altenator pulley ratio to crank

west coast · 12-31-2010, 11:32 AM

I am in process of buying a new altenator and I am wonder what kind of ratio to use will have to buy a new crank pulley or make one. Only turning the motor 7000 rpm.

Dragsinger · 12-31-2010, 09:47 PM

A general guide line for full alternator output is to overdrive the alternator 30% - 50%

Example; a 5" crank pulley combined with a 3" alternator pulley = 40% overdrive. In this example, 1500 engine RPM will equal about 2100 alternator RPM

If the alternator is of the proper amperage output for your load the above example would have full battery voltage to everything with an engine speed of 1600 - 1800 RPM

This type setup will allow you to race all day without battery charging.

Ed Wright · 12-31-2010, 11:20 PM

I just bought a low-mount alternator mount & pulleys from Jegs, and a pully set, meant for street rods. Has worked very well.

Tom Goldman · 01-01-2011, 11:29 AM

East Coast Auto Electric recomends a 2 to 1 ratio .
Most pulley kits made specificaly for drag racing are around this ratio.
I have run higher ratios in the past with no problems.

Robert Simpson · 01-01-2011, 02:07 PM

Does anyone run a cog belt set up for a low mount sbc 69 camaro? Just curious...Thanks

Tom Goldman · 01-01-2011, 06:52 PM

Quote:

Originally Posted by Robert Simpson

Does anyone run a cog belt set up for a low mount sbc 69 camaro? Just curious...Thanks

I run a low mount cog on my BBC.
Check out Jones Racing Products in Ottsville ,PA.
They have a huge selection of cog drive parts..
Almost every circle track racer runs their stuff.
Tom

Wade_Owens · 01-02-2011, 08:50 PM

Quote:

Originally Posted by Tom Goldman

East Coast Auto Electric recomends a 2 to 1 ratio .
Most pulley kits made specificaly for drag racing are around this ratio.
I have run higher ratios in the past with no problems.

x2, I have an east coast alt. also. 3" crank, 5" alt. no issues at all.

Wade O

west coast · 01-02-2011, 11:04 PM

Wade are your pulley numbers backwards or is it just me. I have found pulleys for my crank with ratio of 2.26 and 2.10 for my altenator pulley size. Thanks guy's for the helpjust need to make brackets now.

Bob Bender · 01-03-2011, 10:33 PM

Quote:

Originally Posted by Wade_Owens

x2, I have an east coast alt. also. 3" crank, 5" alt. no issues at all.

Wade O

Me too.......................

12-31-2010, 11:32 AM	#1
west coast Senior Member Join Date: Dec 2008 Location: Rainy Washington Posts: 609 Likes: 12 Liked 223 Times in 73 Posts	altenator pulley ratio to crank I am in process of buying a new altenator and I am wonder what kind of ratio to use will have to buy a new crank pulley or make one. Only turning the motor 7000 rpm.

12-31-2010, 09:47 PM	#2
Dragsinger VIP Member Join Date: Jul 2008 Location: Liberty City [East Texas] Posts: 1,760 Likes: 5 Liked 99 Times in 60 Posts	Re: altenator pulley ratio to crank A general guide line for full alternator output is to overdrive the alternator 30% - 50% Example; a 5" crank pulley combined with a 3" alternator pulley = 40% overdrive. In this example, 1500 engine RPM will equal about 2100 alternator RPM If the alternator is of the proper amperage output for your load the above example would have full battery voltage to everything with an engine speed of 1600 - 1800 RPM This type setup will allow you to race all day without battery charging. __________________ Larry Woodfin 471W

12-31-2010, 11:20 PM	#3
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: altenator pulley ratio to crank I just bought a low-mount alternator mount & pulleys from Jegs, and a pully set, meant for street rods. Has worked very well. __________________ Ed Wright 4156 SS/JA

01-01-2011, 11:29 AM	#4
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,474 Likes: 885 Liked 859 Times in 234 Posts	Re: altenator pulley ratio to crank East Coast Auto Electric recomends a 2 to 1 ratio . Most pulley kits made specificaly for drag racing are around this ratio. I have run higher ratios in the past with no problems. __________________ Tom Goldman 1500 SG , 1506 STK

01-01-2011, 02:07 PM	#5
Robert Simpson Senior Member Join Date: Aug 2004 Location: Jacksonville, Florida Posts: 808 Likes: 7 Liked 20 Times in 12 Posts	Re: altenator pulley ratio to crank Does anyone run a cog belt set up for a low mount sbc 69 camaro? Just curious...Thanks

01-02-2011, 11:04 PM	#8
west coast Senior Member Join Date: Dec 2008 Location: Rainy Washington Posts: 609 Likes: 12 Liked 223 Times in 73 Posts	Re: altenator pulley ratio to crank Wade are your pulley numbers backwards or is it just me. I have found pulleys for my crank with ratio of 2.26 and 2.10 for my altenator pulley size. Thanks guy's for the helpjust need to make brackets now.

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