E46 Track Car Weight Loss

[MrMuddle]

Hi All, just looking for some advice on what else I could possibly remove or even cut out to remove some more weight from my E46 Compact 325ti?

I'm making it into a track car but it still needs to be road legal(mostly!) here in the UK.

So far I've removed the following and been weighing it all as I go...

Carpet - 16.5kg
Front Floor Mats - 2.3kg
Centre Console lower section - 0.9kg
Centre Console Armrest - 1.7kg
Front Door Sill Plastics - 0.5kg
Front Seats - 25.6kg each
Front Sun Visors - 0.35kg each
Rear Seat Backs - 20.8kg
Rear Seat Bench - 5.3kg
Rear Seat Carpet 1.6kg
Rear Door Cards and Corner Trim - 5.5kg
Spare Wheel - 11.8kg
Boot Interior - 12.2kg
Boot Soundproofing - 6.3kg
Boot Tools incl Jack - 2.7kg
Rear Washer Bottle - 0.2kg
Rear Seatbelt Tensioners - 2kg
Rear Speakers - 2.3kg
Bolts and Clips - 1.2kg
Roof Lining - 1.9kg
Roof Insulation - 1kg
Oh Shit Handles - 0.1kg for all 3
Front Seat Belt Panels - 0.4kg x2
Roof Screw/Fittings - 0.1kg
Rear Wiper & Motor - 1.5kg

Total so far 151.1kg removed. I'll be fitting two bucket seats on rails so that'll probably be about 20kg back in at some point!

Here's what it looks like so far inside(taken before roof lining removed)...





I'd like retain a few things like heaters, AC if possible, maybe the stereo and some of the dash for switches etc. Long term I'm thinking about running FRP front and rear overfenders to be able to run wider tyres, as a 235/40/17 currently scrubs on a rear E39 9J et20 wheel. So hoping I can replace front wings with wider FRP ones and cut a section out of the rear wings for FRP overfenders, also possibly an FRP bonnet.

I guess what I'm wondering is what else can be removed or could be safely cut out, like inner boot skin etc to save more weight. I'll also look into battery options but not sure I'll be able to go for a fully lightweight battery if I'm still running most electrical stuff.

Thanks in advance
Rob

[Matt330LS]

You can swap out the factory battery for an Optima, if available in the UK, and it'll still run your electrics and be roughly half the weight. Also, immediately aft of your seatbelts you can take out the sheetmetal pieces that are sort of bowl-shaped. Those should just be attached by screws. They don't weigh much, but every little bit helps.

EDIT: If you're intent on keeping the stereo you could ditch all the BMW gear in the rear and put in a smaller, lighter aftermarket amp to run your speakers. Should free up some space and, in theory, should be a bit lighter, although I don't know what the exact weight savings would be.

[MrMuddle]

Thanks very much, I'll take a look into the battery. I weighed the stock one and it was 17.7kg!
Ok great, I'll take a look at those sheetmetal pieces as well.

For the stereo I was thinking about removing the CD changer and just fitting a single din stereo with CD player. Tbh I'll have to see what it's like when I actually drive it, as if I can't hear anything with all the road noise etc, I'll just remove all of the stereo stuff.
I'm not sure if the compact has anything else in the rear other than the CD changer and two rear speakers. I'd seen people comment before on amps behind the seats but none of that is there in the compact!

What about the front and rear bumper supports/braces(whatever they're called). Would it be safe to remove some material from them with a hole saw. I'm guessing they're thick and heavy. Or maybe replace them with a bash bar like you see on drift cars, if that would be lighter!

[Matt330LS]

Can't speak knowledgeably about lightening the bumper supports. I left mine as-is. However, if you're trying to keep your car road legal you might want to make sure what your laws will allow before you go with a bash bar or modified crash impact structures.

[AvusMPower]

It's not cheap, but I recently put an antigravity ATX-30 in my daily driver and it's been working great. Weighs 2.6 kg.

You could probably get away with a cheaper/lighter model too.

[MrMuddle]

Thanks very much both. On the lightweight batteries, have you had any issues with them powering all the usual components like lights, heaters, fans etc? Also are you having to charge them regularly out of the car or do they cope with just the usual in-car charging?
I was looking at some yesterday and even a 7kg battery would save me 10kg over what I have now!

[AvusMPower]

I've only had the battery installed for a few weeks, but my car is full dd and I haven't had any issues. Sitting for a few days, leaving it on battery for half an hour to run codes, short trips with restarts, etc. The batteries that came in the e46 were enough to crank it repeatedly in near arctic conditions. We can get by with a lot less.

[MrMuddle]

That sounds positive, thanks very much.

[jakermac]

I've run my 93 325is on a self assembled 1.4kg LiFePo battery pack for 8 years. It copes just fine with running the electric things in the car. It has a reserve capacity of 9.2ah, but is fast charging and works very well with the alternator in the car. Mine has no charge/discharge protection, so I have to be careful with leaving lights on, doors not closed tight, etc... And since the battery is so small, I mounted it in the engine bay and eliminated the 2.5 meter run of cable from the trunk area to the engine bay. So my net savings was near 20kg.

[MrMuddle]

Thanks very much, think I definitely need a lightweight battery then, even if I just use it for track days, as the car sits unused quite often. That's a crazy weight saving over the current battery!

One other question, are they safe to jump start as well, so if it does run flat, it wouldn't cause any issues jumping it off a normal battery?

[Def]

You've got to be careful slamming a small LiFePO4 battery with tons of charging current when it's completely dead, but if it's just done a few times in its life it should be fine if it's not super cold.

I killed a LiFePO4 batt that was around 8.4 Ahr when I drained it down cranking my engine when it was about -3 to -5 C. The battery was super cold soaked, and it got hit with full alternator amps for a long period of time and it swelled up a bit and I think killed a cell or two in the pack. It wouldn't start the engine up at all after that. This is why EVs have thermal management systems and clever programming to make sure they don't slam a battery with tons of charging current when cold/hot etc.

But in general, they're pretty robust, and will last longer than a lead acid battery if you don't abuse them.

[AvusMPower]

^ that's good info there thanks for sharing

I had read that in cold conditions, you actually want to turn the ignition to on and burn the headlights or something for a bit to warm up the lifepo4 battery before you try to start

[Def]

^ that's good info there thanks for sharing

I had read that in cold conditions, you actually want to turn the ignition to on and burn the headlights or something for a bit to warm up the lifepo4 battery before you try to start

It does help the battery provide more current, and does keep it from that failure mode to some degree. But there's just not going to be that much heat being generated pulling starting current for a brief bit from the batt or running the head lights for a while.

In my case, I think trying to start the really cold car a few times on an already weak battery drained it down. Then when it finally did catch it get slammed with amps and was still fairly cold.

The next iteration I used an even smaller LiFePO4 battery protected by a resistor (0.5-1 ohm or something like that?) with an ultracapacitor bank to do most the starting. It worked well on a warm engine, but still struggled on a cold engine and was kinda slow to recharge the cap bank (~10 seconds or so to get to ~12.5 V). Deleting the charging resistor would make it work much better, but would expose the battery to more charging amps when low.

If I were redoing it, I'd get some big capacity LiFePO4 cells and use no charging resistor. Something like 20 Ahr is fine to let it see full alternator charging at idle IMO on occasion.

[aeronaut]

I'm using an AntiGravity AT12BSHD, and the car starts fine when temps are in the upper 20's. (Track car only, so I don't see starting it when below that.)