Technical How many CCA to fire up a flathead?

Since I just can't run down the street and ask for a battery for my 36', whats the census on minimum cold cranking amps to fire off a flathead w/12v conversion using a 6 v starter, no creature comforts what so ever like air, radio, and any other shenanigans like that, just fire off the engine, maybe a few lights now and then.... plmk, thx

 

I just fired up a late model merc flathead strapped to a dolly. Used the 12 volt battery from my John Deere 4300 diesel tractor. Its a small size battery out of a Honda if IRC and the flattie fired right up as soon as I hit the starter ****on. I don't have CCA numbers but they can't be very high based on the little battery I was using.

 

Generator or Alternator equipped? Believe it or not the "official" metric for adequate starting is 1 CCA per CI, most people obsess over CCA. If you live in Saskatoon or Regina you probably need more though. "Gulf Coast" doesn't sound too taxing. Generally a heavier battery (reserve ampere capacity) is needed in generator equipped rods because (unlike an alternator) the entire electrical system is supported solely by the battery at times.

 

I have a full race motor: bored .155 with 3/8 stroker and I use a garden tractor batteryfrom tractor supply—about $30—works well. I have compression readings of 150-170. Motor is in 32 cabriolet and runs 80 in 1/8 mile. Flatheads Forever!

 

The cheapie from Walmart

 

Flatheadjohn47 I like that! I have a zero turn mower that I just pulled the battery out of and I might try it out in the flattie in my roadster. Its bored an 1/8" over with a 4 inch crank so it should work ok.

 

Should have noted it has an alternator, that was converted too, thanks Gents

 

And still not a single actual CCA number? I'd also like to know.

 

Considering stock flathead V8's had the option of being started with a hand crank, I'd guess the minimum number is fairly low. Depends on engine mods and condition......mine starts easily on 6v with 500 CCA.

 

Quoting Truck64's post from above "Believe it or not the "official" metric for adequate starting is 1 CCA per CI" that's what I found in searching for info when I was deliberating over battery size for my T roadster.

I ended up using two jetski/motorcycle batteries in parallel because of space limitations and they work fine with my tiny 215 Olds V-8. Sorry, but I don't recall the CCA number on them.

Lynn

 

'Course that guide won't really hold true for high compression engines (or Diesels), but odds are if you were to walk into Hank's FleetFarm and grab a battery blindfolded it would be fine.

 

Don't remember the CCAs but I used a small riding mower battery in my T bucket. Bought it at Homer's IIRC and it was about $40.

 

I start the 385 horse ZZ-4 in my Boss Hoss bike with an Odyssey PC 680

 

The one in my coupe has 650 CCA (group65 battery maybe) not sure what the minimum required is but that's what i am using and it works fine...every time… quick bump on the starter and she fires right off.
Chappy

 

You'd be fine with something "conventional" that will fit. Odds are it'll likely be about 525-550. Reserve capacity is a better measure for batteries. Why? You're a 1/2 hour from home at night and it stops charging. You need lights and ignition to make it back. The bigger the better at that point. So if you want a number, in my opinion, try to go a minimum of 500. As long as you can keep it charged a battery is one of the few things on this stuff where "more is better". I can get away with a 6V 800 CCA in the Duesy we're restoring but I'm fitting it for a 1050 (1/2" taller).

 

Just using CCA without any further data makes it very blunt.

Cold Cranking Amps is all about the current a battery can deliver at 0F (-18C), and as you probably know batteries loose alot of capacity when cold and engines turn over and start much harder in the cold too. You may need one size of battery to start your flathead in the middle of the winter when you've just dug it out of 3 feet of snow, while you may be fine using way less than half that size on a hot summer day.

My strategy is simple, I like to have the margins on my side. If there's room for a bigger battery I want a bigger battery. Within reason ofcourse.

 

I have a lot of shenanigans on mine so I flatter my flathead with this little monster

It is small, light, powerful, requires no venting and throws an impressive 900 PHCA for the first 5 seconds.

 

Is the flathead a brand new build where everything is nice and tight, or does it have a bunch of miles on it and is loosey-goosey? I never put anything in my cars with less than 900 CCA, 1050 is prefered, but then I live in the northern plains and expect my stuff to fire up at -20 F, and hopefully start at -40 F. The gulf coast doesn't have that problem, so your mileage may vary....

 

Keep in mind that a 'typical' V8 will draw about 250 amps @ 12V when starting if everything is in good shape. Large motors and/or high compression can bump that up by 100 amps, but there are a lot of variables; a OEM type series-wound starter will draw more than a permanent-magnet gear reduction starter, all else being equal. Cold climates will require more because of reduced output from the battery, hot climates may require more due to 'heat soak'. While most any lead-acid battery can produce short bursts of high amps, it's ampere-hours that defines what the battery's reserves are. Personally, I wouldn't go below 40 AH capacity.

To put this in some perspective, a 1100CC motorcycle will draw about 90 amps when starting.

 

I’m using a 650 Cranking amp in my merc it works quite well with the 6 volt starter it only turns about half a crank and starts up

 

I'm different than most as I never consider the "cheapest" one when I look at batteries but go for the highest rated one that fits in the space I am putting it in.
Still if you go cheap go Walmart as friends have pretty good luck with them.
You have X by X by X inches to work with battery box wise, what size of battery fits in that space? Too much info to print out but this chart will let you figure out what group size of battery will fit.
https://www.jegs.com/Sizecharts/bcigroup.html

 

been running an optima red for 18 years in my blown flathead P/U with 6v starter just changed to 12v starter as I got tired of replacing bendix springs and starter drive bolts every coupla years, was gonna put wing nuts on starter..............

 

Exactly what I got, I figured I can always use it in my zero turn if my flattie doesn't like it, your the 2nd or 3rd person to recommend this exact battery so for $100 and "agm", its done, thanks.

Will advise how it works in a follow up down the road, not pun intended

 

I'm also a big fan of the Odyssey PC 680 battery.
I've had one in my 32 with a big inch flathead for 6+ years.
It's great. Cost was about $ 120.00 delivered. Weighs about
11# . I have it under the rear seat in my Tudor on it's side.
I run an alternator off the driveshaft to charge it.
Wouldn't hesitate to buy another.
Jim

 

x2.......really GREAT little battery. I have used them in several of my rods.

 

On the other hand; a regular old 24, 34, etc battery will do the job; plus you'll never have to be hunting down a "special" battery in the time of need.

 

I’m also using the Odessey PC680 on my Flathead. Mounted under the seat. Plenty of power. Zero issues. Price is right.

 

Just remember all those figures, cca , reserve capacity etc are for when the battery is new. The battery starts deteriorating the day it is made, not the day you buy it. I always check the manufactured date on any battery I buy, I have seen year old batteries sold as” new”. So.. if you start out with a battery that is just barely big enough, it will fail before a larger battery would. Just my .02.


Bones