I've been using a lawn tractor battery in my Roadster for over 5 years now -
and it's never let me down. Cost well under $20, and weighs about a third
what a group 24 weighs. I don't exactly treat it with kid gloves either. It
has to start the car up to 20 times in an afternoon at an Autocross, and
power a high pressure fuel pump, electric cooling fan, ECU and fire the
injectors...plus a 160watt heater blower on cold days. During cold weather
it sits (almost 2 months this year) outside in the cold without a charger.
Still, it starts the car every time, usually on the first try.
Sure, it helps that I have fuel injection and a gear reduction starter...but
the same battery was in the car for about 6 months with a tired old starter
and SU's...and it started every time. Plus, with EFI the cranking voltage
cannot drop below about 9 volts or the ECU will not function.
If any of you have access to an ammeter that can read cranking amps - like
one with an inductive pick up - test just how many amps are needed to crank
your roadster or any other car. You may be surprised how little current is
actually needed. My Roadster only draws about 90amps when cranking at about
60deg F. The highest reading I ever measured was about 200amps, on a 13.5:1
compression L28 (280Z) race engine.
Of course, if your Roadster is hard to start for whatever reason...or you
tend to leave the radio/lights/etc on for extended periods with the engine
off...by all means get a big heavy battery. Maybe even two of 'em. But if
your Roadster starts easily and you like the idea of cheap, light and small,
give a lawn tractor battery a try.
Rob Robinson
CSP 67 2000
Roanoke, VA
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