LeX2K

Soldering with heat shrink is very reliable, even though some say it will fail with "vibration" or something along those lines. No it won't, diodes in an alternator are soldered. Practice makes perfect I have no doubt you're an expert at soldering.
Been burned too many times, for critical stuff I won't use anything but OEM.*
And the wire is actually 100% copper which is becoming harder and harder to find.

*Toyota is now sourcing more and more components from China, sad to see. Nothing against China but in general components make in China are done to a very low price point and the quality follows.

Bimmerbill

Hey Craig,
I need some advice (help). You had mentioned that I should use a slow blow fuse when I install my extra cables (BIG THREE) and this will not be a problem. My question - In the future I do plan to install my battery in the trunk and I have perused every Big Three conversion on You Tube that I could find. None of these had a battery in the trunk, so do I run a cable from the alternator to the positive side of the battery in the trunk or?
Bare in mind I would be the first to admit to you and anyone else that I am not an electrical guru or engineer. But I have been working on cars for a ton of years (and still learning) especially from your notes to other Club Members.
Craig, thank you for your help on this problem.
Bill

KahnBB6

iTrader: (5)

Bill,

I must admit to you just the same that I am also not an electrical guru or engineer despite all the electrical documentation that I've added in this and some other threads. It's not my main field but just like you I have worked on cars for most of my years (in a non-professional capacity) and have learned and continue to learn whenever I need to solve a problem of some kind.

That said, my understanding of the "slow blow" type high capacity fuse in a Big Three setup is to certainly provide the needed circuit protection based on theoretical maximum amperage draw (remember that even if an alternator is, say 130A capacity you won't actually see that on the circuit UNLESS there are enough components in the system drawing that much current) but it is strongly recommended to choose a "slow blow" fuse on that alternator positive cable (close to the battery) because you don't want the whole circuit going out from only a very, very brief spike to the fuse's max load capacity.

In other words from my understanding you want this Big Three slow blow fuse to actually blow when there is a definite *sustained* too-high amperage draw on the circuit.

You'll also note that even Lexus specifies the stock alternator fuse for the SC300 and SC400 respectively at around +20A higher than the stock alternator's max amperage capacity. So this is also why I paired my 130A SC430 alternator's Big Three additional circuit with a 150A "slow-blow" MegaFuse (made by the Littelfuse company I believe).

....

Now, as to a trunk mounted battery there is a bit of added complication over a normal setup with a front engine bay mounted battery. Some highly modified turbo 2JZ SC builds have such a setup. I have seen more Supra MKIV builds with a rear mounted battery (in the rear hatch area for an MKIV Supra.

While there are some weight distribution advantages to doing this for racecars I was advised by Aaron who owns and operates Driftmotion to NOT pursue a trunk mounted battery setup. Not that he said it couldn't be done-- certainly it can be. But he cautioned that due to the extra distance that the electrical current needs to travel from the front of the car to the rear and then back again, if not done exactly right there can be some electrical abnormalities introduced.

Then again I reason that the truth may be somewhere in the middle. For a normally driven street car, even if you're pushing 800whp I don't personally think it makes much sense to do a trunk mounted battery setup. I never wanted to pursue this myself.

However if you wish to, here's what I recommend based on what I have learned so far:

.......

First, go onto SupraForums and look at the trunk/hatch mounted battery setups in their build threads section to get some understanding of how most people do this in the SC/MKIV/Soarer style chassis. Supra MKIV electrical systems from the engine bay backward are a bit simpler than ours and have less overall individual body ECUs doing different things. Which means SC bodies draw a bit more current overall than MKIV bodies do irrespective of which engine is powering either of them.

Next, when you do a Big Three cable upgrade to support an upgraded alternator what you are actually doing is installing large gauge cables, sized according to total length of the circuit paths to the maximum assumed alternator amps output to the assumed standard voltage drop that those lengths will encounter.

The greater the length of the wire(s) for a given amount of maximum amps drawn... the larger/thicker the cable gauge will need to be. This is actually true for ANY electrical circuit and you can observe this throughout the entire stock Toyota/Lexus electrical system if you inspect wires and connectors closely for each of their specific purposes.

...

When it comes to doing a rear mounted battery setup with an upgraded alternator you will not only be doing a Big Three upgrade but you will be installing a VERY, VERY thick gauge set of cables from the engine bay electrical connections all the way back to the trunk. This is necessary because at that distance and with something like 130A up from the standard 100A (SC300 stock alternator) if you undersize those long cables you will run the risk of an electrical fire if the current draw at maximum exceeds the ability of the copper wires to handle that much current at 12V-14V (voltage is basically a measurement of pressure, remember).

