t-von

iTrader: (8)

I think this a missed and very important modification especially for heavily modified Fds. Here's why!!

When Mazda designed the Fd Rx7, they had the Mitsubishi Alternator Co. build the alternator based on the Fds max load capabilities. This is basically everything turned on MAX. Engine WOT, blower motor at max, cooling fans on MAX, all lights on w/ brake lights, and Bose sound system with all it's little amplifiers. What they came up with was 100amps max electrical load. For a mid 90's car that's plenty of power however, is it adequate with all the additional electrical loads we are adding while modifying our cars?

Now just because the alternator is capable of producing 100amps doesn't mean it's designed to do so for lengthy periods of time. It's just like injector duty. There's a reason we strive not to go past 80% duty on injectors. The internal regulators are designed to only allow the alternator to supply the needed current based on the loads it receives. The regulators secondary function if to keep the alternator from over heating. But what happens when those loads are exceeded? Short answer is voltage drop.

Lets take a look at the additional electrical loads we are adding to our 7's while in quest for more power.

1.Bigger fuel pump!

A lot you know this but I'm gonna go over it anyways. We all know that average base fuel pressure is around 38psi. Under normal cruising or engine vacuum conditions, the fuel pressure actually drops because the vacuum/boost line is pulling a vacuum on the internal spring or diagram of the fuel pressure regulator (FPR) which cause it to relieve more pressure. So while we are cruising around under vacuum, fuel pressure is lower (lets say 33-34psi). At this level the electrical loads are minimal. As we accelerate the opposite happens. The vacuum becomes less as we reach atmospheric pressure so the spring or diaphragm start to return to the original set pressure (again were at 38psi). Now since were talking stock Fd Rx7, were talking something that's boosted. As we get into boost, the vacuum/boost line to the FPR becomes more of a boost line. Under boost conditions, the pressure added to the spring or diaphragm causes the relief passes to close. This of course allows the FPR to relieve less fuel so the fuel pressure increases. In most cases FPR increase on a 1 to 1 ratio with boost. So a stock Fd is now running 48psi at 10psi boost pressure. Now what about a modified Fd? Not only are we running a BIGGER fuel pump, but we are also running more boost. Lets say we are now running 20psi with base fuel pressure set at 38psi. At 20 psi we are now at 58psi. The electrical demands on a BIGGER fuel pump at that PSI level are much higher than stock. Soooo do you think your stock alternator is gonna keep up? Maybe?

Ignition amplifier.

So now that we have more fuel potential to the engine, we need a way to combust all that extra fuel to make us more power. That's were that ignition amplifier comes in. With more power comes more responsibility on that stock alternator. The stock alternator be like "what the hell enough already!!!!" But wait were still not done yet!! I need to control my boost so I don't creep.


Electronic boost controllers

Here we have something else for the poor stock alternator to handle. This thing is duty cycle based and is putting even more electrical load stress on that alternator. Your alternator is really starting to get pissed. But we still aren't done yet!

Water injection.

Now I want to make sure I don't detonate and blow my engine we add yet another electrical motor in the form of a water pump and solenoids so we can spray a cooling mist down our engines throats. The engine may love you but your alternator is now saying F*CK YOU. Oh we still aren't done yet!

Stereo system.

Yep gotta have the ice to go with at that vroom vroom. Lets see big amplifier and 7" display. Your alternator has just thrown in the towel as it running constantly near it's peak output. Can you say blown engine from voltage drop to the fuel pump?

This is something you guys may want to think about next time you start having voltage drop problems due WOT on the dyno. Ask yourself " do I really have enough load producing capability out of my charging system to handle all this stuff"? If your still running the stock alternator, I seriously doubted it!

I see 20b guys doing the exact same thing. We add a bigger engines with 6 ignition coils to fire and all the above mods yet, some still run the stock alternator. Not me I recently upgraded to a 150amp once I started doing research. Jump in guys and lets upgrade those alternators.

capt. bill1

And remember just upping the size of the alternator my not solve the issue. If you have bigger current draws you need to up the size of the wires handling them as well.

