[tscdennab]

Lately i developed a mini-obsession for lightweight, since this is a very healthy way to improve the car's performance. To keep a car 100% streetable yet make it lightweight is not easy, especially when financially constrained.

One of the mandatory things because of the good price/weight reduction ratio is a lightweight battery. I researched many options for this and I think I have found the perfect compromise for my street car.

The 4 parameters to keep in mind when choosing a lightweight battery are technology, weight, cranking power and reserve power.

Technology

AGM (Absorbent Glass Mat - non spillable maintenance free lead acid battery) is the best OEM battery technology today (lithium is expensive and not widespread). From the pictures of some e90 and MINI batteries I realized that earlier e90 cars do NOT have AGM batteries and the later ones feature AGM batteries. If you have a 90Ah battery with a charge indicator (like a small round lens which is green when battery is charged) chances are that it's not an AGM battery. My car has an Exide 80Ah AGM battery, weighting 22.5kg (50lbs). The problem is, the optimal alternator charge voltage is different for AGM and non-AGM batteries, and it is best to replace a non-AGM battery with another non-AGM battery and if you have AGM to replace it with another AGM battery (like for like). This is because the alternator is set up to charge either an AGM or standard battery. However, an AGM battery can replace a non-AGM but not always. The opposite is not true.

Cranking power

To start an engine, a rule of thumb is that one "cold cranking amp" is needed for every cubic inch of engine displacement, so the N54 needs about 200CCA to start (240CCA according to another online calculator). The problem is that the battery cranking power drops with the temperature. So if you want the car to also start in the winter, you need about double the minimum required CCA for the engine. 400CCA would be ok for a 3 liter engine, I guess.

Weight and Reserve Power

These are directly related. The more weight, the more reserve power. Reserve power is the battery capacity to sustain prolonged loads, like running the radio with the engine stopped. A 15lbs battery is unlikely to start after a few minutes of listening to the radio with the engine off.

Battery registration

After installing a new battery, you can reset battery adaptation with the BT cable, in order for the new battery to be charged correctly and have a maximum life. I didn't do this yet but I will do it in a few days.

So, what are the options for the e90 ?

1. Braille - these expensive batteries are in fact rebadged and re-marketed Deka AGM motorcycle batteries, sold as lightweight racing batteries. I would recommend the 21lbs battery, no less. It costs like $180. Add the $100 fitment tray and the price becomes stupid. Too much when there are so many other options.

2. Deka - ETX30L is the Braille 21lbs battery. It costs about $95. I would recommend this battery together with a SAE terminal conversion kit ($15) which convers from motorcycle terminals to car terminals. Braille is a Deka with the car terminals attached.

3. Big Crank ETX30L - rebadged Deka batteries, sometimes even cheaper than Deka.

The problem with the above batteries is that if you want good fitment you need a special tray from Macht Schnell or HP Autowerks which costs $100 or so, and also weights about 2 lbs. Insane price. You can also do a Mr.5-style tray from some plywood (search the forum).

4. MINI OEM battery - it's a 55Ah battery which weights 36lbs. Too much for my liking, and too expensive from my dealer.

And the winner is...

5. Intact 45Ah / 450CCA AGM Power Battery. Ideal battery for a lightweight yet streetable car. It weights 29lbs for a total of 21lbs weight savings compared to the stock battery. The width and height are identical to the OEM battery, only the length is smaller, but the e90 battery compartment has perfect adjustment holes. The downside is that it is not available in the US

Below are some pictures from my install. The fitment is 100% OEM, including all the connectors and plates from above the battery.

[Rotorocious]

Very cool

[scottp999]

Good write up. The Braille 21lb was ok for me but started to fade after only a year of use. I would constantly get low battery warnings, even if I charged it fully, the second time i started it, the low battery warning would be back again. Not sure if I got a dud, or that it would need to be replaced on a regular interval.

I currently put the original battery back in.

[tscdennab]

Originally Posted by scottp999

Good write up. The Braille 21lb was ok for me but started to fade after only a year of use. I would constantly get low battery warnings, even if I charged it fully, the second time i started it, the low battery warning would be back again. Not sure if I got a dud, or that it would need to be replaced on a regular interval.

I currently put the original battery back in.

If originally you had an older, non-AGM battery in the car, your alternator would probably not provide the correct charging voltage to the Braille AGM battery. The Braille battery should have also been "registered" with the BT tool (or at the dealer). However, I suppose that 2-3 years it's about the normal life period for such a small battery in such a big car

[vasillalov]

Nice find! While I do generally agree that weight reduction is a good thing, it has to be done carefully. We are adding heavier intercoolers in the front, installing lighter batteries and mufflers in the rear. Some even remove the rear seats as well.

All this upsets the 50/50 weight distribution and makes the car nose heavy. A nose heavy car is more prone to understeer.

Just food for thought...

[tscdennab]

Originally Posted by vasillalov

Nice find! While I do generally agree that weight reduction is a good thing, it has to be done carefully. We are adding heavier intercoolers in the front, installing lighter batteries and mufflers in the rear. Some even remove the rear seats as well.

