[highrisk]

I have read through numerous threads on this subject, but thought I would ask for advice since every build is different.

I am doing a frame off restoration on a 65 GTO. All of the wiring harnesses will be stock 65. The engine, as well as all of its mounting brackets, alternator straps, power steering, water pump, etc, is a 69 428.

What I am wondering is what size alternator I will need for my requirements and possible upgrades. I do not mind bypassing the external regulator if an internal regulator is better than an external. I have also seen where some have recommended the 12si. This is also not a problem as long as it will fit the 69 brackets without the need to modify.

This is what I have and my future plans for the car. It has a Mallory electronic ignition. It will be getting a Vintage Air Conditioning System. It will be getting electric windows. The radio is rated at 240 watts total, in the future I might add an amplifier. The one I am looking at is rated at 1200 watts, not sure what the actual power requirements are. It will not be used to drive anything huge like woofers, just two 6x9 Alpine speakers in the back and two 6 1/2 Alpine speakers up front. My intent is to drive the speakers more efficiently to make them clearer and not to make it loud, I like my hearing just fine. I also want the available power in case I have to upgrade to electric fans for the radiator. The ones I am looking at are rated from 12 to 50 amps peak draw. I have seen some that go as high as 80, but that is really over kill. It is more realistic for the 12 to 25 amp range, 50 at most. I really think the stock fan and shroud will keep this car cool since I am installing a Griffin two row 1 1/4" radiator and Evans pump, but I just want to have the ability in the alternator in case I need the electric fans.

I also know it is recommended to upgrade the power cable from the alternator to handle the increased power. Where can you get these and what is recommended? I do not see anything like that listed with our host or other sights like AMES and OPG.

Thanks for all of the help,
Dale

[george kujanski]

If you consider electric fans in the future go with a 12SI, 94 A now, or certainly get it later. if you consider the short term approach, a standard 62A, with either an external reg or internal in a 10SI will do the job.

With electric fans you will need the low RPM higher currnt output of the 12SI, 94A.

George

[GT182]

Dale, I bought my interally regulated alternator at a parts store here. One near you should be able to give you suggestions as my parts guy did. Get one that replaces your old alternator but puts out more power. Save the fan and pulley off yours to reuse.

There's instructions here on PY on how to wire it so you can keep the external regulator on you firewall. To help..... You'll need jumpers on the external regs spades.... top and bottom spades jumpered, and 2 middle spades jumpered. I cut the wires inside my ext reg so there's no power flowing thru it. That's the reason for the jumper wires you'll solder on. Wiring plugs on to it as it did before.

[highrisk]

Originally Posted by george kujanski

If you consider electric fans in the future go with a 12SI, 94 A now, or certainly get it later. if you consider the short term approach, a standard 62A, with either an external reg or internal in a 10SI will do the job.

With electric fans you will need the low RPM higher currnt output of the 12SI, 94A.

George

George,
Thanks for the advice. Does the 12si bolt up to the 69 brackets without any problems? Also, other than rewiring the external regulator and replacing the alternator pigtail with one for an internal regulator, is there any other wiring issues I need to be aware of? You had mentioned to another individual that he may need a bigger wire coming from the alternator to handle more amps. Is this something I need to do?
Thanks for your time,
Dale

[highrisk]

Originally Posted by GT182

Dale, I bought my interally regulated alternator at a parts store here. One near you should be able to give you suggestions as my parts guy did. Get one that replaces your old alternator but puts out more power. Save the fan and pulley off yours to reuse.

There's instructions here on PY on how to wire it so you can keep the external regulator on you firewall. To help..... You'll need jumpers on the external regs spades.... top and bottom spades jumpered, and 2 middle spades jumpered. I cut the wires inside my ext reg so there's no power flowing thru it. That's the reason for the jumper wires you'll solder on. Wiring plugs on to it as it did before.

Gary,
Good talking to you again. Thanks for the wiring tip. My old external regulator was going out when I started tearing the car down so it will be a great candidate for the modification.
Dale

[george kujanski]

I don't know if there is something peculiar about the '69 brackets, but I know that the 10SI and 12SI are drop in mechanically compared to the original 10DN, Hence the advantage of using the higher output 12SI units developed and tested by Delco.

Since the original cabling was designed to handle a max output alternator of 62A, perhaps even a smaller cable for cars originally equipped with the 37A alt, upgrading to a larger output cable is good advice when going to a 94A.

These alts actually sense and control the voltage at the battery, but a small output cable will cause a larger voltage drop between the alt output and the battery. The result is loads connected closer to the alt output will have a slightly higher voltage than the battery, and this effect is minimized when larger cables are used.

Also for this reason, when fans are installed, they should be operated thru a relay (as most probably are), the relay power connection should be at or near the alternator electrically. This removes the fan current from going thru the harness and fusible link, which was sized for the original alternator. The fan and relay circuit should also then be fused to handle the fan current.

