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increasing the amp output on a factory 10SI alternator ??

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Old November 9th, 2018, 07:41 AM
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increasing the amp output on a factory 10SI alternator ??

Hi.
Has anyone increased the alternator output of their factory 10 SI GM alternator, using their original housing?
I see there are kits available to up the output from the aftermarket, has anyone used one?
Anyone use factory parts to increase the output?

Thanks
Bernhard

Last edited by Bernhard; November 9th, 2018 at 07:45 AM.
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Old November 9th, 2018, 08:35 AM
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Bernhard, is your stock alternator dead? If so, you could always replace it with a later model 10 SI alternator with a higher amp rating. If it's just one of those MAW projects then hopefully someone can give you some feedback on those kits.
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Old November 9th, 2018, 01:25 PM
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Originally Posted by Olds64 View Post
Bernhard, is your stock alternator dead? If so, you could always replace it with a later model 10 SI alternator with a higher amp rating. If it's just one of those MAW projects then hopefully someone can give you some feedback on those kits.
Berndard wrote:

The alternator works fine and is numbers correct
I just want to increase the output to ensure that the battery remains at near full capacity
The car is a project build and I will be going through the entire car
The alternator has to be able to keep up to a electric fuel pump and a UHV type of ignition system
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Old November 9th, 2018, 02:48 PM
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In my experience, the limiting factor in the 10SI frame is cooling capacity. If you limit the alternator to a range below 70 to 80 A, you won't exeed the cooling capacity. Otherwise overheating will shorten the life of the windings and electronic bits.
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Old November 9th, 2018, 03:21 PM
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how many amps will your pump and ign be drawing?
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Old November 9th, 2018, 04:43 PM
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Old November 10th, 2018, 09:10 AM
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Originally Posted by stellar View Post
how many amps will your pump and ign be drawing?

I don't have the pump or complete ignition system, I'm still souring parts for the ignition system. I did try to find the amp draw of the pump but have not found it listed on line yet.
The alternator will be running a under drive pulley as it will spend most of the time at the race track.
You are correct I should do a amp load calculation before sizing the alternator.
I forgot to include gauges, line lock , dash lights, dome light, headlights, wiper motor, maybe a data logger.
The car will be a a full delete car, No radio,No heater,no power windows, etc so the increase in amp load will be coming from the electric fuel pump and UHV ignition system.
Since I'm rebuilding the alternator anyway I would rather have some extra capacity to cover a possible increase in load.
Thanks for the reply
Bernhard

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Old November 10th, 2018, 10:41 AM
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Originally Posted by VC455 View Post
In my experience, the limiting factor in the 10SI frame is cooling capacity. If you limit the alternator to a range below 70 to 80 A, you won't exeed the cooling capacity. Otherwise overheating will shorten the life of the windings and electronic bits.
100% true. I had a Chrome 10SI case rated at 100 amps, pretty sure output was more like 80 amps. Other than changing the voltage regulator once it gave 0 issues till the truck burnt to the ground from a shorted block heater cord. The other 10SI chrome alternator's that actually put out 100+ amps lasted maybe 5 years at the most. Why manufacturer's didn't copy the better 12SI fan and case must be they want the alternator's to last a short time. My BIL used a 94 amp upgrade on a 12SI case, lasted till he sold the car. Try it, just don't expect it to last for 20 years, 5 years will be pushing it in my experience.
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Old November 10th, 2018, 11:21 AM
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From your post I am guessing the alternator will have a large diameter pulley. This alone will reduce alt output especially at low RPM. If you want to use original alt cases, you will need to change the following parts (.Rectifier.) This should have diodes with 35 or 40 amp rating. 40 is better.( Regulator.) This should have a set point between 14.6 and 14.8. ( Stator.) This should be rated at 94 to 105 amps.( Rotor.) This should be rated at least 78 amp to 94 amp. 94 is better. The rotor is critical when using a higher output stator, especially for low RPM output. If you don't need to use the original cases, you should buy a stock 94 amp 12SI alt. It will bolt right up and probably cost less than changing your stock 10SI alt.
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Old November 10th, 2018, 04:28 PM
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Originally Posted by stellar View Post
From your post I am guessing the alternator will have a large diameter pulley. This alone will reduce alt output especially at low RPM. If you want to use original alt cases, you will need to change the following parts (.Rectifier.) This should have diodes with 35 or 40 amp rating. 40 is better.( Regulator.) This should have a set point between 14.6 and 14.8. ( Stator.) This should be rated at 94 to 105 amps.( Rotor.) This should be rated at least 78 amp to 94 amp. 94 is better. The rotor is critical when using a higher output stator, especially for low RPM output. If you don't need to use the original cases, you should buy a stock 94 amp 12SI alt. It will bolt right up and probably cost less than changing your stock 10SI alt.
Thanks for the reply
I would like to use the stock housing as I would like it to appear completely stock.
I know most guys charge the battery between rounds because the cars don't have much run time and like you said with the larger pulley the charging rate is low.
I should have also mentioned that I will be using a factory starter and the comp ratio will be around 11.5 .