All this upsets the 50/50 weight distribution and makes the car nose heavy. A nose heavy car is more prone to understeer.

Just food for thought...

I knew this would come

Just think about the difference in weight distribution between a full tank of gas and a 10% tank...it's really a non-issue at these weight reduction levels.

[Q4P]

Originally Posted by vasillalov

Nice find! While I do generally agree that weight reduction is a good thing, it has to be done carefully. We are adding heavier intercoolers in the front, installing lighter batteries and mufflers in the rear. Some even remove the rear seats as well.

All this upsets the 50/50 weight distribution and makes the car nose heavy. A nose heavy car is more prone to understeer.

Just food for thought...

Yes! This may be an appropriate way of weight reduction for drag racing but not for handling or track driving. It would be best to remove the weight from the front to make the car a little rear heavy but it is impossible to remove almost any weight from the front albeit a crash bar.

[vasillalov]

Originally Posted by tscdennab

I knew this would come

Just think about the difference in weight distribution between a full tank of gas and a 10% tank...it's really a non-issue at these weight reduction levels.

True, and at the same time, the 50/50 weight distribution is quote with half of tank of fuel.

[tscdennab]

Originally Posted by vasillalov

True, and at the same time, the 50/50 weight distribution is quote with half of tank of fuel.

So do you always drive with half a tank of fuel, or are you almost always "inbalanced" ?

[dzenno]

Great find man, good stuff...where did you get it from?

[tscdennab]

Originally Posted by dzenno

Great find man, good stuff...where did you get it from?

I have imported it from Germany to my country. I got it specifically from www.basba.de, but many battery shops in Germany, including eBay stores, carry it.

[Q4P]

I think the point being made is thats it's a nice project and all but in the end you saved yourself 9 kgs. What difference will that make (pure logic speaking). lol Put a few books in the car or someone slightly heavier in the car as driver and the advantages are offset. I see very few things that can be done to this car to make it lightweight and keep it luxurious / streetable. But hey, in the end its your project.

[tscdennab]

Originally Posted by Questforpower

I think the point being made is thats it's a nice project and all but in the end you saved yourself 9 kgs. What difference will that make (pure logic speaking). lol Put a few books in the car or someone slightly heavier in the car as driver and the advantages are offset. I see very few things that can be done to this car to make it lightweight and keep it luxurious / streetable. But hey, in the end its your project.

Just participate at some competitions and you will quickly realize what it's all about.

You can keep the car streetable and still shave like 150lbs:

- Replace front seats with Recaro Pole Position (60lbs savings)
- Get a lightweight hood (20lbs savings)
- Get a lightweight battery (21lbs savings)
- Get lightweight 17-18" rims (20lbs of ROTATIONAL weight saved)
- Get a lightweight carbon fiber trunk (10lbs savings)

Below is an example of streetable, luxurious but 60lbs less weight in the center of the car.

[Q4P]

Originally Posted by tscdennab

Just participate at some competitions and you will quickly realize what it's all about.

You can keep the car streetable and still shave like 150lbs:

- Replace front seats with Recaro Pole Position (60lbs savings)

Questionable due to comfort, I have sat in those seats... many would disagree with this.

- Get a lightweight hood (20lbs savings)
Agreed but most of the time they are carbon fiber and don't look stock and/or are not in the color of the vehicle.

- Get a lightweight battery (21lbs savings)
Sure but that's only 20 pounds and BMWs dont seem to like Batteries other than stock, see guy that had his explode.

- Get lightweight 17-18" rims (20lbs of ROTATIONAL weight saved)
By far biggest one and the only one that I would recommend.

- Get a lightweight carbon fiber trunk (10lbs savings)
See hood comment above.

Below is an example of streetable, luxurious but 60lbs less weight in the center of the car.

So sure, you save 150 lbs but that is like driving with an average sized passenger, wouldn't adding more power (via tune or meth) and stiffer springs do about the same for someone who daily drives their car? Now if you only track the car - then it is a very heavy car to begin with.

[Syndicategt]

Don't forget about:

Exhaust - 20 lbs
Rear seat delete - 80 lbs
Upgraded Rotors - 5 lbs each

And you could always do a supermodel diet of cigs, diet coke, and cocain to lose some weight

[tscdennab]

Originally Posted by Questforpower

So sure, you save 150 lbs but that is like driving with an average sized passenger, wouldn't adding more power (via tune or meth) and stiffer springs do about the same for someone who daily drives their car? Now if you only track the car - then it is a very heavy car to begin with.

Adding power and saving weight are not mutually exclusive, but in fact, complementary. It would be a pity to leave performance on the table by only adding power. You could always increase performance by going lightweight, regardless of how much power you have.

The e90/e92 is not a heavy car at all. Look at the M3, it weights alot and still performs. Or even better, look at the M3 CSL and M3 GTS or the M3 CRT sedan.
They increased power, but they also reduced weight.

[Q4P]

Originally Posted by tscdennab

Adding power and saving weight are not mutually exclusive, but in fact, complementary. It would be a pity to leave performance on the table by only adding power. You could always increase performance by going lightweight, regardless of how much power you have.

