Boy, mention the word autocross and TR4 in the same sentence and I could
go on for a bit. I'll try to stick to the basics, and not too long winded.
The main difference between the 4 and the 4A is the frame. The frame on
the 4 is really not much more than a widened TR2/3 frame. Other than the
steering gear, the front suspension is the same on the 4 as the 3. The 4A
on the other hand has a whole new frame design which continued unchanged
through the 5,250 and 6. There were some minor differences in the various
models, but the layout is the same.
The 4A was available in either a solid axle model or the new (at that time)
independent rear suspension, IRS. The solid axle was set up pretty much the
same as the 4, with differences in the brake mounting, bump stops, and so on.
The IRS car featured coil springs in the rear, massive aluminum trailing arms
and a rather limited range of suspension travel. The IRS stayed virtually
the same until the demise of the TR6, with some differences in the mounting
brackets and spring rates as the cars got heavier. Some folks contend that
the solid axle car handles just as well if not better than the IRS design.
The White Car, my current autocrosser, is a solid axle design. I would like
to try a 4A IRS sometime, just to see the difference.
One of the big differences in the improved suitability of the 4A over the 4
for competition is the front suspension. The parts are pretty much the same,
the big changes were made in the mountings. In the older 4s, the lower arms
pivot on pins which are firmly attached to the bottom of the front spring/shock
towers. From the 4A onward, the lower arms pivot on brackets which are mounted
to the frame rails. The big difference here is adjustability. The old style
suspension came from the factory with 2 degrees positive camber as the one and
only setting. To change this would require offset bushings or reworking the
suspension links themselves. The later cars changing camber, as well as the
caster, is a matter of shims between the brakcets and frame. Where the Rust
Rocket was running about 1.5 degrees positive camber, The White Car has about
1.5 degrees negative. The front sticks much better that way.
Another difference is the exhaust manifold. The 4s used the same type of
cast iron exhaust manifold as the 3, while the 4A had a much better flowing
4-2-1 almost-a-header setup. I have been running a stock 4A manifold, and
am just now putting a set of headers on my car. The stock one gives pretty
good low and mid range power, but with the number of big, long course we run
out here I decided to try the header and get more top end.
Well to sum it up, the 4A is a more competitive car right out of the box,
is a bit more rare as something like 28,000 were made versus the 50,000 or
so 4s. Those numbers are just off the top of my head, may be off by quite
a margin. The bodies use all the same panels, the trim is a bit different.
Both have the same motor, 2138cc, unless you get a 4 that had the 1998cc
motor as an option. It was avialable as an option for those who wished
to run their cars in classes with a 2 liter displacement limit. Given a
choice, I'd get a 4A.
mjb.
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