Alternator Size - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Pirate83 · 08-25-2022, 10:09 PM

Hey fellas,

I have 90 amp alternator on my SBC 350 with HEI, Vintage Air, FiTech EFI & Pump, 17" Electric Fan, and radio and I am having a lot of issues with the truck just staying running.

I am thinking about going to a bigger alternator. What amp should I go to?

Thanks!

**The Rocknrod** · 08-25-2022, 11:13 PM

Do you know the total amps your pulling at any one time in a normal day? That is, have you added the amps up on the above listed items?

**The Rocknrod** · 08-26-2022, 10:23 AM

If you don't get an answer here I can see about moving this to the Electrical section - http://67-72chevytrucks.com/vboard/f...splay.php?f=64

LVPhotos · 08-26-2022, 12:20 PM

I run a Mechman in Dodge 370 amp. They have a 170 with V belt or rib. Custom ones can be made to order
https://www.mechman.com/alternators/...let/1963-1985/

vin63 · 08-26-2022, 06:19 PM

Like Rocknrod LVPhotos mentioned, add up your amp draw to get a better idea of what you need. I run a 160 amp Hi-Torque alternator that kicks on at a low RPM. I run a lot of accessories that draw significant amps: MSD Digital 6 ignition, 2 HO radiator fans, 1 HO trans cooler fan, Vintage Air AC unit, MagnaFuel EFI pump, air suspension compressor, etc.

franken · 08-27-2022, 07:43 PM

Might want to measure the voltage at several places such as battery, fans and alt.

slorio · 08-27-2022, 10:48 PM

Pirate:
Few of questions:

* What size pulley are you running on crank? Performance (i.e. smaller) crank pulley results in alternator turning slower and water pump running slower. Causes problems for street car with cooling and charging.
* Is cooling fan running continuously or only when engine exceeds temp? Running it all the time needlessly taxes charging system.
* What is battery voltage when engine is running?

Short answer is 90 amp alternator is unlikely to be the source of your problem.

Hope this helps.
Regards
Steve

**Accelo** · 08-28-2022, 01:35 AM

Quote:

Originally Posted by Pirate83

I have 90 amp alternator on my SBC 350 with HEI, Vintage Air, FiTech EFI & Pump, 17" Electric Fan, and radio and I am having a lot of issues with the truck just staying running.
I am thinking about going to a bigger alternator. What amp should I go to?
Thanks!

I agree, I doubt it's your alternator.
Take your belt off and see if it runs any better off the battery.
Motor will not cool, i.e no fans or water pump.
However, running a short time on a fully charged battery should not hurt anything and it may eliminate the alternator as the source of your problem.

**MT65** · 08-28-2022, 10:33 AM

I agree with vn63, you’re running a bit of a load, fuel oump, ac, etc, personally I use minimum off 100 amp with less than that…the difference in cost for a bigger/better alternator is minimal…think of it this way, a 6 cylinder will move your vehicle, and use more fuel because it works harder doing the same thing as a properly tuned v-8….

08-25-2022, 10:09 PM	#1
Pirate83 Registered User Join Date: Sep 2016 Location: Phoenix, AZ Posts: 22	Alternator Size Hey fellas, I have 90 amp alternator on my SBC 350 with HEI, Vintage Air, FiTech EFI & Pump, 17" Electric Fan, and radio and I am having a lot of issues with the truck just staying running. I am thinking about going to a bigger alternator. What amp should I go to? Thanks!

08-25-2022, 11:13 PM	#2
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Alternator Size Do you know the total amps your pulling at any one time in a normal day? That is, have you added the amps up on the above listed items? __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

08-26-2022, 10:23 AM	#3
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Alternator Size If you don't get an answer here I can see about moving this to the Electrical section - http://67-72chevytrucks.com/vboard/f...splay.php?f=64 __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

08-26-2022, 12:20 PM	#4
LVPhotos Registered User Join Date: Jan 2013 Location: Las Vegas, NV Posts: 1,853	Re: Alternator Size I run a Mechman in Dodge 370 amp. They have a 170 with V belt or rib. Custom ones can be made to order https://www.mechman.com/alternators/...let/1963-1985/ __________________ 1962 shortbed 408cui small block, TKO 600 5-speed, bagged Porterbuilt suspension. 18" Salt Flats http://www.cardomain.com/ride/332579...t-c-k-pick-up/ http://67-72chevytrucks.com/vboard/s...d.php?t=560081

08-26-2022, 06:19 PM	#5
vin63 It's Better With Nitro Join Date: Apr 2008 Location: Chino Hills, CA Posts: 2,261	Re: Alternator Size Like Rocknrod LVPhotos mentioned, add up your amp draw to get a better idea of what you need. I run a 160 amp Hi-Torque alternator that kicks on at a low RPM. I run a lot of accessories that draw significant amps: MSD Digital 6 ignition, 2 HO radiator fans, 1 HO trans cooler fan, Vintage Air AC unit, MagnaFuel EFI pump, air suspension compressor, etc. __________________ 1963 C-10: Deluxe-optioned cab, shortbed, fleetside Pontiac 462 ci, Kauffman D-Port alum. heads 4L80E, narrowed sheetmetal Ford 9-inch Tubular front and rear suspension Custom 6-piston front disc and 4-piston rear disc brakes

08-27-2022, 07:43 PM	#6
franken Registered User Join Date: Jun 2013 Location: Somewhere Posts: 3,058	Re: Alternator Size Might want to measure the voltage at several places such as battery, fans and alt.

08-27-2022, 10:48 PM	#7
slorio Registered User Join Date: Sep 2006 Location: Louisiana Posts: 373	Re: Alternator Size Pirate: Few of questions: * What size pulley are you running on crank? Performance (i.e. smaller) crank pulley results in alternator turning slower and water pump running slower. Causes problems for street car with cooling and charging. * Is cooling fan running continuously or only when engine exceeds temp? Running it all the time needlessly taxes charging system. * What is battery voltage when engine is running? Short answer is 90 amp alternator is unlikely to be the source of your problem. Hope this helps. Regards Steve

08-28-2022, 10:33 AM	#9
MT65 Senior Member Join Date: Sep 2020 Location: Kila mt Posts: 437	Re: Alternator Size I agree with vn63, you’re running a bit of a load, fuel oump, ac, etc, personally I use minimum off 100 amp with less than that…the difference in cost for a bigger/better alternator is minimal…think of it this way, a 6 cylinder will move your vehicle, and use more fuel because it works harder doing the same thing as a properly tuned v-8….



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