So Close! Alternator Upgrade
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I've been putting many hours into this project, lately. Because the Suburban looks like a Suburban, now, and because I've driven it. I feel the need to get this thing into a condition where it's practical for family use.
At the moment, I'm still messing around with a number of things.
I'm not happy with the brakes, even though I've got a good vacuum system in place. Under normal use they are OK. Hard braking, however, shows that things get mushy and fade fast. I think that the vacuum assist is OK, but I haven't bled the system, yet. I'll try that, and see whether that's the issue.
I've got some clunks I'm sorting out, but these are getting cleared up. I've shifted the exhaust and intake a bit, but those self-tapping screws that I used to attach the shifter boot are a little too long. I might just pull them out and trim off the drill points.
The pyrometer and boost gauges are necessary safety items, as I will be playing with the max fuel screw soon.
It's a little anemic on acceleration, but I've instrumented the system to monitor EGTs and boost and will be tweaking the max fuel screw shortly (after I fix the brakes!).
This post's main issue: Alternator Upgrade. One issue that I found last weekend, while charging the air conditioning, was that I was actually discharging the battery. This was caused by a number of factors, including:
The engine's idle was extremely low -- much lower than a gasoline engine would ever be
I was using a CS 130 alternator that came with the Suburban, but had maintained the Isuzu's large 3 1/4" diameter dual-belt pulley
I had front and rear air conditioning units running full blast -- a considerable load on the system
Running the air conditioning triggers both 16" fans in the radiator -- another considerable load on the system
Thanks to being a relatively small alternator with a big pulley, this CS-130 wasn't keeping up with power demands at idle.
So, after messing around with things that afternoon, I found out that I had drawn the battery down to 9 volts, and couldn't even start the engine. I put the battery maintainer on it and did some calculations. I don't think the engine was idling at the normal 800 rpm (though I haven't hooked up the alternator, just yet), but I did my calculations based on that rpm. The engine pulley is 6 1/2" and the alternator pulley is 3 1/4". So, at 800 engine rpm, the alternator would be spinning at only 1600 rpm. The alternator curves I found online showed that these alternators don't produce any current below 1200 rpm. They also indicated that this CS 130 (a 100 amp alternator) would only produce around 35 amps at this speed.
It was time to look at another solution. I looked at some overpriced 160 and 200 amp alternators and found some "overdrive" pulleys that were smaller and would increase the alternator rpm. I decided to go with a remanufactured GM CS 144 alternator from Napa rated at 140 amps, combining it with a 2.6" diameter pulley from Great Water. In this case, an engine turning at 800 rpm would turn the alternator at 2000 rpm. At this rpm, the CS 144 curves I found showed that this would produce a remarkable 90 amps at idle.
This remanufactured alternator had produced 145 amps in testing -- 87 of them available at 2000 rpm.
When I brought the unit home from Napa, I found out that the factory had tested the alternator after rebuilding it, and provided a data sheet showing the results. They showed that this alternator had produced maximum of 145 amps at 6000 rpm, with 87 amps available at 2000 rpm.
A size comparison between the CS 130 and CS 144 alternators.
I pulled the serpentine pulley from the larger alternator and put the Great Water pulley on it. 17mm shafts are standard on these, so there were no fit issues. Here's a comparison of the two alternators side-by-side -- showing how much larger the CS 144 is. The 144 is known for durability and reliability. Though 130s can be wound for high output, the 144 will still typically provide more current at lower rpms. CS means "charging system," while the numbers indicate the armature size. Note that even with the case size differences the mounting ears are in the same places--allowing many GM owners the ability to upgrade to a larger alternator. My homemade angle-iron brackets required some modification to fit the larger case, but it didn't take too long for me to get it mounted.
The CS-144 was mounted, along with a smaller 2.6" pulley. Testing of this alternator showed that it should produce 87 amps at idle.
Once I did, I was pleased to see that I could run front and rear a/c units on full blast and both of my 16" radiator fans, while the voltmeter in the dash continued to read 14v.
--Putting the "engine" back in "engineering!"