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Re: Autocross car preparation.

To: Lancer7676@aol.com
Subject: Re: Autocross car preparation.
From: Scott Fisher <sefisher@cisco.com>
Date: Tue, 18 May 1999 14:16:45 -0700
Cc: spridgets@autox.team.net
Organization: Cisco Systems
References: <c5035f0a.2472b35a@aol.com>
Reply-to: Scott Fisher <sefisher@cisco.com>
Sender: owner-spridgets@autox.team.net
Lancer7676@aol.com wrote:
> 
> My questions are:
> (1)  Considering the 1973 [...] Can anyone tell me the order of work that I
> might get the most payback from doing on this car, in terms of turning it
> into a non-street, strictly Autocross car?  That is assuming I do the
> bodywork first.

Yes.  Do the bodywork last.  (Structural rust repairs not included.) 
Start with suspension and tires, then engine work, then gearing.  You
will have more fun, learn more, and eventually drive faster in a car
that has completely stock but 100% sound suspension than in a car that
has 75% trick racing sh--uh, stuff bolted onto wonky bushings and rusted
bolts.

Others have suggested picking a class first and then preparing to the
rules for that class.  It's the right choice.  I echo their
recommendations of DSP (esp. since the Midget will be moved to ESP next
year).  Basically, SCCA autox runs four categories of autocross cars:

Stock: just what it says, changes very limited.
Street Prepared (SP): some suspension changes, bolt-on engine
modifications
Prepared: basically, Production-category road-racing rules (slicks,
high-compression engines, wild cams, "real" race cars, which pretty well
have to be trailered to the track)
Modified: Must have four wheels and there are weight/displacement
limits, but this is where you get things like Spridgets with rotary
engines, old Formula cars running Outlaw Sprinter wings, and the like.

Within each category there are classes based more or less on
displacement; Corvettes, for example, run in A Stock, while Spridgets
run in H Stock, and cars with displacement/performance somewhere between
run in B through G.  There are fewer SP classes than Stock classes, and
DSP -- the Spridget's current category -- tended to have lots of cheap,
fast cars in it and was therefore very competitive, at least in my
region (San Francisco).   It'll be interesting to see how it fares in
ESP next year.

I haven't reviewed the SCCA rules in about 10 years, but they used to
allow (in the SP classes) the replacement of lever shocks with tube
shocks.  This was a worthwhile improvement, but would depend entirely on
how worn your '73's Armstrongs are at present.  Do the bounce test; grab
one corner, shake it up and down, and if the car settles on the first
bounce, keep your shocks. 

Your first order of business is to make the car reliable and predictable
in handling.  Have you autocrossed before?  It's a very specialized
skill, and there's a steep learning curve even in cool cars like
Spridgets.  You'll have much more fun -- and stay with it and improve
more rapidly -- if your car is consistent.  I'd recommend a beginning
autocrosser do the following, in this order:

1.  Rebuild the front end, using harder-compound bushings.  If possible,
install the tubular front shock conversion; I used the Werace kit on my
'74 Midget 12 or 13 years ago.  Worked great once I figured out not to
use the stock sway-bar mounting holes -- that cracked my A-arms!  You
*have* to drill out new holes where the template says.  I don't know
what's available today, though, and there may be something better.  You
may choose to go with lower springs, since you say you're planning to
trailer it; I ran springs that dropped my Midget 1" at the front, and
actually got better handling when I replaced the stock springs and went
with a 3/4" anti-roll bar (but that was also when I got the shock
geometry right, which would make a BIG difference).  But low springs on
a street-driven Midget mean you learn to drive around tall objects in
the road, like, say, dimes. :-)  

BTW -- yes, I know Fred Puhn and Carroll Smith and everybody say that if
you put on a stiffer front anti-roll bar, you get more understeer. 
They're right, assuming you're talking about a race car.  If you're
talking about a hopelessly shot old British sports car using Morris
Minor front suspension components, adding a front anti-roll bar
*reduces* understeer.  Took me a while to figure out why: on a Midget,
increased body roll causes increased positive camber (called "camber
gain").  If you reduce body roll, you reduce camber gain, keeping the
tire planted more firmly on the asphalt, reducing front-end slip angles
-- hence, reducing understeer.  Put on a 3/4" front anti roll bar and
the car will get *more* pointable with the gas.  BTDT.

2.  Rebuild the rear suspension, using hard bushings and spring plates. 
I used the no-longer-available Nylatron components on an MGB several
years ago, and that tightened up action and removed any slop at the
rear; I've seen the modern equivalent in the Moss catalog, you know
where to look.  If the rear Armstrong lever dampers are shot, consider
replacing them with the adjustable Spax units I've seen in the Moss
catalog.  Adjustable shocks give you some tuneability; I'll explain more
later if you need it.  Don't bother with stiffer rear springs yet, but
when the time comes talk to the folks at Winner's Circle.

If you don't swap out the Armstrong dampers for tubular shocks, then at
least drain them and fill them with the right shock oil.  Don't use STP
or heavy-duty motor-oil in them, as it'll dissolve the seals.  

3.  Wider wheels and tires.  Chevy Vega/Monza rims, as you may already
know, fit the Midget bolt pattern, or there are the Moss alloys for $139
apiece.  You may need either to modify the backspacing at the rear to
clear the spring/inner fender, or not, depending on the wheels you use. 
I ran 185-60HR13 tires on my stock Rostyles with my '74, and got minor
rubbing on hard turns with bumps (e.g., going up a steep driveway) till
I installed 1/4" wheel spacers at the rear.  In DSP you can use Hoosier
Autocrossers (or whatever they're calling 'em now, AS02 or something
equally silly) or A008RSII.

