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Subwoofer/car audio influence on tuning

Understanding AFR

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Knowing that injector response, ignition strength and sensors in general are relying on voltage. How would I go about tuning, having about a 6000watts RMS worth of car audio loading the alternator and electrical system?

There is a noticeable loss of throttle response or even power loss when my system is at full tilt on the highway for example.

I have done the big 3 upgrade which makes it more stable and I isolated the system as much as possible using separate 0 gauge runs to lithium banks. The voltage does not drop below 12.4 volts. I assumed it would have been sufficient enough, but it isn't.

The car will be running a megasquirt standalone next week, so hopefully I can correct the injectors using the voltage compensation table. But how about the ignition? Any further input is sincerely appreciated ;)

Very Kind Regards,

Cedric from belgium

Well, the actual draw on the electrical system won't be as great as the total draw, but variable, which doesn't help.

If I were you, I would run a dual battery setup with one dedicated to the engine and one to the ICE - there will still be some voltage fluctuations, but it should be reduced. The greater the alternator current rating, the lower the fluctuations should be. I assume you are already running substantial smoothing capacitors for the transitional loads?

There are other folks battling a similar problem, and this is definitely a good read on it - make particular note of the need for high amperage power AND ground/earth cabling! -

European folks could check out Demontweeks,, and the like, listings for alternators and follow up with the makes/brands mentioned there.

To do it properly, I would recommend two independent systems, with two alternators*, so there should be negligible interaction.

*as packaging can be a problem, I seem to remember some - rather expensive - specialist dual output alternators which are basically two independant alternators in a single housing and I'll have a look to see if my aging mind is playing tricks or if they are actually available and in 12V.

[edit] Only info' seems to lead to dead end links, might have been a solution looking for a problem others solved with splitters or dual alt'rs. If anyone has updates or sources, please post them here.

Thank you for your reply!

I do have 2 separated electrical circuits. Using 2 lithium banks in the back with separate runs of 0 guage power and groundm and an uprated carbattery in the front for engine management. It purely is the alternator load I'm worried about which has an effect on power like all belt driven accessories from the crank have. Ofcourse when 'racing' / pulling the ICE would be turned of. It is the cruising area I am worried about.

Going with 2 alts is quite impossible in my engine bay as the engine lays transverse. This is however the first time I've heard about 2 alts in one. Might need to take a look into that.

Thanks again!

Kind Regards,


Part of the problem is the way the alternator works with the batteries - the electrical system basically runs off the alternator when the voltage is above the batteries charged level and if there is too much load for the alt'r to meet, it will drop to battery voltage that meets the current demand.

So, even with isolators a heavy auxiliary demand will pull the voltage down.

Thinking on this, it might only be solved by incorporating a high current ZENER based voltage feed to the ECU and it's components. been rather a long time but might be able to figure something out, but there may be 12V voltage stabilised options out there.

Alternatively, you may be able to get a friend who is into electronics to make something up. What I have in mind is using a regulator to maintain a, for example, fixed 12V to the vehicle electronics that holds it there regardless of whether the regulator is getting a higher voltage. That way fluctuations in the alternator/battery supply 'shouldn't' affect the ECU voltage as long as it is still getting a minimum of 12V (plus whatever drop there is across the device).

Oh, the only references I found to a "2 in 1" alternator referred to a company that seems to have folded - if you do find one, please bring it up here, I expect there are others in a similar position as you.

I think I may have found exactly what you need, a converter series that takes noisy "12V" and converts to regulated 13.2V - - it would seem it would be the ideal device for the ECU, etc?

It may also be of benefit to others chasing similar regulation issues.