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| Re: Time for a new clutch setup A15t/Toyota T50 |
Subject: Re: Time for a new clutch setup A15t/Toyota T50
by jmac on 2010/4/10 8:27:30
Over the years, any solid axle rear will cause the right side left (or coil) to sag more - because every time you accelerate there's some %ag of the force trying to twist the diff, and raise the right rear.
Even with std new springs, this force will lift the right rear and is why you'll see single spinner burnouts almost always only ever being right hand rear. Once you add in some years of use, then that right rear spring has sagged more than the left and so it'll spin up the right rear easier and easier as it progresses ver the years.
As mentioned, even std new springs and level ride height will still experience right rear lifting under acceleration (esp in first, and esp with a setup with probably 3 times the output of any factory engine (maybe more than 3 times).
So - stock springs - spin right rear
more power and stock springs, spin right rear easier.
sagged/used springs spin right rear easier
sagged plus more power, massively right rear spin-up
So the goal, with identical springs, for dragging, would be to run about 0.25-1 inch lowering block on the left hand rear. This would then mean that at a standstill there is a slight bias of downforce - more on the right rear. Then when you launch, it lifts the right rear, but with enough spring bias, you won't raise it to the pint it loses grip, instead, optiamlly, it raises the right to the point that you can get good grip off of both tyres.
Since the springs often have sagged, technically a lowering block wouldn't be needed. What you'd do is simple (some cars it's impossible since springs are mirror images, not identical) - swap over the rear springs left to right and right to left. Automatically has a slight bias of download on the right rear that becomes neutral under launch.
Another thing you can do, possibly combined with this, is to run an air shocker on the right rear, and have dead level springs, for better handling (or more consistent on right and left turns) and just add air to that right rear shock to get the launch perfect. With a bit of trial and error, you could find the pressure that suits.
Very very very generally, you'd not want to use lowering blocks at all, as it raises the axle centreline vs the front spring eye (or pivot point on more complex front spring locators) The lower the axle centreline vs the front spring pivot point, the more it tries to lift the rear/body as it launches, and the body wll attempt to travel rearward/down due to it's own inertia, which basically means that such a rear susp angle leads to the rears being pushed down VERY hard during launch, with maximum loading (remembering there is a difference between where/how the body might roll and where the load/downforce/weight transfer might be targetted.
Even without that, lowering blocks give less support to leaf springs at the axle tube brackets, and move axles away to all conspire to wrapping up the springs/axle tramp.
SO basically the 'go' is to swap rear springs side to side, and generally that does the trick.
Another alternative to an air shocke is a rear sway bar. You can have one adjustment (or disconnect it altogether) on the street, but for the track, you can 'stack' washers and bushes to bias and give more downforce on the right rear.
The point of all this is that even with an LSD or locked diff, there's still some potential to be had from even downforce on the drive wheels under launch, and one of the best ways to sus that out is to test somewhere safely with an open diff, practising launches, and dialling in a touch more preload/added downforce to the right rear, untill it no longer spins the right rear up to buggery (or reduces it to a bare minimum, and then marking/recording this settting and then fitting an LSD or locked centre, you'll get the most out of it.
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