I believe this is basically the concern that Aaron @ DM was voicing to me.

Some cars are designed from the factory with a rear mounted battery (the recent GR Yaris for instance) and the same principles apply but in those cases an OEM has millions spent on a ground up design for the entire electrical system to be designed that way reliably from the start.

When people like us do a trunk mounted battery conversion or Big Three additional cable upgrade when uprating the alternator output we're piggybacking on the the standard electrical system design.

....

I don't have all my Big Three cable measurements that I used just offhand but I did start with some very, very large (thick) gauge cables that were hard to work with in the engine bay and eventually recalculated the expected maximum electrical load to cable distance and stepped back a size or two and had a much easier time routing everything.

I used an excellent voltage drop calculator here for pretty much EVERY wiring project I did in my car including my Big Three cable addition: https://www.wirebarn.com/Wire-Calculator-_ep_41.html

.....

Bottom line... personally unless you'll be building an SC up into full track/race spec I don't see any major advantage to doing the rear battery conversion. But you certainly can. Just take some cues from MKIV Supra setups that have also done this since they are the most common to find with rear battery conversions.

If you're thinking of this because you are having trouble finding additional free space for additional circuits that you want to install into our tight engine bays then I can recommend you a few ultra-compact and OEM quality miniature fuse and relay boxes which can fit into far more compact locations in our engine bays than your average aftermarket automotive universal fit electrical boxes can accommodate.

Several of those I already used earlier in this thread.

And I used that same wire calculator website page in order to determine my wire sizes when installing them all.

.....

Once again I find it hard not to make a long post reply for something but I hope this info can help you out, Bill!

Bimmerbill

Craig,
Thank you so much for the wealth of information. I now plan on going ahead with with the Big Three and a 150 watt slow blow fuse. I will go ahead with the 2 gauge wire. The reason I wanted to put the battery in the trunk is for weight reduction from the front end. I have finally accumulated all parts to install LS460 front brakes and Supra Turbo rear. I have not weighted the front rotors and calipers but they are plenty heavy. I may add a couple of other things. I have a BMW with a battery in the factory location in the trunk which I have always liked that idea. I have friends with BMW's that have the battery under the back seat which is the ideal location - polar moment. I will, starting tonight review all the information on the Supra forums re battery in the trunk.
Thank you again, but don't go anywhere I could just pop up anytime.
Bill

CLass of 1

Great stuff, gentlemen.

Bill, I am planning to do the very same for a few reasons:

1) Weight distribution (as you already pointed out), positioning the battery where the stock CD player is now, offsets the weight of a driver. But, of course the affect is amplified by removing weight from the very front of the vehicle, too.

2) Engine bay space. Whether doing a 2JZ build or my eventual V12 aspirations, having that front corner open for intercooler piping or an air box is a huge advantage. Battery’s are also hold heat, and get in the way of accessing the headlights!

3) Moving the battery to the trunk allows the stereo’s amplifiers to be extremely close to the battery, which is a benefit for their performance. This is minimal, but still worth noting.

4) If doing any fuel pump upgrades, the same principal applies. Having the battery right next to the fuel pump with a fuse and relay, will ensure that the fuel pump always sees 14+ volts and will maintain high output and high flow, protecting your engine.

Craig rightly points out that there are a number of complications and potential pitfalls if not done correctly, but in my view, the pros outweigh the cons. So long as the battery is SECURE in the trunk and the wiring has been both chosen correctly, and properly safeguarded, then go for it!!

You may have luck going on top of the transmission tunnel to pass through the cabin, though this may necessitate a new hole in the firewall. That 0 or even 2 gauge wire is usually pretty stiff and hard to work with. There are more flexible options out there but they’re costly.

Also, one other thing to consider, if you’re going through the trouble of relocating the battery, you may want to look into adding an auxiliary fuse panel for any new electronics added to the car. By doing this, you’re reducing the chances of having electrical issues when tapping in to 12v power all over the car. You can have everything, all the way down to a boost gauge, wired into the new fuse panel. No electrical gremlins to worry about and your life becomes easier when troubleshooting failures of these devices.

By the way, Bill, I have the exact same brake setup, but I haven’t installed yet. Very eager to see yours all done!!

Nick

Bimmerbill

Nick,
Thanks for the kind words. My caliper adaptors should be here from Australia this week. I did not want the aluminum ones made here in the States (and more expensive) and elected to go with the steel one from down under. When I have everything , will start painting and a friend with a rack comes in very helpful. So I am shooting for next week and will send you a picture.
Best of luck,
Bill

KahnBB6

iTrader: (5)

Nick and Bill-- I understand where you are both coming from wishing to relocate the battery. Nick, especially in your case whether you move forward with your 1GZ V12 project or a custom built 1UZ twin turbo you will indeed want all the additional space up front that you can get.

