Looks like I’m going to be needing a 250A alt. Read somewhere here on the forum that a version of a 250a makes a lot of juice at idle which is an important check for me. I’m going to be doing the Big Three at the same time and I’d like to ask if there’s any addition heavy ga wiring that needs to be done at the time of alt install or before. Any tips or suggestions appreciated.

 

my mechman 170 worked great in my z06... would buy again!

you can drop in a bigger wire but it also creates resistance.... just gotta do the math on the gauge wire....

 

A larger diameter wire would decrease the resistance and lower the voltage drop from point A to point B, Bigger is better just heavier.
Adding additional grounding is part of the whole package.

 

I'm old and maybe memory failing but when I bought my Mechman I thought I was told the larger amperage alternator had lower output at idle.

 

the 240a unit has a lower output at idle but they apparently have a new 250a that makes about 200a at idle. Along with regular C6 draw I have B&M fanned trans cooler 15A , stereo amps( 80 & 50), BAP 40A. The 170 wouldn’t cut it, the 240 wouldn’t give me the juice I need at idle but this new 250 might be the one.

 

You are correct, and back to the op, are you sure that you need a 250amp alternator to begin with? The 170amp Mechman puts out 45+ amps at idle, while the oem unit only put out about 14 amps at idle isntead. The 250 will put out more amps at full tilt, but lower amps at idle instead.

Also, keep in mind that the OEM cable from the alternator to the starter solenoid is smaller gauge wire to begin with, and has a fuse link in it, that is two gauges smaller yet for that inch of section. So stock cable may hold and work for the stock 140 amp alternator somewhat with slightly more load, but will never be enough for the 250amp full load isntead. For that, will need to add in a secondary cable with fuse to handle the demand of the additional accessory load to the battery, without blowing the stock cable fuse link.

 

Supporting vendor here BlownBlueZ06 is selling new 250A that he said makes about 200A at idle. I have a good bit more of amps needed then the 45 at idle from the 170 I believe. I think you posted before you saw my numbers needed to run things. I was hoping you’d chime in with your extensive knowledge.

 

Just because a BAP is rated at 40amps, it does not mean the current draw will be 40. The current draw will be the fuel pump draw the BAP is feeding. Same as your stereo. Unless you have it cranked flat out, the current draw is less. In other words, you cannot go 15+80+50+40 will be my current draw. The best thing is to buy a cheap DC tong and turn all your accessories on that you would normally use and measure the current draw at idle. Things like headlights, AC and make sure the radiator fan is running. A tong is a meter that clamps around a cable or cables and measures current draw.

 

Just saw this,

https://www.corvetteforum.com/forums...lternator.html

And if such is the case, and the alternator is not going to burn itself out quickly from the amount of heat/less cooling with its internal fan blades moving slower at idle, may just be the ticket.
What I can not seem to find, is the warranty time on the unit.
Mechman gives two year, but unable to see what RTK is giving/covering for warranty since seems like the unit is tweaked from them after the fact instead (not sure if just internals, or changing pulley size).
https://www.mechman.com/warranty-returns/
https://www.mechman.com/alternators/...-0l/2006-2013/

 

Don't state if you are running a dual radiator fan set up, but it would be pulling around 45 amps, while the oem fan only pulls 18amps isntead.
But yes, bumping hard on the stereo at a stop light at idle, will be taxing the battery hard, since the 170 amp would never keep up with the demand with it only putting out around 45 amps.

Also, de-rate the oem alternator to starter terminal to 50 amps, and this will give you an idea of what you will need for the secondary wire from alternator to battery.
Lets call it 7 feet, so with alternator able to put out 260, that means we need the secondary wire to carry 210 amps, so 1/0 gauge copper or 2/0 CCA AWG wire for the secondary wire, with 250 amp fuse.
https://www.mechman.com/content/inst...structions.pdf

Also, since your path of all the ground current back is through the alternator bracket/motor, would run a secondary ground wire from the alternator to at least the engine ground point, if not to the chassis if you are grounding the amps there. Hence in your set up, it really the stereo amps that are drawing most off the power, and really need to be tapped at the secondary alternator positive wire end location for the positive side, and then reinforce the ground circuit side from the amps ground, back to the alternator body itself to carry the load as well.
Note, flow of DC current is from the ground to the positive, so you don't want to choke out what the ground side can handle to begin with.

 

I understand what you’re saying, I’m just taking the advice from others here and elsewhere to add up all the fuses and use that as a guide to how much current can be used at one time and get an alternator which puts out more then that. Worst case scenario type of thing, little headroom as opposed to shorting something out or not providing enough juice, seems to make sense to me. Maybe I’m mistaken, all this electrical stuff is head scratching. Thanks for your help.

 

I will ask about the warranty and possible pulley size difference on the 250 when I talk to them, important tips, thanks.

Don't have a dual fan yet but it seems I’m heading in the direction. Lost an A6 already due to overheating already and temps are ok most of the time but on hot summer days in traffic they creep up higher then I would like. Heavy Traffic is a concern where I am and temps often climb over 90* in the summer and it’s a pain in the *** to constantly be concerned with overheating the engine and also watching the current usage. I’d like to enjoy my car and not have to be worried so much about turning the volume down all the time with slow airflow and creeping engine speeds. When I got all the sound gear I was more or less oblivious to how much of an issue it would become, it is what it is and just trying to find the best way to deal with it.
Thanks for that link and your concise explanation, it’s appreciated and will help me get it done properly.

 

Racetronics heavy fuel pump wiring kit is a nice addition to the big three

 

Got home to a box waiting at my door. Ordered it from BlownBlueZ06 just four days ago and it made it from Cal to NY in that time. Bret had it boxed up and shipped out the next morning he would have shipped the same day but I called him too late to get it out. Alt was nicely packed and it’s a nice looking unit. I got the black painted cast unit and it looks great compared to stock unit. It’s a Mechman and it comes with a little smaller pulley and a two year warranty. Test tag on the unit states at 800rpm it made 198A and at 1800rpm it did 259A. Healthy numbers.
Also have a 1/0 Big 3 kit with a 250A fuse to pair it with and hopefully I’ll bolt it on in the next couple weeks.

Thanks to all who took the time to offer advice, it’s much appreciated, and thanks to you Bret for giving me the time to chew your ear and for getting it out so quick.