JoeNova

Has anyone here had issues with low power when dynoing without an alternator, or with an alternator that stops charging above a certain RPM?

The problem has came up fairly often recently with turbo cars peaking at 4000 RPM and then power falling off afterwards, to notice in the logs that battery voltage is dropping down to ~11.80. These are 78-80mm turbo 5.3 cars at 20+ PSI with healthy cams. We're talking 600whp at 4000 and then 500whp by 5000 RPM and still falling.

I have an engine going on the engine dyno soon, and I had originally wanted to run with no alternator and an electric water pump to make things easier, since I can't run my normal belt setup (power steering, etc). I was going to run on the 12v dyno batteries and get it tuned but now there are concerns of spark strength and retuning for 14 volts once its back in the car.

big hammer

Yes, if you want to be running without an alternator you should be switching to a 16v system.

JoeNova

I only want to run without an alternator on the engine dyno but its just a 12v system.
I'll see about upgrading to a 16v system on the dyno but its probably not in the budget right now. This has never really been an issue until we started noticing major power losses on the chassis dyno with failing alternators with turbo LS engines. I'm assuming its a spark issue.

big hammer

Could just use a fully charged 16v battery and no alternator. That way your voltage would be up where it should be

G Atsma

Would keeping the battery(s) on a charger while testing screw things up? That would at least keep the voltage up..

pantera_efi

iTrader: (1)

Hi Joe, Greg has the correct "tech" with my services asked by those who operate a Bench Dyno to provide a Quality DC Power Supply set at 14.37 Volts.

YOUR answer is YES, great problems found when Battery Voltage is LOW.

SURE the PCM has Bat.Comp.

The problem is your Fuel Pump with low voltage WILL heat the fuel when Voltage is LOW.
The SAME with the Coils/Injectors as they TOO will run hotter, NOT a good thing for the Bench Calibration cost.

NEXT, the PCM Voltage read of 11.8 is AT THE Battery.

The wire length of the Coils/Injector harness ADDS a Voltage Drop due to resistance laws.
A scope read of the instant coil voltage is much LOWER than the PCM read.

Lance

tug686spd

iTrader: (11)

Pretty sure this is my alternator crapping the bed on the dyno. After this pull the car was shut down like normal because base tune was done. Unstrapped car and fired it up, turned over slow but figured it was due to being hot. Drove out of building and around it to load on trailer to bring it home. Got home car wouldnt crank to pull off trailer. Was a new build so I went through motor anyways but only problem found was the dead alternator.