Mazda seemed to have used smaller diameter wires in their harnesses to help keep the overall weight of the car down.

Howard Coleman

iTrader: (6)

an excellent post and the foundation for a valuable thread. lets hear more on the subject.

i have an upgraded alternator from Rich and don't remember the specific output.

i can also attest to the need for lots more alternator output.

for instance, as we find we can make 500+ hp with increased reliability, we find we are using larger fuel pumps.

the newer higher output pumps from Walbro:

9000262 gasoline
9000267 E85

should be fused for 30 amps.

fuel pump output is VERY dependent on elec input.

if your input to the pump does decrease in boost due to overload you could have a fatal engine problem. that's why i believe almost all modded FDs should have a digital fuel pressure sensor and LOG FUEL PRESSURE.

the cute little analog gauge will tell you nothing at 7000 RPM when it counts.

if you are currently logging, the additional expense should be under $100 and you will then KNOW fuel pressure where it counts... at high power levels.

lets hear from others as to what you run and what it draws current-wise..

i run both a Kenne Bell Boost A Pump (16 V to the pump in boost) and a Kenne Bell Boost A Spark (15 V to plugs in boost).

all our additional modules add up, especially in boost when it counts.

what do you have that sucks amps and what are the alternator options?

howard

Howard Coleman

iTrader: (6)

"Mazda seemed to have used smaller diameter wires in their harnesses to help keep the overall weight of the car down."

weight, or lack thereof, is one of the many beauties of the FD. i wouldn't have been surprised to find they drilled holes in the wires to lighten them... the FD was aggressively designed and it delivers.

ReddRex7

iTrader: (4)

What vehicle is this 150 amp alternator found on, it would help to locate one.

$lacker

iTrader: (9)

I'm also interested - when my car idles, the amp doesn't appear to be producing enough
My gauges dim with the same frequency as my blinkers lol

misterstyx69

iTrader: (142)

With a little modification,a Ford Taurus alt fits on an FC,so I can't see why it wouldn't fit on an FD..it is 130 amps.
The pulley shaft is the same size too.(for FD)

ReddRex7

iTrader: (4)

Thanks for adding that info, let the hunt begin. What needs to be modified to make this fit?

djseven

iTrader: (56)

Most FD owners would be well served to remove their shiny aftermarket underdrive pulleys from the alternator and install a factory one. This alone will make a noticeable difference at idle and low rpm cruising.

0110-M-P

iTrader: (10)

This is a very good point...get a proper idler pulley kit when you remove your airpump instead of a pulley kit that underdrives the alternator.

capt. bill1

True. But small wires won't deliver big amps. ( As I'm sure you know Howard.) At least not for long without the need for you to break out your shinny chrome fire extinguisher that is. :-)

Here's a link to a DC wire size chart at the Engineers Tool Box site. (Which has a lot of other great info as well.)

Amps and Wire Gauge - 12V Circuit

And remember folks, when calculating DC wire runs you have to account for the return to ground leg as well. So if the run from the power source is say 10 feet, you have to double that to get the correct gauge wire to use. And it never hurts to go up one size if your calculations put you at the higher limit of a wires amp carrying capacity.

Slow2k

iTrader: (9)

I know IRP sells an alternator upgrade for the FD. I think it's 120 amps.

RENESISFD

iTrader: (13)

Another important factor to consider is idle amperage. Peak amperage that is usually quoted does not tell the whole story. The alternator I will run on my car puts out over 100 amps at idle and 180 at full output. This is with the alternator at operating temp.

People with crazy fuel systems like 2 id1000 and 4 id2000 injectors should also consider the alternator amperage and voltage output because injectors are sensitive to operating voltage.

