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by Mike Sheldon a.k.a.
Muffler Mike
This
article assumes that most who will read this wants to or has a real street car
not running slicks and has 200 or less hp.
The whole idea is to get as much weight transfer to the rear wheels and keep it
there. There are many things that can be done to accomplish this. First and the
easiest way would be to add 90/10 front shocks. (This produced a tenth of a
second better 60ft time when I was using 165 radials. Best 60 ft with these
tires was a 1.90 and a best of 12.47) These shocks let the front of the car
raise up easy and tries to hold the front end up by not letting the front come
down nearly as fast. (Chrysler 64-74 model works great on ball joint and an
adapter/extension will be needed on a link pin) The first thought that a lot of
people have is drill out the existing shocks so it will come up easier. Well
this does accomplish the up travel and yanks the front end up but most of us
don’t have enough power to carry it. Thus, the front end comes right back down
and unloads the rear tires. In most cases, a little tire spin will out 60ft a
wheelie any day. Don’t take this the wrong way, because there are exceptions,
and even I have experienced this exception. If you try to do a wheelie and bog
the motor with a bigger than normal cam, the rpm will drop right out of its
power band and your time goes right out the window. The whole idea is to have a
little tire spin and keep the weight on the rear tires and it will move out.
Another area to look at is the front beam itself and how your adjusters are set
up. E.g.: I use the old (very old) style select-a-drop. This keeps the bottom
leaf springs in their stock location and pulls or twists the top leaf springs
down. This crates a binding situation. When putting a jack under the front end,
the tires will not fall all the way down. With out down travel, you have
defeated the whole point, unless you have the hp and rear tires to pull. Verify
that the front will drop out all the way.
The rear end is pretty much a simple set up. There really is no need for big
aftermarket torsion bars or any other fancy items. Although when using in the
area of 190-200 and above with slicks, and a heavy car, this is around the cut
off of when to switch to some bigger torsion bars. If you don’t have enough
power when using aftermarket torsion bars, the car will have a tendency to
unload and bounce back up and this is not what you want. You are looking to keep
the rear end squatted. Front up and rear down. At what height should you set
your rear end up? Well in my opinion, it’s not all that critical. I personally
have my car set at a slight positive camber. But more importantly is the down
stop that is needed to keep most of the tread on the ground. I have been using
some old bus snubbers. A better bet would be to make some adjustable snubbers
using the type 1 rubber. There has been talk about the bus snubbers being too
soft and the rear bouncing off and unloading. So this will be on a car to car
basis of what works best. Another good reason to have some sort of positive stop
is to keep the fulcrum angel of a swing axle from becoming to great and hurting
parts. Obviously an IRS suspension is another story all together. When using
more rear travel, you have reduced the shock load in the gearbox as well. It
takes longer to come up to full load on the gearbox as the suspension is going
into compression. The longer you can delay the full weight of your car on the
gearbox the longer it should live. One of Gary Larsen’s methods of setting rear
ride height is can you stick a finger between the snubber and the stop and
that’s right about where I have mine. A good set of stock shocks should be
adequate but 10/90s are definitely not out of the question. This is something I
am looking into.
I have noticed that during a good launch seen on video and pictures that the
rear end will squat and then slightly unload. So this is telling me that it is
not perfect. If at all possible, get as much video from the side as possible.
This is a great tool, especially if you don’t have any knowledgeable crewmembers
helping you out. In other words get that friend or wife to take that camera out
there. A couple of other items that will help keep a consistent launch will be
the use of a heavier flywheel and even a heavy front pulley. My personal
technique of driving out of a heavy spin is to just blip the throttle and put my
foot back in it. Using a heavy flywheel will keep your motor from just falling
on its face completely. Using a heavy flywheel also accomplishes the option of
using a lower launch rpm which in turn, give the tires time to plant themselves
instead of just shocking them into a spin, and the motor will not die off
because the weight of the flywheel will keep the motor spinning.
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