Battery replacement

[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

[Vince Caldicott]

Thanks Graham and Rob, I've tested the battery after a short run out and it reads 12.66 volts. I still need to test the alternator. I believe The compression ratio is quite high at 10.8 to 1. The car turns over quite well when cold on a fully charged battery and starts can take 30 seconds. When I switch it off it tends to over run for a couple of seconds which may have something to do with the difficult restarting. I'm tempted to purchase a higher Ah battery and hope that solves the problem when hot starting.
Vince

[Rob.Hendriks]

Vince
You may have just given us the cause for the starting problems. Over-running or dieseling is not good for your engine and needs to be addressed asap. It occurs when there is no ignition source i.e. the key is turned off and the remaining fuel/air mix is ignited by a hot spot within the cylinder. This hot spot can be carbon build up (which would be unlikely in a newly built engine), the timing being too far advanced or the mixture being too lean making the engine run hot and thus causing the plugs to overheat. Sluggish starting when hot is also a symptom of the timing being too far advanced. Would carry out a few checks:

Spark plugs
First take out all the spark plugs and examine them carefully. Look at the electrodes and the nose of the insulator for any signs of overheating. The plugs should have a light brown coating all over - if they appear white or glazed they have been overheating

Check engine timing
If the spark plugs aren't at fault, you should next check the timing. Usually, you will have had other warning of over advanced timing, such as pinking under hard acceleration or hard/sluggish turn over when starting hot

Air leaks
If dieseling persists, your next avenue of investigation is the fuel system. The problem may be caused by a weak fuel/air mixture because of a badly adjusted carburettor or air leaking into the inlet manifold. A weak fuel/air mixture can make the engine run much hotter than it should.

[Vince Caldicott]

Hi Rob, thank you for your reply and sorry for the delay in responding, I've been away on a family holiday and banned from the internet. I will forward your response to my mechanic who looks after my car for him to check out the possible causes you highlight. I will respond with results of his checks. Thanks again.
Vince

[AC Ventura]

Vince, you mentioned difficult restarting, presumably from hot? With an FE side oiler this is almost certainly vapour lock (fuel vaporising in the carb feed line) caused by engine bay heat. You can rectify this with a fuel return line to the tank.
Also a high compression FE needs a high torque mini starter.

[westcott]

Vince, beside the battery You shoud check the charging situation at idle.

After swapping engines from different engine families sometimes I made the experience that the new pulley ratios are a little bit off and the cooling and or charging circuit is affected.

In tjhe past I had situations in different engine swap projects were the alternator needed some kick on rpm to start charging at idle.

If the situation is like this the battery will discharge slowly at idle because the carry over alternator pulley is too big by diameter in the new constellation and rpm is not sufficient for charging.

A fix for that will a bigger pulley on the crank and or a smaller pulley for the alternator.

If your altenator sees enough rpm at idle it will charge the battery directly after the start and everything is perfect, voltage at idle measured at the battery poles should be 13,8-14,0 V.

   

[Flyinghorse]

I have used the attached calculator to figure this out in the past. (not mine -credit to KRC)

[Vince Caldicott]

Thanks everyone for the helpful info, I will pass all this on to my mechanic for when I next take it in, it does seem a bit better since installing the larger battery but not as easy to start as I would like. I do have the right starter and alternator so most likely the fuel vaporisation is the culprit. Vince