Has anybody heard of, or thought of, using either a WOT switch or a vacuum switch with a couple of 5-pin relays, to interrupt the circuits for the AC compressor clutch and the alternator? The idea is so when you stand on the gas, drag from the alternator and AC compressor (if applicable) would practically go away. I got the idea while working on a '96 Isuzu Rodeo 4-banger. The engine is so weak on that truck, in order to squeeze every last bit of efficiency they can out of it, they use the ECM to interrupt the alternator at full throttle. I figure nobody runs at WOT long enough to drain a battery... Worth a try? Or not enough drag to make a difference on a V8?
It wouldn't be any trouble really. An hour's work maybe. I can think of a couple of ways it could interrupt the alternator... Either directly cut the charge wire, or fool the voltage regulator by bridging/cutting the dash light, etc. The AC compressor doesn't pull enough power to notice anything going up a hill, at least not for me, although that was the idea on the Isuzu. I'm thinking less for going up hills, and more for those times when sudden acceleration is called for. :16suspect
I think that's a great idea. I like it more for avoiding driving the compressor at high RPMs than for power saving/efficieny. Lots of times I'll just turn off the AC when down shifting at highway speeds. If you do it, please post your design. Would be good to be able to adjust the vacuum cutoff point.
This was standard practice back in the 60s and 70s. The only downside I can think of in cutting out the alternator is if you have an aftermarket ignition box. Some of them like to have a full 14.5 - 15 volts, regardless of what the manfacturer says. A weak spark could negate any power gains from cutting it out.
I know for a fact it would effect the MSD 6 box. I lost a belt going down the road when I had all MSD ignition on my 71 F100 and it started misfiring with in a minute or two. I think it would be a good and relatively easy idea but like bmcdaniel I would be more concerned about the AC. I always wondered how many RPM's they could take since there is no control at all for that. Clint
I do have an MSD box, the old 6A type. I know from past battery/alternator/VR problems that it will still run at greatly diminished voltage. I don't know if it was performing badly though...
Yeah, I think a minute or two would be longer than I would typically run at WOT though. I was thinking more like 13-14 seconds at a time. I know I can run my AC at 6000 RPM without blowing it up. Probably not the greatest thing to be doing though. And I bet I could get to that point on the tach a bit sooner without the compressor running...
I thought some of the small, weak, 4 cylinder import cars already did this (for A/C)? I like the idea.
Was a good seller back then. J C Whitney I think sold the vacuum kit to shut off ac. Alternator aint worth bothering with, talk to drag racers,, nobody pickups up anything worth while on that,, better to have full voltage an shutting off alt. is hard on charging system an may leave you stranded. AC has gotten more efficient than years ago, system cycles off much more. You do have a good idea, vacuum switch works good, a electric switch is good if you go to drag strip,,, NOBODY wants ac water on the track
Well, I'll leave the alternator out of it then, and focus on the AC. Now I know I have a vacuum switch around here somewhere...
ford had done that on alot of mustangs. ive seen on the 80s carbed ones a full throttle switch that would turn off the alt at full throttle. i found it when i replaced an alt. and it still wouldnt work. i traced the wireing and found the switch. in the 4.6 cars the ac is shut off at full throttle. ive wired eletric fans to turn off at full throttle on some cars ive done. id recomend useing the full throttle to shut off the ac and the eletric fan. leave the alt working so your ignition spark stays strong.
Just have to find out if you pull less vacuum at WOT than you do at idle. If you do, then the vac switch should work. If not, then a WOT switch like you'd use for nitrous may be the answer. I'd definitely use an adjustable vac switch if I go that route. I used one once for a 700R4 transmission in a carbed GM application, to disengage torque converter lockup under acceleration. I experimented with a few different switches, but settled on one from a Volvo because it was consistent and it was easy to adjust until it "felt" right.
Some carbureted K-Cars had WOT switches, I'd rather use a WOT switch instead of a low vacuum switch. Atmospheric pressure and weather conditions affect an engine's behavior, you wouldn't like having a dead battery when cruising at highspeeds.
