bad launches..

[CHB]

yesterday went to do some testing on my KE70. i found out that it launch stupidly sideway at first 2 gears with the car barely moving. it just wheel spins and move sideway toward driver side. my car has open diff 4.3 toyota E series axles.
i can clearly see there were 2 tires marks on the pavement, does this means both tyres having traction? if that is not the case, can a welded diff improve the first 2 gears launch better?

[feral4mr2]

lesser boost in the 1st and/or second gear will help sideways launches, maybe you should invest in a dual stage boost controler....

[CHB]

thanks for the tip. i currently running very low boost at 14psi only. yes it may be true that low boost on 1st and 2nd gears will help launch but i was wondering if the suspension works have something to do with it?

[Draven]

is it primarily a drag car?

If so, softening up the rear suspension will help... but if it's track/street, the compromise may not be worth it.

[NME308]

Hi mate,
If you have 2 tire marks on the pavement on launch then it sounds like both wheels spinning. On an open wheeler diff that may or may not signal trouble down the track but is besides the point here!
Your car will be trying to head right on launch because it is doing the normal trick of lifting the drivers side wheel thus leaving most of the tractive effort being put down by the passenger side wheel.
To counteract this I use a heavy duty swaybar which I preload so the drivers side wheel is being planted into the road/racetrack. It will depend on how your swaybar mounts (if you already have one) as to how you accomplish the preload. On my old setup the swaybar mounted directly to the lower trailing arms so I was able to use a threaded rod and a bunch of nuts to force the arm down on one side (sway bar was held captive in 2 places to each trailing arm - bolted at the front and u clamped at the back).
The aim is that when you measure dead centre under the diff and jack the rear up using a socket between diff and jack to allow pivot the passenger side wheel should lift off the ground first and have about an inch of clearance before the drivers side wheel comes off the ground.
If you hadn't guessed this will of course leave the car with a slightly lopsided - down on the left rear - look but is the simplest way of getting both wheels driving to the bitumen and a straight launch. You may be able to make a simple setup to allow quick preload when you know some drag launches are in order!
Racers with adjustable coil overs in the rear can adjust spring preload to compensate but this can be dangerous in the braking area when the power is suddenly backed off and the car will want to swing back hard to the left...

Cheers,
Jason

[rob]

is the car lowered and does it have a panhard rod?

if its lowered and you dont have an adjustable panhard rod then the diff will be slightly off centre.

[CHB]

yes it is lowered and yes it has a panhard rod. i've centered the axle when it is on the ground and worked out how long the panhard rod should be. now the axle is dead center when the car is on the floor.
is softening the rear suspension means use a softer spring or softer absorber?

[Smokey228]

Maybe try less revs or stickier tyres???

I mean at 7k and street slicks on a semi prepped track, even my car will break out...

If you want to drag race, you want soft springs and shocks to suit in the rear, you then want special front shocks so that the front comes up and then slowly comes down to keep weight over the back wheels...

For track work, you obvisouly dont want this, so if you wanna try both things, try slipping the clutch more and giving it less revs...

Cheers,
Jase

[4DaDrift]

Edited Post.

[NME308]

Attachment 8056

The above picture shows (I think) an AE86 with probably slightly modified rear supsension. I believe it will still be similar to your corolla however in having the panhard rod and round trailing arms.
For a sway bar mounted similar to this you need to lenghten the right hand side connector rod to the chassis so that the drivers side wheel is pushed downwards as the sway bar tries to counteract. For simplicity you could modify the connector rod useing a length of threaded rod with a nut either side of the sway bar to provide adjustment.

Attachment 8057

This picture above is quite similar to the setup I used to run on my kingswood before installing a full crome molly kit. The sway bar here mounts purely to the lower trailing arms. Not visible will be a clamp holding the sway bar just in front of the spring and a bolt through the sway bar close to the front of the arm. On this style of setup you can once again use a length of threaded rod to lever the front end of the sway bar on the right side to force the drivers wheel down.

As mentioned in my post above to test the preload the rule of thumb is that when jacked up perfectly in the middle the passenger side wheel should come off the ground about an inch before the drivers side wheel. With both tyres contacting the road with the same pressure you will be have traction from both tyres and as a bonus if you are spinning the wheels the car will still move ahead in a straight line.

This of course may only be the first step. If you continue to experience major traction loss (even though this will now be in a straight line) you may need to review your cars ride height. A rule of thumb here with factory 4 link style rear ends is that lowering the car generally lowers the angle of intersection of the diff trailing arms. The lower on the car the lines meet generally the more wheel spin you will encounter. If you draw an imaginery line along your car following the direction the upper trailing arm points and another line following the direction of the lower trailing arm ideally they need to meet around the middle of the drivers seat back. On a standard car this can be hard to achieve however sometimes a set of raised springs (yes raised) can get this instersecting angle closer to ideal!

Cheers,
Jason

[Hen]

At the simple end of things, it sounds good (for now) that you're getting two black marks, that means both tyres are spinning. I'd recommend a locker for a drag car so you know both wheels will always spin, but it has many downsides on the road.

But to get a better launch (without changing your setup, that's been well covered above) you need to balance your clutch and throttle so you take off smoothly without the engine bogging down or too much wheelspin. You may find you aren't able to floor the throttle until midway through second, otherwise it just ends in crazy wheelspin.

Hen

[CHB]

At the simple end of things, it sounds good (for now) that you're getting two black marks, that means both tyres are spinning. I'd recommend a locker for a drag car so you know both wheels will always spin, but it has many downsides on the road.
Hen

thanks for the recommendation but here in Malaysia, i think it is impossible to get a decent locker without having to import it myself, which i need to pay massive import tax. i think welded diff should works for me

beside that, it is Toyota E-series van axle, so i think it is impossible for me to find a LSD to suit it. so i may end up weld the diff.

but back to topic, if i can get 2 tyre marks on the pavement during the launch, it means that both wheel having the same surface friction right? does this means i don't need a welded diff yet?

[Hen]

Yeah, I agree. Sorry it was a bit hard to understand, but I meant just welding up your current centre. I have heard rumours of a rare E series LSD, but personally I don't believe them.

And yes, you have both wheels spinning now, but maybe with a smoother (but also faster) launch will you start to get a single wheel spinning. So I think you need more "testing" before deciding to weld or not.

Hen

[CHB]

well i'm trying to borrow a pair of semi slick and see if can archieve the handling on the launch or not. we'll see

[Smokey228]

Man, weld it if its for drag, wether it single legs now or not, power isnt even until its fully locked. Even an LSD will slip differently between wheels...

You want full power to both wheels to ensure limited wheelspin and maximum thrust (im pretty sure thats the name of a porno)

And if you are running slicks, run a lower tire pressure, small burnout (dont want to delaminate) and soft rear suspension to allow the car to bog...

Cheers,
Jase