George

[highrisk]

Originally Posted by george kujanski

I don't know if there is something peculiar about the '69 brackets, but I know that the 10SI and 12SI are drop in mechanically compared to the original 10DN, Hence the advantage of using the higher output 12SI units developed and tested by Delco.

Since the original cabling was designed to handle a max output alternator of 62A, perhaps even a smaller cable for cars originally equipped with the 37A alt, upgrading to a larger output cable is good advice when going to a 94A.

These alts actually sense and control the voltage at the battery, but a small output cable will cause a larger voltage drop between the alt output and the battery. The result is loads connected closer to the alt output will have a slightly higher voltage than the battery, and this effect is minimized when larger cables are used.

Also for this reason, when fans are installed, they should be operated thru a relay (as most probably are), the relay power connection should be at or near the alternator electrically. This removes the fan current from going thru the harness and fusible link, which was sized for the original alternator. The fan and relay circuit should also then be fused to handle the fan current.

George

George,
Thanks for all of the information. I am sure there is no difference in the alternator brackets as far as what size alternator they take. I was not aware the 10SI and 12SI were made on the same platform as the 10DN. This is good stuff to know.

I can easily make a new heavier wire for the alternator. What size wire would you recommend upgrading to to be able to handle the higher amps?

The 12SI alternators I have found on Summit that are made by PowerMaster are actually rated at 100amps. Are these the same as the ones you are talking about that are rated 94 amps? I know you are talking about an AC Delco with a rating of 94 amps but I have not had any luck locating one on the internet.

Thanks again,
Dale

[george kujanski]

Mid 80's Camaros had 94A 12SI, I believe. Members have purchased them from the parts stores.

Don't know about the PowerMaster units from summit. If they are true 12SI they would be fine. There also are aftermarket alts that are made or retrofitted from 10DN and 10SI units rated as high current, around 100A. I'm suspicious of those... they may be fine, but the 12SI had improved cooling and diodes to be able to handle the higher output...Delco didn't just upgrade the earlier frames for a reason. I don't have any experience with those, but if I can get a true Delco 12SI rated 94A, with 40 or 50A available at idle, why bother with others? That's my opinion.

Going a gauge number smaller on the cable almost doubles the current handling rating, so that's a good starting point. In fact, 3 gauge numbers changes the current rating by a factor of 2, but since wire usually is available in even numbered gauge, go to 8 or 6 if you have a 10 gauge cable, etc. Obviously, the cable gets larger and more stiffas the gauge number gets smaller.

George

[highrisk]

George,
Thanks again. I did find the 12SI once I realized I needed to look at mid 80's GM. I found one of your old posts where you had mentioned that. Autozone and Oreilly sells remanufactured units with lifetime warranties. They are aroung $90. Thanks for the great advice.

I also did some deeper research on the PowerMaster. They advertise their 100 amp as having 70 amps at 2400 RPM and their 140 amp as having 80 amps at 2400 RPM. Are these overkill and would the original, tried and proven, GM 12SI still a better choice?

I will have to cut a piece of wire off my old harness so I can take it in and see what size it is. Jegs and Summit recommends 10ga or 8ga for 65 to 140 amps. Anything over that they recommend 6ga. At least I have a starting point now.

Thanks,
Dale

[george kujanski]

I also took a look at the Summit site last nite. I need to check the Powermaster site to get clarification on the housings they use...i.e. 10SI or 12SI and how they rate their output.

2400 RPM, if engine speed, should be about 5000 RPM alt shaft speed, at which the alt should put out it's max rating. If 2400 is the alt shaft speed, that would equate to about 1200 engine RPM (assuming a 2:1 pulley ratio). So if it's the latter, that's fairly good output since you need high output current running fans at or near idle, otherwise the battery won't be charging with the hgih fan load.

With heavy idle loads like fans you need 50 to 60 amps available near idle; that's the critical spec. Max output current doesn't mean much for that application.

Another point on specs: alts should be rated for output at higher temps, which is the underhood environment. Ratings done with surrounding air at room temp will always be higher, but are not representative of reality.

Back when I worked in charging systems, we rated all of our alts with the machines hot, with surrounding air at least at 50 degrees C. IIRC.

Just some info gathered over the years.......

George

[highrisk]

George,
Good point on the RPM, I was assuming it was engine speed and thought it was not enough amps for that speed. I did not think they could have been talking alternator speed, but that makes more sense. I will see if I can contact PowerMaster and see what they say. If you find out anything, let me know. As of right now I am leaning towards the rebuilt Delco unless these prove to be more efficient at idle.

Some of the PowerMaster cases look like 10SI/10DN and some others look like 12SI. But that doesn't mean anything.

