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Battery replacement

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Vince Caldicott:
I have recently  installed a 427 side oiler into my cobra and I need to replace the battery, can anyone advise the best make and output battery for this engine.
Vince

Rob.Hendriks:
Firstly, you need to determine the battery size or group i.e. the battery size that will best fit the physical dimensions and terminal locations for your application

If you live in colder climes, then consideration needs to be given to the Cold Cranking Amps (CCA), which define a battery's ability to start an engine in cold temperatures. The rating refers to the number of amps a 12-volt battery can deliver at -17C (0F) for 30 seconds while maintaining a voltage of at least 7.2V

Consideration then needs to be given to:
•   Maintainability/serviceability – most of our batteries are tucked away in a quite difficult to access location and most us do not look at the battery until it goes flat, therefore consider a battery that requires minimum maintainance i.e. a sealed gel or AGM type battery
•   Use of the vehicle – is it used daily, only in fair weather or once a year, this will reflect on battery selection
•   Mechanical aptitude of the owner – an owner that is less mechanically adept, is more likely to never look at the battery until it is dead
•   Battery age – take care when purchasing a battery that the manufacturing date is within the past 6mths. This is usually on the case or label and is indicated by letters and digits; A = January, 0=2000, 1=2001, etc.
•   Electrical devices – is there an electric clock, that runs even with the ignition off
•   Isolation – is the battery able to be totally isolated
•   Wiring – age and condition of the wiring and connections; are they in good condition, no corrosion, all connections are tight, etc.

Once you have determined the above and the selection has been made I would recommend fitment of a charger/maintainer like the C-TEK MXS 3.8 (https://www.ctek.com/products/vehicle/mxs-3-8).
These can be directly wired to your battery, with a small 10x12x30mm sealed waterproof and dust-proof connection discreetly located for easy access. I my case access is through the engine side vent; when the car is not in use the C-TEK is permanently connected (sometimes for several months) and when disconnected the connector is pushed back through the vent out of sight

Vince Caldicott:
Rob , thank you for your very helpful and detailed reply. I have currently a 77AH Varta  battery which I tend to fully charge when I return from a road trip. My concern is this, if I start from cold it can't take 20 to 30 seconds to fire the engine, I then go out for say half an hour, park up for an hour and then the battery seems to struggle to turn the engine over. Is this because the battery is underrated for such a big engine or is it correctly sized and just worn out. Does 77Ah sound about right for a 427 FE?

Vince

Rob.Hendriks:
Vince

I’m no sparkie, but here are a couple of basic tests to carry to determine if your battery is charging and/or holding a charge

Using a digital multimeter, set the dial to DC voltage to low range e.g. <24VDC
Next, take your multimeter’s black lead to the negative battery terminal and the red lead to the positive terminal. Hold each one firmly until the multimeter provides a voltage readout.

12.66+ battery is 100% charged and in good shape
12.45 - 75% charged
12.24 - 50% charged
12.06 - 25% charged
11.89 - 0% charged

If you’re seeing 12.45 volts or higher, your battery is in good shape and it’s time to check other common culprits. If you’re below a 75% charge, your battery might still bring the car to life, but not reliably. Below this threshold, your battery may need recharging or even replacing depending on its age.

Now start the engine and carry out the same test, the reading should be between 13.7 – 14.7, showing your battery is receiving charge from the alternator

Flyinghorse:
Vince I would also look at why your engine is taking so long to start (fuel pressure /carb/plugs/ignition)--as I recall you had it rebuilt.
We assume here that your alternator is recharging the battery/the battery taking the charge --its odd that the battery appears drained after a run--usually 30mins on an alternator is sufficient to recharge the battery.
It may be that the compression ratio of the new build  is to much for the standard starter /battery combination and a hi-torque starter is required.
I am looking at optimate spiral wound  gel battery for my car (If I can find a way to secure it)/possible hi torque starter (Stroked 302 to 347")
Real steel (And summit) list a master torque  for the 427FE  #9606
There does seem to be a switch to iridium plugs for some of the MKiV CRS and recently documented on the Ace site for Bristol engines.

Graham

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