It seems back in the day a/c was looked at as incompatible with cars designed for performance. My assumption has always been the components weren’t durable enough and would be prone to failure. Anyone ever pushed the limits with an a/c car and how far did you go? Only interested in OEM stuff from 67-73, I realize modern components are completely different.
I do not believe it had much to do with durability or part failure. It was more that it was one more belt that the engine needed to turn and that took power away from going directly to the rear wheels. That was also the thinking behind not ordering power steering. Another part of the thought process was that adding A/C and/or power steering also added more parts to the car, and more parts equaled more total weight of the car. With less weight and less power robbing accessories the car should go faster.
Randy Goodling
CCOA #95
I think that it had to do with the axle ratio and engine RPM’s, at higher road speeds. Crank and water pump pulley diameters normally changed with the addition of air conditioning. So did radiator cooling fan selection. The C9OE-H Super Cobra Jet fan was double reinforced.
I considered that as well, but my gut feeling is you would tear up a compressor if you’re turning high RPM’s and pushing your engine to the limits. Maybe that isn’t correct, that’s why I asked the question.
I guess to get into the specifics, I want to use my tribute stroker build in the X code which is an a/c car. Being fond of creature comforts I’d still like to have the a/c. I’m not concerned about losing a few HP or the extra weight.
I didn’t consider different pulley diameters. The fan shouldn’t be an issue, I’ll be running a larger radiator with the C9 fan. Maybe details I left out in the GT-E thread.
If you are not planning to race the car then I would think you will be fine. And if you ever do decide to run the car down a track you could just remove the A/C belt and have some fun.
Randy Goodling
CCOA #95
parasitic drag is typically the main reason ac becomes the concern of lost hp. Modern engines today actually turn off the a/c compressor under heavy acceleration to cut down on the drag of the compressor if it happens to be engaged. Then you have the electric waterpumps and no power steering you find on drag strip only cars for the same principle.
Today it seems crazy to think of ordering a car without AC as a standard option especially in a hot climate. Even the some of the highest performance cars today have ac in them. back then a car with AC was an option most could live without and save money on not having.
I beat on them pretty hard back in the day, and everything that I owned was AC equipped. I would normally turn the AC off if I was going to go down the drag strip for example. Never had any problems with AC stuff.
By the way that '67 in my signature photo went down the drag strip many times. I was always cool on the way home from Green Valley with the AC turned down low. That’s me circa 1977.
Of course you were “cool”. You were driving a Cougar. 
The compressor is really only creating drag if the AC is on. When it’s off, the pulley just free-wheels.
I agree that the thought (or at least my thought/hope) was less belts would mean less drag on the pulley. I would routinely remove the AC & PS belts on my 351C-4V when drag racing back in the day. Never proved this with a dyno - that would be interesting to show (that equipment is much more available now vs. in the late 70’s).
I would think the AC and even PS components add a small weight, but I did not see any need/desire to remove them, as it was definitely an advantage to be able to reconnect and use them the rest of the time. It was also too much easier to use other ways to remove or move weight to the rear…
Never had enough guts to remove the ALT belt - most of the time we ran at night & also may not be able to replace right away if we had to leave the area quickly,
CougarCJ mentioned the axle which reminded me… didn’t the factory change the axle ratio to 3.0 when AC was ordered? I’ve been wondering why so maybe the engineers knew the AC compressor would not like the higher revs in shorter geared cars?
When my GT-E was purchased the original owner (that I bought it from) had the dealer install and AM FM Stereo radio and under dash AC. When he picked the car up he was informed that the AC would invalidate the warranty on the car. He was outraged and wrote Ford demanding an explanation. Ford wrote him back saying the dealer was mistaken, the warranty on the car was still valid, it was the AC warranty that was not valid. Th reason was that the engine could turn at higher RPMs than the compressor was rated to handle. Ford also sent a schematic diagram showing how to wire a switch to turn the compressor clutch off. The letter advised him that he could leave the AC blower fan on but he should always turn the compressor off during “performance situations”. This was with a 3.50 rear axle ratio, so I suspect that the redline of the 427 was a big factor.
Interesting. That seems to agree with what I was thinking. Thanks Bill.
We had an issue with local Falcon GTs that had a/c. They used to throw the a/c belt at sustained high revs because of the length of the belt and the growth in the belt from heat and slippage. They were York compressors so it probably had something to do with the 351C turning 6500 rpm
This was the reason Ford would not let a car with the Drag Pak option have air conditioning. The stress on that small compr piston/rod and long belt. A former Ford dealer owner told me in 69 they tried to order a Mach 1 with a 3.91 rear which would have been a SCJ with A/C. Ford would not accept the order unless they dropped the A/C or went to a below 3.50 gear.
Echoing the others. A/C & rears numerically higher than 3.25 don’t work if you plan on seeing revs over 5k.
A bigger issue is that there is no place for the AC hoses to go through the radiator core support due to the oil cooler hoses using that hole. Both sets of hoses won’t physically fit in the same car.
So this has always been weird to me …
“A/C & rears numerically higher than 3.25 don’t work if you plan on seeing revs over 5k.”
It doesn’t really matter what gears are in the rear-end, the transmission has gears and can certainly get over 5k in 1st and 2nd no matter what the rear gears (within reason). So if we’re talking sustained RPMs, then you’re talking cruising speed and such – were people really cruising around at 5k rpms ?
I think someone else touched on this, but maybe it wasn’t the actual RPMs or sustaining them that was the issue but rather the rate of acceleration. With the 3.91 gears the motor won’t be working nearly as hard to accelerate everything and will climb through the rev range much faster. This is what is going to stretch and pull on the belts rather than a steady state (especially if someone leaves the a/c or defrost on).