Slow2k

iTrader: (9)

Good point John. Is your alternator going to be something completely custom or are you going to tell us where you're getting it?

angel824

iTrader: (8)

Love this subject and where this thread is going. A quick search found this:

http://www.maniacelectricmotors.com/19rx7140amph.html

Any one have experience with or input in general on it?

RENESISFD

iTrader: (13)

It is a custom alternator however fitment is for a 2006 subaru sti. It mounts simmilar to the fd alternator.

Manufacturer is dc power engineering.

t-von

iTrader: (8)

You are 100% right as I forgot to bring that up. I also upgraded to 2 gauge wiring through out. Also don't forget to add a secondary fuse to carry the total output load of the alternator. That long slender fuse box in the engine bay has a 100amp fuse. Well there's an empty spot right next to it to add another. The factory wiring is such that any current the alternator creates has to go through that fuse. Well since I added 50 more amps of current capability to the electrical, I also added another 50amp fuse so the alternator isn't being restricted and can pass it's max potential. If you don't match the fuse and wiring to the total output, you will never get the full benefits of the upgrade as the internal regulator will always reduce the output when it hits that resistance.

t-von

iTrader: (8)

I bought the 150amp mazda from unit off ebay. It's a direct fit no mods. Do an eBay search for" rx7 amp alternator" and you will find upgrades for all generation rx7s.

t-von

iTrader: (8)

+1. Some alternators, if you underdrive they turn off at idle.

SA3R

This is why I do not run shiny under drive pulleys on any of my vehicles. Ever. Nothing wrong with the stock pulleys.

capt. bill1

I may not be reading this correctly. But adding a 50a fuse inline with the 100a fuse isn't the same as replacing the 100a fuse with a 150a one.

Nor is adding a fuse inline with another fuse going to alleviate any restriction. Only increasing the wire size can do that. And I'm not just talking about the main battery cables and cable feeding the fuse block. In fact the whole fuse block may need to be replaced if it isn't rated to handle over 100a total current to it. Then there is the issue of the wires going from the fuse box to all those systems/loads that now may have a new higher current demand devices attached to them.

But like I said, perhaps I'm misreading you. :-)

IRPerformance

iTrader: (41)

This is why I have been offering our 140 amp upgrade for some time. The stock 90 amp unit does not cut it once you start adding gauges, larger/additional fuel pumps, stereo, etc. I use the stock case but install a larger stator with more windings and a corresponding voltage regulator. I also prefer NOT to underdrive the alternator. I run the stock pulley with an aux idler like the Pineapple or Tweakit. I know there are some alternators out there claiming higher output. The issue is most of these have to be spun faster to make that output, and as a result can suffer from charging issues at idle/low rpm. Its kind of like running a big turbo. You have to rev the car higher before boost comes on and you start making power. I found that 140 amps is the best compromise between low speed charging ability and maximum output. Otherwise you have to get into a custom bracket and do something like a side mount alternator.

Monkman33

iTrader: (28)

Capt. Bill is right. Adding a fuse inline only reduces the capabilities to the maximum of the weakest link. Whether it be fuse or wire.

Most don't realize that a fuse is there to keep the wire from melting down and catching fire.

Individual components are protected at the components themselves.

t-von

iTrader: (8)

Actually in this case it does as it's a parallel setup and not series like your thinking. It's just like doubling up on the wiring will increase the current capability because now you have two paths of travel to the same location. Go take a look at that long fuse holder in the engine bay and you will see the double plate that's attached to the main fuse. That empty section has the metal tab so you can screw another 10mm bolt into it. Adding a secondary fuse here gives another path of travel to the other side of that block where all your electricals are connected.


Edit: Now that I think about it, I'm going to need to upgrade the main wire on the other side of my fuse block if I want to carry the additional load to the interior panel. Otherwise my added fuse is doing nothing right now.

t-von

iTrader: (8)

The added fuse is not inline, it's parallel.