Since I chose to keep a very OEM 2JZGTE setup in my engine bay with stock intercooler piping, a stock TT airbox and other OEM hardware the available space was already at a premium when I was looking to add a few additional circuits in a clean way.

This is why I went with a couple of compact custom power distribution boxes made by Littelfuse. I ordered everything part-by-part from Mouser Electronics. I covered my notes for that a few pages back when I was revising my auxiliary electric cooling fan circuit and just chose to revise all my other add-on circuits as well.

The little PDU boxes fit nicely with some custom steel brackets I made right around the brake booster area up near the driver's side shock tower. I then used a dedicated negative wire termination box (intended for installing additional auxiliary circuits into police car electrical systems) that went down to its own single wire going to the battery negative post. This was covered in those same posts a few pages back.

But with the factory battery tray area freed up you can certainly install any number of aftermarket power distribution boxes for additional fuses and relays. Littelfuse makes several great OEM-like examples and there are others out there. Check the Mouser Electronics catalog online-- their inventory of ultra-specific automotive electrical parts is impressive. You just have to order EVERY part you need piecemeal from them.

....

And yes, as you said Nick the main concern with any battery from front to trunk relocation project is the careful selection of wire from the engine bay to the battery. I'd definitely study several *clean* MKIV builds with trunk mounted battery setups to see how people consistently do it the right way. The worst thing you can do is undersize. And yeah, with cables that thick the stock firewall grommet is not going to fit through there.

I easily fit a 10GA wire for my TT Denso OEM fuel pump install but there is no way something like a 2/0 gauge cable is going to clear there... or be easy to work with.

I actually have some leftover and terminated high quality 2/0 cable leftover from my first Big Three installation that I'm going to get rid of soon if either of you may be interested. I have been so busy with house renovations this year I just hadn't gotten around to pulling it out and listing it yet.

I bought it all from Driftmotion as a pre-made kit.

Not enough length to go all the way to the trunk but I have plenty that is long enough to work in the engine bay area.

2/0 cable turned out to be overkill for my setup but it is the ideal gauge to send power to and from a trunk mounted battery in these long vehicles.

....

I am sure those braking kits you both have will be awesome! The slight added weight will be greatly offset by the improvement in stopping power.

Toyota just discontinued the front OEM Supra TT brake pads (but not the OEM rear pads yet) and so it looks like I may go back to my tried and true Hawk HPS pads or perhaps something else.

It's a shame because the Supra TT OEM brake pads, while not good for a track, are excellent all around at resisting fade under most everyday driving situations and have great initial bite that other good quality high performance street pads probably won't quite match. But every unique setup can be adjusted to by the driver.

It'll probably be the Hawk HPS pads for me since I am already familiar with their characteristics. Or maybe Stoptech pads since I haven't tried a set of those yet.

Can you both get a set of matched front and rear aftermarket pads for those braking setups?

CLass of 1

Bill: The brackets I got from XAT are steel. I actually wanted aluminum to keep the weight down and had even considered trying to reengineer these as my uncle in law works at a specialized metal shop with a water jet CNC, I was considering having him make me a copy out of aluminum…

Craig: I think your electrical setup is perfect for your car and ideal for 90+% of anyone wanting to improve their electric system, in particular because you have the 130 amp upgrade.

As for pads, no. I couldn’t find a match with the type of behaviors I was looking for. I wanted pads that were easy to live with, not necessarily for performance. So, I chose Akebono ceramics for the (LS460) front, but could not find a match for the (Supra) rears. I wanted ceramic so the dust would be at an absolute minimum. The reality is, I am not competing or driving the car hard. For the rear pads, I went with OEM Toyota. I would have preferred a ceramic and may still go that route as I think Brembo makes a ceramic pad for the rear.

The stock setup is 2 piston front 11.6” and 1 piston rear 12”. I’ll now have 4 piston front 14” and 2 piston rear 12.7” so even though they’re ceramic, my hope is the stopping power will be stronger than stock.

My only real concern with this setup - and perhaps you felt the same way, Bill - was the front/rear bias. When you look at the stock setup, the fronts are smaller than rears. I was hoping to find some kind of BBK option to use the Supra calipers but a larger rotor, perhaps something in the 13.5” range, but struggled to find anything.