Are the stator and rotor from a GM AC / Delco 12SI or are they sourced from the aftermarket ?
Thanks again
Bernhard
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Old November 10th, 2018, 06:00 PM
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Originally Posted by Bernhard View Post
The alternator will be running a under drive pulley...
Presumably this is to save horsepower. There are two things to consider in this regard.

1. Racers sometimes overestimate the amount of horsepower used by the alternator. At the most, let's say you need 50 A. At 14 V this is a 700 W output. This is less than one horsepower. Even if the alternator is only 80% efficient, that load would represent 1.2 horsepower.

2. Compare your standard 10SI with standard pulley to an enhanced 10SI with underdrive pulley. Let's say the standard 10SI with standard pulley would keep the battery charged under racing conditions. You want to slow down the alternator but raise it's maximum output so it, too, would keep the battery charged. If you succeed, both alternators would be putting out the same amperage and both would have the same horsepower consumption. You are spending money but not saving horsepower.
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Old November 10th, 2018, 08:43 PM
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Originally Posted by Bernhard View Post
Thanks for the reply
I would like to use the stock housing as I would like it to appear completely stock.
I know most guys charge the battery between rounds because the cars don't have much run time and like you said with the larger pulley the charging rate is low.
I should have also mentioned that I will be using a factory starter and the comp ratio will be around 11.5 .

Are the stator and rotor from a GM AC / Delco 12SI or are they sourced from the aftermarket ?
Thanks again
Bernhard
They can come from either OE 12SI or aftermarket.
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Old Yesterday, 10:21 AM
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Originally Posted by VC455 View Post
Presumably this is to save horsepower. There are two things to consider in this regard.

1. Racers sometimes overestimate the amount of horsepower used by the alternator. At the most, let's say you need 50 A. At 14 V this is a 700 W output. This is less than one horsepower. Even if the alternator is only 80% efficient, that load would represent 1.2 horsepower.

2. Compare your standard 10SI with standard pulley to an enhanced 10SI with underdrive pulley. Let's say the standard 10SI with standard pulley would keep the battery charged under racing conditions. You want to slow down the alternator but raise it's maximum output so it, too, would keep the battery charged. If you succeed, both alternators would be putting out the same amperage and both would have the same horsepower consumption. You are spending money but not saving horsepower.
This is a very good point.
The reason I want to run the pulley is more about looks as a lot of racers back in the day ran the GM Chevy pulley.
Many guys were running a field on/off switch in Stock in the early 80's, that was not legal to run at the time looking for the 1 hp.
Their are many racers saying the 1hp gain could be a net loss if the fuel pump and ignition system were not delivering the performance needs of the engine.
Thanks for the reply
Bernhard
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Old Yesterday, 10:32 AM
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Originally Posted by stellar View Post
They can come from either OE 12SI or aftermarket.
Thanks for the reply.
Are the 12 Si rotor and stator a direct bolt in or do they require modification to fit in the 10 Si housing?
Thanks
Bernhard
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Old Yesterday, 10:44 AM
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Direct bolt in. The regulator is also direct bolt in. The rectifier (diodes) are not.
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Old Yesterday, 11:54 AM
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Originally Posted by stellar View Post
Direct bolt in. The regulator is also direct bolt in. The rectifier (diodes) are not.
Thanks for the reply this is very helpful !
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