I called M&H Electric Fabricators, they make the stock type replacement harnesses, and they said they use a 12ga wire for the alternator power supply, which according to them is what the stock harness has. So a 10ga, and definitely an 8ga, would be a big improvement.

Thanks again,
Dale

[highrisk]

George,

I just got off the line with the tech guy at PowerMaster and this is what I found out. The 7294 series is their 12SI that are designed to look stock. The 7295 is the 12SI with a smooth look, more modern looking. The basic 7294 is rated at 100 amps at full RPM, he said more like 105, and at idle is 70 amps. They consider idle as 2400 RPM alternator speed so if you are running stock crank pulley he said it would be around 800-1000 engine RPM, depending on crank pulley size. The 47294 is their 140 amp 12SI which is rated at 80 amps at idle. He said these actually test out between 80 to 95 amps and the 80 is a low side figure. He also recommended an 8ga wire ran directly to the battery from the alternator. He really recommended the 140 amp because the cost is not that much more and it gives a lot of room for added electrical devices. He also said they have considered phasing out the 100 amp version because the 140 amp is so much more popular. So do you think the 100 amp or the 140 amp would be a better choice?

So here is another question. If I run an 8ga wire directly to the battery can you leave the stock wire from the wiring harness connected to the alternator and starter? The guy from M&H actually recommended leaving the original hooked up and to run an 8ga or 10ga directly to the battery.

Thanks again,
Dale

[ponjohn]

I ran an alternator from an 84 z28 ho. It is 94 amp and it is a direct replacement. You won't have to worry about swapping pullies on the side of the road.

It is internally regulated and worked great. Ran an electric fuel pump, Mark 8 fan and an MSD box.

[highrisk]

Originally Posted by ponjohn

I ran an alternator from an 84 z28 ho. It is 94 amp and it is a direct replacement. You won't have to worry about swapping pullies on the side of the road.

It is internally regulated and worked great. Ran an electric fuel pump, Mark 8 fan and an MSD box.

Thanks for the first hand experience. Did it produce enough at idle to run the fans and other electrical items? That is the big reason I was looking at the PowerMaster. Their 100Amp is rated at 70Amps at idle and their 140 is rated at 80Amps at idle. The tech rep said the 140 actually does 85 to 90 at idle, the 80 is the minimum they accept at idle. George was saying the AC/Delco 12SI 94 Amps produce 40 to 50Amps at idle and I was just curious if this is able to run your high electrical demand at idle and keep the battery charged? This car had absolutely no options but when I am done it will have an electronic ignition, electric windows, Vintage Air, electric antenna, rally gauges, and a stereo with a 1200 watt amplifier. I want to make sure there is enough room in the alternator to add additional items in case I need to add electric fans and an electric fuel pump. Do you think the 94Amp alternator would be able to handle all of this at idle and still keep the battery charged?

Thanks for taking the time to respond,
Dale

[george kujanski]

A while back I posted the output curve from a 94A 12Si...I'll see if I can resurrect it.

The big killers are the high-duty cycle devices, i.e. electric fans, electric water pumps. Short term loads when added together such as operating at the same time, may temporarily overload the alt at idle, but as soon as the load goes off, the system will recover and charge the batt again. With the fans, etc. they run for quite a while, and if the alt can't keep up, the battery drains during the on time. Hi power stereos also don't really add to the load much since the really hi power peaks are transient in nature....1200 WATTS thru the speakers continually will damage your brain.

George

[ponjohn]

Originally Posted by highrisk

Thanks for the first hand experience. Did it produce enough at idle to run the fans and other electrical items? That is the big reason I was looking at the PowerMaster. Their 100Amp is rated at 70Amps at idle and their 140 is rated at 80Amps at idle. The tech rep said the 140 actually does 85 to 90 at idle, the 80 is the minimum they accept at idle. George was saying the AC/Delco 12SI 94 Amps produce 40 to 50Amps at idle and I was just curious if this is able to run your high electrical demand at idle and keep the battery charged? This car had absolutely no options but when I am done it will have an electronic ignition, electric windows, Vintage Air, electric antenna, rally gauges, and a stereo with a 1200 watt amplifier. I want to make sure there is enough room in the alternator to add additional items in case I need to add electric fans and an electric fuel pump. Do you think the 94Amp alternator would be able to handle all of this at idle and still keep the battery charged?

Thanks for taking the time to respond,
Dale

I didn't experience a problem but you have more to run that I did. 1200 watts is an enourmous amount of power. I'd bet if your read the spec's of the amp it is probably 1200 wats into 2 ohms for a split second ( unless it is a high end piece).

Most amps are designed to run at 75-80% volume not 100%.

FWIW- I also ran and electric w/p with a red top battery.

If I were you, I'd be inclined to add all the currents up and then check off the loads that will be likely running at the same time to come up with a low and high value.

IE- you know that the cooling fan and a/c will always be on together.

Then buy an alternator based off that info.

