Alternator for 302

[simon]

What should I buy?
Don't need too much power obviously but does it matter what I get?
Simon

[SimonP]

Simon,
It's down to a case of whatever will fit and has an output of about 60 Amps.

A bit of info:
You may need more power than you think!
You need to "budget" something like this:
Performance ignition system, 10-15A
Lighting, 12A max. (add 5A per spotlight or front fog, if fitted)
Wipers, 5-8A
Heater blower, 5-8A
Cooling fans, 10A each.

You can ignore any intermittent loads, like indicators, brake/reverse lights, screenwash and horn.

Unlike a dynamo system, an alternator is usually sized to FULLY supply ALL electrical loads, with a little reserve left to charge the battery in the "worst case" situation.

I'd reckon about 60 Amps would be about right.

If you fit a bigger alternator than is absolutely necessary, it won't really matter. All the alternator tries to do is maintain the battery at around 14V (13.8 to 14.4V).
A bigger alternator will simply have more reserve and recharge the battery more quickly to recover from starting.

Once the battery is recharged, a 100-Amp alternator will drain roughly the same horsepower from your engine as a 50-Amp alternator when supplying an average 25-Amp load.

The only issue with an alternator is that they can usually provide near enough their full output at idle speeds. With a carburetted engine, this can "load down" the idle speed and sometimes stall the engine. Obviously on your 5-litre engine it isn't as drastic as with a 1-litre engine!
With EFI systems, the idle speed control system makes up for this increased loading.


Simon

[BenBaron]

How would I know what output my alternator is?


cheers
Ben

[SimonP]

There should be a plate attatched with either a rating, model number or both.
If the alternator came from a donor car, the manual or handbook should show which type was fitted to those models.

If you have a standard Lucas type on your RV8, it will probably have a number like "17ACR" or "20ACR". Look for a tag around the body, where the black plastic cover meets the casting.

Once you have the type number, you can look up it's spec.

If it's only about 30 or 40 Amps, it may still be adequate for your car, and will probably only be an issue if you run a specialist ignition like MSD, do a lot of night driving, and your electric fan(s) run more than 50% of the time.

Simon

[crendonman]

Simon,

I've running a Cleveland 351C and I bought a new alternator for a Rover Metro £59 from a company in Bradford :tu

(no exchange necessary)

Let me know if you are interested and I will give you details

Regards

david

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[BenBaron]

Hi Simon,

looked all over but no markings or anything on the alternator.
Its a chrome one I picked up second hand, so I didnt bother asking..

Is there anyway I can tell before I wire it in and have my engine running?


cheers

Ben

[SimonP]

Ben,
What sort of connections does it have? Is it:
Lucas style 3-spade connector (2 big, 1 small), or
2 stud terminals (1 big, 1 small), or
1 stud terminal, 2 spade terminals (maybe under rubber plug)?

You can't tell it's rating just by looking at it, but I'd hazard a guess at it being a Delco model with "different clothes on".

Can you post a picture? Maybe somone could recognise it and let you know.

Simon.

[VinceGledhill]

My advice is to determine your loads, I.E. Swich everything on and measure it with an ameter. Not got one? Then bring it here and I'll check it.

Once you've determined what loads you have (amps used when everything is on) then you need an alternator to balance that load (in other words give you more than you are capable of using)

Everyone tends to over compensate when it comes to alternators. It's not an alternator for a 302 or a 351 but simply one that will charge your battery when everything in the car is swiched on.

Look for similar threads on this site, I have written many times about the subject. Suffice to say, you do not need to spend more than £30.00 on an alternator for a cobra.

Don't forget there's no rear screen heater, no air conditioning, etc that put a drain on your battery.

Remember, Volts are the speed at which the gremlins are running. Amps is the amount of gremlins running down the wire. Your alternator will supply a number of amps (amount of gremlins) into the battery, greater than the number of amps that are coming out (amount of gremlins being used)

That is all.

So.... in breif... measure it..... get one a bit bigger... save some brass.... buy Vince a beer..... sorted.


Regards
Vince
Time served Auto Electrician
Lucas Leeds 1979-1983

[BenBaron]

righty ho,

think from your descriptions that it is a lucas style one (from memory)

I will take a photo of it and post...


thanx for the help
Ben