pulse cranking amps

C

chinga

Junior Member
I have ordered Snyder’s gear reduction 12 v starter for my 29 racer. H & H touring build on 31 block (zero Hour) with Snyder 5.5:1 head, inserts, cam and oversize stainless valves. Been looking at 2 different lightweight Braille batteries:

B2317, 17 LB, Pulse Crank Amps = 1191, Amp hour = 23

B3121, 21 LB, Pulse Crank Amps = 1380, Amp hour = 31

Which one should crank the engine well?

Do you recommend a different lightweight battery?\
 
Probably more of a HAMB question 'cause this is a stock A site, but I'll give your inquiry a shot- The starter amperage draw is directly related to load. Your Model A with the relatively low 5.5 CR head you have chosen needs little torque to crank. The 12V gear reduction starter is way overkill and will likely only draw 75 amps or less with 11 volts at the starter terminal. The starter you have chosen is built on a motor intended to crank 4 or small 6 cyl cars. It is not a high amperage rotor build like the gear reduction starters sold for big V8's and diesels.

A 23 amp-hour AGM battery cranking an 80 amp load (start + ign) to the point of temporary plate ion starvation (faster than the AGM can keep up, then the voltage falls quickly off) would continuously crank the engine approximately 3.9 minutes. Of course that gear drive starter will smoke if you run it continuously that long. A better way to look at it is 20 second cranks with a minute cool down between attempts. This will allow the AGM electrolyte to normalize, avoiding the early fall-off wall. You would get over thirty 20 second cranks. Is that sufficient?

Since weight seems to be an issue to you and nobody needs more than a half dozen 20 second cranks out of a speedster battery, I'd recommend an entirely different Braille battery. THIS ONE. It's only 5.9 lbs.
 
Hey Mike,

Thanks for the analysis, detailed explanation and very light but very expensive battery recommendation.

Wish I had that much to invest in saving ten pounds. All of this is very interesting. I think thirty 20 second cranks will be more than sufficient.

For weight someone suggested not using a starter but stick a cranking motor in the front on the crank pulley and spin the engine there.
 
I see a number of MOTORCYCLE BATTERIES are about four pounds with low CCA's and 12 volts. I do not know the racing rules, but could you use a JUMP BOX to start the car and then use the four pound motorcycle battery to run it?
 
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