My wheel design doesn’t help either as the bolts and nuts for the 3 piece wheels interfere with other BBK options, such as ISF or RCF calipers.

Nick

Bimmerbill

Hey Craig, I am still reading, eyes just about worn out, maybe new glasses on the horizon.
You mentioned the 2 gauge wire. If Nick has not said anything about it, I will take it just let me know how much for cable and shipping. Send a PM and I will ck back this evening.
Thanks,
Bill

CLass of 1

All yours, Bill!

Nick

KahnBB6

iTrader: (5)

Bill,

Okay, I'll pull them out and get you measurements of all the lengths and pictures and figure out shipping once I find a good shipping box for it all.

And it's not 2-gauge wire. It's 2/0 AWG wire. MUCH thicker. The only 2/0 cable out of the kit that I kept was for my additional engine block to battery negative ground connection... which would be very easy for you to source and match.

http://www.batterycable.co/automotive_cable_gauge.html

You're familiar with the cutting, termination and heat shrink methods for big cables like these, right? I will include some leftover new 3/4" heat shrink tubing (red color) and a 150A in-line fuse with clear plastic holder. Also a couple of special angle cable ends. I used an anvil tool with a small one-handed sledgehammer in order to terminate my cable ends in the right orientation and a heat gun to get the heat shrink tubing on.

When cutting the wires you must use a special set of cutters designed to cut copper wire uniformly in the round. Very common and easy to buy off Amazon.

This cable will work well for all your engine bay Big Three connections. You will need more 2/0 AWG in order to cover the distance from engine bay to the trunk for your battery conversion.

I'll get you figures and pictures later tonight or by midday tomorrow.

KahnBB6

iTrader: (5)

Nick -- I had thought it was only the 1992-1997 SC300's which got the smaller rotors in the front than in the rear. I didn't realize that SC400's also had slightly smaller rotors in the front than in the rear as well. I know the SC400's for all 92-00 model years and 98-00 SC300's have better front to rear sizing.

I think your plan with the pads is good. Your difficulty finding the same set for both different sets of calipers was my concern but you're right... with that level of stopping power and a set of pads front and rear that are known to heat up at around the same rate you should be fine for street use.

I'll note that on the brake bias concern I did notice a more balanced distribution of braking when I switched from my first MKIV TT calipers & rotors in the front and SC300 92-97 sliding calipers and rotors to all front and rear MKIV TT calipers and rotors.

It was somewhat subtle but I definitely noticed it right away.

You should be able to correct this for your own setup with a manual brake bias valve. However I don't know how well those work with ABS. I do think that keeping ABS in these heavy cars is a very good thing.

CLass of 1

Thanks for the feedback on your setup. It makes me a little worried, but I’ll push on and find out I suppose. I was really hoping to find a larger rear setup, but unless I go to an ISF rear, and shave the caliper a bit to clear the wheel, I don’t think I’ll be able to achieve the ideal balance. Even more reason to throw more weight over the rear axle with that battery relocation!! Haha

Nick

KahnBB6

iTrader: (5)

To be clear about it... I wasn't unhappy at all with just the MKIV TT front calipers and rotors and rear 92-97 SC300 sliding calipers and rotors. I used that setup for a few years with no issues at all and I loved the braking improvement! There was no downside in my opinion.

I just meant that once I added the rear TT calipers I did notice a very subtle new fore-to-aft neutral balance in the braking system. Where before just the front brakes had the most power and bite, now both ends seemed to haul down with more overall balance.

Yet you'd have to have sampled both setups back to back with a couple of intentional high speed slowdowns in order to have noticed this difference in normal street driving.

I would not worry about it if you find that you still get some slight front bias with the front LS460 calipers and rear MKIV TT 2-pot calipers. I think it really will be okay once you get it all installed.

...

The more important thing to me is your pad selection. Akebono is a good brand. Are you sure they don't have a set for 1993-2002 Supra MKIV TT rear calipers? Those TT calieprs have so many pad choices available I think you'll have several options for finding a good match front to rear.

The OEM Toyota TT rear pads are very good so use them for as long as they remain available from dealers. I won't be concerned myself once they finally become discontinued. Many good street performance pads are available for the MKIV TT calipers which means many options if you have just the rears in your SC.

CLass of 1

Well, turns out, they do. Problem was, it isn’t carried by Rock Auto for some reason. So, I didn’t see it. But! There is a silver lining! It turns out that, according to Akebono’s site, not only are the original pads ceramic, but, they are the OE manufacturer! So, in a round about way, I actually do have Akebono ceramic pads on the rear!!

You’re a genius, Craig.

Nick