging" method, there might not have been anything wrong. It is fully expected that the driver top link would go from loose & rattles on it's rod-ends (while hanging) to tight/under a load when placed back on the ground. When back on the ground the load shifts & the pasinger top bar then becomes the loose & rattles bar. So you often get similar results to the 100% on the ground method when using the hanging method. It's just two different ways/methods to end up in or around the same initial ballpark.

Would it be the same to move weight to the RR?? Just curious. That would keep the spring platforms the same, but....does it really matter?

David Willingham wrote:Would it be the same to move weight to the RR?? Just curious. That would keep the spring platforms the same, but....does it really matter?

I guess the truth is most all drag chassis tuning methods out there can be usable in some cases, a lot can boil down to just personal preference.

For example if you did need to move more static weight to the RR, in theory it can be accomplished in many different ways. A person could physically stack more weight there with a weight bar, or do it with the top right 4-link bar length (or right ladder bar adjuster), or with the right anti-roll link length (if it has an A/R), or the right rear spring seat height, or diagonally across with the left front spring seat height. And on a car with limited body-roll capabilities (ladder bar or 4-link + anti-roll) just making a decent jump in engine "at launch" HP/TQ numbers can in effect also increase the weight numbers the RR sees (not static/at rest, but during launch loading) from the increase in rotational torque output.

So which of these ways is "best" to add weight to the RR?........ just depends on who you talk to and personal preference/personal experience.


It's kinda like your concern about bump-steer in another thread. If you ask 20 racers how much they could live with, and how much is too much, you would get many different answers. A tiny little amount of bump-steer might not ever be noticed by some drivers, and never ever bother them. But that same small amount might still scare the crap out of some other drivers. Personal preference/personal experience comes up a lot in racing.

The suspension was working perfectly now and the new car was going
straight. So I was really excited to start testing the NOS system. I
had it setup with 150 shot I'd previously tested on the dyno. So I
set the base timing back, filled the aux tank with 118 gasoline, and
headed out to Cordova to make some NOS runs in their Quick 8 race.
Car went 8.50s on the NOS and I even made it to the finals!!! But
cracked a cylinder in the finals and slowed to settle for the RU spot.
Everything was going so good with the new car..... So now waiting
to resolve the block issue (see Engine Tech thread) and could be
down the rest of the summer? What a bummer!!!!!

Rich