[GT182]

Dale, good to see you around bud. You'll like going the with internal regulator alternator. If your idle isn't quite enough you can always increase it a bit to get a better charge to the battery. I did that with mine. My car was idling at 800 and the battery light would come on once in a while. I bumped the idle up to 1000 and no more warning light.

I also went to an Interstate battery... 1000CA. It's an MTP-24 with 800CCA and 1000CA. Also went with a 2 guage cable to the starter. Engine starts better and the lights are brighter... inside and out.

[highrisk]

Originally Posted by george kujanski

A while back I posted the output curve from a 94A 12Si...I'll see if I can resurrect it.

The big killers are the high-duty cycle devices, i.e. electric fans, electric water pumps. Short term loads when added together such as operating at the same time, may temporarily overload the alt at idle, but as soon as the load goes off, the system will recover and charge the batt again. With the fans, etc. they run for quite a while, and if the alt can't keep up, the battery drains during the on time. Hi power stereos also don't really add to the load much since the really hi power peaks are transient in nature....1200 WATTS thru the speakers continually will damage your brain.

George

George,
Thanks again for the information. The power curve for the alternator would be great. The power amplifier for the stereo isn't for the purpose of blowing my ear drums out, it is to drive the speakers more efficiently and improve their sound at lower settings. It will never see 1200 Watts because I won't have enough hooked up to it to make it use that much. I flew helicopters for 25 years and I am very picky with my hearing. My biggest concern is if I have to add electric fans making sure the alternator will handle the fans, running the Air Conditioner, and the other electric items on a hot summer day while cruising at low RPMs or in stop and go traffic.
Thanks again,
Dale

[highrisk]

Originally Posted by ponjohn

I didn't experience a problem but you have more to run that I did. 1200 watts is an enourmous amount of power. I'd bet if your read the spec's of the amp it is probably 1200 wats into 2 ohms for a split second ( unless it is a high end piece).

Most amps are designed to run at 75-80% volume not 100%.

FWIW- I also ran and electric w/p with a red top battery.

If I were you, I'd be inclined to add all the currents up and then check off the loads that will be likely running at the same time to come up with a low and high value.

IE- you know that the cooling fan and a/c will always be on together.

Then buy an alternator based off that info.

Yeah, I know the 1200 watts is just a number and it will never actually see that. I just want it to make the speakers sound better at lower power settings. I listened to this stereo with the Alpine speakers with and without the amplifier and the quality of the sound was much better with the amplifier, especially at lower levels.

I figured the biggest problem will be when running the AC in stop and go traffic. A good set of electric fans pull as much as 50 amps (Flex-a-Lite dual fans 28 amps, Derale Dual Fans 50 amps), I have no idea what the blower on the Vintage Air unit pulls. Most single fans will pull between 10 to 20 amps, I wouldn't think it should be much more than that. So that gives a range from 38 to 70 for the two systems. B-Man recommends the fans for a 4th generation F-body (Dorman 620-634) but I haven't been able to find their amp draw.

This is why I am curious about the idle rating of the stock 94 amp Delco. If it is making 40 to 50 at idle it will be at its limit at idle keeping up with the demand where the 140 amp PowerMaster will actually have power left over at idle. But, the Delco is a lot less expensive and I don't want to waste money if the bigger alternator is not necessary. The big if is, if I will need electric fans. I am not planning on adding them unless the mechanical fan can't do the job. So if the Delco actually produces 50 amps at idle it might be my best choice and then see how things are if I need to add electric fans. If I see there is a big draw on the battery, then I would have to upgrade at that time.

Thanks for the information to help make this decision easier. Sometimes you just need to look at it with some other input.
Dale

[highrisk]

Originally Posted by GT182

Dale, good to see you around bud. You'll like going the with internal regulator alternator. If your idle isn't quite enough you can always increase it a bit to get a better charge to the battery. I did that with mine. My car was idling at 800 and the battery light would come on once in a while. I bumped the idle up to 1000 and no more warning light.

I also went to an Interstate battery... 1000CA. It's an MTP-24 with 800CCA and 1000CA. Also went with a 2 guage cable to the starter. Engine starts better and the lights are brighter... inside and out.

Gary,
Good hearing from you again.
I am currently running an Optima Red Top battery with 910CA and 720CCA (that's if it is still any good if I ever get this car back together). I am already going to upgrade the cable from the battery to the starter to 2GA and I am going to run a 8GA or 6GA from the alternator directly to the battery. The only thing I am uncertain about is if I should still hook up the stock 10GA wire from the alternator to the starter. I have researched this and I can't really find an answer. I know the wire will need to be connected on the starter side to power the vehicle, but I am uncertain whether to connect it to the alternator or tape it off.
Bumping up the idle a little bit is a good idea especially if I go with the Delco.
Hope all is well with you,
Dale