The e90/e92 is not a heavy car at all. Look at the M3, it weights alot and still performs. Or even better, look at the M3 CSL and M3 GTS or the M3 CRT sedan.
They increased power, but they also reduced weight.

Agreed 100%, but wouldn't it be wiser to leave your car a daily driving beast and buy as light as possible (and cheap) of a car for track duty? You're essentially cheapening your car out with all of these lightweight parts (and making it feel less solid) in a car that is already perfectly balanced and as a luxurious as possible for a car of that class. In addition, I question tracking a BMW due to maintenance costs and the possibility of a very expensive repair in case if anything goes wrong after extended amounts of hard driving. Remember, it's tough to have a combo of lightweight / luxurious and streetable, BMW tries that will all of their cars and reaches a great medium but none of them excel at this. see M5, M6, X6 and X5M, e90 does this best but in the end the M3 is a very heavy track car and gets trumped by lighter alternatives.

[vasillalov]

Originally Posted by Questforpower

Agreed 100%, but wouldn't it be wiser to leave your car a daily driving beast and buy as light as possible (and cheap) of a car for track duty? You're essentially cheapening your car out with all of these lightweight parts (and making it feel less solid) in a car that is already perfectly balanced and as a luxurious as possible for a car of that class. In addition, I question tracking a BMW due to maintenance costs and the possibility of a very expensive repair in case if anything goes wrong after extended amounts of hard driving. Remember, it's tough to have a combo of lightweight / luxurious and streetable, BMW tries that will all of their cars and reaches a great medium but none of them excel at this. see M5, M6, X6 and X5M, e90 does this best but in the end the M3 is a very heavy track car and gets trumped by lighter alternatives.

...and this is why the E36 M3 still remains one of the best dedicated track cars on budget. The interior is nothing special so stripping it down makes sense. It destroys the E46 M3 on the track too. The maintenance on these is much, much lower than the E46 and E90 M3s....

[Q4P]

Originally Posted by vasillalov

...and this is why the E36 M3 still remains one of the best dedicated track cars on budget. The interior is nothing special so stripping it down makes sense. It destroys the E46 M3 on the track too. The maintenance on these is much, much lower than the E46 and E90 M3s....

Bada bing bada boom... and add the E46 CSL as the king of all, although it only weighed 3,050 lbs from the get go and was in no way meant as a daily driver (no ac, radio or real trunk floorboard). Albeit, it would be considerably more to maintain than the older models but certainly cheaper and more reliable than the newer turbod (335i type cars when it comes to tracking).

[tscdennab]

Originally Posted by Questforpower

Agreed 100%, but wouldn't it be wiser to leave your car a daily driving beast and buy as light as possible (and cheap) of a car for track duty? You're essentially cheapening your car out with all of these lightweight parts (and making it feel less solid) in a car that is already perfectly balanced and as a luxurious as possible for a car of that class.

Are you really considering the 335i a "luxurious" car ? Besides the BMW brand and the build quality I can't see any luxury in it. I happen to consider it a technologically advanced chassis which is a perfect basis for car that can perform very well on the street as well as on the track. The costs and marketing reasons prevented BMW to make this a better car, and this leaves us the opportunity to add what is missing. This is the real challenge and fun: to improve this car while keeping it's street character. This is one of the reasons why this forum exists, otherwise people would be all over the e36 M3 forums

PS: is Porsche "cheapening" their Boxter S car (which is not a track car) by offering a supplemental Li-Ion lightweight battery option for $2000, which doesn't even work in the winter and the owner must switch it by himself between seasons ?

[MDORPHN]

FWIW, I've run an Odyssey PC680 in my M Coupe for many years.

Very reliable and robust, and a tremendous value.

Neil

[Q4P]

Originally Posted by tscdennab

Are you really considering the 335i a "luxurious" car ? Besides the BMW brand and the build quality I can't see any luxury in it. I happen to consider it a technologically advanced chassis which is a perfect basis for car that can perform very well on the street as well as on the track. The costs and marketing reasons prevented BMW to make this a better car, and this leaves us the opportunity to add what is missing. This is the real challenge and fun: to improve this car while keeping it's street character. This is one of the reasons why this forum exists, otherwise people would be all over the e36 M3 forums

PS: is Porsche "cheapening" their Boxter S car (which is not a track car) by offering a supplemental Li-Ion lightweight battery option for $2000, which doesn't even work in the winter and the owner must switch it by himself between seasons ?

Yes, for the price it better be a luxury / very solid and heavy feeling car or I'd buy an evo as a track car and an accord as a dd.

Challenge and fun - yes, but there is a point where logic (saving 20 lbs on a battery) and expense of doing so limit themselves.

PS - Any Porsche is essentially a track car from the factory (this is Porsche's pedigree) minus the stupid SUV's and so called Panameras...

Is porsche cheapening themselves out? - Some would argue yes, others no.

Is it stupid to put navigation in a car with a great bose stereo and then use seat belt cloth for a door handle ala Gt3 Rs to save weigh and charge people more - Yes it is. (although it's great marketing)