westwest888

A lead acid battery is like running the AC. Alternator works overtime to charge at 5% efficiency. I've eliminated virtually all electrical draw for recharging the battery. Where other high mileage S4's will need the alternator replaced (a $2000 job), mine will keep humming.

primetime

LOL! Ok if you say so, any data to support that assumption? I haven't seen/heard of any bad alternators yet... My point on performance is still valid regardless... Also, for me and I know I'm not the norm as I'd say you aren't either with all your road racing mileage isn't a concern... My 2010 car has 9,0xx miles... It will be sold before it hits 20K unless I give it to my wife as a daily...

westwest888

Worst case charging efficiency for a lithium battery is 80%. In normal temperature ranges it's over 90%. You can use your engine to force feed electricity into a bucket of acid for hours until it's full. I'm just going to use mine to turn the wheels.

primetime

West, I'm not questioning the battery there is no doubt it's lighter and better, heck I'll probably buy one this spring... Your post and my points are about the intake, you are running a sub optimal setup and it cost more... Why do you always change the discussion to what you feel fits your agenda... Focus...

Bobby Kinstle

That's not true at all. Flooded cell batteries have a charge efficiency around 65% when they are full, and as high as 85% when they are moderately discharged. However, the batter will draw significantly less than one amp when fully charged, so even though the efficiency drops you are still looking at a current draw which is less than the rotational friction of your alternator. If you switched to the VRLA battery I linked to before, you can get charge efficiencies as high as 95% and float currents of around 5 milliamps when fully charged. Not that it will make any difference at all.

When your alternator is outputting at full capacity it consumes around 2 horsepower. Sure you can make it less, but that's a pretty small dial to turn, and turning it all the way to zero results in an insignificant net gain.

Your lithium battery would have a lower peak draw for the 1 minute or so after starting your car but then it would likely draw more current than the original battery for quite some time until it's fully recharged. Yes the charge efficiency is higher, but it's drawing more power from the alternator during a time you might actually care about it.

westwest888

There is useful information here and I thank you for sharing it. Where do you get the 2 HP number for the alternator? Is that a general (classical) figure for alternators, or a specific figure germane to modern luxury sedans with large alternators?

I would have ball parked it at 10 HP.

Bobby Kinstle

I assumed it was a 120A alternator but looking at ECS it looks like we actually have 180A alternators. So lets work out the math:

Output Voltage (lets say) 14V times maximum output current 180A equals power output of 2520W. Modern alternators are around 80% efficient, so that means power input is 3150W. 745.7W per Horsepower means 4.22HP maximum input from the belt. That's assuming the alternator is outputting it's maximum capacity, which it wouldn't except for maybe the first minute after starting the car on a lead acid. Your battery probably can't accept current at that rate.

will13k7

If your unlucky, you'll get some dumb smog guy who thinks he is doing his job and wants to see it all oem under the hood, he'll take one look at that CF tubing and say its modded so it doesn't pass the visual test. he'll not understand or care about the technical points about not modding the air box.

... speaking about being below the law, our tunes modify emission related controls and I think that makes them illegal. I'll be switching to the stock map before getting checked and my oem intake will be back on.

moto-one

As long as there is a CARB sticker on it, it's legal and can not be denied...on the visual.

Mark

will13k7

CARB approval would be nice, none of the players for the B8 S4 platform have this certification. Given how much they charge for them, its pretty lame they don't given lower cost intakes for lower cost cars are CARB certified.