4.  Engine mods are where you get far less bang for your buck, but since
you ask below I'll address them in detail there.

> (2)  Since the car would be utilized only as an Autocross car, and would be
> towed to the events, Is it necessary to replace the lower front door hinge
> posts?  Or would it be acceptable to clean out the rust as much as possible,
> treat it to stop it, connect the door by the top hinge and the door latch,
> then to weld the door solidly shut on the inside?

This, I believe, is illegal in the Street Prepared category.  

> (3)  What type of engine modifications would I need to make in rebuilding the
> 1275 that came with the 1973 to make it the best engine for an Auto cross car?

In Street Prepared, the basic rules are:

You must use the stock cam, compression, valves, springs, pistons and
rockers.  You can only shave a limited amount (typically about 0.25")
off the head for the purpose of "truing" up a head after a rebuild.  You
can overbore your engine no more than something like 0.047" (effectively
limiting you to 40-over pistons, which *does* give you something like a
1308cc engine, not an insignificant bump; furthermore, increasing the
cylinder bore raises the compression ratio a hair, since you're pushing
a larger volume into the same size combustion chamber.

You can only modify the cylinder head ports for 1" from the manifold
gasket.  Read Vizard VERY carefully here -- you can get very real gains
on an A Series engine (or B, for that matter, if anyone cares) by
looking at his diagrams showing heaviest gas flow and by really
understanding his concept of stepping the ports to avoid reverse flow. 
These two things make a HUGE difference on a siamese-port engine.  

You can use any induction and exhaust system you wish.  No, that doesn't
mean connecting the exhaust up to an impeller and using it to force air
into the induction tract under pressure. :-)  It does mean you can use a
Weber and an LCB if you want, but I don't recommend them for the first
year.  Save your money for what you didn't know was going to break till
you got it on course.

To get the best out of the stock exhaust manifold, run your Dremel up
into its ports and clean them up, following Vizard's recommendations on
where the gas flow is.  You can go deeper than 1" here if you need to,
just not the cylinder head.

Oh, and a free tip from the old Abingdon Special Tuning Guide: Set your
valve clearances to 0.015" instead of 0.012".  This effectively delays
the valve opening till the piston speed is a little higher, which
improves the charge velocity enough that it makes a noticeable
difference in power.  I was really surprised at the bump in my torque
curve (over 2800 RPM, anyway) when I did this on my '74.

Remove the belt-driven radiator fan and install an electric unit; Hayden
makes a 13" fan that's ideal for these cars, costs $69 or so at Pep
Boys.  The best installation is to pick something that's always hot
(essentially, right to +12V off the battery) and then install a
temperature-sensing switch in the radiator core that turns the fan on
when the water reaches a set temperature.  

> (4)  I have been told I need a rear end with high ratio--like high 4.+.  Are
> these available as standard rear end ratios or are these specially built
> differentials?

Standard, but may be hard to find.  4.56:1 is the recommended autox
ratio, it'll make your Spridget leap off the line hard enough to whack
your helmet off the roll bar and make you see stars.  Oh, and it'll also
break your axles, right, Miq? :-(  

> (5)  Any other information regarding this possible rebuild 

Basically, if you have the choice of spending money on parts or on an
autocross school, pick the school.  Borrow a car, or drive your RBS, or
rent a Geo, but take as many autocross schools as you can find and
afford.  Then concentrate this year on making the car solid,
predictable, reliable, and then learn how to drive it.  

Doing the *absolute cheapest* things to get a Spridget in shape to have
safe fun for a season's worth of autocrossing, I'd say:

1 - replace bushings front and rear (what, about $100 for all the bits?)
2 - drain and refill the shocks with new shock oil (about $7)
3 - sticky tires on junkyard Vega rims (about $100 per tire, rims depend
on your junkyard but let's budget $25 apiece)
4 - head gasket set (replaced when you pull the head to grind it), what,
$25?
5 - valve clearance to 0.015 -- free
6 - spark advance as far as possible without pinging -- free
7 - front anti-roll bar -- about $100

That brings the total up to about $650, which -- using my wife's rule
for calculating the relationship between my initial estimates and the
actual cost ("double it and add thirty") -- works out to just under
$1500.  Yeesh!  That's more than I've paid for most of my British cars!
:-)

Oh -- brakes!  I completely forgot about brakes; you'll have to make
that determination yourself.  However, note that for autocrossing,
having high-temperature compounds isn't necessary; a typical autocross
run will last 40 to 90 seconds, at speeds probably no higher than 40
mph, and may include two heavy braking "events," in a 1500-lb car. 
Stock rear shoes, new Castrol LMA, and if you really feel flush one
month, Repco MetalMasters up front.  But rebuild your calipers and wheel
cylinders first.

> Thanks guys!!   Your input will help me make a decision about the direction I
> want to go with that '73!

Don't say that, we may give you directions to our garages! :-)

Don't forget -- the most important thing you can do in an autocross is
to have fun.  Keep at it; the first trophy I ever got in autocrossing
came at the end of a season in which my first outing showed me as the
slowest car on course, period, in all classes.  I always figured that
the plaque wasn't so much for my driving skill as for not giving up.

--Scott



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