Home made lifepo4 car battery? 16 volt conversion?
 

I've been trying to find a way to improve my ignition system on my Saturn to improve fuel mileage. I thought about adding a dc to dc converter to increase the voltage to the coils but after further research I stumbled upon an old drag racers trick of converting to a 16 volt system and several great reviews about how it not only improves ignition performance but also every other electrical device works better with the exception of some burned out headlights.
My main concern is will the pcm be able to handle the increased voltage but I will get back to that.

The battery
Most 16 volts batteries are in the $250 range and weight close to 50 lbs and that won't do. I would like to make my own lifepo4 battery using 5 or 6 headway 38120s 10 ah cells from evassemble.com for about $100 and weighing less than 8 lbs

chemical composition

LiFePO4

Nominal Capacity

10Ah

Charging voltage

3.65V

Nominal Voltage

3.2V

Cut-off Discharge Voltage

2.0V

Charging Method

CC/CV

Maximum Discharge Current(continuable)

100A

Maximum Charge Current(continuable)

50A

The alternator
My alternator is due for a rebuild and while I'm at it I can use a 16 volt regulator http://m.ebay.com/itm/Delco-CS130-Al...-/281132793918
Voltage: 16
Set Point: 19.1
Polarity: Negative
Activation: Self-Excited
Notes: •1-Wire
•For Applications With 16V Batteries

12v
For the stuff I would like to stay 12 volts I could make the battery a 3 post ground 12v and 16v but running a wire from the positive side of the 4th cell for 12.8 volts

If all you want to do is boost the ignition system, I'd use a dc-dc converter. They're really cheap, and its easier.

I would not suggest making a 3 post battery. It'll unbalance the cells and you'll have to deal with that.

Other than that, I think a 5 cell setup would be worth a shot, though still pretty high of voltage off a fresh charge (16.75V). Definitely not 6 cell, thats gonna make your voltage too high.

Do no use a 3 post battery with any lithium chemistry.

I have built my own LiFePO4 batteris and converted vehicles over to LiFePO4.

That 10ah lithium battery wont be able to start your vehicle when its cold.
If you attempt to charge a LiFiPO4 battery with a cell temperature than 20'F it will permanently damage its capacity.
Do no expose the LiFePO4 battery to under hood heat, that will ruin them too.
I do not recommend using Lithium starting batteries up north at all.
I live in new mexico and I have to bring my lithium batteries in at night during the late fall, all winter and early spring, I also relocated them inside the vehicle and put them on Anderson connectors to protect them from temperature swings.

I have accidently fried ECMs with as little as 18 volts using a battery charger with 100 amp "starting assist". So don't do it.

I really appreciate the advice I have not been able to find any articles about making your own lithium battery so any advice I can get on that is great. I was planning on locating the battery in the dash or trunk because of the heat I was not aware of the sensitivity to low temperatures only heat I might just stick to running a 10 lb motorcycle battery during the warmer months and a dc to dc for the coils. The higher voltage would be nice for the starter allowing a smaller battery though. As for the dc to dc converter I'm wondering how reliable it would be and how much voltage I would safely be able to run to the coils or how much the spark plugs could be gapped for the increased voltage?
I'm not completely off the idea of running a 16 volt system though just more reading to do. I would mainly worry about restricting the power to the pcm

Starters crank an engine over pretty good with the LiFePO4 battery 4 cell configuration with 13.2 volts.

Problem with putting the battery in the trunk is you have longer run of cable and more voltage drop. I put them behind the seat.

For powering the coils I say get a constant voltage booster and turn it up to 14.6V, that is the highest voltage I have seen on a vehicle electrical system.
That way when the engine is cranking and battery voltage is at say 11 volts the starter will see get a constant 14+ volts.

This is my battery build:
DIY: BYOB, for more power, a lot less weight - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Maximum amps is 100 on those cells? You're going to toast them pretty quickly replacing your cars lead with them... I'd bet you're going to draw twice that starting.

For engine cranking you only want to run the batteries at about a 5C rate.
Chances are cranking a 4cyl engine with a 10ah battery will likely use between a 10C and 20C discharge rate. 20C is the absolute max on most LiFePO4 batteries.